Machining characteristics of micro EDM in water using high frequency bipolar pulse

Micro EDM using conventional pulse generators such as the RC type or transistor type with water as the dielectric fluid suffers from poor accuracy of machined structures due to electrolytic corrosion. In this study, a new high frequency bipolar pulse generator for micro EDM in water was developed in order to prevent electrolytic corrosion. The new pulse generator produced a high frequency bipolar pulse possessing a positive pulse duration of several hundred nanoseconds with a high repetition rate provided to the machining gap. Discharge characteristics of micro EDM using the new pulse generator were investigated. Machining characteristics were also investigated according to machining conditions such as the repetition rate, positive voltage, capacitance and resistivity. Using the new pulse generator, micro holes without electrolytic corrosion were successfully fabricated in deionized water and tap water. Machining time, tool wear and clearance using the new pulse generator in deionized water decreased compared with those using the RC circuit in kerosene.     

A methodology for determining the true stress-strain curve of SA-508 low alloy steel from a tensile test with finite element analysis

The true stress-strain curve of a material should be determined for plastic property input to numerical analysis. This study proposes a simple methodology for determining the true stress-strain curve of SA-508 Grade 3 Class 1 low alloy steel using limited information from a general tensile test with finite element analysis. Measured engineering stresses and strains can be reasonably converted to true stresses and strains under uniform deformation before necking. True stress-strains are difficult to determine after necking because of nonuniform deformation without specialized measurement techniques. Five post-necking strain hardening models are considered, namely, linear, swift, Ludwick, Hollomon-linear (HL) and Hollomon-linear-constant (HLC) models. The equations for each model can be determined using the results of the tensile test, which include the true stress-strain value at the maximum load point and the corrected true stress-strain value at the fracture point plus the Considere instability criterion. The HL and HLC models suggested that the engineering stress-strains from the finite element analysis are consistent with the experimental results.     

Pygidial Gland of Azteca NR. bicolor AND Azteca chartifex: Morphology and Chemical Identification of Volatile Components

The large paired reservoirs of the pygidial gland of Azteca nr. bicolor and A. chartifex represents the largest exocrine structure in the abdomen. The glands produce a secretion with a strong smell, which the ants release when they are disturbed. Analyses of the secretions by gas chromatography–mass spectrometry (GC-MS) revealed a mixture of iridoids and ketones. A. nr. bicolor contains 2-heptanone (8%) and a mixture of three iridodial isomers, with trans-trans-iridodial as the major component (32%). A. chartifex contains 6-methyl-5-hepten-2-one (13%) and the three isomeric iridodials with cis-trans-iridodial as the principal component (32%).     

Preparation and properties of UV-curable polyurethane acrylate ionomers

Ultraviolet (UV)-curable polyurethane acrylate ionomer (PUAI) prepolymers were synthesized from isophorone diisocyanate (IPDI), poly(methylene ether) glycol (PTMG), 2,2-bis(hydroxymethyl) propionic acid (DMPA), triethylamine (TEA), 2-hydroxy ethyl acrylate (HEA), and dibutyl tin dilaurate (DBT) as a catalyst. UV-curable polyurethane acrylate ionomer aqueous dispersion was formulated from the prepolymers, water (30 wt %), and 1-hydroxycyclohexylhenyl ketone (Irgacure 184) as a photoinitiator. The films of UV-cured polyurethane acrylate ionomer were formed by curing the dispersion using a medium-pressure mercury lamp (80 W/cm; λ max = 365 nm). Gel content decreased with increasing water content in the aqueous dispersion. Effects of DMPA content and molecular weight of PTMG and the degree of neutralization on the physical properties were investigated. It was found that the storage modulus increased with increasing DMPA content. Tensile modulus and strength decreased with increasing the molecular weight of PTMG from 650 to 2000. The glass transition temperature shifted to a higher temperature as the content of DMPA increased. As the degree of neutralization increased, the tensile strength and modulus decreased. However, the elongation at break increased. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:2153–2162, 1998     

Syndioselective propylene polymerization: Comparison of Me2C(Cp)(Flu)ZrMe2 with Et(Cp)(Flu)ZrMe2

