Passive Mechanism Research Articles

Study of passive steering mechanism for small Mars surface exploration rovers

Planetary surface exploration rovers are required to have the ability to travel over uneven ground such as sandy or rocky terrain. In addition, to maintain long-term functionality under severe mass constraints, the rover must be highly reliable with a simple configuration. The reduction in the number of actuators will also contribute to a reduction in the number of electrical components involved and improve reliability. This paper proposes a lightweight and simple traveling and steering mechanism that combines a path-following system based on the difference in rotational speed of the left and right wheels when traveling in a curve and a passive Ackermann mechanism without an actuator, assuming a small exploration rover of a size and mass that can be mounted on a Japanese launch vehicle. We also propose a correction method to improve the path-following performance. We also developed a prototype wheeled rover of the target size and weight, and tested and evaluated the effectiveness of the proposed method in following the target path and overcoming obstacle on simulated soil.

ELSMOR European Project: Experimental Results on an Innovative Decay Heat Removal System Based on a Plate-Type Heat Exchanger

This paper summarises the results of an experimental campaign carried out at SIET on the ELSMOR facility built in 2022 to validate a decay heat removal system for the E-SMR. Based on the passive mechanisms of natural circulation, the system aims to dissipate the reactor decay heat to a water pool, using two heat exchangers: a plate-type one coupling the primary side to the secondary side, and a vertical tube one coupling the secondary side to the water pool. Such a system is considered to be the most effective passive system, capable of safely managing the SMR accident and accidental situations, and achieving long-term decay heat removal without the need for electricity or external inputs. A description of the primary and secondary loops of the plant is given, together with the installed instrumentation and data acquisition system. In addition, the paper summarises the tests performed in terms of test procedures, test type and associated objectives, test matrix, test results, achievements, and open issues.

Laser ablation of SiC/SiC ceramic matrix composites: Morphological characterization, component evolution and oxidation mechanisms

SiC/SiC composites play a pivotal role in aerospace and energy applications for their excellent resistance to high temperatures, corrosion, oxidation, and low density. This paper delves into the ablation behavior irradiated by a femtosecond laser, examining both qualitative and quantitative aspects through micro/nanostructure and component analysis. The findings reveal significant disparities in elements, compositions, and chemical states across the ablation zones, transition zones, and marginal zones. Moreover, a detailed discussion on the active and passive oxidation mechanisms in the ablation zone is presented. Notably, the oxidation product SiO2 acts as a barrier, impeding oxygen penetration into the material interior.

Leptospiral lipopolysaccharide dampens inflammation through upregulation of autophagy adaptor p62 and NRF2 signaling in macrophages

Leptospira interrogans are pathogenic bacteria responsible for leptospirosis, a worldwide zoonosis. All vertebrates can be infected, and some species like humans are susceptible to the disease whereas rodents such as mice are resistant and become asymptomatic renal carriers. Leptospires are stealth bacteria that are known to escape several immune recognition pathways and resist killing mechanisms. We recently published that leptospires may survive intracellularly in and exit macrophages, avoiding xenophagy, a pathogen-targeting form of autophagy. Interestingly, the latter is one of the antimicrobial mechanisms often highjacked by bacteria to evade the host immune response. In this study we explored whether leptospires subvert the key molecular players of autophagy to facilitate infection. We showed in macrophages that leptospires triggered a specific accumulation of autophagy-adaptor p62 in puncta-like structures, without altering autophagic flux. We demonstrated that Leptospira-induced p62 accumulation is a passive mechanism depending on the leptospiral virulence factor LPS signaling via TLR4/TLR2. p62 is a central pleiotropic protein, also mediating cell stress and death, via the translocation of transcription factors. We demonstrated that Leptospira-driven accumulation of p62 induced the translocation of transcription factor NRF2, a key player in the anti-oxidant response. However, NRF2 translocation upon Leptospira infection did not result as expected in antioxydant response, but dampened the production of inflammatory mediators such as iNOS/NO, TNF and IL6. Overall, these findings highlight a novel passive bacterial mechanism linked to LPS and p62/NRF2 signaling that decreases inflammation and contributes to the stealthiness of leptospires.

