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The accompanying papers in the first issue of Entropy, volume 5, 2003 were presented at the electronic conference on Foundations of Information Science FIS 2002 (http://www.mdpi.net/fis2002/). The running title of this FIS e-conference was THE NATURE OF INFORMATION: CONCEPTIONS, MISCONCEPTIONS, AND PARADOXES. It was held on the Internet from 6 to 10 May 2002, and was followed by a series of discussions –structured as focused sessions– which took place in the net from 10 May 2002 until 31 January 2003 (more than 400 messages were exchanged, see: http://fis.iguw.tuwien.ac.at/mailings/). This Introduction will briefly survey the problems around the concept of information, will present the central ideas of the FIS initiative, and will contrast some of the basic differences between information and mechanics (reductionism).

A flexible needle has emerged as a crucial clinical technique in contemporary medical practices, particularly for minimally invasive interventions. Its applicability spans diverse surgical domains such as brachytherapy, cardiovascular surgery, neurosurgery and others. Notably, flexible needles find utility in biopsies requiring deep skin penetration to access infected areas. Despite its minimally invasive advantages, the precise guidance of the needle to its intended target, while avoiding damage to bones, blood vessels, organs and tissues, remains a significant challenge for researchers. Consequently, extensive research has been dedicated to enhancing the steering and accuracy of flexible needles. Here, we aim to elucidate the recent advancements, trends and perspectives in flexible needle steering models and path planning over the last 15 years. The discussed models encompass various types, including symmetric-tip needles, curved-tip needles, tendon-actuated needles, programmable needles and the innovative fracture-directed waterjet needles. Moreover, the paper offers a comprehensive analysis, comparing the trajectories followed by these needle models to attain the desired target with minimal tissue damage. By delving into these aspects, the paper contributes to a deeper understanding of the current landscape of flexible needle technology and guides future research directions in this dynamic field.

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.

Summary: Lunar-based equipment plays a vital role in the exploration of the moon because it undertakes the tasks of moving, transporting, digging, and so on. In order to control the gait of lunar-based equipment more precisely and guarantee mobile stability, the contact mechanism between its foot and lunar soil is worthy of in-depth study. In this paper, a contact model is proposed to predict the stress, strain, and displacement both on the contact surface and in the lunar soil when the foot is under vertical load. The axial stress in the proposed contact model is verified through the experiment and its accuracy in the lunar equipment is verified through simulation. The error is in a reasonable range and the influence depth of load conforms to the experiment results. This paper provides a relatively accurate model to describe the contact force between the lunar-based equipment’s foot and the lunar soil and will promote the research of lunar exploration.

Abstract In contrast to single‐phase materials the manufacturing process of composites creates multiscale interfaces among constituent materials and between laminar multilayers. Targeting the interfaces in these composite structures, this paper presents a perspective study on the impact safety of potential future composite rail vehicles. The aim is to conceptually explore the key role of interfacial discontinuities of composite material structures as they are a critical issue affecting the impact performance of future composite rail vehicles. Following a theoretical description, the issues are addressed in two parts. First, composite materials are characteristically analyzed from the perspective of their interfacial discontinuities within the materials and between the laminate multilayers to identify their influence. Second, the structural conditions required for crashworthiness are determined in relation to the dual requirements of global stability and local deformability for efficient energy absorption. The key findings are: (1) The interfacial discontinuities of the material phases and the designed structural assemblies need to be tailored for crashworthiness performance and (2) Global stability and locally deformability are the key dual requirements for the energy absorbing progressive deformations that are essential for application of composite for crashworthiness of rail vehicles. The research conceptually explores a key issue of the impact mechanics of composite structures from the perspective of impact safety of composite rail vehicles.

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.

This paper introduces an open-source pixel-wise Digital Image Correlation tool written in Python and targeting graphics processing units (GPUs) with the help of Cupy and Rapids-cuCim libraries. It is capable of computing the kinematic fields that transform an image into another in an efficient and quick way and it allows to treat large images in the GPU. Even if GCPU_OpticalFlow can be easily used by communities concerned by the estimation of displacement, it is particularly tuned to estimate consistent strain (gradient) field. The detection of a crack in a material is presented in this work as a demonstration.

