Search

Biological structures optimized through natural selection provide valuable insights for engineering load-bearing components. This paper reviews six key strategies evolved in nature for efficient mechanical load handling: hierarchically structured composites, cellular structures, functional gradients, hard shell–soft core architectures, form follows function, and robust geometric shapes. The paper also discusses recent research that applies these strategies to engineering design, demonstrating their effectiveness in advancing technical solutions. The challenges of translating nature's designs into engineering applications are addressed, with a focus on how advancements in computational methods, particularly artificial intelligence, are accelerating this process. The need for further development in innovative material characterization techniques, efficient modeling approaches for heterogeneous media, multi-criteria structural optimization methods, and advanced manufacturing techniques capable of achieving enhanced control across multiple scales is underscored. By highlighting nature's holistic approach to designing functional components, this paper advocates for adopting a similarly comprehensive methodology in engineering practices to shape the next generation of load-bearing technical components. [ABSTRACT FROM AUTHOR]

Organisms in nature have evolved a variety of surfaces with different tribological properties to adapt to the environment. By studying, understanding, and summarizing the friction and lubrication regulation phenomena of typical surfaces in nature, researchers have proposed various biomimetic friction regulation theories and methods to guide the development of new lubrication materials and lubrication systems. The design strategies for biomimetic friction/lubrication materials and systems mainly include the chemistry, surface structure, and mechanics. With the deepening understanding of the mechanism of biomimetic lubrication and the increasing application requirements, the design strategy of multi-strategy coupling has gradually become the center of attention for researchers. This paper focuses on the interfacial chemistry, surface structure, and surface mechanics of a single regulatory strategy and multi-strategy coupling approach. Based on the common biological friction regulation mechanism in nature, this paper reviews the research progress on biomimetic friction/lubrication materials in recent years, discusses and analyzes the single and coupled design strategies as well as their advantages and disadvantages, and describes the design concepts, working mechanisms, application prospects, and current problems of such materials. Finally, the development direction of biomimetic friction lubrication materials is prospected. [ABSTRACT FROM AUTHOR]

In this paper, we propose a mechanical model for a game of tug of war (rope pulling). We focus on a game opposing two players, modelling each player's body as a structure composed of straight rods that can be actuated in three different ways to generate a pulling force. We first examine the static problem of two opponents being in a deadlock configuration of mechanical equilibrium; here we show that this situation is essentially governed by the ratio of masses of the players, with the heavier player having a strong advantage. We then turn to the dynamic problem and model the response of the system to an abrupt change in activation by one of the players. In this case, the system exhibits a nontrivial response; in particular, we compare a sudden pulling and a sudden "letting up," and demonstrate the existence of regimes in which the lighter player can momentarily take the advantage. [ABSTRACT FROM AUTHOR]

Model-based approaches to navigation, control, and fault detection that utilize precise nonlinear models of vehicle plant dynamics will enable more accurate control and navigation, assured autonomy, and more complex missions for such vehicles. This paper reports novel theoretical and experimental results addressing the problem of parameter estimation of plant and actuator models for underactuated underwater vehicles operating in 6 degrees-of-freedom (DOF) whose dynamics are modeled by finite-dimensional Newton-Euler equations. This paper reports the first theoretical approach and experimental validation to identify simultaneously plant-model parameters (parameters such as mass, added mass, hydrodynamic drag, and buoyancy) and control-actuator parameters (control-surface models and thruster models) in 6-DOF. Most previously reported studies on parameter identification assume that the control-actuator parameters are known a priori. Moreover, this paper reports the first proof of convergence of the parameter estimates to the true set of parameters for this class of vehicles under a persistence of excitation condition. The reported adaptive identification (AID) algorithm does not require instrumentation of 6-DOF vehicle acceleration, which is required by conventional approaches to parameter estimation such as least squares. Additionally, the reported AID algorithm is applicable under any arbitrary open-loop or closed-loop control law. We report simulation and experimental results for identifying the plant-model and control-actuator parameters for an L3 OceanServer Iver3 autonomous underwater vehicle. We believe this general approach to AID could be extended to apply to other classes of machines and other classes of marine, land, aerial, and space vehicles. [ABSTRACT FROM AUTHOR]

It is often assumed that in the collapse of the Aristotelian distinction between art and nature that results from the rise of mechanical philosophies in the early modern period, the collapse falls on the side of art. That is, all of the diversity among natures that was explained previously as differences among substantial forms came to be seen simply as differences in arrangements of matter according to laws instituted by the "divine artificer", God. This paper argues that, for René Descartes, the collapse occurs on both sides. Natures are artefacts of God, and human artefacts, under some conditions, can be classified as natures or, at least, continuous within nature. Drawing on developments across both horticulture and engineering in the 16th and 17th centuries, as well as Descartes' mechanical philosophy, this paper explores challenges to the Aristotelian nature/art distinction. The question then is what, in the advent of this collapse, are human artificers doing when they construct artefacts? Are they replicating God's powers by creating new natures, or are they doing something else, and if so, what might that be? It is argued that we should view human invention for Descartes not as creating new natures so much as discovering them. These findings have consequences for how we interpret Descartes' use of the term "nature" in relation to automata and other artefacts produced by human hands. [ABSTRACT FROM AUTHOR]

In this paper, we propose a fully coupled two-phase poroelastic deformation theory for a spherically layered and self-gravitating Earth. The earth model consists of a solid inner core, a fluid outer core and poroelastic mantle and crust. The boundary-value problems are posed in the Laplace-transformed domain using the spherical system of vector functions, and analytical solutions are obtained in each layer using the dual-variable and position matrix method. As an application, the surface loading problem is considered. The undrained and drained limits are discussed with the corresponding governing equations, which are different from the conventional ones where body force is ignored. Numerical examples show that the poroelastic effect can be significant since the difference between the results for undrained and drained limits are large with obvious time-dependent deformation. This newly derived theory for the coupled boundary-value problem will have broad applications, such as displacement and gravity change due to groundwater depletion, poroelastic rebound after an earthquake and risk evaluation of earthquakes induced by water injection. [ABSTRACT FROM AUTHOR]

