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 Performance Indicator for Reduction in Vulnerability Through Stabilization of Plutonium

The US Department of Energy (DOE) is currently storing several metric tons of plutonium in various forms in a variety of facilities throughout the DOE complex. Since the cessation of weapons production in 1990, many of these facilities with plutonium in storage have not operated. Since the shutdown was regarded as temporary, little attempt was made at that time to empty the process lines of plutonium, or to place the plutonium in containers or packages that would provide safe storage for extended periods of time. As a result, the packages and containers providing interim storage are vulnerable to failure through leakage, rupture and other modes, and pose potential hazards to facility workers, the public and the environment. Here, an approach to measuring and tracking the reduction in vulnerabilities resulting from stabilizing and repackaging plutonium is developed and presented. The approach utilizes results obtained by the DOE Working Group on the vulnerabilities associated with plutonium storage

Nuclear uncertainties in the NeNa-MgAl cycles and production of 22Na and 26Al during nova outbursts

Classical novae eject significant amounts of nuclear processed material into the interstellar medium. Among the isotopes synthesized during such explosions, two radioactive nuclei deserve a particular attention: 22Na and 26Al. In this paper, we investigate the nuclear paths leading to 22Na and 26Al production during nova outbursts by means of an implicit, hydrodynamic code that follows the course of the thermonuclear runaway from the onset of accretion up to the ejection stage. New evolutionary sequences of ONe novae have been computed, using updated nuclear reaction rates relevant to 22Na and 26Al production. Special attention is focused on the role played by nuclear uncertainties within the NeNa and MgAl cycles in the synthesis of such radioactive species. From the series of hydrodynamic models, which assume upper, recommended or lower estimates of the reaction rates, we derive limits on the production of both 22Na and 26Al. We outline a list of nuclear reactions which deserve new experimental investigations in order to reduce the wide dispersion introduced by nuclear uncertainties in the 22Na and 26Al yields.Comment: 46 pages, 4 figures. Accepted for publication in The Astrophysical Journa

Cholesterol Corrects Altered Conformation of MHC-II Protein in Leishmania donovani Infected Macrophages: Implication in Therapy

Previously we reported that Kala-azar patients show progressive decrease in serum cholesterol as a function of splenic parasite burden. Splenic macrophages (MΦ) of Leishmania donovani (LD) infected mice show decrease in membrane cholesterol, while LD infected macrophages (I-MΦ) show defective T cell stimulating ability that could be corrected by liposomal delivery of cholesterol. T helper cells recognize peptide antigen in the context of class II MHC molecule. It is known that the conformation of a large number of membrane proteins is dependent on membrane cholesterol. In this investigation we tried to understand the influence of decreased membrane cholesterol in I-MΦ on the conformation of MHC-II protein and peptide-MHC-II stability, and its bearing on the antigen specific T-cell activatio