Search Results (188)

This paper creates a global similarity network between city-level dialects of English in order to determine whether external factors like the amount of population contact or language contact influence dialect similarity. While previous computational work has focused on external influences that contribute to phonological or lexical similarity, this paper focuses on grammatical variation as operationalized in computational construction grammar. Social media data was used to create comparable English corpora from 256 cities across 13 countries. Each sample is represented using the type frequency of various constructions. These frequency representations are then used to calculate pairwise similarities between city-level dialects; a prediction-based evaluation shows that these similarity values are highly accurate. Linguistic similarity is then compared with four external factors: (i) the amount of air travel between cities, a proxy for population contact, (ii) the difference in the linguistic landscapes of each city, a proxy for language contact, (iii) the geographic distance between cities, and (iv) the presence of political boundaries separating cities. The results show that, while all these factors are significant, the best model relies on language contact and geographic distance. Full article

Constructing heterojunctions can combine the superior performance of different two-dimensional (2D) materials and eliminate the drawbacks of a single material, and modulating heterojunctions can enhance the capability and extend the application field. Here, we investigate the physical properties of the heterojunctions formed by the contact of different atom planes of Janus MoSSe (JMoSSe) and graphene (Gr), and regulate the Schottky barrier of the Gr/JMoSSe heterojunction by the number of layers and the electric field. Due to the difference in atomic electronegativity and surface work function (WF), the Gr/JSMoSe heterojunction formed by the contact of S atoms with Gr exhibits an n-type Schottky barrier, whereas the Gr/JSeMoS heterojunction formed by the contact of the Se atoms with Gr reveals a p-type Schottky barrier. Increasing the number of layers of JMoSSe allows the Gr/JMoSSe heterojunction to achieve the transition from Schottky contact to Ohmic contact. Moreover, under the control of an external electric field, the Gr/JMoSSe heterojunction can realize the transition among n-type Schottky barrier, p-type Schottky barrier, and Ohmic contact. The physical mechanism of the layer number and electric field modulation effect is analyzed in detail by the change in the interface electron charge transfer. Our results will contribute to the design and application of nanoelectronics and optoelectronic devices based on Gr/JMoSSe heterojunctions in the future. Full article

Laser ranging technology holds a key position in the military, aerospace, and industrial fields due to its high precision and non-contact measurement characteristics. As a core component, the performance of the photon detector directly determines the ranging accuracy and range. This paper systematically reviews the technological development of photonic detectors for laser ranging, with a focus on analyzing the working principles and performance differences of traditional photodiodes [PN (P-N junction photodiode), PIN (P-intrinsic-N photodiode), and APD (avalanche photodiode)] (such as the high-frequency response characteristics of PIN and the internal gain mechanism of APD), as well as their applications in short- and medium-range scenarios. Additionally, this paper discusses the unique advantages of special structures such as transmitting junction-type and Schottky-type detectors in applications like ultraviolet light detection. This article focuses on photon counting technology, reviewing the technological evolution of photomultiplier tubes (PMTs), single-photon avalanche diodes (SPADs), and superconducting nanowire single-photon detectors (SNSPDs). PMT achieves single-photon detection based on the external photoelectric effect but is limited by volume and anti-interference capability. SPAD achieves sub-decimeter accuracy in 100 km lidars through Geiger mode avalanche doubling, but it faces challenges in dark counting and temperature control. SNSPD, relying on the characteristics of superconducting materials, achieves a detection efficiency of 95% and a dark count rate of less than 1 cps in the 1550 nm band. It has been successfully applied in cutting-edge fields such as 3000 km satellite ranging (with an accuracy of 8 mm) and has broken through the near-infrared bottleneck. This study compares the differences among various detectors in core indicators such as ranging error and spectral response, and looks forward to the future technical paths aimed at improving the resolution of photon numbers and expanding the full-spectrum detection capabilities. It points out that the new generation of detectors represented by SNSPD, through material and process innovations, is promoting laser ranging to leap towards longer distances, higher precision, and wider spectral bands. It has significant application potential in fields such as space debris monitoring. Full article