This paper presents a method that modifies commercial engineering-oriented finite element packages for the modelling of Glacial Isostatic Adjustment (GIA) on a self-gravitating, compressible and spherical Earth with 3-D structures. The approach, called the iterative finite element body and surface force (FEMIBSF) approach, solves the equilibrium equation for deformation using the ABAQUS finite element package and calculates potential perturbation consistently with finite element theory, avoiding the use of spherical harmonics. The key to this approach lies in computing the mean external body forces for each finite element within the Earth and pressure on Earth's surface and core–mantle boundary (CMB). These quantities, which drive the deformation and stress perturbation of GIA but are not included in the equation of motion of commercial finite element packages, are implemented therein. The method also demonstrates how to calculate degree-1 deformation directly in the spatial domain and Earth-load system for GIA models. To validate the FEMIBSF method, loading Love numbers (LLNs) for homogeneous and layered earth models are calculated and compared with three independent GIA methodologies: the normal-mode method, the iterative body force method and the spectral-finite element method. Results show that the FEMIBSF method can accurately reproduce the unstable modes for the homogeneous compressible model and agree reasonably well with the Love number results from other methods. It is found that the accuracy of the FEMIBSF method increases with higher resolution, but a non-conformal mesh should be avoided due to creating the so-called hanging nodes. The role of a potential force at the CMB is also studied and found to only affect the long-wavelength surface potential perturbation and deformation in the viscous time regime. In conclusion, the FEMIBSF method is ready for use in realistic GIA studies, with modelled vertical and horizontal displacement rates in a disc load case showing agreement with other two GIA methods within the uncertainty level of GNSS measurements. [ABSTRACT FROM AUTHOR]

In this paper, the differences in mechanical strength tested during the static tensile and compression test of Scots pine (Pinus sylvestris L.), European larch (Larix decidua) and Norway spruce (Picea abies) wood exposed to continuous soaking in water with a salinity of 7‰ were determined. The value of salinity corresponded to the average salinity on the Polish Baltic coast. This paper also aimed to examine the content of mineral compounds absorbed during four cycles of two weeks each. The essence of the statistical research was to identify the effect of the mineral range compounds and salts depending on the mechanical strength of the wood. Based on the results of the experiments, it can be concluded that the medium used has a specific effect on the wood species' structure. The effects of soaking on the wood parameters depend obviously on the type of wood. A tensile strength test of pine, as well as the tensile strength other species, was enhanced by incubating it in seawater. A native sample's initial mean tensile strength was 82.5 MPa, which increased to 94.8 MPa in the last cycle. It was found that the larch wood had the lowest tensile strength difference (9 MPa) of the woods studied in the current study. Four to six weeks of soaking was necessary to notice an increase in tensile strength. [ABSTRACT FROM AUTHOR]

This paper studies the optimization of mechanics and resource allocation in linear vibration energy harvesters operating under an overall size constraint. In such harvesters, the volume aspect ratio and the stroke direction should be carefully selected to maximize output power and power density. Further, because the proof mass and spring stroke must share the available size along the stroke direction, a mass-stroke design trade-off results; the trade-off is optimized here. The optimization further leads to a universal metric the enables the comparison of linear vibration energy harvesters designed to operate in a limited volume. Examination of this metric results in guidelines and best practices for selecting harvester dimensions and shape for a given volume constraint, all based on the dimensional harvester optimization for maximum size-constrained output power. This paper offers several key contributions. First, it provides an evaluation and optimization of the impact that volume shaping and volumetric resource allocation have on the output power of linear vibration energy harvesters. Second, it develops a “universal normalized surface” relating output power to dimensional harvester design. The surface expresses the performance limit of space-constrained linear vibration energy harvesters in terms of their output power density. This leads to universal guidelines for harvester design. Finally, benchmarking harvesters reported in the literature against the universal surface demonstrates that their output performances lie on or below the surface, despite large variations in their exogenous design variables such as vibration amplitude, frequency, volume etc. Thus, this paper offers an effective method to evaluate mechanical design and optimization in state-of-the-art linear vibration energy harvesters under volume constraints, a scenario suited for IoT applications. [2021-0074] [ABSTRACT FROM AUTHOR]

Tube spinning is a continuous bulk forming technique used to produce seamless tubes. In the last six decades, tube spinning process has been applied to a wide range of engineering products; especially in automotive, aerospace and nuclear industry. However, understanding of the process mechanics is limited. Key references were published about 60 years ago. This paper investigates tube spinning mechanics using physical trials and a numerical model. Mechanisms of material accumulation, wave, bell-mouth and diametral growth in tube spinning are investigated and their mechanisms explained. Numerical model results show that both equivalent plastic strain and plastic strain rate are localised in the region immediately under and ahead of the roller producing highly non-uniform strain distributions and that the process reaches steady-state at an early stage. The stress state is dominated by compressive normal stresses in all three directions. [ABSTRACT FROM AUTHOR]

This is the second paper of the induction theory of gravitational field. In the first paper, a new space-time view, which considers the influence of gravity, was constructed. In the new view of time and space, classical mechanics no longer holds. In this paper, the theory of mechanics and energy is established in the new space-time relation. In this paper, the basic mechanical law in the new space-time relationship is derived from the inertial force of the observed object relative to the reference object. Second, according to this basic law, the new formulas of gravitation and electromagnetic force in the space-time relationship are derived. Third, the influence of the moving of the observation object on the force is discussed. Finally, the new law of mass energy conversion is discussed. [ABSTRACT FROM AUTHOR]

In this paper, a prediction model for the tensile behaviour of ultra-high performance fibre-reinforced concrete is proposed. It is based on integrating force contributions of all fibres crossing the crack plane. Piecewise linear models for the force contributions depending on fibre orientation and embedded length are fitted to force–slip curves obtained in single-fibre pull-out tests. Fibre characteristics in the crack are analysed in a micro-computed tomography image of a concrete sample. For more general predictions, a stochastic fibre model with a one-parametric orientation distribution is introduced. Simple estimators for the orientation parameter are presented, which only require fibre orientations in the crack plane. Our prediction method is calibrated to fit experimental tensile curves. [ABSTRACT FROM AUTHOR]

This paper represents an initiatory investigation into moments of inaction in games. Two types of inaction are defined and discussed: stasis, which is inaction brought on by or through a game's mechanics, and stillness, which is brought on by or through a game's aesthetics. This paper uses gameplay examples from Until Dawn, Mario Party 2, Animal Crossing: New Leaf, and World of Warcraft to demonstrate that moments of stasis and stillness can either be designed features of a game that produce a variety of affective experiences, or playful subversions that are injected into a game by the player. Identifying whether moments of stasis and stillness are designed or injected enables these two modes of inaction to be compared and positioned as part of a broader project that interrogates whether play can be a form of critique. [ABSTRACT FROM AUTHOR]

Comments are provided on the recent paper by Ebadi et al. (2024) which demonstrates that the formulated model that was solved contains misconceptions or errors that render the work unsuitable for describing the evolution of interfacial areas in two-fluid porous medium systems. The need for kinematic equations is described and components of a theoretically consistent approach are summarized. [ABSTRACT FROM AUTHOR]

Battle Royale (BR) games are well known for their ability to not only attract but also retain a large number of players. In this paper, we attempt to identify the common themes which BR players identify as methods of retention through a qualitative thematic analysis with 11 participants. Data was gathered using semi-structured interviews and analysed through thematic analysis. Seven common themes were identified, where (1) draw of new content, (2) mechanics and action of BR games, and (3) reward systems were suggested to impact retention. Additionally, (4) social dynamics and (5) mastery were external factors outside the game that may impact retention in BR games. However, the other themes of (6) aesthetic preference and (7) unique selling points were not contributing factors in our sample. Further work is needed to understand the impact of these retention factors and how to design for these factors in game development. [ABSTRACT FROM AUTHOR]