Deep-sea mining, as a critical direction for the future development of mineral resources, places significant importance on the mechanical characteristics of its transportation pipelines for the safety and efficiency of the entire mining system. This paper establishes a simulation model of the deep-sea mining system based on oceanic environmental loads and the mechanical theory of deep-sea mining transportation pipelines. Through a static analysis, the effective tension along the pipeline length, the maximum values of bending moment, and the minimum values of bending radius are determined as critical points for the dynamic analysis of pipeline mechanical characteristic monitoring. A dynamic simulation analysis of the pipeline’s mechanical characteristics was conducted, and simulation sensor data were obtained as inputs for the prediction model construction. A prediction model of pipeline mechanical characteristics based on the BP neural network was constructed, with the model’s prediction correlation coefficients all exceeding 0.95, enabling an accurate prediction of pipeline state parameters.

Mobile ad-hoc networks (MANETs) and wireless mesh networks (WMNs) are used in a variety of research areas, including the military, industry, healthcare, agriculture, the Internet of Things (IoT), transportation, and smart cities. The swift advancement in MANET technology is the driving force behind this rising adoption rate. Routing over MANET is a critical problem due to the dynamic nature of the link qualities, even when nodes are static. A key challenge in MANETs is the need for an efficient routing protocol that establishes a route according to certain performance metrics related to the link quality. The routing protocols utilised by the nodes in WMNs and MANETs are distinct. Nodes in both types of networks exchange data packets through the routing protocols. For this highly mobile network, the ad-hoc On-Demand Distance Vector (AODV) routing protocol has been suggested as a possible solution. Recent years have attracted researchers’ attention to AODV since it is a routing technique for ad-hoc networks that prevents looping. The architecture of this routing protocol considers several factors, including the mobility of nodes, the failure of connection links, and the loss of packets. In this systematic review, one of the key focuses is bringing attention to the classic AODV, which was developed after discussing the recent development of several versions of AODV. The AODV routing protocol performs a path strength check to generate a more reliable and secure route between the source and destination nodes. In AODV, investigations demonstrate advances in both the format protocol approach and the network simulation-2 (NS-2), and these improvements were made in the same scenario used to revitalise AODV. It has been discovered that the AODV is more effective in several aspects, such as throughput, end-to-end delay, packet delivery ratio (PDR), energy consumption, jitter, packet loss ratio, and network overhead. Furthermore, this paper presents this systematic review based on AODV modifications in the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). It also provides a methodological framework for the papers’ selection.

The paper describes the results of the parametric analysis obtained using the multibody systems. Numerical analysis allows checking different variants of the weapon without the need of building a lot of experimental models. As a part of the analysis, the impact of the slide mass, the recoil spring stiffness, the friction coefficients, the propellant gas pressure, and the force of bullet engraving the barrel on the kinematic characteristics of the weapon were checked. The extreme values of the slide mass and the recoil spring stiffness were selected, after crossing them, the correct operation of the weapon would not be possible. The operation of the pistol was checked for its multiple variants, taking into account its lubrication, lack of lubrication, and lack of friction by appropriate selection of the friction coefficients. The propellant gas pressure variants were selected to reflect the pressure in the barrel during shoot using ammunition manufactured according to different standards and of different quality. The models, taking into account the force of bullet engraving the barrel and those ignoring such force, were developed to check their impact on the kinematic characteristics of a short recoil operated weapon.

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.

In this paper, a detailed validation of the passive material properties of mice carotid arteries and constants of the Fung and Holzapfel hyperelastic material laws is conducted by means of static nonlinear FEM analyses. The response of the carotid arteries in an inflation test is studied here for the following mouse models: wild-type, mdx, sgcd−/−, Eln+/+, Eln+/−, Fbln5+/+, and Fbln5−/−. All FEM computations are conducted on models that have been preliminarily checked for their reliability. The results of the calculations, namely, the relation between the internal pressure and the artery outer diameter, are verified against experimental responses and the applicability of the laws is assessed. New sets of Holzapfel constitutive relation constants are proposed for Eln+/+ and Fbln5−/− mice. Finally, the problem of carotid artery buckling is also discussed. The buckling pressures of the arteries are predicted using FEM models and nonlinear static analyses. These values are compared with the reference experimental results, which allow for further validation of the constitutive relations. The research emphasizes that computations and numerical methods enable an accurate description of bioengineering processes and behaviors but only if the models used are appropriately validated.