Dog clutches are superior to synchromesh units due to much less wear caused by friction but require an external torque source to synchronize the rotation speeds. The current trend in e-mobility to use the driving motor of an electric vehicle as this source just creates another problem, which is known as torque holes. In this work, we propose a novel double-sided dog clutch that synchronizes the speeds electromagnetically by itself avoiding mechanical contact between the parts. A shift sleeve, two coils placed coaxially in their stators, and two complementary rings form an electromagnetic reluctance actuator, which is integrated inside the gearbox between two gearwheels and represents the double-sided clutch. Thus, intermediate parts between the shift sleeve and the actuator are not required. Both actuator sides can produce axial force and electromagnetic torque. However, torques and forces are generated simultaneously on both sides. Therefore, a special control algorithm is developed to keep the resulting axial force approximately equal to zero while the torque is generated in the neutral gear position. After the synchronization, the axial force is applied on the corresponding side to shift the required gear engaging the shift sleeve teeth directly with the slots of the complementary ring mounted on the gearwheel. So, an axial contact of the teeth at an unaligned state, which can lead to unsuccessful shifting, is avoided. A testrig, which includes a clutch prototype and a testing two-speed gearbox, has been designed and built. The developed theoretical ideas have been verified during the experiments under different conditions. The experiments confirm that the actuator can reduce positive and negative speed differences on both sides and subsequently shift the gear without a shift sleeve collision at misaligned angular positions. Full article

Electrothermal actuators, with their simple structure, small size, strong anti-interference ability, and easy integration, have emerged as a promising solution for micro-drive technology. However, deploying them in extreme environments, such as the fuze systems—which demand exceptional reliability under high mechanical overloads. In this study, a device based on multi-electrothermal co-actuation is designed for the fuze system of loitering munition. The overall structure and work principle of the multi-electrothermal co-actuation device is discussed. Considering application environments, the effect factors of V-beam numbers, air gap, type of contact surface, external load force, periodic voltage and gas damping on the output performance of the multi-electrothermal co-actuation device are systematically addressed via simulation and experimental method. Furthermore, the high overload resistance performance of the co-actuation device applied in loitering munition is studied. The results show that the proposed multi-electrothermal co-actuation device could operate stably under a high overload (12,000 g/73.79 μs) environment, fully meeting the demanding requirements of fuze system for loitering munition. In addition, this study identifies laser processing-induced thermal gradients and mechanical stresses as critical fabrication challenges. This study provides significant insights into the design and optimization of multi-electrothermal actuation systems for next-generation fuze applications, establishing a valuable framework for future development in this field. Full article

Ground reaction forces (GRFs) are the primary interaction forces that enable a legged robot to maintain balance and perform locomotion. Most quadruped robot controllers estimate GRFs indirectly using joint torques and a kinematic model, which depend on assumptions and are highly sensitive to modeling errors. In contrast, direct sensing of contact forces at the feet provides more accurate and immediate feedback. Beyond force magnitude, tactile sensing also enables richer contact interpretation, such as detecting force direction and surface properties. In this work, we show how tactile sensor information can be used inside the feedback of the control loop to achieve compliance of legged robots during ground contact. The three main contributions are (i) a fast and computationally efficient 3D force reconstruction method tailored for spherical tactile sensors, (ii) a tactile admittance controller that adjusts leg motions to achieve the desired GRFs and compliance, and (iii) experimental validation on a quadruped robot, demonstrating enhanced load distribution and balance during external perturbations and locomotion. The results show that the peak ground reaction forces were reduced by 55% while balancing on a beam. During a locomotion scenario involving sudden touchdown after a fall, the tactile admittance controller reduced oscillations and regained stability compared to proportional–derivative (PD) control. Full article

This work develops a comprehensive analysis method to examine the nonlinear dynamic response of angular contact ball bearings (ACBBs) with variable clearance. Based on the elastic contact theory and friction principle, the nonlinear contact-impact behavior of the ACBB is systematically investigated. A multibody dynamics model incorporating three-dimensional clearance effects is developed. First, the nonlinear vibro-impact dynamics model of the ACBB is presented considering the influence of variable clearance. Second, the kinematic analysis of the ACBB with clearance is planned, and performance tests are performed under variable conditions, which demonstrate the effectiveness of the proposed method. Furthermore, a comparative analysis of a numerical simulation of the ACBBs with variable clearance is performed. The results show that the increase in rotation speed and external load would cause the high-frequency contact impact between ball and raceway. The decline of the deviation ratio for the cage’s mass center velocity illustrates that the motion trajectory of ACBB would be irregular. Full article