An optimization study of passive flow control mechanism for a seashell-shaped wind turbine

Small wind turbines have a lot of promise in areas that are remote from the power grid. For such small-scale applications, such as off-grid electricity, a spiral wind turbine (SWT), a novel type of horizontal-axis wind turbine, may be employed. Placing wind turbines within a duct is one potential method for increasing the efficiency of wind energy harvesting in low-wind urban locations. In this work, a shroud with a flange at its outlet is created using an optimization approach that attempts to maximize the coefficient of power (CP), which improves SWT performance. An evolutionary algorithm over a Kriging interpolative model serves as the optimizer in use. The shroud's shape is determined using a series of straight lines. Using the commercial code program ANSYS-FLUENT, the Reynolds-averaged Navier-Stokes (RANS) equations are solved along with the SST k–ω turbulence model to determine the turbine CP. The computational results are validated and confirmed with previously published results. The optimal shroud design introduced significant improvements in the CP when applied to the SWT, resulting in a maximum CP of 0.967 (at λ = 3.25), which is 3.6 times the maximum CP of the bare SWT (CP = 0.2668 at λ = 2.5).

Passivation performance and mechanism of coal gangue with different pollution levels based on CaO and calcite

Passivation performance and mechanism of coal gangue with different pollution levels based on CaO and calcite

Chitosan nonwoven fabric composited calcium alginate and adenosine diphosphate as a hemostatic bandage for acute bleeding wounds

Acute bleeding following accidental injury is a leading cause of mortality. However, conventional hemostatic bandages impede wound healing by inducing excessive blood loss, dehydration, and adherence to granulation tissue. Strategies such as incorporating active hemostatic agents and implementing chemical modifications can augment the properties of these bandages. Nevertheless, the presence of remote thrombosis and initiators may pose risks to human health. Here, a hemostatic bandage was developed by physically combined chitosan nonwoven fabric, calcium alginate sponge, and adenosine diphosphate. The presented hemostatic bandage not only exhibits active and passive mechanisms for promoting clotting but also demonstrates excellent mechanical properties, breathability, ease of removal without causing damage to the wound bed or surrounding tissues, as well as maintaining an optimal moist environment conducive to wound healing. In vitro evaluation results indicated that the hemostatic bandage possesses favorable cytocompatibility with low levels of hemolysis. Furthermore, it effectively aggregates various blood cells while activating platelets synergistically to promote both extrinsic and intrinsic coagulation pathways. In an in vivo rat model study involving liver laceration and femoral artery injury scenarios, our developed hemostatic bandage demonstrated rapid clot formation capabilities along with reduced blood loss compared to commercially available fabrics.

Passivation of mild steel embedded in low-heat Portland cement: A comparative study with ordinary Portland cement

This study investigates the passivation behaviour and mechanism of mild steel embedded in low-heat Portland cement (LHC) paste. Results show that, compared to ordinary Portland cement (OPC), LHC has a significantly lower alkalinity at early stage and thus a lower passivity of mild steel embedded is obtained in LHC. This is explained by the formation of thinner passive film with higher contents of Fe2+ oxides in LHC at the early stage. Nevertheless, the passivity of mild steel in LHC becomes higher than that in OPC at later stage due to formation of a passive film in LHC with an identical thickness and higher content of Fe2+ oxide compared to that in OPC.