The piezomagnetic effect is defined as a change in magnetization with applied stress. Changes in the geomagnetic field caused by the piezomagnetic effect, referred to as the piezomagnetic field, have been theoretically estimated and compared by previous studies to interpret observed variations in the geomagnetic field. However, the piezomagnetic field estimated in previous studies may not provide an accurate estimation because they ignored spatial variations in elasticity, leading to only a rough approximation of the properties of Earth's crust. In this paper, a semi-analytical procedure for calculating the piezomagnetic field arising from a point dislocation source embedded in a layered elastic medium is derived. Following a well-established method of the vector surface harmonic expansion, all of the governing equations written in partial differential equations in a real domain, together with the linear constitutive law of the piezomagnetic effect, are converted to a set of ordinary differential equations in a wavenumber domain. Equations in the wavenumber domain are solved analytically, and each component of the piezomagnetic field in the real domain is obtained after applying the Hankel transform. By using the derived procedure, the piezomagnetic and displacement fields due to a finite fault with strike-slip, dip-slip, and tensile-opening mechanisms are estimated for media with layered elasticity structures. Results for a finite fault are obtained by integrating the point source solution over the fault plane. The results of the numerical analysis allow the effect of heterogeneities in rigidity on the piezomagnetic effect to be examined and implications for the findings of previous investigations to be drawn. In cases where the moment-release at the dislocation source is fixed, the effect of the rigidity differences between upper and lower layers on the piezomagnetic field is minor even in the case where the Curie point depth is near the source of dislocation. This result is in contrast to a previous study that assumed the Mogi model and suggested that heterogeneities in the horizontal direction may be of importance when combined with layered rigidity structures. A contrast is seen between the piezomagnetic and displacement fields corresponding to models with layered rigidity structures: the piezomagnetic field is roughly proportional to the moment-release on a source fault, whereas the displacement field is proportional to slip or opening of the fault. Provided that the rigidity of the crust increases with increasing depth, the calculated piezomagnetic field is likely to have been underestimated in many earlier studies, which assumed uniform rigidity and a geodetically inverted size of slip. [ABSTRACT FROM AUTHOR]

This paper reviews the effect of multirotor aerial vehicle designs on their abilities in terms of tasks and system properties. We propose a general taxonomy to characterize and describe multirotor aerial vehicles and their designs, which we apply exhaustively on the vast literature available. Thanks to the systematic characterization of the designs, we exhibit groups of designs having the same abilities in terms of achievable tasks and system properties. In particular, we organize the literature review based on the number of atomic actuation units and we discuss global properties arising from their choice and spatial distribution in the mechanical designs. Finally, we provide a discussion on the common traits of the designs found in the literature and the main open and future problems. [ABSTRACT FROM AUTHOR]

Isostasy explains why observed gravity anomalies are generally much weaker than what is expected from topography alone, and why planetary crusts can support high topography without breaking up. On Earth, it is used to subtract from gravity anomalies the contribution of nearly compensated surface topography. On icy moons and dwarf planets, it constrains the compensation depth which is identified with the thickness of the rigid layer above a soft layer or a global subsurface ocean. Classical isostasy, however, is not self-consistent, neglects internal stresses and geoid contributions to topographical support, and yields ambiguous predictions of geoid anomalies. Isostasy should instead be defined either by minimizing deviatoric elastic stresses within the silicate crust or icy shell, or by studying the dynamic response of the body in the long-time limit. In this paper, I implement the first option by formulating Airy isostatic equilibrium as the linear response of an elastic shell to a combination of surface and internal loads. Isostatic ratios are defined in terms of deviatoric Love numbers which quantify deviations with respect to a fluid state. The Love number approach separates the physics of isostasy from the technicalities of elastic-gravitational spherical deformations, and provides flexibility in the choice of the interior structure. Since elastic isostasy is invariant under a global rescaling of the shell shear modulus, it can be defined in the fluid shell limit, which is simpler and reveals the deep connection with the asymptotic state of dynamic isostasy. If the shell is homogeneous, minimum stress isostasy is dual to a variant of elastic isostasy called zero deflection isostasy, which is less physical but simpler to compute. Each isostatic model is combined with general boundary conditions applied at the surface and bottom of the shell, resulting in one-parameter isostatic families. At long wavelength, the thin shell limit is a good approximation, in which case the influence of boundary conditions disappears as all isostatic families members yield the same isostatic ratios. At short wavelength, topography is supported by shallow stresses so that Airy isostasy becomes similar to either pure top loading or pure bottom loading. The isostatic ratios of incompressible bodies with three homogeneous layers are given in analytical form in the text and in complementary software. [ABSTRACT FROM AUTHOR]

We present a theory of modern, thermally induced deformation in a realistic Earth. The heat conduction equation is coupled with standard elastic deformation theory to construct a boundary-value problem comprised of eighth-order differential equations. The accurate and stable dual variable and position propagating matrix technique is introduced to solve the boundary-value problem. The thermal load Love numbers are defined to describe the displacements and potential changes driven by thermally induced deformation. The proposed analytical method is validated by comparing the present results with exact solutions for a homogeneous sphere, which are also derived in this paper. The analytical method is then applied to a realistic Earth model to evaluate the effects of layering and self-gravitation of the Earth on displacement and changes of potential. Furthermore, the frequency dependence in the thermal load is illustrated by invoking different thermal periodicities in the computation. Thermal anisotropy is also considered by comparing the results obtained using isotropic and transversely isotropic Earth models. Results show that, when simulating thermally induced deformation, invoking a homogeneous spherical Earth leads to results that substantially differ from those obtained using a more realistic Earth model. [ABSTRACT FROM AUTHOR]

In this paper, the free vibration of an aluminum beam coated with imperfect and damaged functionally graded material is investigated. The imperfections consist of porosities, while 4 evenly distributed cracks represent the damage profile. A polynomial function is used to vary the density and elasticity through the thickness of the coating, while the effective elastic modulus and density are found with classical lamination theory. To achieve a truthful modeling, the gradually changing mechanical properties of the coating are modeled with 25 layers of material. The individual layers are isotropic and homogeneous. Numerical solutions are found with the finite element method using Timoshenko beam elements. MATLAB is used to write a finite element code, and the beam natural frequencies are found. To show the influences of porosity, crack depth, coating thickness and the polynomial function index (n) on the natural beam frequencies, a parametric study is conducted. It was found that the natural frequency values were significantly affected by the studied parameters. [ABSTRACT FROM AUTHOR]