Deformation monitoring of deep foundation pits is critical for ensuring construction safety. However, traditional methods (e.g., inclinometers) face inherent challenges such as limited spatial coverage (<30% in large-scale projects), low operational efficiency (requiring 2–3 times longer data acquisition than 3D scanning), and spatiotemporal discontinuity (single-point measurements fail to capture 3D dynamic deformation fields, leading to incomplete mechanical interpretations of soil–structure interactions). In contrast, 3D laser scanning provides rapid, non-contact, and high-resolution data acquisition that can capture comprehensive deformation fields over large areas. Therefore, this study proposes a novel deformation monitoring framework, aiming to expand the monitoring range and enhance the measurement accuracy. The proposed framework combines the extensive spatial coverage of 3D laser scanning with the corrective capability of a backpropagation neural network (BPNN) model. The proposed approach leverages sparse yet high-precision traditional monitoring data to train the BPNN, effectively correcting systematic deviations in laser scanning measurements caused by external disturbances and instrument errors. Validation at an active deep foundation pit site in Hangzhou reveals that the method reduces the mean absolute error (MAE) from 5.2 mm to 1.8 mm, with corrected scanning data consistency exceeding 80 percent compared to conventional monitoring measurements. This work establishes a scalable framework for deformation analysis and sets a technical benchmark for monitoring in large-scale deep foundation pit projects. Full article

This study examined the differences in physiological, metabolic and running dynamics responses between level and inclined treadmill protocols and their implications for accurately determining training intensities. Twenty-three healthy, active adults (18 male and 5 female) from 25 to 59 years old (age: 42.7 years, height: 1.77 m, body mass: 71.9 kg, $V{O}_{2max}$: 54.3 mL·${\mathrm{kg}}^{-1}$·${\min }^{-1}$) completed both protocols. Physiological markers (gas exchange threshold (GET), respiratory compensation point (RCP), $V{O}_{2max}$), metabolic variables (HR, $V{O}_2$, $VC{O}_2$, RER, VE, speed) and running dynamic variables (running economy (RE), stride length (SL), ground contact time (GCT), cadence) were measured and matched for the external work rate at each stage. The data were analyzed using one-way repeated measures ANOVA with Tukey’s post hoc procedure. No significant differences were observed in the physiological markers for the inclined and flat protocols across all the intensities. However, the metabolic variables showed significant differences (p = 0.0333 to <0.0001) between the inclined and flat protocols at higher intensities. The RE was consistently improved in the flat protocol compared with the inclined protocol, with significant differences observed at the high-intensity stages (p = 0.0232 to <0.0001). While the physiological markers remained unaffected, metabolic responses and running kinematics differed significantly between the protocols. These results highlight that training intensity zones derived from inclined protocols may not be appropriate for flat terrain training, underlining the importance of testing specificity in athlete preparation. Full article

In this work, we demonstrate that an external pressure of 15–30 kPa can significantly improve metal halide perovskite (MHP) film thermal stability. We demonstrate this through the application of weight on top of an MHP film during thermal aging in preserving the perovskite phase and the mobile ion concentration, an effect which we hypothesize reduces the extent to which volatile species can escape from the MHP lattice. This method is shown to be effective for a more scalable approach by only applying the weight to a cover glass during the lamination of an epoxy-based resin, after which the weight is removed. The amount of pressure applied during lamination is shown to correlate with stability in both 1 sun illumination and damp heat testing. Lastly, the performance of MHP photovoltaic devices is improved using pressure during lamination, an effect which is attributed to improved interfacial contact between the MHP and the adjacent charge transport layers and healing of any voids or defects that may exist at the buried interface after processing. As such, there are implications for tuning the amount of pressure that is applied during lamination to enable the durability of MHP solar modules toward manufacturing-scale deployment. Full article

The bacterial flagellar motor is one of the few known rotary motors, powering motility and chemotaxis. The mechanisms underlying its rotation and the switching of its rotational direction are fundamental problems in biology that are of significant interest. Recent high-resolution studies of the flagellar motor have transformed our understanding of the motor, revealing a novel gear mechanism where a membranous pentamer of MotA proteins rotates around a cell wall-anchored dimer of MotB proteins to turn the contacting flagellar rotor. A derivative model suggests that significant changes in rotor diameter occur during switching, enabling each MotA₅MotB₂ stator unit to shift between internal and external gear configurations, causing clockwise (CW) and counterclockwise (CCW) motor rotation, respectively. However, recent structural work favors a mechanism where the stator units dynamically swing back and forth between the two gear configurations without significant changes in rotor diameter. Given the intricate link between the switching model and the gear mechanism for flagellar rotation, a critical evaluation of the underlying assumptions is crucial for refining switching models. This review scrutinizes key assumptions within prevailing models of flagellar rotation and switching, identifies knowledge gaps, and proposes avenues for future biophysical tests. Full article

