Mechanical Engineering

Bioactive glasses are widely utilized to regenerate bone tissue and aid bonding of orthopedic implants. Forming composites of bioglass with bioactive polymers allow the mechanical properties and biological response to be tailored. Although several methods for creating bioglass–polymer composites exist, they require dissolution of the polymer, controlled phase separation, and appear to have an upper limit of ∼30 vol.% bioglass. Cold sintering is a novel technique for the densification of ceramics and glasses which utilizes a liquid phase and pressure to allow the production of components at reduced temperatures. We demonstrate that cold sintering (100°C) of Bioglass 45S5 powder produced via flame spray pyrolysis and the fabrication of Bioglass 45S5–polymer composites. Assessment of the in vitro response revealed that composites were not cytotoxic. Solid‐state 31P and 29Si MAS NMR studies of the silicon and phosphorus speciation in the glass powder, as‐received, wetted, and sintered s...

This report examines the current status and the future directions of the field of nanomagnetism and assesses the ability of hard X-ray synchrotron facilities to provide new capabilities for making advances in this field. The report first identifies major research challenges that lie ahead in three broadly defined subfields of nanomagnetism: confined systems, clusters and complex oxides. It then examines the relevant experimental capabilities that are currently available at hard X-ray synchrotron light sources, using the Advanced Photon Source (APS) at Argonne as an example. Finally, recommendations are made for future development in X-ray facilities that will enhance the study of nanomagnetism, including new experimental directions, modifications that would enable in situ sample preparation, and measurements at high magnetic fields and/or low temperatures. In particular, in situ sample preparation is of high priority in many experiments, especially those in the area of surface magnetism.

We review the phenomenology of exchange bias and related effects, with emphasis on layered antiferromagnetic (AFM)-ferromagnetic (FM) structures. A compilation of materials exhibiting exchange bias and some of the techniques used to study them is given. Some of the applications of exchange bias are discussed. The leading theoretical models are summarized. Finally some of the factors controlling exchange bias as well as some of the unsolved issues associated with exchange bias are discussed.

warm robotics systems are characterized by decentralized control, limited communication between robots, use of local information, and emergence of global behavior. Such systems have shown their potential for flexibility and robustness [1]-[3]. However, existing swarm robotics systems are by and large still limited to displaying simple proof-of-concept behaviors under laboratory conditions. It is our contention that one of the factors holding back swarm robotics research is the almost universal insistence on homogeneous system components. We believe that swarm robotics designers must embrace heterogeneity if they ever want swarm robotics systems to approach the complexity required of real-world systems. To date, swarm robotics systems have almost exclusively comprised physically and behaviorally undifferentiated agents. This design decision has its roots in ethological models of self-organizing natural systems. These models serve as inspiration for swarm robotics system designers, but are often highly abstract simplifications of natural systems and, to date, have largely assumed homogeneous agents. Selected dynamics of the systems under study are shown to emerge from the interactions of identical system components, ignoring the heterogeneities (physical, spatial, functional, and informational) that one can find in almost any natural system. The field of swarm robotics currently lacks methods and tools with which to study and leverage the heterogeneity that is present in natural systems. To remedy this deficiency, we propose swarmanoid, an innovative swarm robotics system composed of three different robot types with complementary skills: foot-bots are small autonomous robots specialized in moving on both even and uneven terrains, capable of self-assembling and of transporting objects or other robots; hand-bots are autonomous robots capable of climbing some vertical surfaces and manipulating small objects; and eye-bots are autonomous flying robots that can attach to an indoor ceiling, capable of analyzing the environment from a privileged position to S

Swarms of indoor flying robots are promising for many applications, including searching tasks in collapsing buildings, or mobile surveillance and monitoring tasks in complex man-made structures. For tasks that employ several flying robots, spatial-coordination between robots is essential for achieving collective operation. However, there is a lack of on-board sensors capable of sensing the highlydynamic 3-D trajectories required for spatial-coordination of small indoor flying robots. Existing sensing methods typically utilise complex SLAM based approaches, or absolute positioning obtained from off-board tracking sensors, which is not practical for real-world operation. This paper presents an adaptable, embedded infrared based 3-D relative positioning sensor that also operates as a proximity sensor, which is designed to enable inter-robot spatial-coordination and goal-directed flight. This practical approach is robust to varying indoor environmental illumination conditions and is computationally simple. Relative positioning sensing • Indoor flying robots • Collective operation • 3D sensor • Spatial-coordination • Proximity sensing J.F.R. developed the concept of relative positioning sensing for enabling goal-directed flight on indoor collective flying robots, wrote the manuscript, developed the sensor hardware/firmware, developed the calibration tools and characterised the sensor. T.S. extensively contributed to the sensor firmware and characterisation. J.-C.Z. and D.F. conceived and directed the project sponsoring the work described in the article. They also provided continue support and feedback towards reaching the attained results.