Numerical study of owls' leading-edge serrations

Owls' silent flight is commonly attributed to their special wing morphology combined with wingbeat kinematics. One of these special morphological features is known as the leading-edge serrations: rigid miniature hook-like patterns found at the primaries of the wings' leading-edge. It has been hypothesized that leading-edge serrations function as a passive flow control mechanism, impacting the aerodynamic performance. To elucidate the flow physics associated with owls' leading-edge serrations, we investigate the flow-field characteristic around a barn owl wing with serrated leading-edge geometry positioned at 20° angle of attack for a Reynolds number of 40 000. We use direct numerical simulations, where the incompressible Navier–Stokes equations are solved on a Cartesian grid with sufficient resolution to resolve all the relevant flow scales, while the wing is represented using an immersed boundary method. We have simulated two wing planforms: with serrations and without. Our findings suggest that the serrations improve suction surface flow by promoting sustained flow reattachment via streamwise vorticity generation at the shear layer, prompting weaker reverse flow, thus augmenting stall resistance. Aerodynamic performance is negatively impacted due to the shear layer passing through the serration array, which results in altered surface pressure distribution over the upper surface. In addition, we found that serrations increase turbulence level in the downstream flow. Turbulent momentum transfer near the trailing edge increased due to the presence of serrations upstream the flow, which also influences the mechanisms associated with separation vortex formation and its subsequent development over the upper surface of the wing.

Effective Gene Therapy for Hemophilia a: Novel Re-Dosable Non-Viral Formulation That Provides Stable, and Durable FVIII Expression with Improved Tolerability

Current first-line treatments for Hemophilia A patients are clotting factor replacement or bi-specific antibodies. These treatments require continuous, lifelong infusions, yet many patients have breakthrough bleeds. There remains a high unmet need for safe, effective, and durable therapies. We have developed a liver-directed non-viral in vivo gene insertion approach using the piggyBac® DNA insertion system. Unlike conventional AAV-based gene therapy, our platform enables delivery of large transgenes, the ability to stably and efficiently integrate the therapeutic transgene into the genome, and the potential for re-dosing to titrate to target FVIII activity levels. A key challenge for all gene insertion systems relates to the need to safely and efficiently deliver the transgene DNA. In the current study we evaluated a novel hepatocyte-targeted non-viral platform able to co-deliver both DNA and mRNA with superior safety and specificity relative to the traditional liver-directed LNP concept. We first evaluated a two nanoparticle system using conventional 4-component liver-directed LNPs, with one lipid nanoparticle (LNP) encapsulating the mRNA for the super piggyBac (SPB) transposase (LNP-SPB), and a second LNP encapsulating a plasmid containing the hFVIII transposon DNA (LNP-hFVIII). We subsequently developed a novel co-encapsulated LNP formulation, comprising both SPB mRNA and transposon plasmid DNA (LNP-SPB-hFVIII). In juvenile WT mice we observed a 50% increase in hFVIII antigen expression compared to the dual nanoparticle approach. This was further validated in a severe hemophilia A mouse model (FVIII knock-out). Following a single dose of the co-encapsulated LNP-SPB-hFVIII to adult hemophilia A mice tolerized to human FVIII, we observed ~30% of normal hFVIII expression sustained over the duration of the 7 month study. To further support the concept of re-dosing, we treated immunocompetent adult hemophilia A mice tolerized to human FVIII with repeated administrations every 3 weeks. We observed a dose-proportionate increase in FVIII activity after each administration, reaching an average hFVIII activity of 96% of normal, following 3 repeated doses. Traditional LNPs use several lipid components that typically include an ionizable lipid, cholesterol, a polyethylene glycol (PEG) lipid, and a structural lipid, each with a unique function to effectively encapsulate and deliver the DNA and mRNA required for the piggyBac platform. Cellular transfection of these traditional LNPs has been demonstrated to occur by passive mechanisms such as micropinocytosis or Apolipoprotein E (ApoE)-mediated endocytosis by the low-density lipoprotein receptor (LDLR). However, this can also result in delivery to unwanted cell-types, particularly tissue-resident immune cells. To address this potential failure mode, we explored the addition of a N-Acetylgalactosamine (GalNac)-based targeting ligand to our co-encapsulated LNP formulation (LNP-SPB-hFVIII-G). In immunocompetent animals, targeted LNPs yielded a ~2-3-log reduction in pro-inflammatory serum cytokines (IL-6, IFNɣ) while maintaining high hFVIII expression and no elevation in transaminases (ALT, AST). In conclusion, our results demonstrate the capabilities of the piggyBac DNA insertion system and non-viral approach in providing stable FVIII transgene expression through genomic integration, along with the potential for redosing. Additionally, we have highlighted the tolerability profile of our current generation of liver-targeted non-viral delivery platform. Altogether, these data provide proof-of-principle toward developing an effective and durable therapy for Hemophilia A.

