The Stability of a Precessing and Nutating Viscoelastic Beam with a Tip Mass

AbstractThe present work aims at stability analysis of a uniformly precessing and nutating viscoelastic beam with a tip mass as a simple model of a polymeric mechanical arm. The motion of the beam is described as small deformations superposed on rigid body rotation about a point. The damping in the viscoelastic material is considered to be of non-viscous type. The material is modeled in the time-domain using a Voigt model and Maxwell model in parallel. The resulting parametric equations are derived in a rotating frame and analyzed using a variant of Hill's method. The stability borderlines are generated with precession and nutation speeds as parameters for materials with different frequency versus storage modulus and loss coefficient graphs. It is observed that the beam, which only precesses is also unstable for a certain range of non-zero nutation angles

Performance analysis of a hybrid one-sided magnetic exciter mounted on a piezoelectric stack

Abstract. The present work proposes a non-contact hybrid exciter especially useful for harmonic excitation of lightly damped structures/rotors. In the proposed exciter an electromagnet is placed on a piezoelectric stack and the extension of the piezoelectric stack is made almost equal to the displacement of the structure using a simple tracking control. This largely eliminates stiffness coupling between the structure/rotor and the exciter and non-linearity in the excitation force due to the vibration of the structure/rotor. The stiffness and inertia of the piezoelectric stack is considered in the analysis. A SIMULINK model of the combined structure and the exciter is developed for a full time-domain simulation of the excitation system

A study on the formation of crystalline phases during solidification and crystallization in the bulk metallic glass of Zr₅₃ Cu₂₁ A₁₀ Ni₈ Ti₈ composition

The present paper considers the formation of crystalline phases during solidification and crystallisation of the Zr53Cu21Al10Ni8Ti8 alloy. Solidification was carried out by a copper mould casting technique, which yielded a partially crystalline microstructure comprising a `big cube phase' in a dendritic morphology and a bct Zr2Ni phase. Detailed high-resolution microscopy was carried out to determine possible mechanisms for the formation of the crystalline phases. Based on microstructural examinations, it was established that the dendrites grew by the attachment of atomistic ledges. The bct Zr2Ni phase, formed during solidification and crystallisation, showed various types of faults depending on the crystallite size, and its crystallography was examined in detail. It has been shown that the presence of these faults could be explained by anti-site occupancy in the bct lattice of the Zr2Ni phase

An insight into the outer- and inner-sphere electrochemistry of oxygenated single-walled carbon nanohorns (o-SWCNHs)

The extremely large surface areas as well as connecting nanopores of single-walled carbon nanohorn (SWCNH) aggregates have been tested, for the first time to the best of our knowledge, as metal-free, stable and cheap electrocatalysts for heterogeneous electron transfer reactions involving inorganic redox couples, including f-block elements such as actinides. From systematic studies of heterogeneous electron transfer reactions, the electrochemically reversible outer-sphere heterogeneous surface insensitive electron transfer reaction involving [Ru(NH3)6]3+/[Ru(NH3)6]2+ and the electrochemically near-to-reversible inner-sphere heterogeneous surface sensitive electron transfer reaction involving [Fe(CN)6]3−/[Fe(CN)6]4− on oxygenated SWCNHs (i.e., o-SWCNHs) have been compared to heterogeneous electron transfer involving the quasi-reversible [U(VI)O2(CO3)3]4−/[U(V)O2(CO3)3]5− redox reaction on o-SWCNHs. It was evident that the oxygen containing functional groups of o-SWCNH could catalyze the electron transfer process between uranium species in solution and the working electrode happened by following surface-sensitive inner-sphere electron transfer mechanism. Furthermore, the electrochemical stability, repeatability and reproducibility of the o-SWCNH modified glassy carbon electrode were found to be analytically acceptable for studying the electrochemistry of uranium in alkaline solutions with high ionic strength

Experimental studies on the pathogenicity of Vibrio mimicus strains isolated in Bangladesh

Vibrio mimicus, a newly described species of the genus Vibrio has been isolated from stools of 14 patients with diarrhoea. Live cells of all the 14 strains tested caused accumulation of fluid in rabbit gut loops and diarrhoea in infant rabbits. Culture filtrates of all the strains caused increased capillary permeability in rabbit skin; however, five of the filtrates resembled cholera toxin in that they gave positive reactions in rabbit loops, chinese hamster ovarian and mouse adrenal cell monolayers and GM1 ELISA tests and were neutralized by cholera antitoxin. None of the strains produced heat-stable toxin or possessed invasive capability as determined by Sereny's test. Thus, V. mimicus strains were divided into a group which produced a toxin immunobiologically similar to cholera toxin and the rest producing a heat-labile toxin unrelated to that of V. cholerae