The impact of reducing friction losses on the fuel consumption and CO 2 emissions was investigated through computational simulation of piston ring dynamics. Experimentally determined cylinder bore surface finishes, low viscosity oil and ring coatings response to oil additives were used as simulation inputs. Oil viscosity grades from SAE10W-40 to SAE0W-4 were considered. 3D roughness measurements of regular and "mirror-like" cylinder bores were used to estimate the flow factors coefficients for the average Reynolds equation and asperity contact stiffness. The combination of smooth cylinder bores, low viscosity oils with appropriate additives promoted ring pack FMEP reductions of up to 66% at part load and WOT with consequent CO 2 reductions of up to 10% at part load and 1.5% at WOT.

We propose a direct method to compute the steady state response to cyclic loadings of elastoplastic solids with Armstrong-Frederick nonlinear kinematic hardening. The algorithm obtains the elastoplastic asymptotic cyclic response without true incremental integration. The method performs much faster than using the step-by-step procedure until stabilization. Including nonlinear kinematic hardening in this asymptotic analysis allows modeling the ratcheting phenomenon, which is important in safety assessment of structures under variable loadings. To the best of the authors knowledge, this is the first direct procedure for computing the asymptotic cyclic response of elastoplastic solids with nonlinear kinematic hardening.

In order to estimate the seismic demand by using the nonlinear static procedure, different approximate methods have been developed. One of the most useful methods is called displacement coefficient method (DCM), which is based on some modification factors. One of these coefficients denoted 1 C , concerns the inelastic deformation ratio and usually depends on either the yield-strength reduction factor or the ductility factor. In general the evaluation of the inelastic deformation ratio is based on the response of single degree of freedom (SDOF) systems, where the response of the structure is mainly controlled by the fundamental mode, knowing that the inelastic deformation ratio will not capture the contribution of higher modes in the overall structural response. A developed theoretical approach with the aim of estimating the inelastic deformation ratio for structures, considering contribution of higher modes of vibration, is introduced. In this assessment, the normalized yield strength coefficient (η) and the post-to-preyield stiffness ratio (α) are key factors. The results are compared to the uncoupled modal response history analysis (UMRHA) procedure and some existing formulations for a nine story building subjected to the El Centro 1940 ground motion. It appears that the new theoretical approach leads to enough accurate estimation of the inelastic deformation ratio compared to the UMRHA one.

Measuring the velocity of an arrow in flight is a task of interest to archers, but can be difficult without specialized equipment. We show how accurate velocity measurements can be made by recording the sound made by the arrow as it travels over one or more microphones. Useful recordings can be made with a data acquisition system or with the sound recorder built into most PC operating systems. Estimates of the drag coefficient of different arrows can be made using several microphones to record each shot.

The purpose of this research is to highlight how the diffusion of innovative new RET's renewable energy technologies, such as solar and wind, in Western Balkan countries as transition economies, could have a significant impact on reaching the EU Green Deal energy transition targets of "no net emissions of greenhouse gases by 2050" and the Paris Agreement to cut greenhouse gas emissions (GHG) and transition of these economies to low-carbon development paths [1]. The purpose of this analysis is to present sufficient evidence regarding the reliability and viability of the adapted renewable energy technologies, specifically solar PV and wind technologies. Additionally, it aims to assess the diffusion of innovation in these technologies and predict the extent to which the growth of these innovative technologies is contributing to the achievement of national energy transition objectives for Western Balkan countries. This research will utilize diffusion models dual phase logistic (bi-logistic) and Gompertz for the objective of analysing the adoption and forecasting RET's wind and solar PV, since it has been shown to be effective in previous research studies [2]. The proposed methodology will be utilized to examine the cumulative capacity (measured in megawatts MW) of renewable energy technologies (RETs) wind and solar PV throughout the previous ten-year period for WB6 and from 1990 for Germany. The utilization diffusion models simulation scenarios will enable the projection of solar PV and wind technologies penetration up until the year 2035 and 2050.

The test procedure for characterizing the tribological behavior of lubricants and materials for the system "piston ring/cylinder liner" outside of engines is now operational and validated. The test parameters presented in this paper (F N ¼50 N; v ¼ 0.3 m/s, s ¼ 24 km) may act only as an indicator and should be used to the tasks regarded. It allows the check prior expensive engine testing, if a tribomaterial, tribocouple or new lubricant will reach a satisfactory engine performance. The introduction of piston ring segments and cylinder liner as specimen into the test rig as well as the volumetric wear determined by means of stylus profilometry represented a big step forward in order to increase the transferability of "tribotests" to engine tests on an acceptable level.

