Analytical approach to the transition to thermal hopping in the thin- and thick-wall approximations

The nature of the transition from the quantum tunneling regime at low temperatures to the thermal hopping regime at high temperatures is investigated analytically in scalar field theory. An analytical bounce solution is presented, which reproduces the action in the thin-wall as well as thick-wall limits. The transition is first order for the case of a thin wall while for the thick wall case it is second order.Comment: Latex file, 22 pages, 4 Postscript figure

Vibration Control Analysis of Aircraft Wing by Using Smart Material

Many of the mechanical systems exposed to undesired vibrations. These vibrations are removed by using active vibration control (AVC) and hence stability the response of the system. Smart structure technology is used for vibration reduction. Therefore the aircraft wing is embedded by Piezoelectric as a sensor and actuator. This material has fast response times and generates large amounts of force. Active vibration control was achieved by used output feedback control. An aircraft wing is numerically modelled with a used shell element and a couple filed analysis on piezoelectric between the displacement and the voltage. Output feedback control has been inserted to a finite element method by using ANSYS parametric design language (APDL). The control of free and forced vibration for smart structure was investigated. Free vibration is produced by aerodynamic force (lift force) at maximum speed of the aircraft and by the initial condition. Harmonic excitation (sin wave) is considered in the forced vibration control by using a piezoelectric shaker. Active vibration control was studied with different control gains and actuation voltages which affected the vibration control. The effect of changing the position of PZT, collected pair on mass and stiffness of smart structure as passive control (Control OFF) was investigated and then the optimal location was found. Experimental works for active vibration control of smart structure have been presented to verify the closed loop simulations. Free vibration, force vibration and natural frequency are obtained for experimental works by LABVIEW programs. It was observed that APDL ANSYS results were well matched with the experimental results. Settling time for free vibration, when the control OFF, is 15s, and when the control ON it is 3s. Displacement Amplitude for force vibration when the control is OFF it is ± 0.04m and when the control is ON it is ± 0.0005m. Keywords: Smart material, Aircraft wing, Active vibration control

Synthesis and Characterization of New Mesomorphic Azo Compounds and Study their Photoluminesecence Properties

The preparation of a new Azo compounds of highly conjugated dimeric and polymeric liquid crystal to achieve the crystalline characteristics Which have structures assigned based on elemental analysis, IR 1HNMR and CHNS-O while mesogenic properties have been set for DSC and hot-stage polarizing optical microscopy. The compounds show enantiotropicnematic phase being displayed. The compounds show photoluminescence properties in the organic solution at room temperature, with the fluorescence band centered around 400 nm

A location aided fast handoff protocol for the next generation wireless systems

An important and challenging issue in the nextgeneration wireless systems (NGWS) is to support seamless handoff while moving between different integrated networks. This paper presents a location aided fast handoff protocol which is an improvement over the pre-registration low latency handoff proposed by the IETF. Pre-Registration requires layer 2 information that might not be present in the access technology being used. By processing geographical data information acquired through GPS related to mobile node movement and the coverage area of each foreign agent intelligent handoff decisions can be made, allowing more control over the actual handoff latency and buffering requirements

Finite Element Analysis and Modelling of Perlon - Fiberglass of a Prosthetic socket

Finite element analysis can be a useful tool in investigating the mechanical interaction between the residual limb and its prosthetic socket, and in computer-aided design and computer-aided manufacturing of prosthetic sockets. The intention of this paper was to analyze prosthetic socket of distinct materials and for different geometry for optimum design solution by finite element analysis. The finite element method (FEM) is a very powerful tool for analysing the behaviour of structures, especially when the geometry and mechanics are too complex to be modelled with analytical methods. A modified three dimensional finite element model of socket was developed in workbench of ANSYS 14.0 to find out the stress distribution and deformation pattern under functionally appropriate loading condition during normal gait cycle.  A variety of materials were used for the analysis of the socket like The optimization technique results showed that the best optimal design of the prosthetic above knee socket is in lay-up 4perlon 2fiber glass 4perlon design under temperature 20 . This study focuses on the analysis of patellar tendon bearing prosthetic sockets with integrated compliant features designed to relieve contact pressure between the residual limb and socket. In this study, the numerical results of stress distribution model of the prosthetic above knee socket showed that the values of maximum stress according to Von-Mises criterion results are increased with the increasing of temperatures. The best designs results of the prosthetic above knee socket are (94.64%) in lamination lay-up 4-2-4 under 20  where it took from pervious study. The procedure developed through this work can be used by future researchers and prosthetic designers in understanding how to better design transfemoral prosthesis. Keywords: Prosthetic; Safety factor; Finite element model; Socke