Many recent studies have tried to determine the influence of geometry of faults in earthquake mechanics. However, it still remains largely unknown, and it is explored mainly with numerical models. In this paper, we will try to understand how exactly does the geometry come into play in the mechanics of an earthquake from analytical perspective. We suggest a new interpretation of the effect of geometry on the stress on a fault, where the curvatures of the fault that multiply the slip play a major role. Starting from the representation theorem, which links the displacement in a medium to the slip distribution on its boundary, and assuming a 3-D, homogeneous, infinite medium, a regularized boundary-element equation can be obtained. Using this equation, it is possible to separate the influence of geometry, as expressed by the curvatures and torsions of the field lines of slip on the fault surface, which multiply the slip, from the effect of the gradient of slip. This allows us to shed new light on the mechanical effects of geometrical complexities on the fault surface, with the key parameters being the curvatures and torsions of the slip field lines. We have used this new approach to show that, in 2-D static in-plane problems, the shear traction along the fault is mainly controlled by the gradient of slip along the fault, while the normal traction is mainly controlled by the slip that multiplies the curvature along the fault. Finally, we applied this new approach to re-interpret the effect of roughness (why there is a need for a minimum lengthscale in linear elasticity, how to study mechanically the difference of roughness measurements with the direction of slip, scaling of slip distribution versus geometry), bends and kinks (what is the difference between the two, are they sometimes equivalent), as well as to explain further the false paradox between smooth-and-abrupt-bends. This unified framework allows us to improve greatly our understanding of the effect of fault geometry on the mechanics of earthquakes. [ABSTRACT FROM AUTHOR]

Understanding the fluid dependence of the poroelastic stiffness constants of a layered porous package is of great importance in subsurface exploration and development. While the effects of the pore-fluid distribution caused by coarse-scale heterogeneities within an isotropic medium have been studied for several decades, the role of these heterogeneities on the poroelastic constants of a finely layered package is still largely unexplored. In this study, we apply the poroelastic upscaling methods to estimate the fluid-dependent poroelastic stiffness constants of a layered package at the coarse scale. The numerical results show that the refined Gassmann's fluid substitution formulae presented in this paper is applicable if a single fluid phase is uniformly saturated within a layered package. The stiffness constants (⁠|${c_{11}}$| and |${c_{33}}$|⁠) of the layered package with patchy saturations are always higher than or equal to those obtained for the medium with homogeneous saturations, the stiffness constants predicted by the refined fluid substitution formulae for the package simultaneously saturated with different fluids fall between them. Experimental results confirm the relationship between the undrained vertical stiffness constant and the effective pore-fluid bulk modulus for the patch saturated package, indicating that a reasonable result can be achieved by properly choosing an effective poroelastic model that accounts both for the fluid hydraulic communication and the anisotropy of the medium. The results improve the understanding of the coarse-scale fluid dependence of the poroelastic stiffness constants of a layered package, and therefore, it can be used to interpret the seismically inverted elastic parameter for the petrophysical properties in heterogeneous reservoirs. [ABSTRACT FROM AUTHOR]

A compliant beam subjected to large deformation is governed by a multifaceted nonlinear differential equation. In the context of theoretical mechanics, solution for such equations plays an important role. Since it is hard to find closed-form solutions for this nonlinear problem and attempt at direct solution results in linearising the model. This paper investigates the aforementioned problem via the multi-step differential transformation method (MsDTM), which is well-known approximate analytical solutions. The nonlinear governing equation is established based on a large radius of curvature that gives rise to curvature-moment nonlinearity. Based on established boundary conditions, solutions are sort to address the free vibration and static response of the deforming flexible beam. The geometrically linear and nonlinear theory approaches are related. The efficacy of the MsDTM is verified by a couple of physically related parameters for this investigation. The findings demonstrate that this approach is highly efficient and easy to determine the solution of such problems. In new engineering subjects, it is forecast that MsDTM will find wide use. [ABSTRACT FROM AUTHOR]

Archimedes' statics is considered as an example of ancient Greek applied mathematics; it is even seen as the beginning of mechanics. Wilbur Knorr made the case regarding this work, as other works by him or other mathematicians from ancient Greece, that it lacks references to the physical phenomena it is supposed to address. According to Knorr, this is understandable if we consider the propositions of the treatise in terms of purely mathematical elaborations suggested by quantitative aspects of the phenomena. In this paper, we challenge Knorr's view, and address propositions of Archimedes' statics in their relation to physical phenomena. [ABSTRACT FROM AUTHOR]

In this paper, we model the crack growth in an elastic medium constituted by two welded half-spaces with different rigidities. We implement a 2-D boundary element method (BEM) computing shear and normal tractions acting on the crack and the slip accommodating stress drop from an arbitrary initial configuration to a final frictional configuration. The direction of crack growth follows the criterion of maximum energy release (strain and gravitational energy) provided that it overcomes the surface fracture energy and the work dissipated by friction. The energetic criterion leads to estimates of the dip angle of seismic faults depending on the amplitude of the initial stress and it includes the classical Anderson's results as a particular case. Moreover, in presence of a sharp rigidity contrast, the direction of crack growth is strongly deflected. The model simulates non-planar, complex, fault geometries, as in the case of detachment and listric faults and it explains the increase of dip angles for both normal and reverse faults, when they enter soft sedimentary layers. [ABSTRACT FROM AUTHOR]

Effective medium theory plays an important role in the characterization of fractured reservoirs. The main goal of this paper is to assess the accuracy of three classical effective medium theories (compliance-based non-interaction approximation, Hudson theory and anisotropic self-consistent approximation) and investigate their applicable frequency range. To evaluate the crack density limitation of these models, we construct a series of physical models with crack density varying from 0 to 12 per cent. To satisfy the long-wavelength approximation of effective medium theory, we consider a crack diameter and aperture of 3 and 0.12 mm, respectively. To study their appropriate high-frequency laboratory condition, we use the ultrasonic transmission method to measure the elastic wave velocities at frequencies of 500, 250 and 100 kHz. The experimental results are then compared with the effective medium theories to discuss their accuracy. We also highlight and compare the accuracy of these theories for the inversion procedure to quantify the crack density. [ABSTRACT FROM AUTHOR]

This work explores the collision process at foot contact in models of legged robots. In particular, we highlight that for legged systems the widely used assumption of no sliding of the contact points can yield inconsistent outcomes. For certain contact configurations and system parameters, neither the assumption of lift-off of the trailing foot nor the assumption that it stays fixed on the ground yield valid solutions. The foot will slide, even if an infinite coefficient of friction is assumed. In a related effect, we present configurations in which the solution of the collision process is ambiguous. These behaviors are examined for the models of a minimalistic biped, a passive dynamic walker, and the five-link bipedal robot RAMone. The paper provides background for these non-intuitive behaviors and investigates the influence of system parameters onto the collision behavior of a passive dynamic walker. By studying bipedal models that range from minimalistic to physically accurate, this paper establishes a bridge between the theoretical study of unilateral contact in multibody dynamic simulations and the application of these simulation methods in the modeling of ground contact in actual legged systems. [ABSTRACT FROM AUTHOR]

