Spatial and attentional aftereffects of virtual reality and relations to cybersickness

Virtual Reality - Cybersickness describes the nausea and discomfort that frequently emerges upon exposure to a virtual reality (VR) environment. The extent to which cybersickness leads to temporary...     

Multi-objective optimization of functionally graded materials,thickness and aspect ratio in micro-beams embedded in an elastic medium

Optimal design of micron-scale beams as a general case is an important problem for development of micro-electromechanical devices. For various applications, the mechanical parameters such as mass, maximum deflection and stress, natural frequency and buckling load are considered in strategies of micro-manufacturing technologies. However, all parameters are not of equal importance in each operating condition but multi-objective optimization is able to select optimal states of micro-beams which have desirable performances in various micro-electromechanical devices. This paper provides optimal states of design variables including thickness, distribution parameter of functionally graded materials, and aspect ratio in simply supported FG micro-beams resting on the elastic foundation using analytical solutions. The elastic medium is assumed to be as a two-layered foundation including a shear layer and a linear normal layer. Also, the size effect on the mechanical parameters is considered using the modified strain gradient theory and non-dominated sorting genetic algorithm-II is employed to optimization procedure. The target functions are defined such that the maximum deflection, maximum stress and mass must be minimized while natural frequency and critical buckling load must be maximized. The optimum patterns of FG micro-beams are presented for exponential and power-law FGMs and the effect of theory type and elastic foundation discussed in details. Findings indicate that the elastic foundation coefficients and internal length scale parameters of materials have the significant influences on the distribution of design variables. It is seen that the optimum values of inhomogeneity parameter and aspect ratio for E-FG micro-beams predicted by the modified strain gradient theory are larger than those of the classical continuum theory. Also, the multi-objective optimization is able to improve the normalized values of mass, maximum deflection, buckling load and natural frequency of P-FG micro-beams.     

Control strategies on stable manifolds for energy-efficient swing-ups of double pendula

Optimal control problems for mechanical systems often arise in technical applications. To find solutions with minimal control effort, the system’s natural, uncontrolled dynamics can be used. Promising candidates to be considered for energy-efficient trajectories are highly dynamic, but uncontrolled motions on (un)stable manifolds of equilibria. In this contribution, we propose a control strategy for mechanical systems which sequences uncontrolled trajectories on (un)stable manifolds with short control manoeuvres to design a feedforward control. In particular, we present optimal swing-up solutions for a double pendulum which are based on trajectories on the stable manifold of the pendulum’s up–up equilibrium. To demonstrate the advantages of our approach compared to a black-box optimisation, we perform a post-optimisation with the optimal control sequence as an initial guess. The numerical results are evaluated in a simulation environment for the double pendulum on a cart and applied to a real test rig.     

Quasi-Binary Transition Metal Dichalcogenide Alloys: Thermodynamic Stability Prediction,Scalable Synthesis,and Application

Transition metal dichalcogenide (TMDCs) alloys could have a wide range of physical and chemical properties, ranging from charge density waves to superconductivity and electrochemical activities. While many exciting behaviors of unary TMDCs have been demonstrated, the vast compositional space of TMDC alloys has remained largely unexplored due to the lack of understanding regarding their stability when accommodating different cations or chalcogens in a single-phase. Here, a theory-guided synthesis approach is reported to achieve unexplored quasi-binary TMDC alloys through computationally predicted stability maps. Equilibrium temperature–composition phase diagrams using first-principles calculations are generated to identify the stability of 25 quasi-binary TMDC alloys, including some involving non-isovalent cations and are verified experimentally through the synthesis of a subset of 12 predicted alloys using a scalable chemical vapor transport method. It is demonstrated that the synthesized alloys can be exfoliated into 2D structures, and some of them exhibit: i) outstanding thermal stability tested up to 1230 K, ii) exceptionally high electrochemical activity for the CO₂ reduction reaction in a kinetically limited regime with near zero overpotential for CO formation, iii) excellent energy efficiency in a high rate Li–air battery, and iv) high break-down current density for interconnect applications. This framework can be extended to accelerate the discovery of other TMDC alloys for various applications.     