Hardmetal coatings prepared by high velocity oxy-fuel (HVOF) spraying represent an advanced solution for surface protection against wear. In the current systematic study the high-temperature oxidation and unidirectional sliding wear in dry and lubricated conditions were studied. Results for a series of experiments on self-mated pairs in dry conditions as part of that work are described in this paper. Coatings with nominal compositions WC-10%Co4%Cr, WC-(W,Cr) 2 C-7%Ni, Cr 3 C 2 -25%NiCr, (Ti,Mo)(C,N)-29%Ni and (Ti,Mo)(C,N)-29%Co were prepared with an ethylene-fuelled DJH 2700 HVOF spray gun. Electrolytic hard chromium (EHC) coatings and bulk (Ti,Mo)(C,N)-15%NiMo (TM10) hardmetal specimens were studied for comparison. The wear behaviour was investigated at room temperature, 400 and 600 • C. For the coatings sliding speeds were varied in the range 0.1-1 m/s for a wear distance of 5000 m and a normal force of 10 N. In some cases the WC-and (Ti,Mo)(C,N)-based coatings showed total wear rates (sum of wear rates of the rotating and stationary samples) of less than 10 -6 mm 3 /Nm, i.e., comparable to values typically measured under mixed/boundary conditions. Coefficients of friction above 0.4 were found for all test conditions. The P × V values as an engineering parameter for coating application are discussed. The microstructures and the sliding wear behaviour of the (Ti,Mo)(C,N)-based coatings and the (Ti,Mo)(C,N)-15%NiMo hardmetal are compared.

Two new substoichiometric titania (TiO x ) coatings designated for cylinder liner application were deposited on specimen of grey cast iron GG20HCN with high carbon content by plasma spraying. First, a Ti n O 2n-1 coating was prepared by atmospheric plasma spraying (APS) using a sintered and agglomerated Magnéli-type spray powder. Second a TiO 1.95-x coating was deposited with a vacuum plasma spray (VPS) process using a commercial, fused and crushed TiO 1.95 powder. The tribological behaviour of these coatings under lubricated conditions was compared with uncoated specimen of this grey cast iron. As counter bodies a widespread used APS-sprayed Mo-NiCrBSi piston ring coating (MKP81A ® ), an advanced HVOF-sprayed WC/Cr 3 C 2 -based (MKJet502 ® ) ring coating as well as non-commercial prototype APS-sprayed Ti n O 2n-1 and APSsprayed (Ti,Mo)(C,N) + 23NiMo (TM23-1) coatings were tribotested. The interaction of the pairs with prototype engine oils based on esters and polyglycols were studied under mixed/boundary lubrication using the BAM test method. Lubricants were factory fill engine oils, ester-containing lubricants with low-SAP (sulphur-ash-phosphor) and/or bio-notox properties as well as polyglycole-based lubricants. The ester and polyglycole-based engine oils respond both to bio-no-tox criteria and are polymer-free. They follow different strategies to reduce zinc, phosphorus and sulphur to assure a low ash content. Both TiO x coatings designated for cylinder liners meet or exceed the wear resistance of the grey cast iron with high carbon content when paired with APS-sprayed Ti n O 2n-1 or Mo-NiCrBSi piston ring coatings. Overall, in nearly all pairs the wear rates of the APS Ti n O 2n-1 coating were lower than those of the VPS TiO 1.95-x coating. In order to characterize the tribological behaviour under oil-off, dry-running conditions, additional tests were performed under unlubricated unidirectional sliding conditions at 22 and 400 • C for a sliding speed of 1 m/s against sintered polycrystalline Al 2 O 3 as stationary specimen.

The effects of nickel (Ni) content on the mechanical properties and microstructure evolution in the weld metals of commercial K65 oil and gas pipeline steel were studied. Increase Ni content could significantly improve the strength and low temperature impact toughness (-40 °C and -60 °C) of the weld metal. The above influences of Ni were attributed to the formation of predominant acicular ferrite (AF), at the expense of grain boundary ferrite (GBF), ferrite side plates (FSP) and martensite/austenite (M/A) constituent in weld metal. EBSD results indicated that GBF keeps K-S or N-W relations only with the prior austensite grain that belongs to one side of the grain boundary and the variants belong to the same bain group which always forms low angle boundary. Moreover, the retained austenite as one part of M/A constituent was mainly found in the weld metal with lower Ni content. It indicated that the transformation process could be promoted more completely by the increase of Ni content. The mechanism of the toughness improvement brought by Ni increasing was ascribed to the relatively uniform transformation to final microstructure, which reduces the appearance of GBF and M/A constituents.

A systematic approach to joint state and time-varying parameter estimation for nonlinear systems is proposed in this paper. Applying the sector nonlinearity transformation to both the system nonlinearities and the time-varying parameters, the original system is equivalently rewritten as a Takagi-Sugeno system with unmeasurable premise variables. A joint state and parameter observer whose parameters are designed by solving an LMI optimization problem is then proposed. The target application is a realistic model of an activated sludge wastewater treatment plant, being an uncertain nonlinear system affected by a time-varying parameter.

