Passive Method Research Articles

Enhanced surface acoustic wave microfluidic performance through FDTS self-assembled monolayers on [formula omitted]

Microfluidics technology has been extensively applied in biochemical analysis and medical diagnostics, where precise and efficient control of microfluids is crucial. However, existing passive microfluidic control methods (e.g., microchannels) and active strategies (e.g., optical, thermal, magnetic field, and electrokinetic manipulation) are often hindered by complex device structures and operational uncertainties. Surface acoustic wave (SAW) microfluidic manipulation offers a promising alternative, providing flexible and efficient digital microfluidic control through the modulation of input signals. Nevertheless, the intrinsic hydrophilicity of substrates such as LiNbO3 results in inefficient microfluidic driving and jetting, primarily due to high surface tension. In this study, we employed chemical vapor deposition (CVD) to coat LiNbO3 substrates with 1H,1H,2H,2H-Perfluorododecyltrichlorosilane (FDTS) self-assembled monolayers (SAMs), creating hydrophobic surfaces with a contact angle of approximately 120°. In comparison to commercially available Glaco hydrophobic coatings, which reduce SAW amplitude by approximately threefold and increase substrate temperature by up to 1.5 times, FDTS SAMs exhibit negligible impact on SAW properties. Furthermore, when compared to untreated SAW devices, FDTS SAMs-coated devices demonstrated a sixfold increase in droplet driving speed under low power input (e.g., 0.5 W), enabling faster and more precise liquid jetting at velocities reaching 5 m/s. This work highlights the potential of FDTS SAMs in enhancing the performance of SAW-driven microfluidic devices, particularly in applications requiring high-efficiency droplet manipulation.

Airborne microplastic monitoring: Developing a simplified outdoor sampling approach using pollen monitoring equipment

A novel, yet simple, airborne microplastic (MP) sampling approach using global pollen monitoring equipment was applied to identify, characterise and quantify outdoor airborne MPs for the first time. Modification of Burkard spore trap tape adhesive provided particle capture and facilitated downstream spectroscopy analysis. 36 polymer types were identified from a total of 21 days sampling using Burkard spore traps at two locations (United Kingdom and South Africa). MPs were detected in 95 % of daily samples. Mean MP particle levels were 2.0 ± 0.9 MP m-3 (11 polymer types) in Hull (U.K.), during March, 2.9 ± 2.0 MP m-3 (16 types) in Hull in July, and 11.0 ± 5.7 MP m-3 (29 types) in Gqeberha, (S.A.) in August 2023. The most abundant polymer type was nylon (Gqeberha). The approach was compared with two passive sampling methods whereby 27 polymer types were identified and of these, 6 types were above the limit of quantification (LOQ), with poly(methacrolein:styrene) (PMA/PS) the most abundant. Irregularly shaped MPs < 100 µm in length were predominant from all sampling approaches. For the first time, airborne MPs were chemically characterised and quantified using volumetric pollen sampling equipment, representing a viable approach for future airborne MP monitoring.

Ultra-high brightness Micro-LEDs with wafer-scale uniform GaN-on-silicon epilayers

Owing to high pixel density and brightness, gallium nitride (GaN) based micro-light-emitting diodes (Micro-LEDs) are considered revolutionary display technology and have important application prospects in the fields of micro-display and virtual display. However, Micro-LEDs with pixel sizes smaller than 10 μm still encounter technical challenges such as sidewall damage and limited light extraction efficiency, resulting in reduced luminous efficiency and severe brightness non-uniformity. Here, we reported high-brightness green Micro-displays with a 5 μm pixel utilizing high-quality GaN-on-Si epilayers. Four-inch wafer-scale uniform green GaN epilayer is first grown on silicon substrate, which possesses a low dislocation density of 5.25 × 108 cm−2, small wafer bowing of 16.7 μm, and high wavelength uniformity (standard deviation STDEV < 1 nm), scalable to 6-inch sizes. Based on the high-quality GaN epilayers, green Micro-LEDs with 5 μm pixel sizes are designed with vertical non-alignment bonding technology. An atomic sidewall passivation method combined with wet treatment successfully addressed the Micro-LED sidewall damages and steadily produced nano-scale surface textures on the pixel top, which unlocked the internal quantum efficiency of the high-quality green GaN-on-Si epi-wafer. Ultra-high brightness exceeding 107 cd/m2 (nits) is thus achieved in the green Micro-LEDs, marking the highest reported results. Furthermore, integration of Micro-LEDs with Si-based CMOS circuits enables the realization of green Micro-LED displays with resolution up to 1080 × 780, realizing high-definition playback of movies and images. This work lays the foundation for the mass production of high-brightness Micro-LED displays on large-size GaN-on-Si epi-wafers.