Quasistatic legged locomotion over uneven terrains requires characterization of the legged robot equilibrium postures as well as an understanding of the non-static motion modes that can develop at the contacts. This paper characterizes the frictional multi-legged equilibrium postures on a generic class called ‘tame stances’, which satisfy a generalized support polygon principle. To characterize the equilibrium postures, the paper lumps the legged mechanism’s kinematic structure into a rigid body having a variable center of mass and maintaining the same contacts with the terrain. The equilibrium postures associated with a given set of contacts correspond to the locations of the center of mass at which the body is supported in static equilibrium by the same contacts under the influence of gravity. This paper thus characterizes the feasible equilibrium region of a rigid body having a variable center of mass and supported by multiple frictional contacts under the influence of gravity. The paper establishes that the feasible equilibrium region forms a convex set which has five types of boundary curves. These boundary curves are formulated analytically, illustrated with graphical examples, and associated with the onset of five non-static motion modes at the contacts. The paper also compares the analytical results against experimental measurements conducted on a legged mechanism prototype. [ABSTRACT FROM AUTHOR]

Multiphase reactive transport processes are ubiquitous in igneous systems. A challenging aspect of modelling igneous phenomena is that they range from solid-dominated porous to liquid-dominated suspension flows and therefore entail a wide spectrum of rheological conditions, flow speeds and length scales. Most previous models have been restricted to the two-phase limits of porous melt transport in deforming, partially molten rock and crystal settling in convecting magma bodies. The goal of this paper is to develop a framework that can capture igneous system from source to surface at all phase proportions including not only rock and melt but also an exsolved volatile phase. Here, we derive an n -phase reactive transport model building on the concepts of Mixture Theory, along with principles of Rational Thermodynamics and procedures of Non-equilibrium Thermodynamics. Our model operates at the macroscopic system scale and requires constitutive relations for fluxes within and transfers between phases, which are the processes that together give rise to reactive transport phenomena. We introduce a phase- and process-wise symmetrical formulation for fluxes and transfers of entropy, mass, momentum and volume, and propose phenomenological coefficient closures that determine how fluxes and transfers respond to mechanical and thermodynamic forces. Finally, we demonstrate that the known limits of two-phase porous and suspension flow emerge as special cases of our general model and discuss some ramifications for modelling pertinent two- and three-phase flow problems in igneous systems. [ABSTRACT FROM AUTHOR]

The formation of fold-thrust belts at convergent margins is a dynamic process. Accretion of weak sediments to the front of the overriding plate results in crustal thickening and continued flexural subsidence of the underthrusting plate. Fold-thrust belts are often treated as a Coulomb wedge having self-similar geometries with a critical taper, and either a rigid or isostatically compensated base. In this paper, we build upon this work by developing a new dynamic model to investigate both the role of the thickness and material properties of the incoming sediment, and the flexure in the underthrusting plate in controlling the behaviour and evolution of fold-thrust belts. Our analysis shows that the evolution of fold-thrust belts can be dominated by either gravitational spreading or vertical thickening, depending on the relative importance of sediment flux, material properties and flexure. We apply our model to the Makran accretionary prism and the Indo–Burman Ranges, and show that for the Makran flexure must be considered in order to explain the dip of the sediment–basement interface from seismic reflection profiles. In the Indo–Burman Ranges, we show that incoming sediment thickness has a first-order control on the variations in the characteristics of the topography from north to south of the Shillong Plateau. [ABSTRACT FROM AUTHOR]

In this paper, we derive analytical expressions for the dislocation Love numbers (DLNs) for a layered, spherical, transversely isotropic and self-gravitating Earth. This solution is based on the spherical system of vector functions (or the vector spherical harmonics) and a new propagating matrix method called the dual variable and position method. The DLNs can be obtained with high accuracy to an arbitrarily high degree, thereby allowing a wide range of applications based on high resolution earth models. Compared to the traditional numerical integration approach, the present analytical solution is at least 3 orders of magnitude faster. Our calculation also indicates that, compared to the isotropic PREM model, the effect of anisotropy is small, with a relative error about 5 per cent for DLN h 12 at degree n  = 69 with source located at depth 100 km. We provide MATLAB code for computing the analytical DLNs in the supplementary materials section, along with a user manual. [ABSTRACT FROM AUTHOR]

This paper reports asymmetric features of normal and reverse faulting from the point of view of earthquake dynamics. It is assumed that the fault's strength is governed by Coulomb friction, namely depending on normal stress, and numerical simulations are carried out using a boundary domain method, a hybrid coupling between the boundary integral equation and finite difference methods. Under the same uniform initial stress loaded on a fault, simulations reveal that stress perturbations from the ground surface accelerate rupture of a reverse fault but decelerate that of a normal fault when approaching the ground surface. Furthermore, the overburden stress increases with depth. A Mohr–Coulomb diagram constrains the possible stress accumulation, as the Mohr-circle should not exceed the static Coulomb friction. In such case, shear stress can be loaded sufficiently on reverse fault at any depth, while the stress accumulation is limited at a shallow depth of a normal fault. This difference leads to further favouring of reverse faulting at shallow depths and makes normal faulting difficult near the ground surface. The results suggest the importance of the initial stress conditions and dynamic stress perturbation for understanding earthquake mechanics and assessing potential earthquake scenarios in seismic hazard studies. [ABSTRACT FROM AUTHOR]

The question of how to obtain information on the dynamic, spatiotemporal characteristics of crustal stress is of significant concern, especially to elucidate plate tectonics and earthquakes. In this paper, we develop a new method to measure the magnitude and direction of stress changes via temperature distribution. We derive the theoretical relationship between the temperature in the vicinity of a hole and the outer stress according to the principles of rock mechanics and thermodynamics. To verify the theoretical result, we conduct an experiment on the temperature variations in a rock sample with a hole during biaxial loading under dry conditions. The rock sample was a 300 mm × 300 mm × 50 mm block of granodiorite, in which a borehole with a radius of 50 mm was drilled. Platinum resistance thermometers were used to measure the temperatures along the hole during biaxial loading. The loading modes included monotonic loading/unloading and sine wave loading. The experimental results indicate that the temperature around a hole responds sensitively to changes in the stress, following the theoretical expectations. The average temperature response to changes in the stress on the granodiorite was 1.17 mK MPa−1 at room temperature. Therefore, the stress change at the surface of a hole can be determined by detecting the temperature, after which the changes in the outer stress can be deduced based on the relationship between the interior stress in the hole and the outer stress loading on the object. Thus, the temperature distribution could be applied to monitor dynamic changes in the crustal stress, including its magnitude and orientation. This method could be largely helpful for exploring changes in the states of stress along seismogenic faults. [ABSTRACT FROM AUTHOR]