How were unskilled workers selected and hired in preindustrial labor markets? We exploit records from the rebuilding of St Paul 's Cathedral, London (1672-1748), to analyze the hiring and employment histories of over 1,000 general building laborers, the benchmark category of "unskilled" workers in long-run wage series. Despite volatile demand, St Paul's created a stable workforce by rewarding the tenure of long-standing workers. More senior workers received more days of work each month, preference when jobs were scarce, and the opportunity to earn additional income. We find the cathedral's strategy consistent with reducing hiring frictions and turnover costs. J ust over 350 years ago, St Paul's Cathedral was destroyed in the Great Fire of London. Under the guidance of Sir Christopher Wren, the Cathedral was entirely rebuilt between 1672 and 1711. This pre-industrial mega-project left not only a legacy on the London skyline, but also detailed individual-level records of the employment and remuneration of building laborers. With these records, unparalleled in continuity and scope for this period, we reconstruct and analyze the employment histories of over 1,000 workers employed as general laborers during a 70-year period. We find that St Paul's hiring practices encouraged retention and reduced turnover, giving a core group of laborers more work, priority in rehiring after slowdowns, and access to additional ways to earn. Despite the volatility that characterized pre-industrial labor demand, St Paul's was able to establish a stable workforce by incentivizing tenure and rewarding long-standing laborers. These patterns of organizing worker hiring and retention have not been recognized in earlier studies of early modern labor markets.

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A near-shore oscillating water column (OWC) device with a surging front-wall, which can be conveniently mounted on various cliff-like shores or coastal structures, is proposed to improve the pneumatic efficiency of wave energy extraction. Based on linear potential theory, the interaction between ocean waves and the OWC device is solved by the matched eigenfunction expansion method (MEEM). Auxiliary functions, expanded in orthogonal polynomials, are introduced to approximate the singular behaviors of fluid field in the vicinity of the salient corner. The effects of the dimensions of lip-wall and the stiffness of the spring on the hydrodynamic performances, such as the response amplitude operator (RAO), average inside free-surface elevation, phase difference between the motions of lip-wall and inside free-surface, and optimum conversion efficiency are taken into consideration. The numerical results show that the existence of a freely surging lip-wall can considerably improve the performance of the device over a wider bandwidth, especially for the intermediate and short wavelength regimes, compared with the fixed one.

We address the following sensor selection problem. We assume that a dynamic system possesses a certain property, call it Property D, when a set Γ of sensors is used. There is a cost c A associated with each set A of sensors that is a subset of Γ. Given any set of sensors that is a subset of Γ, it is possible to determine, via a test, whether the resulting system-sensor combination possesses Property D. Each test required to check whether or not Property D holds incurs a fixed cost. For each set of sensors A that is a subset of Γ there is an a priori probability p A that the test will be positive, i.e., the system-sensor combination possesses Property D. The objective is to determine a test strategy, i.e., a sequence of tests, to minimize the expected cost, associated with the tests, that is incurred until a least expensive combination of sensors that results in a system-sensor combination possessing Property D is identified. We determine conditions on the sensor costs c A and the a ...

In discrete-event systems, diagnosis consists in determining in bounded time and with certainty whether a fault has occurred given a sequence of observations . In fact, if some events internal to the system are not observable from outside, then a given observation sequence can correspond to several executions, some of which are faulty and other non-faulty. The simplest formalism for this problem is finite automata, and algorithms were given to check if a given model is diagnosable. However some systems carry an intrinsic ambiguity and the observations are not sufficient for diagnosing faults. Active diagnosis was suggested to overcome this issue . It consists in controlling the system by activating some events, and disabling some others, so that all induced executions can be diagnosed: whether a fault has occurred in the controlled system can be determined by looking at observations. The only objective in the active diagnosis problem is to control the system to make sure that any fault is diagnosed. But the computed controller does not guarantee any other property on the controlled system; for instance, a controller that makes sure that a fault always occurs is a possible solution to active diagnosis since it guarantees diagnosability. Some partial solutions were given, e.g. in , where it is required that the controller guarantees non-faulty behaviors with positive probability. In this internship, we suggest improving the active diagnosis problem to address this issue. We will consider diagnosability as an additional and secondary objective to be taken into account in controller synthesis with a given primary objective. Roughly, the controller should try to satisfy its primary objective, such as trying to avoid faults, and give additional diagnosability guarantees if this is not possible. The proper formalization of this idea is one of the objectives of this internship. For instance, what does it mean for a controller to try to avoid a fault? There are several directions that can be followed. One can explore the possibility of computing controllers that make sure that no fault occurs for a maximal subset of states, while ensuring diagnosability for the rest of the states. One can also formulate the problem in a quantitative way and look for controllers that minimize the time to fault. A third possibility is to use game theoretic notions to compare control strategies: for instance, a controller that ensures a fault immediately is worse than a controller that avoids any fault for k steps, and then possibly allow a fault without forcing it. Several classical notions from game theory, such as rationality, dominance, and regret, can be applied here to capture reasonable controllers. The direction to be explored can be chosen according to the intern's interests.