Peningkatan Keaktifan Siswa Melalui Penerapan Problem Based Learning (PBL) pada Materi "Aku Memiliki Kemampuan" di SMP Negeri 7 Sintang

Student engagement in learning plays a crucial role in enhancing material comprehension and learning motivation. Active students are more likely to engage in critical thinking, participate in discussions, and solve problems presented to them. However, in many schools, student engagement remains low due to passive teaching methods, such as lectures. To address this issue, the Problem Based Learning (PBL) method is implemented. PBL encourages students to actively solve real-world problems relevant to their lives, thereby increasing their involvement and participation in the learning process. This research aims to improve the engagement of grade VIII students at SMP Negeri 7 Sintang on the Aku Memiliki Kemampuan topic through the application of PBL. The results indicate that PBL successfully enhanced student engagement, with student participation increasing from 30% in the initial condition to 85% after two learning cycles. Additionally, the students' average scores significantly improved. Thus, PBL is proven effective in enhancing both student engagement and learning outcomes.

A Low-Cost and Lightweight Real-Time Object-Detection Method Based on UAV Remote Sensing in Transportation Systems

Accurate detection of transportation objects is pivotal for enhancing driving safety and operational efficiency. In the rapidly evolving domain of transportation systems, the utilization of unmanned aerial vehicles (UAVs) for low-altitude detection, leveraging remotely-sensed images and videos, has become increasingly vital. Addressing the growing demands for robust, real-time object-detection capabilities, this study introduces a lightweight, memory-efficient model specifically engineered for the constrained computational and power resources of UAV-embedded platforms. Incorporating the FasterNet-16 backbone, the model significantly enhances feature-processing efficiency, which is essential for real-time applications across diverse UAV operations. A novel multi-scale feature-fusion technique is employed to improve feature utilization while maintaining a compact architecture through passive integration methods. Extensive performance evaluations across various embedded platforms have demonstrated the model’s superior capabilities and robustness in real-time operations, thereby markedly advancing UAV deployment in crucial remote-sensing tasks and improving productivity and safety across multiple domains.

Improvement of thermal environment in the outdoor atrium by employing the spray system

Outdoor atriums have recently been applied with increasing frequency for natural illumination, but they produce a harsh thermal environment easily in summer. Moreover, overheating of the outdoor atrium necessitates air-conditioning to moderate indoor thermal comfort. Simultaneously, the substantial heat emissions from air-conditioning outdoor units worsen the outdoor thermal environment, creating a vicious cycle. Traditional passive evaporative methods involving water and greenery, while capable of regulating the thermal environment, suffer from low evaporative efficiency and pose significant challenges. To improve thermal environment in outdoor atriums, the spray system was employed due to its high cooling efficiency, especially in open or semi-open spaces. In this study, a comparative experiment was conducted to evaluate the effectiveness of using a spray system for evaporative cooling in open outdoor spaces. Furthermore, employing high-efficiency evaporative cooling through spraying to disrupt the vicious cycle of indoor and outdoor thermal environments. The dual goals include regulating indoor and outdoor thermal conditions while also mitigating the local heat island effect. Temperature and humidity distribution within the atrium and adjacent hallways were monitored, along with the impact on air-conditioning operation consumption in neighboring offices. Results showed that the spray system significantly improved the thermal environment in the outdoor atrium, reducing the average and peak air temperatures by 0.94–2.83 °C and 2.92–5.21 °C, respectively. It also resulted in a drop in the average temperature by 0.56–1.62 °C and the peak temperature by 2.31–3.25 °C in adjacent hallways. This effectively eased the issue of overheating in these areas while raising the comfort level in adjacent office spaces. The predicted mean vote decreased from 1.46 to 0.87, indicating a significant improvement in thermal environment in neighboring offices. Furthermore, the daily energy consumption was reduced by 10.6–12.4% in neighboring offices. This study provided the valuable guidance for improving thermal environments within outdoor atrium.