Theoretical and experimental approaches verifying the fluidic operation of a partially shielded digital microfluidics device are presented in this paper. This paper is motivated by recent demand from the synthetic biology community for electrowetting on dielectric (EWD) enabled in-droplet electroporation, but is generalizable to a range of EWD applications that require shielding structures to be patterned on the EWD. An electrode patterned in an additional metal layer on the insulator that supports EWD actuation reduces the effective strength of the EW force due to dielectric shielding at the droplet contact line. A numerical model was developed to predict the impact of the partially shielding electrode on threshold voltage, EW force, fluid velocity, and droplet transport time. Compared with a batch of devices lacking the extra electrode, the presence of the added metal layer resulted in a 29% increase in threshold voltage, an 82% increase in transport time, and a 44% decrease in average transport velocity. Each trend agrees with the simulation results obtained from the fluid transport model. These results support the development of design rules for microfluidic devices that require partially shielding metal layers to integrate with EWD device architectures. [2016-0034] [ABSTRACT FROM PUBLISHER]

This paper presents a new design of finger proposed by the ROBIOSS team of the PPRIME Institute: it is a fully actuated bio-inspired four-degree-of-freedom (DOF) finger driven by four actuators. It has been developed with the aim to replicate fine manipulation with fingertips with a high degree of interaction with the environment. This paper proposes to realize a robotic hand for inside-hand fine manipulation and adaptive grasping. The robotic hand is equipped with fingers whose design is based on a human anatomical finger model. Thus, several fingers can be assembled for building a human-sized dexterous hand with an anthropomorphic look. The modular design offers the ability to choose the number of fingers to be used as well as to adjust finger placement based on the manipulation task requirement. The tendon-based actuation presents a routing of the tendons that minimizes friction, kinematic, and static coupling between different finger axes in the transmission from motors to joints. Unlike many existing robotic hands, including our first anthropomorphic hand, we address the difficulties by decoupling joint motions with a new solution for the universal joint at the base of the finger. The results obtained demonstrate an excellent dynamic behavior and accuracy of the finger motion. Finally, the new finger design led to the development of a fully actuated mechanical hand with four fingers and with 16 DOF: the ROBIOSS hand. The hand was embedded on an industrial robot. A manipulation task that uses simultaneously abduction–adduction motion and flexion–extension motion of the finger demonstrates the potential of the hand for accurate manipulation. [ABSTRACT FROM PUBLISHER]

This paper is the second part of our recent paper 'Historical and Epistemological Reflections on the Culture of Machines around the Renaissance: How Science and Technique Work' (Pisano & Bussotti 2014a). In the first paper--which discussed some aspects of the relations between science and technology from Antiquity to the Renaissance--we highlighted the differences between the Aristotelian/Euclidean tradition and the Archimedean tradition. We also pointed out the way in which the two traditions were perceived around the Renaissance. The Archimedean tradition is connected with machines: its relationship with science and construction of machines should be made clear. It is enough to think that Archimedes mainly dealt with three machines: lever, pulley and screw (and a correlated principle of mechanical advantage). As underlined in the first part, our thesis is that many machines were constructed by people who ignored theory, even though, in other cases, the knowledge of the Archimedean tradition was a precious help in order to build machines. Hence, an a priori idea as to the relations between the Archimedean tradition and construction of machines cannot exist. In this second part we offer some examples of functioning machines constructed by people who ignored any physical theory, whereas, in other cases, the ignorance of some principles--such as the impossibility of a perpetuum mobile--induced the attempt to construct impossible machines. What is very interesting is that these machines did not function, of course, as a perpetuum mobile, but anyway had their functioning and were useful for certain aims, although they were constructed on an idea which is completely wrong from a theoretical point of view. We mainly focus on the Renaissance and early modern period, but we also provide examples of machines built before and after this period. We have followed a chronological order in both parts, starting from the analysis of the situation in ancient Greece. Therefore, in the first part, we have examined the relations between the Aristotelian/Euclidean and Archimedean traditions from ancient Greece to the early modern age. In this second part, we analyse the relations of Archimedean tradition/ construction of machines from ancient Greece to the 19th century, focusing on the mentioned period. We remind the reader that our aim is to prove an epistemological thesis, not to provide a complete historical endeavour. As a correlated article, the reader will find three previous paragraphs in the first above-mentioned article (Pisano & Bussotti, 2014a). [ABSTRACT FROM AUTHOR]

The ocean load in glacial isostatic adjustment (GIA) modelling is represented by the so-called sea level equation (SLE). The SLE describes the mass redistribution of water between ice sheets and oceans on a deforming Earth. Despite various teams independently investigating GIA, there has been no systematic intercomparison among the numerical solvers of the SLE through which the methods may be validated. The goal of this paper is to present a series of synthetic examples designed for testing and comparing the numerical implementations of the SLE in GIA modelling. The 10 numerical codes tested combine various temporal and spatial parametrizations. The time-domain or Laplace-domain discretizations are used to solve the SLE through time, while spherical harmonics, finite differences or finite elements parametrize the GIA-related field variables spatially. The surface ice-water load and solid Earth's topography are represented spatially either on an equiangular grid, a Gauss–Legendre or an equiarea grid with icosahedron-shaped spherical pixels. Comparisons are made in a series of five benchmark examples with an increasing degree of complexity. Due to the complexity of the SLE, there is no analytical solution to it. The accuracy of the numerical implementations is therefore assessed by the differences of the individual solutions with respect to a reference solution. While the benchmark study does not result in GIA predictions for a realistic loading scenario, we establish a set of agreed-upon results that can be extended in the future by including more complex case studies, such as solutions with realistic loading scenarios, the rotational feedback in the linear-momentum equation, and by considering a 3-D viscosity structure of the Earth's mantle. The test computations performed so far show very good agreement between the individual results and their ability to capture the main features of sea-surface variation and the surface vertical displacement. The differences found can often be attributed to the different approximations inherent in the various algorithms. This shows the accuracy that can be expected from different implementations of the SLE, which helps to assess differences noted in the literature between predictions for realistic loading cases. [ABSTRACT FROM AUTHOR]

The proof of the stability of the solar system has been customarily presented as the solution of a great riddle originated by Newton and completed by Laplace. In this paper, I suggest a different narrative. I argue that Newton considered the stability of the solar system more a theological problem than a physical one and that he never raised the question whether the system is stable or unstable. After the introduction of analytical techniques, astronomers and mathematicians, concerned especially with practical problems such as the behavior of the Moon and with the improvement of perturbation theory, also largely neglected the issue of stability. It was only in 1781, when the cultural and scientific conditions were ripe, that Lagrange, not Laplace, finally set and solved, according to the standard of the time, the stability problem. [ABSTRACT FROM AUTHOR]