Abstruct-Fault detection and isolation is a crucial and challenging task in the automatic control of large complex systems. We propose a discrete-event system (DES) approach to the problem of failure diagnosis. We introduce two related notions of diagnosability of DES's in the framework of formal languages and compare diagnosability with the related notions of observability and invertibility. We present a systematic procedure for detection and isolation of failure events using diagnosers and provide necessary and sufficient conditions for a language to be diagnosable. The diagnoser performs diagnostics using online observations of the system behavior; it is also used to state and verify off-line the necessary and sufficient conditions for diagnosability. These conditions are stated on the diagnoser or variations thereof. The approach to failure diagnosis presented in this paper is applicable to systems that fall naturally in the class of DES's; moreover, for the purpose of diagnosis, most continuous variable dynamic systems can be viewed as DES's at a higher level of abstraction. In a companion paper [20], we provide a methodology for building DES models for the purpose of failure diagnosis and present applications of the theory developed in this paper.

A discrete time stochastic feedback control system consisting of a nonlinear plant, a sensor, a controller, and a noisy communication channel between the sensor and the controller is considered. The sensor has limited memory and, at each time, it transmits an encoded symbol over the channel and updates its memory. The controller receives a noise-corrupted copy of the transmitted symbol. It generates a control action based on all its past observations and all its past actions. This control action is fed back to the plant. At each time instant the system incurs an instantaneous cost depending on the state of the plant and the control action. The objective is to choose encoding, memory update, and control strategies to minimize an expected total cost over a finite horizon, or an expected discounted cost over an infinite horizon, or an average cost per unit time over an infinite horizon. A solution methodology for obtaining a sequential decomposition of the global optimization problem is developed. This solution methodology is extended to the case when the sensor makes an imperfect observation of the state of the plant.

The emergence of Industry 4.0 has brought about remarkable technological progressions, leading to substantial transformations in work environments. This has created a globally shared vision that the educational and training systems should be improved to offer high-quality, inclusive, and accessible digital education to develop essential skills and abilities that guarantee job readiness and assimilation into the current labour metamorphoses of era 4.0. In Europe, the reform of education at all levels in response to the concepts of University 4.0 and Education 4.0 is outlined as a key priority. In this regard, outlining the factors for successful inclusive digital education, as well as the barriers to its implementation, is crucial. This paper presents some of the main results of a survey conducted in Bulgaria, Greece, Italy and Latvia, aiming to determine the readiness of universities to provide inclusive Industry 4.0 education.

This paper focuses on a topic that is frequently used nowadays namely 3D printing. The term 3D printing encompasses several manufacturing technologies that build parts layer-by-layer an inconvenience of this process is that the deposition of material takes place in the plane (2D space) then by applying a constant increment on the third axis it is moved to the next plane. The deposition of material is taking part in a 2D space. There are many types of 3D printing such as FDM (fused deposition modeling), SLA (stereolitography), SLS (selective laser sintering), DMLS (direct metal laser sintering), DLP (digital light process), EBM (electron beam melting). Typically these applications involve lowvolumes and complex geometries. Often, components for aerospace and medical applications are ideal candidates for production 3D printing. This paper proposes a new approach to the 3d printing process by using a robotic arm to ensure more than 3 degrees of freedom and deposition paths with spatial orientation. One propose two types of working: nonplanar with the tip normal to the working plane and nonplanar with the tip normal to the trajectory.

Sculptural or painted representations of Surya or the Sun God and temples solely dedicated to him are rare in Kerala, There are a few Sun temples  owned by Brahmin familes and some of which after abandonment came to be renovated and now under collective protection. Most of the sculptures and temples dedicated to him owe their orgins to the late medeival period and some such are being discussed in this paper

A parameter analysis is performed on an analytical penetration model which has been recently developed. Figures are plotted to show how the disturbed zone size, parameters of displacement and stress fields and dynamic section pressure are dependent on soil compressibility, shear strength and mass density. Main results are presented and discussed.

This study presents a solution for the dynamic response of a porous saturated medium to a harmonic motion of a rigid inclusion where an elastic type intermediate layer is located at the interface. The problem has been solved using the Neumann series which terms are obtained by means of recurrence relationships of simple iteration type. To perform regularization we consider every singular integral as an integral in sense of finite part by Hadamard. A modified Shanks transform was used to accelerate the series convergence. The method allows avoid the solution of large system of the linear algebraic equations with densely filled matrix. However, for problems with complicate boundary, which includes segments with large curvature, the requested number of series members sharply increases. The approach is valid for problems which potential satisfied to the Hölder-Lipschitz condition of the first order. Using the proposed approach the problem of a linear harmonic motion of the circular inclusion was investigated and the effect of the frequency on the contact stresses has been studied. It was found that for this specific example, when the vibration frequency increases the maxima of both contact normal stress and porous pressure decrease, while the maximum of the contact shear stress remains almost unchanged.