The kinetics and stereochemical control of propylene polymerization initiated by syndiospecific isopropylidene(1-η⁵-cyclopentadienyl)(1-η⁵-fluorenyl)-dimethylzirconium–methyl aluminoxane (1/MAO) and (1-fluorenyl-2-cyclopentadienylethane)-dimethylzirconium–MAO (2/MAO) were investigated. The influence of MAO concentration and polymerization temperature (T_p) on polymerization kinetics and polypropylene properties, such as molecular weight, molecular weight distribution (MWD), and stereoselectivity, have been studied in detail. The activity of both catalytic systems is very sensitive to the concentration of MAO. The 1/MAO and 2/MAO catalysts record maximum activity when [Al]/[Zr] ratio is around 1300 and 2500, respectively. The activity and the degree of stereochemical control are also sensitive to T_p. The 2/MAO catalyst is much more thermally stable than 1/MAO catalyst; the former shows maximum activity at 80°C, whereas the latter shows maximum activity at 20°C. The cationic active species generated by 2/MAO is not so stereorigid as those by 1/MAO so that 2/MAO catalyst produces sPP of broad MWD (4.43–6.38) and low syndiospecificity at high T_p. When T_p is above 50°C, 2/MAO catalyst produces completely atactic polypropylene. The results of fractionation of sPP samples produced by 1/MAO and 2/MAO demonstrate that 1/MAO catalyst is characterized by uniform active sites, but 2/MAO is characterized by multiple active sites. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 973–983, 1998     

A framework for sharing product information across enterprises

Collaborative product commerce (CPC) is a newly emerging technology to support inter-enterprise collaboration through the product life-cycle. From the point of view of information technology, CPC is a software technology to integrate products, processes and resources of different enterprises using web technologies. In this paper, we propose a framework for integrating product information across enterprises, which is being developed by the Electronics and Telecommunications Research Institute (ETRI) as a part of a CPC project. The product metadata represented by an XML schema, which is compatible with the ISO STEP PDM (product Data Management) schema standard, is presented to semantically and schematically integrate distributed product information. Web services technologies are discussed to support the interoperability of application systems related to the product development, such as computer-aided design (CAD) and PDM, where most of these applications run in a distributed environment. Finally, we implement the framework to integrate distributed product information and application systems.     

Spigot Algorithm and Root Computing

The word spigot indicates that the "digits" (generally in a widened meaning) of the result number are extracted successively from left to right (as if pumped through a spigot) by using only integer arithmetic, as opposed to the iterative approach, where the result number as the whole is improved after each iteration step by using (high-precision) floating-point arithmetic. The approach of spigot computing as used in papers by S. Kamal Abdaly (Comm. ACM 13(1970)), S. Rabinowitz and S. Wagon (American Mathematical Monthly 102(3) (1995)), A. H. J. Sale (Comput. J. 11(1968)) is now systematized and correctness is formally proved; the way for achieving an arbitrary accuracy is shown.Then a method for computing roots of arbitrary rational numbers is developed. If a root is not rational, spigot approach is used to compute its decimal approximation with an arbitrary given accuracy; if the root is rational, its numerator and denominator are computed exactly. This method for root computing is absolutely reliable: it is both formally proved and tested by numerical examples.     

An automatic diabetes diagnosis system based on LDA-Wavelet Support Vector Machine Classifier

In this paper, an automatic diagnosis system for diabetes on Linear Discriminant Analysis (LDA) and Morlet Wavelet Support Vector Machine Classifier: LDA–MWSVM is introduced. The structure of this automatic system based on LDA-MWSVM for the diagnosis of diabetes is composed of three stages: The feature extraction and feature reduction stage by using the Linear Discriminant Analysis (LDA) method and the classification stage by using Morlet Wavelet Support Vector Machine (MWSVM) classifier stage. The Linear Discriminant Analysis (LDA) is used to separate features variables between healthy and patient (diabetes) data in the first stage. The healthy and patient (diabetes) features obtained in the first stage are given to inputs of the MWSVM classifier in the second stage. Finally, in the third stage, the correct diagnosis performance of this automatic system based on LDA–MWSVM for the diagnosis of diabetes is calculated by using sensitivity and specificity analysis, classification accuracy, and confusion matrix, respectively. The classification accuracy of this system was obtained at about 89.74%.     

Encapsulation of organic light-emitting devices by means of photopolymerized polyacrylate films

For encapsulation of organic light-emitting devices (OLEDs) built on glass substrate, photopolymerizable blend consists of pentaerythritol triacrylate (PETIA) and HSP188 (photoinitiator) was spin-coated onto an OLED and then cured to form a cross-linked passivation layer. The electroluminescence (EL) and the rate of degradation were examined to compare the electrical and the emissive properties of the device before and after forming the passivation layer. In this case, wet process encapsulation, which did not influence the EL characteristic of the device, enhanced the lifetime of the device in air.