For the design and construction of the extended-reach well, the ultimate elongation capacity of the extended-reach well was studied. Given the drilling practice of extended-reach well, the extension limit prediction criterion of extended-reach well is established. In this paper, based on the drilling practice of extended-reach well, by the finite element method, the gap element method and the dynamic finite element method of the whole drill string, static analysis model of the extended-reach well and the mechanicsꞌ analysis model of drill string vibration are established. The frictional resistance condition and strength condition of the limit extension of the extended-reach well are solved respectively, and the extended limit prediction criterion of the extended-reach well is established. The software was prepared based on the model and theory, the model and software were validated with the example of drilling, and the average error of the calculated value is 6.94% when compared with the measured values in the field. It can meet the needs of drilling engineering and study of the extension capability of the extended-reach wells.

Design parameters are a crucial element of the product design process. However, design parameter models are often used to solve specific design problems. Generalizing design parameters is an approach to tackle more design problems. This study contributes to resolving certain limitations associated with modeling and representing the design parameters. This paper presents a generalized table of parameters (GTP) for modeling system parameters. This table is linked to a contextual database based on data and information collected from scientific databases, experts' interviews, and Computer-Aided Design (CAD) and Finite Element Modeling (FEM) software analysis and usage. The proposed representative table shows the robustness of integrating multiple sources of information to present a holistic and generalized view of the design system. The quality of the provided data in the table is assessed by applying certain evaluating dimensions and indicators. A case study will be presented on the lattice structure within a specific context in the mechanical field.

The control of a homing flying object, which a guided aerial bomb (GAB) is, takes place in the earth’s atmosphere, which may feature various atmospheric phenomena that are disturbances to the GAB control. The atmospheric disturbances include air turbulences, wind pockets, and wind gusts. For the purpose of the research discussed in this paper, the atmospheric disturbances were qualified as a stochastic process of power spectral density according to the Dryden model. This paper presents a method of controlling a GAB in motion through a turbulent atmosphere of the earth. The GAB was homed to a moving ground target by the most universal method of proportional navigation. The research discussed in this paper included an analysis of the effect of atmospheric disturbances on the target striking accuracy of a GAB moving along a vertical plane, the GAB flight trajectory, the values of force inputs which controlled the GAB flight, the values of actual attack angles, the values of kinematic transverse overloads, and the control errors input to the guidance controller. The numerical simulations were completed during the research in Matlab/Simulink, and certain results thereof are represented in a graphical format.

The paper presents the problems of applications of stratospheric systems to increase the tactical and reconnaissance capabilities of the Polish Armed Forces. The paper contains the results from examples of simulations which were designed to determine the cost/performance ratio of the production and operation of aerostats with strictly identified technical parameters in the context of their operational capabilities. It also describes the principles of operation of aerostats for the support of intelligence collection and the limitations imposed on aerostats by the specificity of tropospheric and stratospheric regions.

An analysis of application feasibility of a special method for surface-to-air missile (SAM) control during homing on an airborne target was carried out in this paper. A prior implementation of the method was motion control for a gyroscope axis with three degrees of freedom [1, 2] at the stages of spatial seeking and tracking of a detected target. The positive results obtained during that research led to a conclusion that the proposed control method would be appropriate for the determination of the control forces for missile guidance. This method consists of the application of the phase trajectories of control errors. Switching over of the control forces at suitable phase plane points reduced the control errors to zero and facilitated a proper flight path of the SAM. This paper presents a switching algorithm, equations of the kinematics and dynamics of SAM flight, and a number of examples of numerical simulations of the problem contemplated herein. The simulation results were represented in a graphic format.

Oil-immersion transformer plays an important role in the operation of power system, and its reliable operation is the basis of the safe and economic operation of power system. Transformer internal failure will not only cause the transformer to stop, but also damage, affecting the proper operation of the power system. The transformer is often in a high-temperature and high-pressure environment during its operation, so it is difficult to effectively and accurately protect the transformer from failure in the harsh working environment. Because the existing methods can not detect and protect the faults of transformer equipment sensitively and accurately, based on this, this paper carried out the research on the detection and protection of oil immersed transformer. By analyzing the calculation results, the relationship between the temperature rise of the transformer structure and the ambient temperature is discussed. It is found that the higher the ambient temperature of the transformer, the greater the harm to the equipment. High temperature area is mainly concentrated at the pull plate of transformer. This provides a reference for making the starting strategies of transformers in different environments, and helps to avoid mechanical structure damage and insulation aging damage caused by temperature.

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.