The elasto-plastic theory of a shallow two bar truss is developed. The behavior of this structural system under tension loading or compression loading is formulated, as well as for reversal loading, where the structure undergoes loading, unloading and reloading. The simple straightforward expressions enable one to correlate the external work to the central displacement and follow the elasto-plastic stresses and strains in the bars along the loading history.

The microstructure and corresponding tensile properties of both plain and Nb-microalloyed grades of ultrathin cast strip (UCS) low alloy steel produced using the CASTRIP Ò process were studied. Both as-cast and hot-rolled strip cast steels with various levels of Nb microalloying were manufactured and investigated in this study. Hot rolling had little effect on the yield strength of Nb microalloyed UCS specimens for a given chemical composition, but resulted in a slightly finer microstructure. The effect of Nb microalloying was significant, and this is attributable to the promotion of finer, tougher austenite transformation products such as bainite and acicular ferrite at the expense of large polygonal ferrite grains. A fine dispersion of Nb solute clusters was observed in all Nb-containing steels following hot rolling, and it is suggested that this also contributes to the observed strengthening.

Multidimensional structure warp-knitted spacer fabrics (WKSFs) are integrated with polyurethane elastomers (PUEs) to fabricate shear-resistant reinforced composite materials, demonstrating a 58% enhancement in shear strength compared to pristine PUEs. We quantitatively evaluated the interface thickness and adhesion between WKSFs and PUEs to assess the influence of the physical and chemical properties of the interface on stress conduction and dispersion. The results demonstrate that the stress transfer efficiency and overall reinforcement are highly dependent on the interface quality and the mesh structure of the WKSFs. Finite-element analysis reveals a multidimensional stress dispersion mechanism within the structure, leading to a more effective stress distribution from a theoretical perspective. The findings provide insights into the stress dispersion in different directions of warp-knitted spacer fabric fibers and offer practical guidelines for designing advanced high-performance, energy absorbing, and shear-resistant materials for applications such as protective systems, structural reinforcement, and energy storage.

The effect of tendons viscoelastic stiffness on the dynamic response of the cat's tibialis anterior muscle under isometric conditions was determined. It was shown that the dynamic response model of the muscle derived under sinusoidal contraction-relaxation in the range of 20-80 % of its maximal isometric tension was not statistically different before and after the disection of the whole distal tendon. It was suggested that under isometric conditions in the force range of 2c-80 % of the maximal, the tendon acts as a very stiff force transmission linkage without significantly modifying the muscle's performance.

Muscle surface displacement is a mechanical event taking place simultaneously with the tension generation at the tendon. The two phenomena can be studied by the surface mechanomyogram signal (MMG) (produced by a laser distance sensor) and the force signal (from a load cell). The aim of this paper was to provide data on the reliability of the laser detected MMG in muscle mechanics research. To this purpose it was veri"ed if the laser detected MMG was suitable to estimate a frequency response in the cat medial gastrocnemius and its frequency response was compared with the one retrieved by the force signal at the tendon level. The force and MMG from the exposed medial gastrocnemius of four cats were analysed. The frequency response was investigated by sinusoidally changing the number of orderly recruited motor units, in di!erent trials, in the 0.4}6 Hz range. It resulted that it was possible to model the force and MMG frequency response by a critically damped second-order system with two real double poles and a pure time delay. On the average, the poles were at 1.83 Hz (with 22.6 ms delay) and at 2.75 Hz (with 38 ms delay) for force and MMG, respectively. It can be concluded that MMG appears to be a reliable tool to investigate the muscle frequency response during stimulated isometric contraction. Even though not statistically signi"cant, the di!erences in the second-order system parameters suggest that di!erent components of the muscle mechanical model may speci"cally a!ect the force or MMG.

Repetitive lifting in the workplace has been identified to be a cause of low back disorders. Epidemiologic data further supports an hypothesis that higher repetition rate (i.e. frequency) is an added risk factor. The objective of this study was to provide experimental data testing the above hypothesis. An in vivo feline model was subjected to 20-min of cyclic lumbar loading at frequencies of 0.1 Hz and 0.5 Hz while monitoring the EMG from the L-3/4-L-5/6 multifidus muscles and the creep at the L-4/5 level. Seven hours of rest were allowed after the cyclic flexion/extension was terminated. During this rest period, a single test cycle was performed every hour to assess recovery of EMG and lumbar creep. The results demonstrate that cyclic lumbar flexion elicits a transient neuromuscular disorder consisting of EMG spasms during the cyclic loading and initial and delayed muscular hyperexcitabilities during the rest period. Cyclic loading at 0.5 Hz resulted in significant (po0:05) increase in the hyperexcitability magnitude and duration during the recovery period. It was concluded that repetitive lumbar loading at fast rates is indeed a risk factor as it induces larger creep in the lumbar viscoelastic tissues which in turn intensify the resulting neuromuscular disorder.