High lift devices using compliant surfaces

Stall delay and lift enhancement play a crucial role in modern aircraft performance. This is commonly achieved by devices such as slats or flaps located at the leading edge or trailing edge of an aircraft's wing. In this paper, we report a feasibility study of using light-weight compliant surfaces for novel high lift devices. The effects of compliant flags with one end fixed or both ends fixed near the leading edge and trailing edge of an airfoil were studied by force, flag deformation, and flow field measurements in a wind tunnel. When a flag is placed near the leading edge, the excitation of the separated shear layer from the leading edge is the main mechanism in increasing the lift at the post-stall angles of attack. In contrast, the trailing-edge flag with an excess length and both ends fixed could increase the effective camber and the circulation around the airfoil in a time-averaged sense. The mechanism is similar to that of the conventional Gurney flap effect, and equally effective at pre-stall and post-stall angles of attack. When used together, the compliant flags can delay stall angle by 8° and increase the maximum lift coefficient by 67% in the parameter range tested presently. Compliant surfaces require no external power as a passive method. If they are to be used as active methods, they are light weight, and can be stored and deployed easily.

Aircraft icing detection via flow-induced ambient random noise: from theory to wind tunnel experiments

Aircraft icing is a serious threat to flight safety. This paper presents a passive approach to detect ice accreted on an airfoil using flow-induced random noise considering spatially-inhomogeneous transient excitations. Under the assumption of diffuse-field, by computing the cross-correlation of ambient vibration measured at two receivers and band-pass filtering it, the guided wave dispersion curve of the structure can be well-reconstructed, by which one can estimate the ice thickness by matching the reconstructed dispersion curve with its theoretical model. In practice, however, the diffuse-field assumption may not hold as spatially-inhomogeneous strong transient excitations exist. The associated directional wave propagation generates additional peaks in the cross-correlation and this contaminates the ice detection result. Therefore, this paper proposes a signal processing technique to identify and suppress the contributions from the transient source in the measurements, by which a reliable dispersion curve reconstruction and an accurate ice detection can be retrieved. The proposed method is shown to be efficient via a wind tunnel experiment. The passive ice detection method is specifically suitable for aircraft online monitoring because only passive sensors are needed which can be tiny, light, and mounted on the internal surface of fuselage skin without any influence on aircraft aerodynamics.

Study and modeling of the ultrasonic ambient noise induced by the fluid-structure interaction in a pipe

An elastic guided wave-based structural health monitoring (SHM) system consists in examining the integrity of a structure through the propagation of elastic waves. In this context, passive methods turn initial hindrances into advantages by making use of the ambient ultrasonic noise in a structure in operation, through the cross-correlation. Although they have been empirically applied in several configurations, no model is available to predict the link between the flow regime and the convergence of the ambient noise correlation towards the impulse response of the system. Considering the different parameters involved in the case of a pipe, a physical approach of this issue may be studied through the turbulent boundary layer, which has long been described by the Corcos model. Corcos-like models have essentially been applied so far on the audible range, below 1 kHz, where we are interested in frequencies around 100 kHz, typical for SHM applications. The semi-empirical model allows to determine a wall boundary pressure, which, applied at the pipe's inner boundaries, acts as a source term for ultrasonic elastic waves propagating in the pipe. Our goal is then to study if such a model can be used at these high frequencies to reproduce the experimental observations.

Enhancing Pediatric Dental Care: The Influence of Virtual Reality.