This paper addresses the identification of the inertial parameters and the contact forces associated with objects making and breaking frictional contact with the environment. Our goal is to explore under what conditions, and to what degree, the observation of physical interaction, in the form of motions and/or applied external forces, is indicative of the underlying dynamics that governs it. In this study we consider the cases of passive interaction, where an object free-falls under gravity, and active interaction, where known external perturbations act on an object at contact. We assume that both object and environment are planar and rigid, and exploit the well-known complementarity formulation for contact resolution to establish a constrained optimization-based problem to estimate inertial parameters and contact forces. We also show that when contact modes are known, or guessed, the formulation provides a closed-form relationship between inertial parameters, contact forces, and observed motions, that turns into a least squares problem.Consistent with intuition, the analysis indicates that without the application of known external forces, the identifiable set of parameters remains coupled, i.e. the ratio of mass moment of inertia to mass and the ratio of contact forces to the mass. Interestingly the analysis also shows that known external forces can lead to decoupling and identifiability of mass, mass moment of inertia, and normal and tangential contact forces. We evaluate the proposed algorithms both in simulation and with real experiments for the cases of a free falling square, ellipse, and rimless wheel interacting with the ground, as well as a disk interacting with a manipulator. [ABSTRACT FROM AUTHOR]

Variable pitch and variable helix (VPVH) milling tools are usually utilized to mitigate regenerative chatter vibrations by destroying the vibration phases between adjacent teeth. But this chatter suppression mechanism may considerably be disturbed by the inevitable tool runout, which could also change the phases, even to a larger extent. Thus the cutting performance of VPVH tools in terms of mechanics and dynamics should be re-evaluated by taking runout into consideration. This paper firstly sets up the mechanistic model for VPVH tools and then presents a combined nonlinear optimization procedure to identify the cutting coefficients and runout parameters. Secondly, the dynamic system of VPVH tools considering runout is modeled by a periodic-coefficient delay differential equation with multiple underdetermined delays. Afterwards, the generalized Runge-Kutta (GRK) method is extended to tackle the runout-induced multi-regenerative effects and thus to analyze the milling process stability. The accuracy and efficiency of the GRK method is validated using published numerical examples. A series of cutting experiments with a commercially available VPVH tool are performed to verify the presented mechanistic and dynamic models. It confirms that runout cannot be neglected when evaluating the cutting performance of VPVH tools. Finally, the joint influences of runout and pitch/helix angles on cutting forces and chatter stability of VPVH tools are discussed in detail based on the proposed approach. [ABSTRACT FROM AUTHOR]

This paper introduces the iRobot-Harvard-Yale (iHY) Hand, an underactuated hand driven by five actuators that is capable of performing a wide range of grasping and in-hand repositioning tasks. This hand was designed to address the need for a durable, inexpensive, moderately dexterous hand suitable for use on mobile robots. The primary focus of this paper will be on the novel simplified design of the iHY Hand, which was developed by choosing a set of target tasks around which the hand was optimized. Particular emphasis is placed on the development of underactuated fingers that are capable of both firm power grasps and low-stiffness fingertip grasps using only the compliant mechanics of the fingers. Experimental results demonstrate successful grasping of a wide range of target objects, the stability of fingertip grasping, and the ability to adjust the force exerted on grasped objects using high-impedance actuators and underactuated fingers. [ABSTRACT FROM AUTHOR]

[Display omitted] • In this paper, the mechanical and friction experiments of composite hydrogels used in biomedical field in recent 3 years are summarized. • In this paper, the shortcomings of mechanical and friction experiments of biological hydrogels in recent 3 years were evaluated. • A more comprehensive method for testing the properties of biological hydrogels is put forward in this paper. Hydrogel is a porous three-dimensional network material that is insoluble in water and can store a large amount of water. This material has excellent mechanical properties, such as medical fields, wastewater treatment and other fields, and are widely used. With the development of modern science and technology, the research on hydrogel, a new kind of biomaterial, is increasingly extensive. Many researchers have carried out research on bone tissue-related engineering based on the advantages of hydrogel, such as adjustable mechanical properties, convenient production and combination with bioactive factors. The researchers mainly focus on the mechanical properties and biocompatibility of hydrogel made of composite materials. The disease causes extensive trauma, broken bones and cartilage damage that does not heal on its own, while traditional surgical treatments can bring side effects such as infection, inflammation and pain. As a new kind of biomaterial, hydrogel has controllable mechanical properties and biocompatibility, and is widely used in bone tissue engineering as scaffold material for growth factor transport and cell adhesion. In order to make hydrogels more suitable for local treatment of orthopedic diseases, the excellent properties of hydrogels are combined with synthetic materials with advanced technologies in different fields. In this paper, the test methods used in the study of mechanical and tribological properties of bone repair hydrogels are reviewed, and the shortcomings of experimental methods in the study of cartilage repair hydrogels are pointed out. the application of the combination of mechanics and tribology in the study of cartilage repair and cartilage replacement was discussed, and the research progress of molecular dynamics in characterizing the micromechanical state of hydrogel was summarized. [ABSTRACT FROM AUTHOR]

This paper develops a multi-scale mechanical-electrochemical model which enables fully coupled mechanics and electrochemistry at both particle and electrode levels. At the particle level, solid diffusion is modeled using a generalized chemical potential to capture the effects of mechanical stress and phase transformation. At the electrode level, the stress arising from particle interaction is incorporated in a continuum model. This particle interaction stress is in addition to the traditional concept of intercalation stress inside isolated particles. The particle and continuum electrode levels are linked by the particle interaction stress as loads on the particle surface, and by consideration of stress on the electrochemical reaction rate on the particle surface. The effect of mechanical stress on electrochemical reaction results in a stress-dependent over-potential between particle and electrolyte. Stress gradient in an electrode leads to inhomogeneous intercalation/deintercalation currents for particles depending on their interaction stress with neighbors, resulting in stress gradient induced inhomogeneous state of charge. Conversely, non-uniform intercalation/deintercalation currents in an electrode lead to stress between particles. With this model we have an important finding: an electrochemically inactive region in an electrode causes stress built-up. This model provides a powerful tool to address various problems such as fracture in-between particles. [ABSTRACT FROM AUTHOR]

In general mechanics, systems must follow the mechanical equilibrium principle, the minimum potential energy principle, and the minimum dissipation power principle. This paper confirms that a rotating drill string in a wellbore follows these three principles. The study presents three main findings. (1) As the rotary speed of a rod string increases, its deflection decreases nearer to the borehole center. (2) There exists a whirl-state transition critical rotary speed. If the rotary speed is below this critical rotary speed, the dissipation power increases as the rotary speed increases. If the rotary speed is higher than this critical rotary speed, the dissipation power first decreases rapidly as the rotary speed increases and the deflection of the rod string abruptly decreases, and then the dissipation power increases as the rotary speed increases. (3) As the viscosity of the liquid increases, the whirl-state transition critical rotary speed decreases. As the axial load increases, the whirl-state transition critical rotary speed decreases. [ABSTRACT FROM AUTHOR]