Objectives. To determine the rest duration required for full recovery of re¯exive muscular activity and laxity/creep induced in the lumbar viscoelastic structures (e.g., ligaments, discs, etc.) after 50 min of cyclic loading, and to develop a model describing such recovery. Background. It is well established that steady, cyclic or vibratory loading of the lumbar spine induces laxity/creep in its viscoelastic structures. It was also shown that such viscoelastic creep does not fully recover when subjected to rest equal in duration to the loading period. Rest periods of 24 h, however, were more than sucient to allow full recovery. The exact period of time allowing full recovery of viscoelastic laxity/creep, and its pattern is not known. It is also not known what is the duration required for full recovery of re¯exive muscular activity lost due to the laxity/creep induced in the spine during cyclic loading. Methods. The lumbar spine of `in vivo' feline preparations was subjected to 50 min of 0.25 Hz cyclic loading applied via the L-4/5 supraspinal ligament. At the end of the loading period the spine was subjected to prolonged rest, interrupted by a single cycle loading applied hourly for measurement purposes until the laxity was fully recovered (>90%). Re¯exive EMG activity was recorded with wire electrodes from the L-1±L-7 multi®dus muscles. A biexponential model was ®tted to the load and EMG recorded in the recovery period in order to represent viscous and elastic components of structures with dierent architecture (e.g., disc vs. ligament). Results. Full recovery of the laxity induced by 50 min of cyclic loading at 0.25 Hz required 7 h and was successfully ®tted with a biexponential model. Similarly, EMG activity was fully recovered in 4 hours, and often exceeded its initial value during the following 3 h. Conclusions. Full recovery of laxity induced in the lumbar viscoelastic structures by a given period of cyclic loading requires rest periods, which are several folds longer than the loading duration. Similarly, re¯exive muscular activity requires 4 h of rest in order to be restored. Meanwhile, signi®cant laxity can be present in the joints, exposing the spine to potential injury and low back pain. Increased EMG activity at the end of the recovery period may indicate that pain was possibly induced in the spinal structures, inducing hyperexcitability of the muscles during passive loading. Although the data was derived from a feline model, and its extrapolation to the human model is not straightforward, the general pattern of decreasing re¯exive muscular activity with cyclic loading is expected in both species. Therefore, workers who subject their spine to periods of cyclic loading may be exposed to prolonged periods of laxity beyond the neutral zone limits, without protection from the muscles and therefore the risk of possible injury and low back pain. Pain and muscle hyperexcitability could also be a factor associated with cyclic loading, being expressed several hours after work was completed.

Objective. To determine if creep developed in the lumbar viscoelastic tissues during a period of static flexion elicited changes in the muscular responses of the flexion-relaxation phenomenon. Background. Static lumbar flexion is a risk factor in workers, yet the physiological biomechanical and histological processes active in the evolution of the consequent low back disorder were not demonstrated experimentally. Controlled animal studies show that static lumbar flexion develops creep in the associated viscoelastic tissues and elicits spasms and modification of muscle function. Such neuromuscular changes are to be investigated in this study while assessing normal human subjects via the flexion-relaxation phenomenon. Methods. Male and female subject groups performed three bouts of lumbar flexion-extension before and after a 10 min period of static lumbar flexion. The surface electromyographic from the erector spinae muscles as well as flexion angle were recorded. The angle in which electromyographic diminished during flexion and initiated during extension was determined and subjected to ANOVA ANOVA with repeated measures to determine any significant changes in the flexion-relaxation response. Results. The erector spinae were active through a significantly larger angle during flexion and initiated activity significantly earlier during extension after static flexion. Females demonstrated more pronounced changes than males. EMG amplitude did not change significantly. Spasms were recorded in more than half of the subjects during the static flexion period. Conclusions. Creep developed during a short static lumbar flexion elicited significant changes in the muscular activity pattern of the flexion-relaxation phenomenon. The muscles seem to compensate for the loss of tension in the lumbar viscoelastic tissues, while spasms suggest that some micro-damage was incurred to the viscoelastic tissues. Static lumbar flexion is shown experimentally as an activity that constitutes an occupational risk factor for the development of low back disorder.