This paper presents the results of numerical simulations of non-stationary heat transfer in a 35 mm anti-air gun barrel cover made of composite materials. The cover protects the gun against weather conditions, including sea water effects, and serves as a protection against mechanical damage. It was assumed that heat coercion in this problem will be the heat condition reached by the material of the barrel with the cover removed, after firing three bursts of 7 shells each, 120 s after opening fire. It was assumed, that in the second 120, the gun crew installs the gun cover and at this point, the heating process begins, followed by cooling of the cover material. The problem of initial and boundary value in the barrel with a cover installed system was solved as a three-dimensional initial and boundary problem. The initial and boundary value model adopted for the coverless barrel and the calculation results for the first burst of seven shells was presented in paper [7]. To obtain the heat condition of the barrel in the second 120, it was necessary to perform calculations for the second and third bursts, and for the barrel cooling processes starting in the second 120. The calculations were performed with a finite element method in the COSMOS/M software [9]. The cover material temperature values obtained during the numerical simulation are well below the temperature of 387K, which could form the upper limit of the composite applicability temperature range.

“RT-400” rocket aerial target system is described in the paper; research method of its simplified external ballistics characteristics is presented and the obtained results are discussed. This system was designed, tested, and produced by a research team of the Institute of Defence Technologies at Kaunas University of Technology and successfully implemented in practice. One of main aims of this paper was to develop external ballistics’ model of a rocket propelled aerial target which would enable obtaining various ballistic parameters of the investigated vehicle such as its acceleration, velocity, flight angle, flight range and trajectory using as input the internal ballistics data obtained at earlier experimental research of the “RV-12K” rocket motor in a static horizontal test stand for thrust measurements and determination of other internal ballistics’ characteristics such as combustion chamber temperature and pressure. During the experimental research process of the vehicle, under test site conditions, the main aim was to compare accuracy of the obtained external ballistics simulation data with the data obtained during experimental approaches using additional measurement techniques such as radar tracking and crash site and launch site GPS coordinates marking.

Duplex stainless steels come under the difficult-to-machine category, considering the loss of the sensitive balance between the constituent phases due to thermal and mechanical working effects. Selective laser melting is emerging as an additive process for achieving near-net shape manufacturing solutions with these steels. Nevertheless, post-printing machining is essential to varying degrees and the machinability responses of the laser melted duplex stainless steels need sufficient attention. This paper addresses this gap, considering the experimental evaluation of the mechanics of machining with laser melted duplex stainless steels. Specimens printed with the most promising laser melting process conditions are evaluated for machinability, comparing with the wrought counterparts and also ascertaining the differential responses between the as-built and solution annealed states. Cutting forces and thermal measurements confirm better machinability with the laser melted samples which is an interesting finding considering the possibility of laser melting, machining, and post-process heat treatment as the best possible sequence of processing duplex stainless steels to circumvent the difficulties in machining.

This paper presents a selection of deliverables of a research project intended to develop a technology demonstrator for an active protection system smart counterprojectile. Numerical simulations were completed to analyse the effects of geometry and weight of the counterprojectile warhead on the counterprojectile flight (motion) parameters. This paper investigates four variants of the counterprojectile warhead shape and three variants of the counterprojectile warhead weight. Given the investigated geometric and weight variants, the PRODAS software environment was used to develop geometric models of the counterprojectile warhead, followed by the determination of the model aerodynamic characteristics. The final deliverable of this work are the results of the numerical simulation of the counterprojectile motion along the initial flight path length. Given the required activation of the active protection system in direct proximity of the protected object, the analyses of counterprojectile motion parameters were restricted to a distance of ten-odd metres from the counterprojectile launching system.

This paper presents the most important information and describes the activities of the 6th Congress of the Serbian Society of Mechanics which was held on mountain Tara, on 19- 21 June, 2017. The Congress was organized by the Serbian Society of Mechanics. Brief summaries of the plenary lectures and some of 99 accepted papers, which admittedly attracted the most interest were shown as well.