The purpose of this study was to assess the effects of virtual reality (VR) in reducing pain and anxiety levels in children. The study also compared active and passive distraction methods using VR during the delivery of inferior alveolar nerve blocks (IANBs) in dental procedures in children. The study comprised 45 preschool patients, aged between 4 and 6 years, with no prior dental anesthetic experience. The participants were randomly assigned to three groups based on the sort of management style: Group A used the tell-show-do technique, Group B engaged in passive distraction by watching cartoons using a VR headset, and Group C participated in active distraction by playing games using a controller with the VR headset. Pain and anxiety were evaluated using physiological measurements, namely by analyzing the variations in blood pressure, heart rate, and oxygen saturation before and after the administration of IANB. Psychological assessments were conducted using the Wong-Baker faces scale, Modified Dental Anxiety scale questionnaires, and Revised Face, Legs, Activity, Cry and Consolability scale after administering IANB. The physiological outcomes revealed no statistically significant differences in blood pressure and oxygen saturation. However, there was a statistically significant increase in the heart rate in group A compared with groups B and C. In terms of psychological measurements, groups B and C exhibited a significant improvement in pain experience and a decrease in anxiety. This study concluded that VR reduced pain and anxiety levels in its passive and active forms.

Optimization Design of Bionic Leading-edge Protuberances on Horizontal Axis Wind Turbine Blades

Abstract The complex operating environments of horizontal axis wind turbines has made the phenomenon of blade flow separation more obvious. As a passive flow control method, the bionic humpback whale leading-edge protuberances have been shown to effectively enhance the performance of the wind turbine. This study employs a multi-objective genetic algorithm and Computational Fluid Dynamics method to analyse the impact of leading-edge protuberances on the aerodynamic performance and flow characteristics of the blades. The results indicate a significant improvement in blade performance after optimization in the wind turbine’s output power. The streamwise vortices generated by the bionic protuberances not only reduce the suction surface pressure, but also suppress the spanwise flow over the blade surface. The length of the flow separation Region is reduced from 0.410 to 0.368 radius. In the process of wind speed change, the tangential forces on the bionic blade exhibit a wave-like variation. The bionic protuberance alters the pressure coefficient of the position. Compared with the original blade, the pressure coefficient of the trough sections on both sides of the bionic blade protuberance is improved. In this study, the bionic protuberance applied to the leading-edge of horizontal-axis wind turbine blades is proposed for the first time, and holds practical value for guiding practical applications.

Passive Design Strategy of Vertical Housing for Optimizing Energy Efficiency

Abstract Passive design is crucial for sustainable building, maximizing comfort while minimizing energy use and environmental impact. It optimizes heating, cooling, ventilation, and lighting through natural energy sources like sunlight and wind, promoting responsible energy consumption. As the Indonesian economy continues to grow, urbanization rates in major cities are rapidly increasing, leading to urban sprawl. One proposed solution is densification through vertical housing construction. However, a concern with vertical housing is the energy consumption for thermal and lighting comfort, particularly in Indonesia’s tropical climate. Passive design presents an effective energy efficient solution for optimizing comfort in vertical housing. This study explores various passive design strategies based on six basic principle. Firstly, it presents local climatic conditions. Then, it discusses lessons learned from traditional buildings and modern buildings. Finally, it introduces a passive design method for high-rise housing, focusing on six points: massing and orientation, building envelope, passive cooling, thermal mass storage, natural air circulation and daylighting. The study presents results and potential recommendations for passive design to optimize energy efficiency.

Vibration Control for Laminated Composite Spherical-Cylindrical-Combined Shells: Theory and Experiment

Considering the structural damage and instability due to extensive vibrations, the present investigation focuses on the dynamic characteristics analysis and vibration control for aerospace structures such as rocket stages and aircraft cowling, modeled as laminated composite spherical-cylindrical-combined shells (SCCSs). The theoretical model of the SCCSs is established by a series of artificial connection and boundary springs. The proposed method’s validity is confirmed through finite element analysis and experimental validation. Nickel-titanium-steel wire ropes (NiTi-STs) are then introduced as a passive vibration control method for the SCCSs. Both circumferential and axial NiTi-ST laying schemes demonstrate good vibration control capabilities on the SCCSs. For similar lengths of NiTi-STs, the vibration control effect of circumferential laying schemes is superior to that of the axial one. Furthermore, the vibration control effect of the circumferential schemes is found to be dependent on the number and positioning of NiTi-STs. The influence of the NiTi-ST structural parameters on the vibration control performance is also analyzed; adjusting the structural parameters appropriately is helpful to improve the vibration reduction effect.

