3D FE simulation for temperature evolution in the selective laser sintering process

A thermal model of selective laser sintering (SLS) has been developed. The model allows for the non-linear behavior of thermal conductivity and of specific heat due to temperature changes and phase transformations. The temperature evolution and the formation of the sintered part are simulated by a 3D finite element analysis based on continuous media theory. It is shown that the effect of sintering has a strong influence on thermal evolution through changing the thermal properties of the material. The results of the model were experimentally tested and confirmed by temperature measurements.     

Thermodynamic calculation of the O-Ti system

The O-Ti binary system has been assessed to produce Gibbs energy parameters for the condensed phases and were evaluated as representations of thermodynamic models. The liquid phase was described in terms of an association model with one associate, the bcc, A 2; cph, A 3 and fcc, A 1 phases were described as interstitial solid solutions, and the O₂Ti, O₃Ti₅, O₃Ti₂, and OTi oxides were considered to be stoichiometric compounds. The thermodynamic parameters were optimized taking into account experimental phase diagram and thermodynamic values from the literature. The phase diagram and the thermodynamic properties were calculated and compared with experimental data.     

The hydrogen evolution reaction on iron corroded in dilute and very dilute solutions of sulfuric acid

Permeation transients for hydrogen, generated by corrosion of iron in dilute solutions of sulfuric acid, were recorded with an improved electrochemical permeation apparatus.The mechanism of the hydrogen evolution reactions is coupled discharge hydrogen recombination for all methods of hydrogen generation, low current anodic polarization, cathodic polarization and corrosion.The experimental hydrogen transient was compared with that predicted theoretically.It is concluded that electrochemical hydrogen permeation is a sensitive tool for investigating processes on metal surfaces which are of engineering importance.     

Thermodynamic optimization of the AgCl-KCl and BaCl2-LiCl systems

The values of the thermodynamic properties of the liquid phase of the AgCl-KCl and BaCl₂-LiCl systems were optimized taking into account all the available experimental thermochemical and phase diagram information from the literature. Each liquid was described as a substitutional solution, and a Redlich-Kister formalism was used for the excess Gibbs energy.     

Public Key Cryptography in Action

This article discusses data security and controls, primarily in the context of data base management systems (DBMSs), with an emphasis on basic principles and mechanisms that have been successfully used by practitioners in actual products and systems. The general discussion does not focus on particular products, although a later section does review several products to illustrate previously discussed concepts. The discussion of data bases is limited specifically to relational DBMSs, which store data in relations that have specific mathematical properties. All examples given are in SQL. It is assumed that readers are familiar with rudimentary concepts of relational data bases and SQL.

This article begins with a review of basic security objectives, followed by a discussion of access controls in the current generation of commercially available DBMSs. The problem of multilevel security is then introduced, including a review of techniques developed specifically for multilevel security.     

Three-dimensional surface reconstruction using meshing growing neural gas (MGNG)

The neural network method, a relatively new method in reverse engineering (RE), has the potential to reconstruct 3D models accurately and fast. A neural network (NN) is a set of interconnected neurons, in which each neuron is capable of making autonomous arithmetic and geometric calculations. Moreover, each neuron is affected by its surrounding neurons through the structure of the network. This work proposes a new approach that utilizes growing neural gas neural network (GNG NN) techniques to reconstruct a triangular manifold mesh. This method has the advantage of reconstructing the surface of an n-genus freeform object without a priori knowledge regarding the original object, its topology or its shape. The resulting mesh can be improved by extending the MGNG into an adaptive algorithm. The proposed method was also extended for micro-structure modeling. The feasibility of the proposed method is demonstrated on several examples of freeform objects with complex topologies.     

Magnebike: A magnetic wheeled robot with high mobility for inspecting complex‐shaped structures

This paper describes the Magnebike robot, a compact robot with two magnetic wheels in a motorbike arrangement, which is intended for inspecting the inner casing of ferromagnetic pipes with complex‐shaped structures. The locomotion concept is based on an adapted magnetic wheel unit integrating two lateral lever arms. These arms allow for slight lifting off the wheel in order to locally decrease the magnetic attraction force when passing concave edges, as well as laterally stabilizing the wheel unit. The robot has the main advantage of being compact (180 × 130 × 220 mm) and mechanically simple: it features only five active degrees of freedom (two driven wheels each equipped with an active lifter stabilizer and one steering unit). The paper presents in detail design and implementation issues that are specific to magnetic wheeled robots. Low‐level control functionalities are addressed because they are necessary to control the active system. The paper also focuses on characterizing and analyzing the implemented robot. The high mobility is shown through experimental results: the robot not only can climb vertical walls and follow circumferential paths inside pipe structures but it is also able to pass complex combinations of 90‐deg convex and concave ferromagnetic obstacles with almost any inclination regarding gravity. It requires only limited space to maneuver because turning on the spot around the rear wheel is possible. This high mobility enables the robot to access any location in the specified environment. Finally the paper analyzes the maximum payload for different types of environment complexities because this is a key feature for climbing robots and provides a security factor about the risk of falling and slipping. © 2009 Wiley Periodicals, Inc.     

Aniline hydrogenolysis on nickel: effects of surface hydrogen and surface structure

Fluorescence yield near-edge spectroscopy (FYNES) above the carbon K edge and temperature programmed reaction spectroscopy (TPRS) have been used as the methods for characterizing the reactivity and structure of adsorbed aniline and aniline derived species on the Ni(100) and Ni(111) surfaces over an extended range of temperatures and hydrogen pressures. The Ni(100) surface shows appreciably higher hydrogenolysis activity towards adsorbed aniline than the Ni(111) surface. Hydrogenolysis of aniline on the Ni(100) surface results in benzene formation at 470 K, both in reactive hydrogen atmospheres and in vacuum. External hydrogen significantly enhances the hydrogenolysis activity for aniline on the Ni(100) surface. Based on spectroscopic evidence, we believe that the dominant aniline hydrogenolysis reaction is preceded by partial hydrogenation of the aromatic ring of aniline in the presence of 0.001 Torr of external hydrogen on the (100) surface. In contrast, very little adsorbed aniline undergoes hydrogen induced C-N bond activation on the Ni(111) surface for hydrogen pressures as high as 10^–7 Torr below 500 K. Thermal dehydrogenation of aniline dominates with increasing temperature on the Ni(111) surface, resulting in the formation of a previously observed polymeric layer which is stable up to 820 K. Aniline is adsorbed at a smaller angle relative to the Ni(111) surface than the Ni(100) surface at temperatures below the hydrogenolysis temperature. We believe that the proximity and strong -interaction between the aromatic ring of the aniline and the surface is one major factor which controls the competition between dehydrogenation and hydrogen addition. In this case the result is a substantial enhancement of aniline dehydrogenation relative to hydrogenation on the Ni(111) surface.