The aim of this paper is to described some teaching procedures that have been applied in the education on structures for architecture stu- dents at the National Autonomous University of Mexico (unam). Even though most of the architecture curricula at Mexican higher education institutions include the subjects of mechanics and geometry, they are taught separately and are not applied to architectural concepts and struc- tural design. In order to mitigate these undesirable teaching conditions, a group of professors has attempted to simultaneously incorporate me- chanics and geometry into the conception and design of structures. In response to the aforementioned circumstances, 'Mechametry' was cre- ated as a new subject in the unam architecture curriculum. Mechametry has been offered for 10 years to undergraduate students, as well as to students in the Design of Lightweight Structures specialization course. Nowadays, many former students are working for companies in Mexico and around the world and are directly involved in the design and con- struction of shells and other spatial structures, primarily tensile surface structures. Some selected projects by these students will be shown and described in this paper, as will projects that have received awards in inter- national contests for architecture students.

Flexible structures (FS) are thin shells with a pattern of holes. The stiffness of the structure in the normal direction is reduced by the shape of gaps rather than by the choice of the material based on mechanical properties such as Young’s modulus. This paper presents virtual prototyping of 3D printed flexible structures with selected planar patterns using laboratory testing and computer modeling. The objective of this work is to develop a non-linear computational model evaluating the structure’s stiffness and its experimental verification; in addition, we aimed to identify the best of the proposed patterns with respect to its stiffness: load-bearing capacity ratio. Following validation, the validated computational model is used for a parametric study of selected patterns. Nylon—Polyamide 12—was chosen for the purposes of this study as an appropriate flexible material suitable for 3D printing. At the end of the work, a computational model of the selected structure with modeling of load-bearing capacity is presented. The obtained results can be used in the design of external biomedical applications such as orthoses, prostheses, cranial remoulding helmets padding, or a new type of adaptive cushions. This paper is an extension of the conference paper: “Modeling and Testing of 3D Printed Flexible Structures with Three-pointed Star Pattern Used in Biomedical Applications” by authors Repa et al.

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.

The paper contains a literature review of studies on several firearms operation systems and a review of articles on modern methods of calculating the kinematic characteristics of weapons. It includes the presentation of the short recoil operated 9 mm PW INKA pistol numerical model. The model was created in the MCS Adams software which uses the multibody systems. The boundary conditions for each part were specified and their implementation was determined. As the preliminary results of numerical investigations, the slide and barrel velocity and displacement curves were obtained. Comparison of a numerical solution with the literature data allowed for its qualitative verification.

Based on investigation of existing folding wheelchairs’ usage, this paper analyzed wheelchair size and material in human-machine system model. The importance of new environmentally friendly materials’ application on wheelchair component producing in recent years was also explained. On the basis of strength and stiffness theory and calculation, applied materials were determined and rod mechanical calculation were carried out. The calculated results will have certain theoretical significance for wheelchair research and design.

Reluctance coil guns are electromagnetic launchers having a good ratio of energy transmitted to actuator volume, making them a good choice for propelling objects with a limited actuator space. In this paper, we focus on an application, which is launching real size soccer balls with a size constrained robot. As the size of the actuator cannot be increased, kicking strength can only be improved by enhancing electrical to mechanical energy conversion, compared to existing systems. For this, we propose to modify its inner structure, splitting the coil and the energy storage capacitor into several ones, and triggering the coils successively for propagating the magnetic force in order to improve efficiency. This article first presents a model of reluctance electromagnetic coil guns using a coupled electromagnetic, electrical and mechanical models. Four different coil gun structures are then simulated, concluding that splitting the kicking coil into two half size ones is the best trade-off for optimizing energy transfer, while maintaining an acceptable system complexity and controllability. This optimization results in robust enhancement and leads to an increase by 104 % of the energy conversion compared to a reference launcher used. This result has been validated experimentally on our RoboCup robots. This paper also proves that splitting the coil into a higher number of coils is not an interesting trade-off. Beyond results on the chosen case study, this paper presents an optimization technique based on mixed mechanic, electric and electromagnetic modelling that can be applied to any reluctance coil gun.

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.

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.

This paper presents the examples of fuze explosive trains designing methods, on the example of 25-mm ammunition fuze. There have been described two, possible to choose, design methods for explosive trains of fuzes. The first method relies on existing solutions using the serial-produced fuzes. The second one is to develop a completely new design explosive train. This paper focuses on the second method of design of explosive trains which can be implemented in two different ways. The first way is very time consuming, long-lasting and needs an experimental work to be done. In this method, we obtained the desired result by „trial and error method”. Second method uses mutually interrelated analytical calculation methods, computer simulations, experiments, and tests. In the case of this explosive train of fuze for 25-mm ammunition, the second method for design was used. As a result of that, the operating principle of explosive train of this fuze and subsequent stages of work on its components was described. The results of experimental tests and live tests on proving ground with the use of 25-mm ammunition was described as well.

