Rigid Parts Research Articles

N-terminal cleavage of cyclophilin D boosts its ability to bind F-ATP synthase

Cyclophilin (CyP) D is a regulator of the mitochondrial F-ATP synthase. Here we report the discovery of a form of CyPD lacking the first 10 (mouse) or 13 (human) N-terminal residues (ΔN-CyPD), a protein region with species-specific features. NMR studies on recombinant human full-length CyPD (FL-CyPD) and ΔN-CyPD form revealed that the N-terminus is highly flexible, in contrast with the rigid globular part. We have studied the interactions of FL and ΔN-CyPD with F-ATP synthase at the OSCP subunit, a site where CyPD binding inhibits catalysis and favors the transition of the enzyme complex to the permeability transition pore. At variance from FL-CyPD, ΔN-CyPD binds OSCP in saline media, indicating that the N-terminus substantially decreases the binding affinity for OSCP. We also provide evidence that calpain 1 is responsible for generation of ΔN-CyPD in cells. Altogether, our work suggests the existence of a novel mechanism of modulation of CyPD through cleavage of its N-terminus that may have significant pathophysiological implications.

Dynamics modeling and analysis of a down-hole drill string multibody system based on the absolute coordinate formulation

Abstract Drilling system dynamics is the basis of studying the interaction between components in drilling process, which needs to solve many difficult problems such as geometric nonlinear dynamics of drill string, contact between drill string and wellbore, solving timeliness and so on. The existing research on establishing dynamic unit of local drilling tool structure has low solution efficiency, and it is difficult to meet the requirements of directional trajectory control and drilling speed increase analysis efficiently. Dynamics model of a downhole drill string system is established by using the multibody system dynamics method in this study. The natural coordinate formulation and the absolute nodal coordinate formulation are adopted to describe the rigid parts and the flexible beams, respectively. The presented model can be used to analyze the dynamic characteristics of the drill string system and the interaction between the drill string and the environment such as the wellbore and rocks in the drilling process. Finally, through comparative analysis with on-site test data, the correctness of the multibody dynamic model of the drill string system established in this paper was preliminarily verified.

Development, implementation, and evaluation of a 3D‐printed high‐fidelity pediatric mannequin with expected hard‐to‐intubate airway

AbstractClinical simulation is fundamental for the healthcare staff to learn and enhance their procedural skills without causing harm to the patients. Despite its importance, in literature appears a deficiency of pediatric pathological mannequins, especially those simulating difficult airway management due to the obstruction of the passage of tubes, fiberscopes, or catheters. Given the importance of simulating complex scenarios in the medical staff's training, the authors decided to realize a modular high‐fidelity pathological mannequin with nasal access using reverse engineering and additive manufacturing techniques within T3Ddy, a joint laboratory between Meyer Children's Hospital of Florence and the Department of Industrial Engineering of the University of Florence. The mannequin is developed from diagnostic images of a significant 30‐month‐old polymalformative patient also affected by Pierre‐Robin syndrome modifying the tracheobronchial tree to reproduce an abnormal status. Rigid parts and silicone cast molds are manufactured using 3D‐printed ABS/ASA while platinum‐cure‐silicones are used for the soft ones. Meyer's anesthesiologists collaborated to the realization providing feedback during design and production. The device is evaluated with a 5‐point Likert scale questionnaire and results in a useful tool for the training of procedural skills related to difficult intubation as its realism, anatomical geometry, and tactic feedback are positively evaluated.

Utilization of the Resonance Behavior of a Tendon-Driven Continuum Joint for Periodic Natural Motions in Soft Robotics

Continuum joints use structural elastic deformations to enable joint motion, and their intrinsic compliance and inherent mechanical robustness are envisioned for applications in which the robot, the human, and the environment need to be safe during interaction. In particular, the intrinsic compliance makes continuum joints a competitor to soft articulated joints, which require additional integrated spring elements. For soft articulated joints incorporating rigid and soft parts, natural motions have been investigated in robotics research to exploit this energy-efficient motion property for cyclic motions, e.g., locomotion. To the best of the author’s knowledge, there is no robotic system to date that utilizes the natural motion of a continuum joint under periodic excitation. In this paper, the resonant behavior of a tendon-driven continuum joint under periodic excitation of the torsional axis is experimentally investigated in a functional sense. In the experiments, periodic inputs are introduced on the joint side of a tendon driven continuum joint with four tendons. By modulating the pretension of the tendons, both the resonant frequency and the gain can be shifted, from 3 to 4.3 Hz and 2.8 to 1.4, respectively, in the present experimental setup. An application would be the rotation of a humanoid torso, where gait frequencies are synchronized with the resonant frequency of the continuum joint.