Turning Trash into Treasure: Additive Free MXene Sediment Inks for Screen-Printed Micro-Supercapacitors

Printed functional conductive inks have triggered scalable production of smart electronics such as energy-storage devices, antennas, wearable electronics, etc. Of particular interest are highly conductive-additive-free inks devoid of costly postdeposition treatments to eliminate sacrificial components. Due to the high filler concentration required, formulation of such waste-free inks has proven quite challenging. Here, additive-free, 2D titanium carbide MXene aqueous inks with appropriate rheological properties for scalable screen printing are demonstrated. Importantly, the inks consist essentially of the sediments of unetched precursor and multilayered MXene, which are usually discarded after delamination. Screen-printed structures are presented on paper with high resolution and spatial uniformity, including micro-supercapacitors, conductive tracks, integrated circuit paths, and others. It is revealed that the delaminated nanosheets among the layered particles function as efficient conductive binders, maintaining the mechanical integrity and thus the metallic conductive network. The areal capacitance (158 mF cm⁻²) and energy density (1.64 µWh cm⁻²) of the printed micro-supercapacitors are much superior to other devices based on MXene or graphene. The ink formulation strategy of “turning trash into treasure” for screen printing highlights the potential of waste-free MXene sediment printing for scalable and sustainable production of next-generation wearable smart electronics.     

Security of internet of things based on cryptographic algorithms: a survey

Wireless Networks - Internet of Things (IoT) is a new concept in Information and Communications Technology and its structure is based on smart objects communications. It contributes to controlling,...     

Random vibrations of functionally graded nanobeams based on unified nonlocal strain gradient theory

Microsystem Technologies - In present study the dynamic response of a functionally graded nanobeam supported by visco-elastic foundation to a stationary random excitation, based on non-local strain...     

Optimization of FX-70 refrigerant evaporative heat transfer and fluid flow characteristics inside the corrugated tubes using multi-objective genetic algorithm

In this study, the heat transfer optimization(evaporation) and the specification of the FX-70 zeotropic refrigerant flow inside a corrugated pipe have been investigated. Despite the low HTC(HTC), this type of refrigerant is highly applicable in low or medium temperature engineering systems during the evaporation process. To eliminate this defect, high turbulence and proper mixing are required. Therefore, using heat transfer(HT) augmentation methods will be necessary and effective. In order to find the most favorable operating conditions that lead to the optimum combination of pressure drop(PD) and HTC, empirical data, neural networks, and genetic algorithms(GA) for multi-objective(MO)(NSGA II) are used. To investigate the mentioned cases, the geometric parameters of corrugated pipes, vapor quality, and mass velocity of refrigerant were studied. The results showed that with vapor quality higher than 0.8 and corrugation depth and pitch of 1.5 and 7 mm, respectively, we would achieve the desired optimum design.     

Multiverse optimizer for structural damage detection: Numerical study and experimental validation

New optimization algorithms have been increasingly developed in the course of the recent years. The accuracy of identified results in optimization‐based damage detection methods depends on the objective function and optimization algorithm. This paper employs multiverse Optimizer (MVO) to solve the optimization‐based damage identification problem. Statistical results obtained by MVO are compared with those of sine cosine algorithm (SCA) and Harris hawks optimization (HHO) in order to perform a comparative study. Two objective functions are used in this optimization problem. The first one is based on the modal assurance criterion (MAC) and the second one on modified total modal assurance criterion (MTMAC). Numerical and experimental examples indicate that the combination of objective function based on MTMAC and MVO algorithm can provide accurate and reliable results in structural damage detection process. MAC is also rejected in competition with MTMAC. While using SCA‐MTMAC, the accuracy of the results is acceptable in some cases. However, HHO‐MTMAC gives weak results in most cases. MVO and SSA are the lowest, and HHO spends significantly more time in terms of computational cost.