The paper continues the authors’ studies on the influence of intermediate ballistics phenomena on increase in the projectile velocity. In a consecutive stage of investigations, studies of the presence of the muzzle brake on acceleration of the projectile in the transitional period are carried out. In the paper, the results of numerical study of the influence of presence and shape of muzzle brake on the projectile velocity increase in the intermediate ballistics period are presented. Numerical simulations of firing of 35 x 228 mm cartridge, with various bullets from the barrel with and without muzzle brake have been performed using the ANSYS FLUENT code. Changes of projectile velocity and changes of pressure and gas velocity inside and outside the barrel were calculated. The simulations indicate that presence of the muzzle brake only in merely degree affects increase in the projectile velocity in the case of the practise missile, while in the case of FAPSDST projectile, the increment of projectile velocity after the output of the barrel is lower when the muzzle brake is mounted on the muzzle. The results will be used in further research related to the modernization of 35-mm naval cannon.

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).

Students’ challenges in learning mechanics are well documented from test situations, and group discussions are considered a fruitful way to meet these challenges. In this paper, we present a study from an authentic teaching setting where upper secondary students in groups solve the task of calculating the acceleration of an elevator by means of a scale. The group work was audio recorded in three groups with different ability levels. Analysis was performed inductively using the analytical tool of semantic gravity and semantic waves. The results reveal multiple challenges solving the task, even among high-achieving secondary physics students. The study shows that for group discussions to be fruitful, students must be able to negotiate for meaning by alternating between different levels of semantic gravity. In this study, only the group consisting of relatively high-achieving students was able to do this. For the groups that did not succeed, this is found to be due to insufficient knowledge base, poor integration of the required concepts in their own language and inappropriate epistemological framing of the situation. It is concluded that more effort should be put into learning basic concepts than curricula and teaching traditions normally provide. This should include tasks carefully adapted to students’ ability, where students can practice alternation between levels of semantic gravity.

The advancement of fundamental sciences in recent decades has led to an increased focus on the prediction of phenomena occurring at the micro and nano scales. Micro- and nanostructures have a wide range of applications in various fields, such as aerospace and automobiles, and are widely used in nano- and micro-sized systems and devices, such as biosensors, nanoactuators, and nanoprobes. The design of these structures relies on a complete understanding of their physical and mechanical behaviors. Mechanics plays a crucial role at the micro- and nanoscales, from the generation of nanostructures to the properties of nanocomposite materials and the manufacturing and design of machines, structures, sensors, actuators, fluidics, and more. This Special Issue aims to bring together high-quality papers that advance the field of micro- and nanostructures and systems through the use of modern computational and analytical methods, in conjunction with experimental techniques, for their analysis, design, manufacture, maintenance, quality, and reliability.

This paper presents implementation and validation of a numerical model of the Twaron® CT709 fabric under impact of the 9 mm FMJ Parabellum projectile (with a soft lead core and a hard brass jacket with a velocity of 365 m/s). The fabric model was made with the use of Autodesk Inventor Professional 2012 program, and computer analysis was conducted with using the ANSYS-Autodyn v12.1.0 program. Geometrical model and strength parameters of the fabric were chosen from literature data. For the numerical analysis of soft body armour three variants of boundary conditions for the fabric were adopted. A sample with the dimensions of 50 x 50 mm made of 16 layers of the Twaron® CT709 fabric was used. The simulations for a quarter of the model with two planes of symmetry were performed. The physically correct behaviour of the fabric under the influence of penetration by a projectile was obtained in the numerical simulations and is demonstrated in this paper.

Measurement of physics processes at new energy frontier experiments requires excellent spatial, time, and energy resolutions to resolve the structure of collimated high-energy jets. In a future Muon Collider, beam-induced backgrounds (BIB) represent the main challenge in the design of the detectors and of the event reconstruction algorithms. The technology and the design of the calorimeters should be chosen to reduce the effect of the BIB, while keeping good physics performance. Several requirements can be inferred: (i) high granularity to reduce the overlap of BIB particles in the same calorimeter cell; (ii) excellent timing (of the order of 100 ps) to reduce the out-of-time component of the BIB; (iii) longitudinal segmentation to distinguish the signal showers from the fake showers produced by the BIB. Moreover, the calorimeter should operate in a very harsh radiation environment, withstanding yearly a neutron flux of 1014 n1MeV/cm2 and a dose of 100 krad. Our proposal consists of a semi-homogeneous electromagnetic calorimeter based on Lead Fluoride Crystals (PbF2) readout by surface-mount UV-extended Silicon Photomultipliers (SiPMs): the Crilin calorimeter. In this paper, we report the mechanical design for the development of a small-scale prototype, consisting of 2 layers of 3 × 3 crystals.