Continuum robotics has rapidly become a rich and diverse area of research, with many designs and applications demonstrated. Despite this diversity in form and purpose, there exists remarkable similarity in the fundamental simplified kinematic models that have been applied to continuum robots. However, this can easily be obscured, especially to a newcomer to the field, by the different applications, coordinate frame choices, and analytical formalisms employed. In this paper we review several modeling approaches in a common frame and notational convention, illustrating that for piecewise constant curvature, they produce identical results. This discussion elucidates what has been articulated in different ways by a number of researchers in the past several years, namely that constant-curvature kinematics can be considered as consisting of two separate submappings: one that is general and applies to all continuum robots, and another that is robot-specific. These mappings are then developed both for the single-section and for the multi-section case. Similarly, we discuss the decomposition of differential kinematics (the robot’s Jacobian) into robot-specific and robot-independent portions. The paper concludes with a perspective on several of the themes of current research that are shaping the future of continuum robotics. [ABSTRACT FROM AUTHOR]

In this paper we describe the experimental implementation of an online algorithm for cooperative localization of submerged autonomous underwater vehicles (AUVs) supported by an autonomous surface craft. Maintaining accurate localization of an AUV is difficult because electronic signals, such as GPS, are highly attenuated by water. The usual solution to the problem is to utilize expensive navigation sensors to slow the rate of dead-reckoning divergence. We investigate an alternative approach that utilizes the position information of a surface vehicle to bound the error and uncertainty of the on-board position estimates of a low-cost AUV. This approach uses the Woods Hole Oceanographic Institution (WHOI) acoustic modem to exchange vehicle location estimates while simultaneously estimating inter-vehicle range. A study of the system observability is presented so as to motivate both the choice of filtering approach and surface vehicle path planning. The first contribution of this paper is to the presentation of an experiment in which an extended Kalman filter (EKF) implementation of the concept ran online on-board an OceanServer Iver2 AUV while supported by an autonomous surface vehicle moving adaptively. The second contribution of this paper is to provide a quantitative performance comparison of three estimators: particle filtering (PF), non-linear least-squares optimization (NLS), and the EKF for a mission using three autonomous surface craft (two operating in the AUV role). Our results indicate that the PF and NLS estimators outperform the EKF, with NLS providing the best performance. [ABSTRACT FROM AUTHOR]

In this paper we present a formal approach to robot motion specification. This motion specification takes into account three elementary behaviors that suffice to define any robot interaction with the environment, i.e. free motion, exerting generalized forces and the transition between both of these behaviors. These behaviors provide a foundation for general motion generation taking into account any sensors, any effectors and the capability to exchange information between embodied agents. This specification can be used both for the definition of robot tasks and implementation of robot control software, hence both of those aspects are presented in this paper. This formal approach was used for the implementation of the MRROC++ robot programming framework. Two-handed manipulation of a Rubik's cube is used as an exemplary task. Extensive experimentation both with the presented formalism and the MRROC++ framework showed that the imposed formal rigor eliminates many errors at the software specification phase, produces well-structured control software and significantly speeds up and simplifies its implementation. These advantages are mainly due to the fact that the proposed formal specification tool is derived from operational semantics used in computer science for the definition of programming languages, thus a close relationship between abstract definition and the implementation of the control system resulted. [ABSTRACT FROM AUTHOR]

A novel robotized tool for percutaneous interventions under CT-scanner guidance is presented in this paper. This teleoperated compact robotic device can be used as an end-effector for an imageguided positioning robot. It is fully compatible with computed tomography constraints. In particular, it is able to manipulate needles that are longer than the overall height of its body. This novel device mimics the manual gesture performed by the physician by grasping and re-grasping the needle. This operating principle enables direct force measurement on the inserted surgical needle and allows efficient teleoperation with force feedback. In the paper, the specifications of this needle driver are presented and the proposed design is explained. Experiments conducted on swine under operating conditions were performed in order to validate both the concept and the design of the proposed insertion device in the context of teleoperated needle insertions with force feedback. [ABSTRACT FROM AUTHOR]

Abstract: This review paper discusses some basics in using continuum mechanics and molecular dynamics to characterize the deformation of single-walled carbon nanotubes (SWCNTs). It identifies that the van der Waals force between SWCNTs in a bundle distributes symmetrically and influences the bundle formation, and that to avoid misleading results from a molecular dynamics simulation, the interaction potential, thermostat scheme and simulation parameters must be carefully selected. The paper then points out that when the necessary condition proposed by Vodenitcharova and Zhang and a compatibility condition for elastic constants are satisfied, the intersect of the bending and in-plane stiffness curves in the modulus-thickness plane can determine a unique effective wall thickness of an SWCNT and hence its Young''s modulus. [Copyright &y& Elsevier]

In the natural world, animals must routinely negotiate varied and unpredictable terrain. Yet, we know little about the locomotor strategies used by animals to accomplish this while maintaining dynamic stability. In this paper, we perturb the running of guinea fowl with an unexpected drop in substrate height (AH). The drop is camouflaged to remove any visual cue about the upcoming change in terrain that would allow an anticipatory response. To maintain stability upon a sudden drop in substrate height and prevent a fall, the bird must compensate by dissipating energy or converting it to another form. The aim of this paper is to investigate the control strategies used by birds in this task. In particular, we assess the extent to which guinea fowl maintain body weight support and conservative spring-like body dynamics in the perturbed step. This will yield insight into how animals integrate mechanics and control to maintain dynamic stability in the face of real-world perturbations. Our results show that, despite altered body dynamics and a great deal of variability in the response, guinea fowl are quite successful in maintaining dynamic stability, as they stumbled only once (without falling) in the 19 unexpected perturbations. In contrast, when the birds could see the upcoming drop in terrain, they stumbled in 4 of 20 trials (20%, falling twice), and came to a complete stop in an additional 6 cases (30%). The bird's response to the unexpected perturbation fell into three general categories: (1) conversion of vertical energy (Ev=Ep+EKv) to horizontal kinetic energy (EKh), (2) absorption of Ev through negative muscular work (-ΔEcom), or (3) converting Ep to vertical kinetic energy (EKv), effectively continuing the ballistic path of the animal's center of mass (COM) from the prior aerial phase. However, the mechanics that distinguish these categories actually occur along a continuum with varying degrees of body weight support and actuation by the limb, related to the magnitude and direction of the ground reaction force (GRF) impulse, respectively. In most cases, the muscles of the limb either produced or absorbed energy during the response, as indicated by net changes in COM energy (Ecom). The limb likely begins stance in a more retracted, extended position due to the 26 ms delay in ground contact relative to that anticipated by the bird. This could explain the diminished decelerating force during the first half of stance and the exchange between Ep and EK during stance as the body vaults over the limb. The varying degree of weight support and energy absorption in the perturbed step suggests that variation in the initial limb configuration leads to different intrinsic dynamics and reflex action. Future investigation into the limb and muscle mechanics underlying these responses could yield further insight into the control mechanisms that allow such robust dynamic stability of running in the face of large, unexpected perturbations. [ABSTRACT FROM AUTHOR]