Advances in Directional Wetting Surfaces for Enhanced Fluid Control: A Comprehensive Review

AbstractControlling surface wettability and directing the flow of working fluids have crucial implications in various natural and engineering contexts. Understanding the fundamental principles of wettability and directional wetting is essential for effectively leveraging these phenomena to enhance the performance of engineering systems, such as microfluidics or heat exchangers. This comprehensive review summarizes of previous research, emphasizing recent advances by categorizing the structures and working principles associated with directional wetting surfaces. The efforts of researchers who have employed diverse strategies to manipulate the wetting behavior of liquids through both passive and active control mechanisms are highlighted. Passive directional transport surfaces require no additional energy while enabling large‐scale and continuous fluid control. Conversely, active directional wetting surfaces offer enhanced flexibility and precise control of liquid movement. Furthermore, insights into recent studies that focused on practical applications are provided and the current challenges that need to be addressed are discussed. This study serves as a guide for future research directions on the development of directional wetting surfaces and offers valuable recommendations for practical implementation.

Hybrid vibration absorber for self-induced vibration suppression: exact analytical formulation for acceleration feedback control

Hybrid vibration absorbers (HVAs) are an effective solution for vibration mitigation. They combine the passive vibration absorption mechanism of tuned mass dampers (TMDs) with feedback-controlled actuators, similar to active mass dampers. This enables them to overcome the performance of both systems in terms of vibration mitigation effectiveness and energy consumption, respectively. This study evaluates the vibration suppression capabilities of an HVA against self-excited oscillations. A single-degree-of-freedom host system encompassing a negative damping term is considered. First, the possibility of enhancing the stability properties of an optimally tuned TMD through a feedback controller is evaluated. The analysis shows that this approach cannot improve the absorber’s performance. Subsequently, simultaneous optimization of all the HVA parameters is considered. Our results reveal that this approach significantly enhances the system’s performance. All analysis is carried out analytically without resorting to approximations. Finally, the absorber is numerically applied to suppress friction-induced vibrations and galloping instabilities.

Enhancing photostability of 2D Ruddlesden–Popper perovskite via molecular acceptor passivation of metallic lead defects

Two-dimensional (2D) Ruddlesden–Popper (RP) perovskites hold great potential for novel optoelectronic applications. However, their unconventional optoelectronic properties are often compromised by a vulnerability to light irradiation, which leads to the formation of metallic Pb (Pb0) defects. This study investigates the passivation mechanism of these Pb0 defects in phenylethylammonium lead iodide (PEA2PbI4) using a strong molecular acceptor, 2,2′-(perfluoronaphthalene-2, 6-diylidene) dimalononitrile (F6-TCNNQ). In situ x-ray photoelectron spectroscopy results demonstrate that F6-TCNNQ effectively removes the light-induced Pb0 states, leading to the recovery of photoluminescence intensity in photodegraded PEA2PbI4 samples and significantly improving the photostability of pristine PEA2PbI4. F6-TCNNQ protects the terrace edge of PEA2PbI4, which is the site of initial degradation, as evidenced by atomic force microscopy and scanning electron microscopy analyses. In situ ultraviolet photoelectron spectroscopy measurements confirm substantial electron transfer from Pb0 to F6-TCNNQ, causing the oxidation of Pb0 to Pb2+. Furthermore, the staggered energy level alignment prevents electron transfer from the valence band maximum of PEA2PbI4 to the lowest unoccupied molecular orbital of F6-TCNNQ, thereby preserving the pristine electronic structure of PEA2PbI4. These findings provide new insights into defect passivation in 2D RP perovskites and offer a design strategy for highly stable optoelectronic devices.

