Vibration analysis of machine tool’s hexapod table

Parallel mechanisms have found new applications in machine tool’s as the end effector carrying the spindle or used as the table of the machine. Investigations on the dynamics and especially the vibration behavior of these mechanisms are in the initial stage. The authors developed a vibration model for the hexapod table of milling machines and machining centers and derived the relevant explicit equations. The eigenvalue problem of the upper platform of hexapod was solved to obtain the natural frequencies of the platform. The results have been verified with FEM simulation. The distinguishing features of the hexapod tables from the view point of dynamic behavior have also been concluded.     

A generic construction to build simple oblivious transfer protocols from homomorphic encryption schemes

The Journal of Supercomputing - Oblivious transfer is a fundamental problem in cryptography where it is required that a sender transfers one of potentially many pieces of information to a receiver...     

Size-dependent nonlinear vibration of an electrostatic nanobeam actuator considering surface effects and inter-molecular interactions

In this paper, the size-dependent nonlinear vibration of an electrostatic nanobeam actuator is investigated based on the nonlocal strain gradient theory, incorporating surface effects. A comprehensive model regarding the von Karman geometrical nonlinearity, inter-molecular forces and both components of the electrostatic excitation (AC and DC) is proposed to explore the system behavior near the primary resonance. Utilizing Hamilton’s principle, the nonlinear equation of motion of the system is derived. The natural frequency and dynamic response of the system, comprising frequency and force response diagrams, are obtained analytically via multiple scales technique in conjunction with the differential quadrature method and validated through a numerical approach. The roles of the nonlocal and strain gradient parameters, surface elasticity, inter-molecular forces and quality factor on the system oscillations are examined. The acquired results unveiled that the size-dependent parameters can significantly displace the multi-valued portions and instability thresholds of the dynamical response. Furthermore, it is deduced that the surface effects induce the stiffness hardening of the nanobeam, whereas the inter-molecular forces impose the stiffness softening effect.

     

Splitting for strength: Manipulating polymerization reactor split ratios to control mechanical and rheological properties in bimodal polyethylene resins

This study integrates advanced mathematical modeling and experimental methodologies to investigate the simultaneous impact of modifications in the split ratio and molecular weight (MW) of chains on the rheological and mechanical properties of bimodal polyethylene (BiPE) resins. The outcomes underscored the viability of fine-tuning the molecular weight distribution (MWD) of a BiPE resin by augmenting the MW of high molecular weight (HMW) chains while simultaneously diminishing their proportion in the final alloy formulation. In addition, the experimental results illuminated the prospect of attaining a targeted melt flow index for the final polymers by elevating the MW of HMW chains alongside an increase in the proportion of low molecular weight chains. Significantly, these adjustments resulted in remarkable enhancements in the shear thinning index and strain hardening modulus of the fabricated resins.