The Effect of Added Wire Mesh on The Thermal Efficiency of the Flat Plate Solar Water Heater Collector

The current study looks into the effects of using wire mesh to expand the flat plate solar collector (FPSC) on the system's thermal efficiency under transient heat-flux without changing its dimensions and its placement to minimise the shadows cast on the collector while utilising passive methods to circulate the working fluid. Thus, the traditional model was investigated numerically (using ANSYS fluent) and experimentally to establish the accuracy of simulation results. Then, the three models, A, B, and C, were tested numerically. In model A, the mesh is used to cover the riser pipe. In model B, the mesh covers the collector plate; in model C, the mesh is placed on both the riser pipe and the plate. The wire mesh placement in all three models improved the thermal efficiency of the FPSC. In addition, model C proved to be paramount to all models under study, classical models A and B, by having a higher thermal efficiency of 41.4%, 14%, and 31.2%, respectively.

Experimental characterization of acoustic damping materials

AbstractDue to their ease of use and low cost, passive damping methods are a preferred mean for the reduction of noise in many engineering applications. This applies in particular to foam materials, which exhibit good acoustic and mechanical damping properties. The selection of suitable materials is usually carried out experimentally and can be very labor‐intensive and time‐consuming. For this reason, it is helpful to develop qualified numerical methodsthat can be used for material design and selection. Hence, foam materials must be characterized experimentally in order to enable a later comparison with vibroacoustic simulations. This contribution, therefore, aims at providing suitable parameters for the use in numerical analyses and their validation. Firstly, the microstructure of a foam specimen is captured by means of a CT scan. In addition to providing the geometry for the multi‐physics simulations, this measurement is also used to determine characteristic foam features, for example, strut thickness and pore size distribution. In the second step, the frequency‐dependent stiffness and damping properties of the material are determined by a special experimental setup utilizing an electrodynamic shaker. Here, the dynamic system is approximated as a single‐mass oscillator, which is sufficiently accurate for low frequencies. These properties will later be used in the numerical model to evaluate different parameter identification approaches. In the third and last step of the experimental campaign, measurements with an impedance tube are conducted to obtain the coefficient of absorption. This material parameter is particularly suitable for comparing experiments and simulations. Finally, the correlation between the experimental results is examined to provide a deeper understanding of the foam materials.

Bio-Based Phase Change Materials for Sustainable Development.

The increasing global population has intensified the demand for energy and food, leading to significant greenhouse gas (GHG) emissions from both sectors. To mitigate these impacts and achieve Sustainable Development Goals (SDGs), passive thermal storage methods, particularly using phase change materials (PCMs), have become crucial for enhancing energy efficiency and reducing GHG emissions across various industries. This paper discusses the state of the art of bio-based phase change materials (bio-PCMs), derived from animal fats and plant oils as sustainable alternatives to traditional paraffin-based PCMs, while addressing the challenges of developing bio-PCMs with suitable phase change properties for practical applications. A comprehensive process is proposed to convert bacon fats to bio-PCMs, which offer advantages such as non-toxicity, availability, cost-effectiveness, and stability, aligning with multiple SDGs. The synthesis process involves hydrolysis to break down fat molecules obtained from the extracted lipid, followed by three additional independent processes to further tune the phase change properties of PCMs. The esterification significantly decreases the phase transition temperatures while slightly improving latent heat; the UV-crosslinking moderately raises both the phase transition temperature and latent heat; the crystallization remarkably increases the both. The future research and guidelines are discussed to develop the large scale manufacturing with cost effectiveness, to optimize synthesis process by multiscale modeling, and to improve thermal conductivity and latent heat capacities at the same time.

Improvement of the Thermal Performance of PCM-Based Heat Sink Used in Electronic Cooling by Adding Nano-Particles

Recently, thanks to the technological advances, electronic devices are getting smaller in size. This causes an increase in the heat generation per unit area. This heat has to be removed from electronic devices for them to be longer-lasting, more efficient and more reliable. There are many active and passive methods designed for this objective. One of them is embedding phase change material (PCM) in the heat sink. PCM, during the phase change stage, absorbs the heat generated in the system and thus aids in keeping the temperature at a certain value. The biggest downside of PCM is its rapid conduction of heat. PCM properties can be improved by using nanoparticles. In this study, nanoparticles such as TiO2 and CuO were added to PCM and such a modified PCM is used in a finned heat sink. The thermal behavior of the PCM with addition of 1%, 2% and 5% TiO2 and CuO was investigated numerically in three dimensions. RT-28HC was used as the PCM in the study. It was shown that as the nanoparticle ratio increases, heat transfer coefficient of the PCM rises and the melting time of Nanoparticle PCM (NPPCM) is less than that of pure PCM. However, it was observed that, the melting time of PCM with CuO added is longer than that of the PCM with TiO2 added.