Microregion Characterization of Grain Boundary Defects and Electron Capture of CsPbI2Br Perovskite

All‐inorganic CsPbI2Br perovskite solar cell shows superior thermal stability, but the power conversion efficiency falls behind organic devices, due to the existence of abundant defects. Halogen and metal ions at the grain boundaries induce the formation of defect states, which increases the probability of carrier recombination. Grain boundaries are also the channels of ion migration. Herein, as relatively simple interface engineering strategy is used at the molecular level, using a multifunctional 2,5‐thiophene dicarboxylic acid to passivate the interface between the perovskite surface and the carbon electrode. The 2,5‐thiophene dicarboxylic acid can effectively coordinate the undercoordinated Pb2+, reduce the defect concentration of perovskite, and suppress the nonradiative recombination. The device with carbon electrode exhibits a power conversion efficiency of 13.4%. The microscopic passivation mechanism is investigated by Kelvin probe force microscopy. It is observed that the surface treatment effectively passivates the defects at the grain boundary and reduces the capture rate of photogenerated carriers of the grain boundary.

Detecting age-related changes in skeletal muscle mechanics using ultrasound shear wave elastography

Aging leads to a decline in muscle mass and force-generating capacity. Ultrasound shear wave elastography (SWE) is a non-invasive method to capture age-related muscular adaptation. This study assessed biceps brachii muscle (BB) mechanics, hypothesizing that shear elastic modulus reflects (i) passive muscle force increase imposed by length change, (ii) activation-dependent mechanical changes, and (iii) differences between older and younger individuals. Fourteen healthy volunteers aged 60–80 participated. Shear elastic modulus, surface electromyography, and elbow torque were measured at five elbow positions in passive and active states. Data collected from young adults aged 20–40 were compared. The BB passive shear elastic modulus increased from flexion to extension, with the older group exhibiting up to 52.58% higher values. Maximum elbow flexion torque decreased in extended positions, with the older group 23.67% weaker. Significant effects of elbow angle, activity level, and age on total and active shear elastic modulus were found during submaximal contractions. The older group had 20.25% lower active shear elastic modulus at 25% maximum voluntary contraction. SWE effectively quantified passive and activation-dependent BB mechanics, detecting age-related alterations at rest and during low-level activities. These findings suggest shear elastic modulus as a promising biomarker for identifying altered muscle mechanics in aging.

Understanding the Effect of Three-Dimensional Design in Tandem Blade

Abstract In order to maximize the pressure ratio and efficiency, compressor designers have tried several unconventional design approaches. Tandem blading is one such unconventional design that promises a higher pressure ratio per stage through a higher diffusion factor. The nozzle shape created between the forward and aft blades of a tandem configuration acts as a passive boundary layer control mechanism. The boundary layer growth over the aft rotor is therefore effectively controlled with the help of this gap-nozzle flow. The flow complexity is likely to increase in the case of a tandem rotor due to the twin leakage vortices, twin wake regions, and their interaction with the hub and casing boundary layers. Modern compressor blades are often designed with three-dimensional blade techniques such as sweep, lean, dihedral, end bent, etc., to reduce the various losses and achieve optimum performance. However, to the best of the author’s knowledge, the effect of 3D blade designs on the performance of tandem rotors has not been fully explored so far. A comprehensive numerical investigation is undertaken to understand the effect of 3D designs on the performance of tandem blades. Axial sweep and dihedral failed to improve the performance of the tandem rotor. Significant improvement in the stall margin is observed for the forward chordwise-swept and negative lean tandem rotors and is largely attributed to lower tip incidence. The performance penalty of the forward-swept and negatively leaned cases can be reduced by integrating compound or variable lean and sweep into the design.

Advancing clinical translation of cardiac biomechanics models: a comprehensive review, applications and future pathways.