Within this research, rheological analysis and thermal properties of two component feedstock based on ceramic and metallic powders are carried out to understand their flow behaviour. Scanning electron microscopy (SEM), Differential Scanning Calorimeter (DSC), Thermogravimetric (TGA) and Capillary Rheometer were employed to set up optimum conditions for moulding, debinding and sintering process. DSC results defined the melting point for both backbone binder components were recorded at the same point, 55 o C. TGA results showed total weight loss of alumina and stainless steel feedstock was 17.4% and 6.43% respectively. Throughout rheological analysis, both feedstock exhibit pseudoplastic behaviour as viscosity reduce with the increase of shear rate, with shear sensitivity index less than 1. The activation energy, E for alumina and stainless steel feedstock had E values in the range of 101.93 -2934.3 J/mol and 7132.3 -10436 J/mol, respectively. For both alumina and stainless steel feedstock, high mouldability index occurred at the highest temperature with shear rate of 96 s -1 and 4070 s -1 which had the value of 47 x 10 3 and 24 x 10 3 respectively. The optimum injection temperature for stainless steel and alumina feedstock should be 190 °C and 230 °C respectively, since the feedstock exhibits the best characteristics for injection.

Magnetic motion control has been actively studied mainly for the purpose of biomedical applications. However, in many cases, many actuator magnets surround a small magnet to be moved, and they consume large electric power. In some cases, complex calculations are required to estimate the control input of the actuator magnets. This study proposes a simple method to move a small magnet to the desired positions. For this, three cylindrical permanent magnets magnetized in the radial direction were positioned as the sides of a triangle; these actuator magnets were rotated using motors. By monitoring the position of the small magnet and through simple feedback control based on the angles of the three actuator magnets, the untethered small magnet could be moved along arbitrary three-dimensional (3D) paths. The control principle was established by calculating the magnetic force and torque acting on the small magnet for some sets of actuator-magnet angles.

l h i r i r a prep~afapaperintendedforpub~~tionina j o d orproceedings Since changes may be made before publication, this preprint i s made available with the ~d e ~b n d i n g that it will not be Cited or reproduced without the permission of the .&r. This document was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor the University of California nor any of their employees, makes any warranty, express or implied, or amme9 any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or the University of California, and shall not be used for advertising o r product endorsement purposes.

In search of materials with better properties, polycrystalline materials are often found superior to their respective single crystalline counterparts. Reduction of grain size in polycrystalline materials can drastically alter the properties of materials, and when the grains reach nanometer scale, the improved mechanical response of the materials make them attractive in many applications. Multicomponent solid solution alloys have shown higher radiation tolerance compared to pure materials. Combining these both advantages, we investigate the radiation tolerance of nanocrystalline multicomponent alloys. We find that the alloys are able to withstand a much higher irradiation dose before the nanocrystallinity collapses, compared to nanocrystalline Ni. Some of the alloys managed to uphold their nanocrystallinity even twice as long as pure Ni.

The ideal picture of a near-perfect 3D microscope often presented regarding Atom Probe Tomography faces several issues. These issues degrade the metrological performance of the instrument and find their roots in the phenomena acting at the atomic to the mesoscopic level in the vicinity of the surface of a field emitter. From the field evaporation process at the atomic scale, to the macroscopic scale of the instrument, the path to model the imaging process and to develop more accurate and reliable reconstruction algorithms is not a single lane road. This paper focused on the numerical methods used to understand, treat, and potentially heal imaging issues commonly affecting the data in atom probe experiments. A lot of room for improvement exists in solving accuracy problems observed in complex materials by means of purely electrostatic models describing the image formation in a classical approach. Looking at the sample at the atomic scale, the phenomena perturbing the imaging process are subtle. An examination of atomic scale modifications of the sample surface in the presence of a high surface electric field is therefore mandatory. Atomic scale molecular dynamic models integrating the influence of the high surface electric are being developed with this aim. It is also demonstrated that the complex behavior of atoms and molecules in high fields, and consequences on collected data, can be understood through the use of accurate ab-initio models modified to include the impact of the extreme surface electric field.

Bronze reacts with oxygen, humidity, and pollutants in the atmosphere so that a patina forms. Natural exposure to an outdoor atmosphere can be simulated and accelerated in order to achieve a patina that mimics outdoor ancient patina. In order to avoid the uncontrolled dissolving of either the natural or artificially formed patina, protection of the patina is needed. In this study, a multi-component fluoropolymer based coating for the protection of bronze patina was developed. In order to provide various functionalities of the coating (such as the hydrophobicity of the coating surface, obtaining interactions within the coating itself as well as a bronze substrate and inhibiting the corrosion processes), a fluoroacrylate coating with appropriate adhesion promoter was suggested, with and without a silane modified benzotriazole inhibitor. The protective efficiency and durability of the applied coatings were investigated electrochemically using potentiodynamic tests and electrochemical impedance spectroscopy in a simulated acid rain solution. All of the developed coatings showed a significant decrease in the corrosion current density. The self-assembled single layer coating (FA-MS) also showed 100% inhibition efficiency. After ageing the coating remained transparent and did not change by UV exposure and/or thermal cycling. The patina and coating investigations using FIB-SEM and EDX showed that the latter coating (FA-MS) successfully covered the surface of the patinated bronze. The mechanism of the bonding was proposed and supported with the spectroscopic observation of a thin and even coating.

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