Allowance distribution and parameters optimization for high-performance machining of low rigidity parts in multistage machining processes

Allowance distribution and parameters optimization for high-performance machining of low rigidity parts in multistage machining processes

A Multi‐layer Solver for XPBD

AbstractWe present a novel multi‐layer method for extended position‐based dynamics that exploits a sequence of reduced models consisting of rigid and elastic parts to speed up convergence. Taking inspiration from concepts like adaptive rigidification and long‐range constraints, we automatically generate different rigid bodies at each layer based on the current strain rate. During the solve, the rigid bodies provide coupling between progressively less distant vertices during layer iterations, and therefore the fully elastic iterations at the final layer start from a lower residual error. Our layered approach likewise helps with the treatment of contact, where the mixed solves of both rigid and elastic in the layers permit fast propagation of impacts. We show several experiments that guide the selection of parameters of the solver, including the number of layers, the iterations per layers, as well as the choice of rigid patterns. Overall, our results show lower compute times for achieving a desired residual reduction across a variety of simulation models and scenarios.

Simultaneous Optimization of Discrete and Continuous Parameters Defining a Robot Morphology and Controller.

The morphology and controller design of robots is often a labor-intensive task performed by experienced and intuitive engineers. Automatic robot design using machine learning is attracting increasing attention in the hope that it will reduce the design workload and result in better-performing robots. Most robots are created by joining several rigid parts and then mounting actuators and their controllers. Many studies limit the possible types of rigid parts to a finite set to reduce the computational burden. However, this not only limits the search space, but also prohibits the use of powerful optimization techniques. To find a robot closer to the global optimal design, a method that explores a richer set of robots is desirable. In this article, we propose a novel method to efficiently search for various robot designs. The method combines three different optimization methods with different characteristics. We apply proximal policy optimization (PPO) or soft actor-critic (SAC) as the controller, the REINFORCE algorithm to determine the lengths and other numerical parameters of the rigid parts, and a newly proposed method to determine the number and layout of the rigid parts and joints. Experiments with physical simulations confirm that when this method is used to handle two types of tasks-walking and manipulation-it performs better than simple combinations of existing methods. The source code and videos of our experiments are available online (https://github.com/r-koike/eagent).

On the glow of cremated remains: long-lived green photo-luminescence of heat-treated human bones.

The long-lived green luminescence of human bone (that has been heated to 600°C for a short duration) is attributed to a carbon quantum dot material (derived from collagen) encapsulated and protected by an inorganic matrix (derived from bone apatite) and is more intense in dense rigid and crystalline parts of (healthy) human bones. The strong collagen-apatite interaction results (upon decomposition) in a protective inorganic environment of the luminescent centers allowing long-lived triplet-based emission of a carbon (quantum) dot-like material at room temperature, as well as resilience against oxidation between 550 and 650°C. The graphitic black phase (obtained upon heating around 400°C) is a precursor to the luminescent carbon-based material, that is strongly interacting with the crystalline inorganic matrix. Human bone samples that have been heated to 600°C were subjected to steady-state and time-resolved spectroscopy. Excitation-emission matrix (EEM) luminescence spectroscopy revealed a broad range of excitation and emission wavelengths, indicating a heterogeneous system with a broad density of emissive states. The effect of low temperature on the heat-treated bone was studied with Cryogenic Steady State Luminescence Spectroscopy. Cooling the bone to 80K leads to a slight increase in total emission intensity as well as an intensity increase towards to red part of the spectrum, incompatible with a defect state model displaying luminescent charge recombination in the inorganic matrix. Time-resolved spectroscopy with an Optical Multichannel Analyzer (OMA) and Time Correlated Single Photon Counting (TCSPC) of these samples showed that the decay could be fitted with a multi-exponential decay model as well as with second-order decay kinetics. Confocal Microscopy revealed distinct (plywood type) structures in the bone and high intensity-fast decay areas as well as a spatially heterogeneous distribution of green and (fewer) red emissive species. The use of the ATTO 565 dye aided in bone-structure visualization by chemical adsorption. Conceptually our data interpretation corresponds to previous reports from the material science field on luminescent powders.