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.

Medical titanium alloy Ti-6Al-4V (TC4) is an ideal surgical implant material for human tissue repair and replacement. TC4 implantation will be in close contact with human soft tissue and has mechanical compatibility problems. In order to solve this problem, the hydrogel was formed on the surface of TC4 by utilizing the adhesion of dopamine, and the storage modulus of the formed hydrogel matched that of human soft tissue. In this paper, the surface of TC4 was first modified with dopamine (DA) and 2-bromoisobutyryl bromide (BIBB). 2-(2-methoxyethoxy) ethyl methacrylate (MEO2MA), oligo (ethylene oxide) methacrylate (OEGMA) and 2-methacryloyloxyethyl phosphorylcholine (MPC) are used as monomers, and methylenebisacrylamide (MBA) is used as cross-linking agent. Thermosensitive hydrogels were formed on the surface of modified TC4 by the ATRP technique. The successful synthesis of initiator and hydrogels on TC4 was demonstrated by Fourier transform infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS). The morphology of the hydrogel was observed by the scanning electron microscope (SEM), and the water absorption and temperature sensitivity were investigated by the swelling property. The thermal and mechanical properties of these gels were measured using thermal analysis system (TAS) and dynamic mechanical analyzer (DMA). The results show that the hydrogel on TC4 has good thermal stability and storage modulus that matches human soft tissue.

The study of social phenomena dominating the society, due to its unique conditions, needs improving and pondering. Although, in the first view, simulating the social phenomena with the mechanical phenomena may be considered illogical due to the complication of social issues, the authors of this paper intend to simulate them through simplicity so that they will demonstrate a more vivid analysis via simpler and more tangible manifestation of social problems and their consequences. To achieve proper and authentic results, the concepts and the definitions of mechanics are borrowed and exerted for the strategy of the investigation, which is conformable with social concepts. It has been tried, based upon the hints of this paper, to review and investigate the country`s social problems by challenging the terms such as stress, fatigue, etc. from two points of view. The first step is to hint the static concepts and their negative consequences and damages, and next, while reviewing dynamic concepts, the dynamic difficulties and awkwardness of the society are explained.

The development of the interior ballistics general model of gun propellant systems by taking into account the specificity of the recoilless propellant system is presented in this paper. The presented expanded physical and mathematical model makes possible the simulation of classical and nonclassical gun systems: two-chamber, mortar, and the considered recoilless one. To solve the system of equations associated with the mathematical model, a computer programme was developed. An analysis was made for two configurations of a recoilless system, differing in the way of arrangement of a propellant charge, i.e., with the propellant charge moving together with a projectile and with the propellant charge burning in a cartridge chamber. The obtained calculation results showed that the system, in which the propellant charge moves together with a projectile, has the maximum pressure and the muzzle velocity higher in comparison with the system with the propellant charge burning in a cartridge chamber. Influence of a way of placement of the propellant charge is the stronger, the higher is the ratio of its mass to the projectile mass. The results of the accomplished calculations, especially the pressure inside the barrel as well as motion parameters of the projectile make the grounds for projecting and construction optimization of the recoilless gun systems.

The conservation of paintings on canvas is closely associated with the understanding of their physico-mechanical properties. Using mechanical testing is essential when developing tools to assess the level of vulnerability and risks of mechanical degradation in paintings. This paper addresses a series of studies highlighting the need of a systemic approach to decision-making for structural treatments.

The conservation of paintings on canvas is closely associated with the understanding of their physico-mechanical properties. Using mechanical testing is essential when developing tools to assess the level of vulnerability and risks of mechanical degradation in paintings. This paper addresses a series of studies highlighting the need of a systemic approach to decision-making for structural treatments.