Cardiac mechanics models are developed to represent a high level of detail, including refined anatomies, accurate cell mechanics models, and platforms to link microscale physiology to whole-organ function. However, cardiac biomechanics models still have limited clinical translation. In this review, we provide a picture of cardiac mechanics models, focusing on their clinical translation. We review the main experimental and clinical data used in cardiac models, as well as the steps followed in the literature to generate anatomical meshes ready for simulations. We describe the main models in active and passive mechanics and the different lumped parameter models to represent the circulatory system. Lastly, we provide a summary of the state-of-the-art in terms of ventricular, atrial, and four-chamber cardiac biomechanics models. We discuss the steps that may facilitate clinical translation of the biomechanics models we describe. A well-established software to simulate cardiac biomechanics is lacking, with all available platforms involving different levels of documentation, learning curves, accessibility, and cost. Furthermore, there is no regulatory framework that clearly outlines the verification and validation requirements a model has to satisfy in order to be reliably used in applications. Finally, better integration with increasingly rich clinical and/or experimental datasets as well as machine learning techniques to reduce computational costs might increase model reliability at feasible resources. Cardiac biomechanics models provide excellent opportunities to be integrated into clinical workflows, but more refinement and careful validation against clinical data are needed to improve their credibility. In addition, in each context of use, model complexity must be balanced with the associated high computational cost of running these models.

Multiple Tuned Mass Dampers and Double Tuned Mass Dampers for Soft Story Structures: A Comparative Study

Recent seismic events have highlighted the vulnerability of reinforced concrete buildings, especially soft-story structures, to damage and collapse during strong earthquakes due to the ground's vibrational response. This study aims to mitigate these adverse vibrations using passive control mechanisms, particularly tuned mass dampers (TMDs). Conventional TMDs require a substantial mass to effectively influence the structure's lateral reactions. The research explores the use of multi-tuned mass dampers (MTMDs) and double-tuned mass dampers (DTMDs) in a soft-story building. The study uses MATLAB to estimate TMD parameters and subject the models to seismic loading. The comparative assessment of these models reveals the potential benefits of using MTMD and DTMD systems to enhance the seismic resilience of soft-story structures.

Improved Efficiency and Stability in 1,5-Diaminonaphthalene Iodide-Passivated 2D/3D Perovskite Solar Cells.

Engineering multidimensional two-dimensional/three-dimensional (2D/3D) perovskite interfaces as light harvesters has recently emerged as a potential strategy to obtain a higher photovoltaic performance in perovskite solar cells (PSCs) with enhanced environmental stability. In this study, we utilized the 1,5-diammonium naphthalene iodide (NDAI) bulky organic spacer for interface modification in 3D perovskites for passivating the anionic iodide/uncoordinated Pb2+ vacancies as well as facilitating charge carrier transfer by improving the energy band alignment at the perovskite/HTL interface. Consequently, the NDAI-treated 2D/3D PSCs showed an enhanced open-circuit voltage and fill factor with a remarkable power conversion efficiency (PCE) of 21.48%. In addition, 2D/3D perovskite devices without encapsulation exhibit a 77% retention of their initial output after 1000 h of aging under 50 ± 5% relative humidity. Furthermore, even after 200 h of storage in 85 °C thermal stress, the devices maintain 60% of their initial PCE. The defect passivation and interface modification mechanism were studied in detail by UV vis absorption, photoluminescence spectroscopy, atomic force microscopy (AFM), scanning electron microscopy (SEM), Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), solid-state NMR, space-charge-limited current (SCLC) mobility measurement, and impedance spectroscopy. This study provides a promising path for perovskite surface modification in slowing their degradation against external stimuli, providing a future direction for increasing the perovskite device efficiency and durability.

Respiratory pressure and split flow data collection device with rapid occlusion attachment

Respiratory model-based methods require datasets containing enough dynamics to ensure model identifiability for development and validation. Rapid expiratory occlusion has been used to identify elastance and resistance within a single breath. Currently accepted practice for rapid expiratory occlusion involves a 100 ms occlusion of the expiratory pathway. This article presents a low-cost modular rapid shutter attachment to enable identification of passive respiratory mechanics. Shuttering faster than 100 ms creates rapid expiratory occlusion without the added dynamics of muscular response to shutter closure, by eliminating perceived expiratory blockage via high shutter speed. The shutter attachment fits onto a non-invasive venturi-based flow meter with separated inspiratory and expiratory pathways, established using one-way valves. Overall, these elements allow comprehensive collection of respiratory pressure and flow datasets with relatively very rapid expiratory occlusion.