A water strider-inspired intestinal stent actuator for controllable adhesion and unidirectional biofluid picking

Soft-bodied aquatic organisms exhibit extraordinary navigation and mobility in liquid environments which inspiring the development of biomimetic actuators with complex movements. Stimulus-responsive soft materials including hydrogels and shape-memory polymers are replacing traditional rigid parts that leading to dynamic and responsive soft actuators. In this study, we took inspiration from water strider to develop a biomimetic actuator for targeted stimulation and pH sensing in the gastrointestinal tract. We designed a soft and water-based Janus adhesive hydrogel patch that attaches to specific parts of the intestine and responds to pH changes through external stimulation. The hydrogel patch that forms the belly of the water strider driver incorporates an inverse opal microstructure that enables pH responsive behavior. The hydrogel patch on the water strider's leg uses a sandwich structure of Cu particles to convert light into heat and bend under infrared light to mimic the water strider's leg simulating the efficient and steady movement of the water strider's leg which transporting the biological fluid in one direction. This miniature bionic actuator demonstrates controlled adhesion and unidirectional biofluid delivery capabilities, proving its potential for targeted stimulus response and pH sensing in the gastrointestinal tract, thus opening up new possibilities for medical applications in the growing field of soft actuators.

Miscibility Studies of Bismesogen CBnCB Forming Nematic Twist-Bend Phase with Cyanobiphenyls nCB.

This work aims to determine how the nematic twist-bend phase (NTB) of bismesogens containing two rigid parts of cyanobiphenyls connected with a linking chain containing n = 7, 9, and 11 methylene groups behaves in mixtures with structurally similar cyanobiphenyls nCB, n = 4-12, 14. The whole phase diagrams are presented for the CB7CB-nCB system. For the other systems, CB9CB-nCB and CB11CB-nCB, only curves corresponding to NTB-N phase transition are presented. Based on the temperature-concentration range of the existence of NTB phase, it was established that an increase in the alkyl chain length of CBnCB causes an increase in the stability of the NTB phase. But surprisingly, an increase in the alkyl chain length of nCB compounds does not change the slope of the NTB-N equilibrium line on phase diagrams. It is slightly bigger when the nCB compound has the same length of alkyl chain as the length of the linking group of a bismesogen. XRD studies were carried out for two mixtures.

A Cost-Effective Approach to Creating Large Silicone Rubber Molds Using Advanced Rigid Polyurethane Foam.

In practical applications, polyurethane (PU) foam must be rigid to meet the demands of various industries and provide comfort and protection in everyday life. PU foam components are extensively used in structural foam, thermal insulation, decorative panels, packaging, imitation wood, and floral foam, as well as in models and prototypes. Conventional technology for producing PU foam parts often leads to defects such as deformation, short shots, entrapped air, warpage, flash, micro-bubbles, weld lines, and voids. Therefore, the development of rigid PU foam parts has become a crucial research focus in the industry. This study proposes an innovative manufacturing process for producing rigid PU foam parts using silicone rubber molds (SRMs). The deformation of the silicone rubber mold can be predicted based on its wall thickness, following a trend equation with a correlation coefficient of 0.9951. The volume of the PU foam part can also be predicted by the weight of the PU foaming agent, as indicated by a trend equation with a correlation coefficient of 0.9824. The optimal weight ratio of the foaming agent to water, yielding the highest surface hardness, was found to be 5:1. The surface hardness of the PU foam part can also be predicted based on the weight of the water used, according to a proposed prediction equation with a correlation coefficient of 0.7517. The average surface hardness of the fabricated PU foam part has a Shore O hardness value of approximately 75. Foam parts made with 1.5 g of water added to 15 g of a foaming agent have the fewest internal pores, resulting in the densest interior. PU foam parts exhibit excellent mechanical properties when 3 g of water is added to the PU foaming agent, as evidenced by their surface hardness and compressive strength. Using rigid PU foam parts as a backing material in the proposed method can reduce rapid tool production costs by about 62%. Finally, an innovative manufacturing process for creating large SRMs using rigid PU foam parts as backing material is demonstrated.

Soft lenses with large focal length tuning range based on stacked PVC gel actuators

A novel tunable lens with large focal length change and driven by stacked polyvinyl chloride (PVC) gel actuators is designed and characterized in this study. The lens rigid parts are 3D-printed and commercially available, whereas the PVC gel membrane is in volume production. Under electrical actuation, the lens attains focal length ranges from 30 to 217 mm within 400 V. A manual regulating mechanism is proposed for the finished lens that dexterously adjusts the initial focus and focal length ranges. In the compound actuation mode, large focus variation over 950% is achieved within 250 V. Under 250 V step input, the lens exhibits practical response time around 291 ms. Focal length tuning ability of the lens is also demonstrated by capturing the images of objects placed in different positions. This tunable lens is promising for various smart optics.