Systems biology postulates the balance between energy production and conservation in optimizing locomotion. Here, we analyzed how mechanical energy production and conservation influenced metabolic energy expenditure in stroke survivors during treadmill walking at different speeds. We used the body center of mass (BCoM) and segmental center of mass to calculate mechanical energy production: external and each segment's mechanical work (Wseg). We also estimated energy conservation by applying the pendular transduction framework (i.e. energy transduction within the step; Rint). Energy conservation was likely optimized by the paretic lower-limb acting as a rigid shaft while the non-paretic limb pushed the BCoM forward at the slower walking speed. Wseg production was characterized by greater movements between the limbs and body, a compensatory strategy used mainly by the non-paretic limbs. Overall, Wseg production following a stroke was characterized by non-paretic upper-limb compensation, but also by an exaggerated lift of the paretic leg. This study also highlights how post-stroke subjects may perform a more economic gait while walking on a treadmill at preferred walking speeds. Complex neural adaptations optimize energy production and conservation at the systems level, and may fundament new insights onto post-stroke neurorehabilitation. This article has and associated First Person interview with the first author of the paper.

Dessert organisms like sandfish lizards (SLs) bend and generate thrust in granular mediums to scape heat and hunt for prey [1]. Further, SLs seems to have striking capabilities to swim in undulatory form keeping the same wavelength even in terrains with different volumetric densities, hence behaving as rigid bodies. This paper tries to recommend new research directions for planetary robotics, adapting principles of sand swimmers for improving robustness of surface exploration robots. First, we summarize previous efforts on bio-inspired hardware developed for granular terrains and accessing complex geological features. Later, a rigid wheel design has been proposed to imitate SLs locomotion capabilities. In order to derive the force models to predict performance of such bio-inspired mobility system, different approaches as RFT (Resistive Force Theory) and analytical terramechanics are introduced. Even in typical wheeled robots the slip and sinkage increase with time, the new design intends to imitate traversability capabilities of SLs, that seem to keep the same slip while displacing at subsurface levels.

The common design of cyclone separators is the cylinder–on–cone design, and the conical shape has a strong effect on the behavior of the vortex core low in the cyclone. The “vortex length” is the distance between the lip of the gas outlet tube and the position at which the core of the vortex attaches to the wall of the cyclone separation space. This occurs spontaneously at an axial position that, at present, cannot be predicted, although it has a profound effect on the cyclone operation, since, if the vortex is too short, it can lead to plugging and wear. In this paper numerical CFD simulations, using advanced turbulence modeling (LES), are the basis for the formulation of models for the vortex length taking into account the geometrical and operational variables influencing it. The work leads to useful models for the vortex length and reveals important information about which variables determine it and the nature of their effects.

One direction of modern artillery ammunition development is to reduce its vulnerability to the effects of mechanical and thermal factors during transport, storage and operation. For LOVA, the reduced vulnerability of propellant explosives intended for loading into this ammunition is usually connected with a higher thermal ignition impulse threshold and reduced burning rate under low propellant gas pressure. Since 2016, work has been under way at the Military University of Technology (Warsaw, Poland), intended to develop a Polish low-vulnerability gun propellant for 120 mm tank ammunition. It was established during the initial stage of research and analysis, that the JA-2 gun propellant (more specifically, its energy and ballistics characteristics and geometrical dimensions of grains) will be the reference propellant for the low-vulnerability propellant in development. To this end, the authors performed closed vessel tests with JA-2 propellant (with seven-perforated grains designated LO5460). This paper contains comparative (with the JA-2 propellant) results of closed vessel tests of several propellant blends developed by the MUT Faculty of New Technologies and Chemistry research team. Closed vessel tests of these propellant blends were performed in the Ballistics Laboratory of the MUT Institute of Armament Technology using a manometric chamber with a volume W0 = 200 cm3. Experimental tests and theoretical analyses were performed based on provisions of the standardisation agreement STANAG 4115 [6], American military standard MIL-STD 286C [7] and original test procedures developed based on [8, 9]. The tests focused mainly on the issue of correlation between the chemical composition of the given propellant blend with the expected values of energy and ballistics characteristics in connection with the required shape of propellant grains.

The paper presents an analysis of the pictures, recorded from the testing ground investigations, obtained with application of the fast-digital camera Phantom v9.1. The analysis was focused on determination of the kinematics of motion of the launcher-missile system. TEMA Motion program was used for motion analysis of the investigated system. The courses of variability of kinematic values characterising motion of the selected points of the launcher were determined. The results analysis showed that the launcher undergoes the linear displacement (X, Y) and angular one (alpha) that cause significant differences in the flight trajectory of the successively launched missiles