NEM-FEM comparison on porthole die extrusion of AA-6082

Porthole die extrusion is a forming process used to manufacture hollow components with different shapes. This forming process is optimized to improve the welding line quality. Process optimization can be achieved by determining the influences that each process parameter has on the pressure along the welding plane. The construction complexity of the die results in research difficulty from an experimental point of view. Even the finite element method (FEM) presents relevant drawbacks primarily because of numerical codes are not capable of simulating the welding phase. Hence, the natural element method (NEM), which allows the joining phase of free surfaces, presents significant advantages. In this work, experimental results obtained using a flexible porthole die are discussed. A suitable 2D geometry was extracted from the die, and both FEM and NEM were conducted. A good agreement among the numerical results was recorded.     

Steady-state mathematical models of battery storage plants withline-commutated converters

Battery storage plants can be interfaced to electric power systems by AC/DC line-commutated converters, whose behavior is strongly influenced by AC and DC side interactions, and which can work in nonideal conditions such as those arising from voltage harmonics and imbalances. Mathematical models of battery storage plants with conventionally and nonconventionally controlled line-commutated converters are presented. The aim is to carry out a complete harmonic analysis in steady-state nonideal conditions. The models, which include the DC side of the converter, can be directly employed in an iterative harmonic analysis of a power system with converters. Numerical simulation results are discussed     

Study of the axially symmetric motion of an incompressible viscous fluid between two concentric rotating spheres

The research reported herein involves the study of the steady state and transient motion of a system consisting of an incompressible, Newtonian fluid in an annulus between two concentric, rotating, rigid spheres. The primary purpose of the research is to study the use of an approximate analytical method for analyzing the transient motion of the fluid in the annulus and the spheres which are started suddenly due to the action of prescribed torques. The problems include cases where: (a) one (or both) spheres rotate with prescribed constant angular velocities and (b) one sphere rotates due to the action of an applied constant or impulsive torque.In this research, the coupled solid and fluid equations of motion are linearized by employing the perturbation technique. The meridional dependence in these equations is removed by expanding the dependent variables in a series of Gegenbauer functions with variable coefficients and employing the orthogonality property of these functions. The equations for the variable coefficients are solved by separation of variables and Laplace transform methods. Results for the stream function, circumferential function, angular velocity of the spheres and torque coefficient are presented as a function of time for various values of the dimensionless system parameters.     

A Reconfigurable High-Speed Optical System for Integrated Local Communications

The introduction of optical fibers in local area networks makes it possible to implement wide-band communication systems integrating all the communication services (telephone, data, images, etc.) foreseen in future office scenarios. This paper describes a reconfigurable high-speed local communication system, which is currently under development at the Centro Studi e Laboratori Telecomunicazioni (CSELT), conceived to attain high reliability and efficiency features, therefore suitable for a wide range of application environments, such as automated offices, integrated manufacturing, hospitals, etc. The access organization is based on a hybrid (i.e., circuit and packet) protocol, which guarantees each type of traffic the required grade of service, while allowing an optimal exploitation of the transmission capacity. Fault-tolerance issues are taken as a guideline in the overall system conception and, in particular, in the transmission subsystem design. The transmission subsystem presently uses available optical technology to implement a loop-shaped bus topology capable of reconfiguring by means of a distributed algorithms, when a link or node fails.     

Assessing soil respiration by means of near-infrared diode laser spectroscopy

High-resolution diode laser spectroscopy in the near-infrared region is applied to the accurate measurement of soil respiration. In particular, the use of a diode-laser-based spectrometer has allowed the implementation, for the first time, of a static accumulation method capable of measuring soil respiration from continuous measurements of CO(2) concentrations, with minor perturbation on soil respiration as well as on CO(2) transport and emission. The system has been tested in a laboratory experiment by detection of CO(2) production from sandy matrices, inoculated with active soil microbes and supplied with different amounts of decomposable plant material. Respiration rates of all samples were then retrieved using a diffusion model. The results of the laboratory tests are in agreement with those expected on the basis of sample composition. Examples of operation with real soil samples are also reported. We discuss the possible field application of the system, in conjunction with closed static soil chambers.     

Electronic and transport properties of silicon nanowires

The electronic, structural and transport properties of silicon nanowires have been investigated with different approaches. The Empirical Tight-Binding model (ETB) and Linear Combination of Bulk Bands (LCBB) method are used to calculate effect of quantum confinement on electronic energies, bandgap and effective masses in silicon nanowires in function of Si cell size. Both hydrogenated and SiO₂ terminated silicon surfaces are studied. Transport properties of nanowires are obtained by applying the Non-Equilibrium Green Function (NEGF) method. NEGF approach has been used to describe nanoMOSFET devices based on Silicon nanowires.     

Designing hypermedia information retrieval systems for multimedia art catalogues

Abstract

Multimedia art catalogues present a number of recurring characteristics in both the type of data and the users involved, and in the type of operations required. Typical data include textual catalogue cards manageable through an information retrieval system (IRS), as well as textual captions, images, video, and speech, organizable as a hypermedia network. In this paper we propose a model for the design of these applications, and discuss its effectiveness in improving the quality of the application. The model exploits a multi-level design approach to organize data and access structures of the IRS, while the Entity-Relationship (E-R) approach, tailored to model hypermedia applications, is adopted to describe the structure of the documents and their links.     

Maintaining certification compliance of equipment used in hazardous (classified) locations

In order to understand how to maintain certification compliance of equipment used in hazardous (classified) locations, one must first have an understanding of what a hazardous (classified) location is and what the requirements are for the equipment certification. These will be explained in Part I by Cheryl Gagliardi, a senior engineer with FM Approvals. Part II will cover recommendations for end-user actions for maintaining the certification compliance and will be provided by Bob Baker, an industry consultant to Emerson Process Management.