Design, modeling and optimization of an adhesively bonded ring joint with U-section for ceramic cylindrical pressure hull of deep-sea underwater vehicles

The brittleness of ceramic increases the risk of damage or collapse when the ceramic cylindrical pressure hull is directly connected with a rigid part, especially under high hydrostatic pressure. To solve the above problem, this paper systematically explores the design, modeling and optimization of an adhesively bonded ring joint with U-section (ABRJ-U) to avoid the direct connection of the ceramic hull of a small hadal glider, Petrel, with the hemispherical metal end caps. The ABRJ-U is comprised of a U-shaped metal ring, a gasket, and epoxy adhesive layer. To optimize the design parameters, a mechanical model of ABRJ-U is established. The stress tests prove that the model has better efficiency in optimization, but lowered accuracy compared with regular finite element method. Considering the difficulty of obtaining a more accurate theoretical model, the optimization efficiency of regular finite element method is selected for further improvement by integrating the response surface methodology and multi-objective genetic algorithm. According to the optimization results, our optimization method considers the stress calibration of both the adhesive and gasket, simultaneously achieving a 20.8% reduction in the mass of ABRJ-U. The proposed methods also provide valuable reference for the design, modeling, and optimization of other bonded joints.

Discontinuous Deformation Monitoring of Smart Aerospace Structures Based on Hybrid Reconstruction Strategy and Fiber Bragg Grating.

A hybrid enhanced inverse finite element method (E-iFEM) is proposed for real-time intelligent sensing of discontinuous aerospace structures. The method can improve the flight performance of intelligent aircrafts by feeding back the structural shape information to the control system. Initially, the presented algorithm combines rigid kinematics with the classical iFEM to discretize the aerospace structures into elastic parts and rigid parts, which will effectively overcome structural complexity due to fluctuating bending stiffness and a special aerodynamic section. Subsequently, the rigid parts provide geometric constraints for the iFEM in the shape reconstruction method. Meanwhile, utilizing the Fiber Bragg grating (FBG) strain sensor to obtain real-time strain information ensures lightweight and anti-interference of the monitoring system. Next, the strain data and the geometric constraints are processed by the iFEM for monitoring the full-field elastic deformation of the aerospace structures. The whole procedure can be interpreted as a piecewise sensing technology. Overall, the effectiveness and reliability of the proposed method are validated by employing a comprehensive numerical simulation and experiment.

Numerical Investigation on the Spatiotemporal Correlation between Hydraulic Loss and Vortex at Turbine Mode of a Pump-turbine

Abstract Hydraulic loss and vortex analysis are two most widely-used methods investigating flow characteristics from macroscopic view and microscopic view respectively although the correlation between these two methods are still not fully clarified. Based on kinetic energy equation and Boussinesq hypothesis, hydraulic loss is resulted from the joint work of the dissipation loss and the transportation loss in flow domain while vorticity can be further divided into local rigid rotational part and deformational part with the help of the newly proposed concept Liutex. Thereafter, enstrophy as well as vorticity transport intensity is selected as the count part of hydraulic loss through dimensional analysis. Finally, the spatial correlation between hydraulic loss and vortex evolution in small guide vane opening at turbine mode is analyzed with the help of SST k–ω model and the temporal correlation at runaway point is analyzed through DES model. For spatial correlation, the dissipation loss and transportation loss are mainly caused by the deformational enstrophy Ω S and the rigid vorticity transport intensity T R , respectively. For temporal correlation, the correlation order nearly remains unchanged while the degree of correlation decreases to some extent. Based on our work, the hydraulic loss caused by different structure of vortex can be quantified and compared.

APPLICATION OF TOPOLOGY OPTIMIZATION ON A 3D-PRINTED SHELF BRACKET

In this study, the topology optimization approach was adopted to reduce the material used in manufacturing. Specifically, the mass optimization technique was deemed suitable. Mass optimization eliminates the parts that don't affect a bracket’s overall strength while under load, resulting in weight reduction and material savings. Two shelf brackets were designed to test this theory and were subjected to mass optimization. A static structural analysis of this optimized model was carried out to confirm the optimization findings. These designs were then manufactured using the 3D-printing process. The yield points were next determined by performing a uniaxial tensile test on the shelf brackets. The outcome of the tests was subsequently compared with the simulation results, and a cost analysis model was created as an output. Ultimately, a reduction of 70% in mass was achieved with acceptable structural strength. In related optimization studies, the connecting part of an unmanned aerial vehicle's landing gear has been optimized resulting in fuel savings. The theory that topology optimization may be used to make both light and stiff parts at the same time has been proven by the results of this research as well as other studies that have been done on the same topic.