Fruits are perishable fresh products with a short shelf life after harvesting. Perishable foods and their shelf lives are directly related to the temperature at which they are stored. Refrigeration is therefore essential in the conservation of fruits, as it allows the temperature to be lowered, helping to delay microbial, physiological, and chemical changes. This work aimed to compare the thermal behaviors of alveoli with different phase change materials (PCMs) placed inside a modular packaging developed for the transport and storage of fruits. The cooling tests were carried out inside a cold storage chamber with the set-point programmed to 2 °C. To simulate the placement in packages exposed to the store environment, heating tests were carried out while the chamber door was opened and the packaging was exposed to external environmental conditions. The phase change materials tested were RT2HC, RT5HC, and RT8HC. The temperature variation in the tests during cooling and heating proved that the new type of alveoli with PCM inside the fruit transport packaging is extremely important, as it can extend the useful life of the fruits after they are removed from the cold chamber, managing to maintain adequate conservation conditions for longer in contact with room temperature. The phase change material RT8HC was the one that showed the best results overall, managing to maintain the temperature of the fruit inside the packaging at a temperature below 10 °C for up to eight hours after being exposed to ambient conditions of 20 °C. Full article

This paper presents a numerical model based on the extended finite element method (XFEM) to tackle the problems of hydraulic fracturing and frictional contact in rock cracks. By considering the water pressure distribution on the crack surfaces and the virtual work principle of frictional contact on the crack surfaces, the governing equations for analyzing hydraulic fracturing and frictional contact problems using the XFEM are derived, and the implementation method of the XFEM with frictional contact and water pressure distribution on the crack surfaces is presented. Taking a single-edge-cracked flat plate as an example, the interaction integral method is employed to compute the stress intensity factor in the case of water pressure distribution on the crack surface. Subsequently, a comparative analysis is carried out between the obtained results and the exact solutions. It is demonstrated that this method can yield highly accurate calculation results. Taking a flat plate with a through crack as an example, the nonlinear complementary method is adopted to solve the frictional contact problem. This contact algorithm can effectively prevent the crack surfaces from interpenetrating, and its results are consistent with those calculated by the finite-element penalty function method. Based on the XFEM, the hydraulic fracturing analysis of a flat plate with a central crack under uniaxial compression is carried out. The critical water pressure decreases as the crack length increases, and the critical water pressure increases as the external axial pressure increases. Taking a gravity dam with an initial crack as an example, the calculation results show that hydraulic fracturing will increase the mode I stress-intensity factor at the crack’s tip and reduce the stability of the crack located in the dam foundation of the gravity dam. Full article

Stick–slip phenomena may manifest at the joints during cyclic vibrations in beam structures connected by some forms of joint. This work incorporates the sticking–slip effect of joint connections into the dynamic analysis framework of multi-beam structures through changes in friction forces. The system characteristic equation is solved using the incremental harmonic balance method, the vibration characteristics of the connected structure are explored through the dynamic response, and the accuracy of the model established in this paper is verified through experiments. The equivalent stiffness and damping changes of a connecting beam under different connection states are investigated for the first time. The research indicates that the “tracking” phenomenon, induced by abrupt damping and resonance frequency variations due to low contact pressure and a low friction coefficient, leads to a relatively stable vibration response amplitude across an extended frequency range. This results in the gradual attenuation of resonance peaks within the frequency response curve, giving rise to a defined resonance frequency range. As connection stiffness diminishes, the system demonstrates characteristics of internal resonance. In addition, the influence characteristics of external excitation and connection joint position on the vibration response of multi-beam structures are also explored. This model provides an effective method for studying the vibration problems of complex beam frame structures. Full article

Hyper-redundant space manipulators (HRSMs), with their extensive degrees of freedom, offer a promising solution for complex space operations such as on-orbit assembly and manipulation of non-cooperative objects. A critical challenge lies in achieving stable and effective grasping configurations, particularly when dealing with irregularly shaped objects in microgravity. This study addresses these challenges by developing a segmented hybrid impedance control architecture tailored to multi-point contact scenarios. The proposed framework reduces the contact forces and enhances object manipulation, enabling the secure handling of irregular objects and improving operational reliability. Numerical simulations demonstrate significant reductions in the contact forces during initial engagements, ensuring stable grasping and effective force regulation. The approach also enables precise trajectory tracking, robust collision avoidance, and resilience to external disturbances. The complete non-linear dynamics of the HRSM system are derived using the Kane method, incorporating both the free-space and constrained motion phases. These results highlight the practical capabilities of HRSM systems, including their potential to grasp and manipulate obstacles effectively, paving the way for applications in autonomous on-orbit servicing and assembly tasks. By integrating advanced control strategies and robust stability guarantees, this work provides a foundation for the deployment of HRSMs in real-world space operations, offering greater versatility and efficiency in complex environments. Full article