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Clearance joint systems exhibit various nonlinear factors, such as freeplay, variable stiffness, bilinearity, which give rise to multiple motion states. Transitions between these motion states are typically non-differentiable, resulting in abrupt changes in the system’s dynamic characteristics. Traditional parameter continuation strategies in the shooting method become invalid at these state transition points. This paper presents an improved shooting method for nonlinear normal mode analysis of clearance joint systems, incorporating an adaptive step size adjustment strategy. First, a hyperbolic tangent kernel function is introduced to smooth the local non-differentiable points in the one-dimensional clearance joint system. Next, a shooting method combined with a pseudo-arclength continuation algorithm is applied to compute and track the relationship between system frequency characteristics and energy. At state transition points, the adaptive step size adjustment strategy facilitates the continuation of periodic solutions. Finally, the stability of the solutions is evaluated using Floquet multipliers. Numerical examples demonstrate that clearances reduce structural modal frequencies and induce multistage behavior in frequency–energy curves. Additionally, clearance with bilinear characteristics generates novel internal resonance tongues.

A novel successive two-stage drying strategy, namely hot air drying with integrated temperature and humidity control (HAD-ITHC) combined with radio frequency (RF) drying, was proposed on large-size Exocarpium citri grandis (ECG) to overcome time-consuming and heat-sensitive component degradation. After optimizing the moisture transition point, two different second-stage drying conditions (hot air drying-assisted RF (HAD-ITHC + RF-HA) and vacuum drying-assisted RF (HAD-ITHC + RF-VD)) were conducted while comparing to HAD-ITHC based on drying efficiency and product quality. The RF heating characteristics during the second stage were improved by decreasing the moisture content during the HAD-ITHC first stage. However, after the moisture content of 40% continuing HAD-ITHC increased the crusting, shrinkage, structural damage, and reduced the RF drying efficiency. As a result, the 40% point was selected as the optimized moisture transition point. The optimal drying conditions for the second stage were electrode gap of 150 mm, hot air temperature of 60 ℃ under RF-HA, and electrode gap of 100 mm, atmospheric-vacuum pressure duration of 4 min:5 min under RF-VD. Compared to HAD-ITHC, introducing RF shortened the drying time (30.01–37.15%) and improved flavonoids content (5.92–9.41%), especially HAD-ITHC + RF-VD. However, the sequential vacuum-atmospheric pressure cycle of RF-VD caused severe crumpling and volatile components (VOCs) losses. The better preservation of flavonoids and VOCs, and uniformity of heating and final moisture distribution were achieved under HAD-ITHC + RF-HA. Overall, HAD-ITHC + RF-HA was a promising successive two-stage drying approach to ECG with higher drying efficiency and better quality. Graphical Abstract

Dry frictions have significant effects on the dynamic responses of engineering systems, due to the strong nonlinear/non-smooth stick and slip properties arising from the contact interactions. To have a valuable insight into the vibration characteristics of dry friction systems, an alternate-state-space shooting algorithm is proposed to effectively calculate the periodic solution and predict the stability. Firstly, a zero-one strategy is introduced to transform the dry friction system into a piecewise stick-slip linear system. Then, the transition points of the dry friction are calculated carefully by the transition criteria. Meanwhile, the alternate state-space framework is established to solve the dynamic solution. Finally, the shooting method based on the alternate state-space framework is applied to get the periodic solution of dry friction systems by further resorting to the periodic boundary condition. The sensitivity analysis of the dynamic response with respect to the initial values is conducted along with the consideration of the sensitivity jumps at transition points. As a by-product, the monodromy matrix is simply acquired from the sensitivity analysis and used to indicate the stability of the solution. Several numerical examples including a mass-spring-belt system, a bilinear hysteretic system, and a structure with Iwan bolted joint models are studied to demonstrate the efficiency and accuracy of the proposed approach.