A piecewise inverse finite element method for shape sensing of the morphing wing fishbone

The shape sensing technology plays a significant role in enhancing the structural performance and flight efficiency of the morphing aircraft by providing feedback to actuation and control systems in real time. The inverse finite element method (iFEM) is a fast, accurate, and robust shape-sensing method based on in-situ surface strain measurements. However, the conventional iFEM becomes less effective when applied to real engineering structures. Thus, this paper proposes a piecewise iFEM (P-iFEM) based on a two-node inverse Hermite beam element (iHB2) for the load-bearing structure of the morphing wing. The P-iFEM method discretizes the structure into a combination of rigid and elastic parts, based on the geometry of the structure when assembling the inverse elements. The Hermite polynomial shape function in iHB2 is adopted to increase the reconstruction efficiency, as only one degree of freedom of deflection is required to achieve the C1-continuity to reconstruct the displacement fields. The high accuracy and efficiency of the proposed method are validated with a numerical fishbone model. Finally, the proposed method is applied to a fishbone structure of a real adaptive deformed wing with high accuracy.

KPA-Tracker: Towards Robust and Real-Time Category-Level Articulated Object 6D Pose Tracking

Our life is populated with articulated objects. Current category-level articulation estimation works largely focus on predicting part-level 6D poses on static point cloud observations. In this paper, we tackle the problem of category-level online robust and real-time 6D pose tracking of articulated objects, where we propose KPA-Tracker, a novel 3D KeyPoint based Articulated object pose Tracker. Given an RGB-D image or a partial point cloud at the current frame as well as the estimated per-part 6D poses from the last frame, our KPA-Tracker can effectively update the poses with learned 3D keypoints between the adjacent frames. Specifically, we first canonicalize the input point cloud and formulate the pose tracking as an inter-frame pose increment estimation task. To learn consistent and separate 3D keypoints for every rigid part, we build KPA-Gen that outputs the high-quality ordered 3D keypoints in an unsupervised manner. During pose tracking on the whole video, we further propose a keypoint-based articulation tracking algorithm that mines keyframes as reference for accurate pose updating. We provide extensive experiments on validating our KPA-Tracker on various datasets ranging from synthetic point cloud observation to real-world scenarios, which demonstrates the superior performance and robustness of the KPA-Tracker. We believe that our work has the potential to be applied in many fields including robotics, embodied intelligence and augmented reality. All the datasets and codes are available at https://github.com/hhhhhar/KPA-Tracker.

Topology optimization for rigid and compliant hybrid mechanisms

This paper proposes a topology optimization method integrating the variable trajectory constraints to design rigid and compliant hybrid mechanisms. The variable trajectory constraints are distributed in the design domain and are uniformly modeled by nonlinear spring model. Each of the variable trajectory constraints has an active or inactive state and different states map various mechanical properties of the nonlinear springs. The nonlinear relation between force and displacement of the spring is formulated. A new group of design variables denoting the states of the springs is introduced into the traditional density-based topology optimization model. The design variables representing the element density of the continuum structure and the states of the variable trajectory constraints are uniformly penalized to avoid intermediate values in order to obtain a physically realizable mechanism. Sensitivity analysis is performed by the adjoint equation method. To demonstrate the versatility and the generality of the proposed method, the typical numerical examples including linear, spline and circular trajectory constraints were implemented. The numerical comparisons between the nonlinear spring model and the actual trajectory constraints verify the accuracy. The proposed method expands the application of topology optimization and can be extensively employed to design the mechanisms integrating both the compliant members and rigid parts.

Design and analysis of a contact-aided flexure hinge (CAFH) with variable stiffness

This paper presents a novel contact-aided flexure hinge (CAFH) with variable stiffness, which consists of a contact-aided segment, a flexible segment and a rigid part. The proposed CAFH can facilitate a compact design and provide an alternative for stiffness-variable designs under any loading conditions. With a mortise-tenon structure, the CAFH is trivially affected by friction. The design and deformation procedures of the CAFH are described in detail, followed by its theoretical kinetostatic modeling using the chained beam-constraint model. The deformation of all segments is considered in the kinetostatic model, which expands the space of design parameters for stiffness-variable designs. Then, the accuracy of the theoretical model and the variable stiffness design are verified by nonlinear finite element analysis (FEA) and experimental tests. In term of stiffness, the maximum relative errors of the theoretical model are 0.76% in Stage 1 and 0.70% in Stage 2, as compared with FEA, respectively. Further, the parameter sweep is carried out, followed by sensitivity analysis to identify the main test error sources. Finally, the multi-material scenarios are investigated preliminarily, and some outlooks are discussed.