The Effect of Length on Free Vibration Response of Cantilever Beam

The point of this study is to find the best value of frictional and structural damping constant for different length of aluminum cantilever beam when applied 30 mm initial displacement at the tip of the cantilever beam, and get the vibration response of cantilever beam. Initial displacement is used to test dynamic characteristics of cantilever beam. This article is based on cantilever beam under initial displacement. For each length of beam there are specific values of mass (frictional) damping and stiffness (structural) damping. The value of stiffness damping will decrease and mass damping will increase at increasing the length of beam. Keywords: Cantilever beam, Finite Element Modeling, vibration response, initial displacement, mass damping, stiffness damping

The Effect of Length on Modal Analysis of Cantilever Beam with and without Piezoelectric

The fundamental technique to determine the dynamic characteristic of engineering structures is the modal analysis. From the modal analysis can determine the natural frequencies and mode shapes. The natural frequencies and mode shapes are determined through finite element modeling (FEM) using ANSYS APDL 15.0 (ANSYS Parametric Design Language). Keywords: Cantilever Beam, Finite Element Modeling (FEM), Modal Analysis

BEM-FEM of Coupling for Prosthetic Socket

In this study, the investigating of the mechanical interaction between the residual limb and its prosthetic socket, and in computer-aided design and computer-aided manufacturing of prosthetic sockets is solving numerically by using FEM-BEM coupling approach. This work tried to improve the deflection of the loading of Socket. The BEM techniques has been used to estimate a deflection at each distance for the main part of loading  that applied on Socket .In addition, a simplified stiffener has been added to optimize a moment of inertia of this main part thereby the deflection will be better , for this purpose a case study has been considered according to international standard for the Socket specification that investigated to illustrate the goal of this work Moreover, a physical problem governed by a linear elliptic partial deferential equation but with a socket (where this paper approximate Socket to shell ) discontinuity in the domain cannot be efficiently solved using the traditional boundary element method. This paper also shows how the Laplace equation can be solved in an interior region containing shell discontinuities by recasting it as an integral equation known as a boundary and shell integral equation and applying collocation to derive a method termed the boundary and Socket element method. Direct and indirect methods are derived and applied to a test problem.  The results show that using stabilized method enables us to get stable and accurate numerical approximations consistent with the physical configuration of the problem over rough mesh by using ANSYS Workbench 14.0 ,AutoCAD and COMSOL 5.2. Keywords: Finite element model; boundary element method; discontinuity; Socke

Generation and Stress Analysis in New Version of Novikov Helical Gear Combining Double Circular Arc and Crowned Involute Profiles

New version of Novikov helical gear combining double circular arc profile with crowned involute profile has been proposed in this paper. Generation of this gear is carried out using the required equations for these two profiles which are programmed using SOLIDWORK. To compare the resulting contact and bending stresses, three models of gear pairs are generated and investigated using finite element software package (ANSYS). The profiles of these models are as following: double circular arc for first model, crowned involute for second model, while the third model formed by combining double circular arc with involute crowned profiles. The results of stress analysis show that the generated stresses are lower in the proposed (combined) gear especially when the contact in the circular arc side. Keywords: Generation of gears, versions of Novikov Gears, circular arc gear, crowned involute gear, stress analysis in gears