Visually impaired individuals are at a high risk of accidents due to sudden changes in walking surfaces and surrounding obstacles. Existing smart cane systems lack the capability to detect pathway surface transition points with accurate distance estimation and danger-level assessment. This study proposes a low-cost smart cane that integrates a novel Pathway Surface Transition Point Detection (PSTPD) method with enhanced obstacle detection. The system employs dual RGB cameras, an ultrasonic sensor, and YOLO-based models to deliver real-time alerts based on object type, surface class, distance, and severity. It comprises three modules: (1) obstacle detection and classification into mild, moderate, or severe levels; (2) pathway surface detection across eight surface types with distance estimation using weighted bounding boxes and depth mapping; and (3) auditory notifications. Experimental results show a mean Average Precision (mAP@50) of 0.70 for obstacle detection and 0.92 for surface classification. The average distance estimation error was 0.3 cm for obstacles and 4.22 cm for pathway surface transition points. Additionally, the PSTPD method also demonstrated efficient processing with an average runtime of 0.6 s per instance.

In the present work, three dimensional numerical study is conducted to investigate the heat transfer and flow characteristics of twisted tubes of different cross section shapes with the Reynolds number ranging from 50 to 2000. The constant wall temperature condition is used in the simulation analysis. The numerical results of twisted square tube are compared with the available previous experimental data. The results indicate that the heat transfer performance of twisted tube is enhanced compared with the smooth tube, while the pressure drop increases as well. One of the key findings is that the transition point of twisted square tube from laminar flow to turbulent flow is identified and located at Re = 500. It is also found that the cross section shape has little effect on the heat transfer of twisted tubes, while it has great influence on the flow pattern. The results also reveal that the twist pitch has remarkable effects on the heat transfer performance of twisted tubes. In addition, the maximum value of PEC of 2.69 is obtained in twisted pentagon tube with twist pitch ratio of 0.17, and the Reynolds number of 350. These results are significant because it will contribute to the development of compact twisted tube heat exchangers.

In this paper, an audio-driven algorithm for the detection of speech and music events in multimedia content is introduced. The proposed approach is based on the hypothesis that short-time frame-level discrimination performance can be enhanced by identifying transition points between longer, semantically homogeneous segments of audio. In this context, a two-step segmentation approach is employed in order to initially identify transition points between the homogeneous regions and subsequently classify the derived segments using a supervised binary classifier. The transition point detection mechanism is based on the analysis and composition of multiple self-similarity matrices, generated using different audio feature sets. The implemented technique aims at discriminating events focusing on transition point detection with high temporal resolution, a target that is also reflected in the adopted assessment methodology. Thereafter, multimedia indexing can be efficiently deployed (for both audio and video sequences), incorporating the processes of high resolution temporal segmentation and semantic annotation extraction. The system is evaluated against three publicly available datasets and experimental results are presented in comparison with existing implementations. The proposed algorithm is provided as an open source software package in order to support reproducible research and encourage collaboration in the field.

The dynamic characteristics of rubber isolation pad (abbreviated as RIP) after service under the high temperature thermal oxygen aging and the variable preloads have preload dependence and thermal oxygen aging dependence, which is a crucial problem for matching the vibration isolation system of air conditioner compressor to reveal the dynamic characteristic mechanism of the RIP with different preloads and thermal oxygen aging conditions. The Peck model is first introduced to characterize the thermal oxygen aging factor, the fractional derivative Kelvin-Voigt thermal oxygen aging-perturbation model (FDKVTPM) and the Coulomb frictional thermal oxygen aging-perturbation model (CFTPM) are established to describe the frequency dependence and the amplitude dependence, respectively. The thermal oxygen aging-dynamic characteristic model of the RIP is built by considering the influence of variable preloads, the model parameters under different preloads are further identified, the validity of the model was examined by the experimental data. The concepts of the stiffness transition point (STP) and the stiffness transition frequency (STF) are innovatively proposed to better describe softening effect of the RIP under variable preload and variable amplitude working conditions. The results show that the static stiffness of RIP increases by 20.7%, the dynamic stiffness increases by 9.3%, and the loss factor decreases by 35% after thermal oxygen aging under different preload conditions, which can lay a theoretical foundation for in-depth study of the stiffness matching and optimization of air conditioner compressor with the RIP.