Numerical simulation for comparison of cold plate cooling and HFE-7000 immersion cooling in lithium-ion battery thermal management

In this work, fluorinated liquids can be used as a new immersion coolant for effective battery thermal management (BTM) because of their insulating and non-flammable inert characteristics. In this research, the liquid chosen for immersion cooling is HFE-7000, characterized by a boiling point of 34 °C. The analysis of bubble kinetics is employed to investigate the heat transfer mechanism in two-phase immersion cooling by examining the behavior of bubbles during the boiling process. The square ternary Li-ion batteries are subjected under loads of 2C and 3C cooled by immersion cooling and a mini-channel cold plate as a comparison. It turns out that immersion liquid cooling modules offer superior thermal performance. Under constant current (CC), the peak temperature is reduced by 4.89 °C and 9.31 °C compared with the mini-channel cold plate cooling (CPC). Under dynamic load conditions, the maximum temperature rise of the battery is reduced by 29.89 % and 43.89 % compared to CPC. As a passive heat dissipation method, two-phase immersion cooling reduces the design requirements for active control. Also, it delivers an efficient battery thermal management system (BTMS) designed for upcoming electric vehicles (EVs).

Field trial of a seismoacoustic method for ice cover parameters monitoring on the Franz Josef Land archipelago

Among the physical parameters of the freezing seas ice cover, ice thickness is of key importance, and its measurement is one of the most important tasks. The increased interest in the state of the sea ice cover as an indicator of global climatic changes, as well as the growth of comprehensive development of the Arctic shelf has caused intensive development of technical and methodological bases for ice observations. Despite the great variety of approaches to ice thickness estimation, all of them are not without weaknesses. Thus, most contact methods imply direct human presence, which significantly complicates the procedure, taking into account, among other factors, the rough weather conditions of the Arctic. Remote methods depend on weather conditions and cannot always provide high spatial resolution. In this connection, it is promising to use satellite observations coupled with the results of autonomous “ground” measurements, which can be seismoacoustic data containing information on the characteristics of elastic waves propagating in the ice-covered sea, is promising. The purpose of this work is to experimentally test a new passive method for monitoring ice cover parameters along long profiles based on the analysis of natural seismoacoustic fields. The article analyzes the data of a full-scale seismoacoustic experiment with a multichannel group of geophones placed on the floating ice of Alexandra Island in the Franz Josef Land archipelago within the framework of a complex expedition of the Russian Geographical Society. The demonstrates that it is in principle possible to use flexural-gravity waves propagating in the floating ice to estimate its characteristics, both in the active mode and by analyzing the ambient noise, is demonstrated. The results of ice parameter reconstruction obtained in a nondestructive manner using seismoacoustic waves and averaged over long profiles are compared with the data of direct contact measurements. This can be further used for monitoring seasonal and multiyear variability of sea ice thickness of freezing seas, including shelf zones.

Air Quality Geospatial Analysis in Vulnerable Areas. Case Study of Valencia (Spain).

The escalating concern over poor air quality, particularly nitrogen dioxide (NO2), poses a critical public health challenge, especially for vulnerable populations, such as children, older adults, and those with chronic diseases. This study aimed to analyze air quality in areas with vulnerable populations through a geospatial analysis of NO2 concentration measured by the passive dosimetry method in 2022. The results reveal high vulnerability caused by areas with over-centralized facilities and high concentrations of nitrogen dioxide, often coinciding with busy avenues. The study emphasizes the urgent need to address air quality disparities, providing crucial insights for public decision-makers to allocate resources effectively and reduce environmental inequalities in the city, ultimately safeguarding the health of at-risk communities.