Interacting many-body systems display enhanced sensitivity close to critical transition points due to diverging quantum fluctuations. This criticality-based enhancement has been suggested as a potential resource for applications in precision metrology. Here we demonstrate many-body critical enhanced metrology for the sensing of external microwave electric fields in a non-equilibrium Rydberg atomic gas. We show that small variations in external driving lead to a large variation in the population of Rydberg states around criticality and to a notable change in the optical transmission signal. For continuous optical transmission at the critical point, we quantify the enhanced sensitivity extracting the Fisher information, which shows a three orders of magnitude increase due to many-body effects compared with single-particle systems. These results demonstrate that critical properties of many-body systems are promising resources for sensing and metrology applications. Interacting quantum systems near criticality have been proposed as potential probes for quantum metrology. An experiment with Rydberg atoms now proves the enhanced sensitivity of critical many-body systems to small variations in external parameters.

Smart hydrogels (SH) were prepared by thermal free radical polymerization of N-isopropyl acrylamide (NIPAAm), acrylamide (AAm) with acrylic acid (A) or maleic acid (M), and N,N′-methylene bisacrylamide. Spectroscopic and thermal characterizations of SHs were performed using FTIR, TGA, and DSC. To determine the effects of SHs on swelling characteristics, swelling studies were performed in different solvents, solutions, temperatures, pHs, and ionic strengths. In addition, cycle equilibrium swelling studies were carried out at different temperatures and pHs. The temperature and pH transition points of SHs are calculated using a sigmoidal equation. The pH transition points were calculated as 5.2 and 4.2 for SH-M and SH-A, respectively. The NIPAAm/AAm hydrogel exhibits a critical solution temperature (LCST) of 28.35 °C, while the SH-A and SH-M hydrogels exhibit the LCST of 34.215 °C and 28.798 °C, respectively, and the LCST of SH-A is close to the body. temperature. Commercial (CHSA) and blood human serum albumin (BHSA) were used to find the adsorption properties of biopolymers on SHs. SH-M was the most efficient SH, adsorbing 49% of CHSA while absorbing 16% of BHSA. In conclusion, the sigmoidal equation or Gaussian approach can be a useful tool for chemists, chemical engineers, polymer and plastics scientists to find the transition points of smart hydrogels.

Quantum phase transitions (QPTs) involve transformations between different states of matter that are driven by quantum fluctuations 1 . These fluctuations play a dominant part in the quantum critical region surrounding the transition point, where the dynamics is governed by the universal properties associated with the QPT. Although time-dependent phenomena associated with classical, thermally driven phase transitions have been extensively studied in systems ranging from the early Universe to Bose–Einstein condensates 2 – 5 , understanding critical real-time dynamics in isolated, non-equilibrium quantum systems remains a challenge 6 . Here we use a Rydberg atom quantum simulator with programmable interactions to study the quantum critical dynamics associated with several distinct QPTs. By studying the growth of spatial correlations when crossing the QPT, we experimentally verify the quantum Kibble–Zurek mechanism (QKZM) 7 – 9 for an Ising-type QPT, explore scaling universality and observe corrections beyond QKZM predictions. This approach is subsequently used to measure the critical exponents associated with chiral clock models 10 , 11 , providing new insights into exotic systems that were not previously understood and opening the door to precision studies of critical phenomena, simulations of lattice gauge theories 12 , 13 and applications to quantum optimization 14 , 15 . A Rydberg atom quantum simulator with programmable interactions is used to experimentally verify the quantum Kibble–Zurek mechanism through the growth of spatial correlations during quantum phase transitions.