Effect of long-chain monoacrylate on the residual monomer content, swelling and thermomechanical properties of SAP hydrogels

Residual monomer is an important factor, particularly in hygienic materials such as superabsorbent polymer (SAP) hydrogels. Recently, we reported different approaches to minimizing residual monomer content in SAPs. In this paper, the effect of a long-chain monomer, poly(ethylene glycol) methylether methacrylate (PEG.MEMA), on the residual monomer content of SAP networks of partially neutralized acrylic acid–PEG.MEMA is investigated. The aim of using PEG.MEMA in SAP synthesis was to reduce the glass transition temperature (T _g) of SAP. As the temperature that is conventionally used to dry SAP (70–110 °C) is lower than the T _g of ordinary SAPs, the polymer is in the glassy state during the heating stage. It was assumed that converting SAP from the glassy state to the rubbery state during drying would facilitate the removal of acrylic acid monomer (AA) from the gel, thus reducing the residual monomer content. The results showed that the use of PEG.MEMA led to a reduction in residual AA when the drying temperature was 100 °C. The residual AA was decreased from 169 to 95 ppm when the drying time was increased from 3 to 15 hours at 100 °C. This positive effect of PEG.MEMA on the level of unwanted residual AA became insignificant at a higher drying temperature (140 °C). The effects of PEG.MEMA content on the thermal and mechanical properties (in the dried state) and the rheological properties (in the water-swollen state) of the SAP hydrogels were also investigated. The swelling capacity and rate was studied in relation to the PEG.MEMA content. It was found that a high level of PEG.MEMA restricted both the absorption capacity and the rate of water absorption.     

A general treatment of piezoelectric double-inhomogeneities and their associated interaction problems

The present paper addresses an analytical method to determine the electroelastic fields over a double-phase piezoelectric reinforcement interacting with an ellipsoidal single-inhomogeneity. The approach is based on the extension of the electro-mechanical equivalent inclusion method (EMEIM) to the piezoelectric double-inhomogeneity system. Accordingly, the double-inhomogeneity is replaced by an electroelastic double-inclusion problem with proper polynomial eigenstrains-electric fields. The long- and short-range interaction effects are intrinsically incorporated by the homogenizing eigenfields. The equivalent double-inclusion is subsequently decomposed to the single-inclusion problems by means of a superposition scheme. The methodology is further extended to the piezoelectric multi-inhomogeneity, where the particle core is surrounded by many layers of coatings of ellipsoidal shapes. Through consideration of various examples, including (1) 2D and 3D interaction problems of a coated piezoelectric reinforcement near a lamellar inhomogeneity and (2) a two-phase spherical particle with thick coating of variable thickness, the validity and robustness of the present theory are thoroughly demonstrated.     

Two- and three-dimensional optical carrier generation determination in crystalline silicon solar cells

Two- and three-dimensional analyses of the distribution of optically generated charge carriers in textured crystalline silicon solar cells of arbitrary geometry have been performed. The simulation algorithm, developed for that purpose, is based on geometrical optics and ray tracing. It determines the dominant contributions to the optical generation within textured silicon exactly. The contribution of weakly absorbed long-wavelength photons is calculated using a Monte-Carlo simulation. The presented algorithm is fast and accurate and can also be used to calculate reflectance and transmittance spectra in excellent agreement with measurements. Two- and three-dimensional generation profiles in single- and double-sided textured solar cells are presented and discussed in detail. Examples for applications are given. Finally, the presented algorithm is compared with a pure Monte-Carlo algorithm.     

Finite element modeling of segmental chip formation in high-speed orthogonal cutting

An explicit, Lagrangian, elastic-plastic, finite element code has been modified to accommodate chip separation, segmentation, and interaction in modeling of continuous and segmented chip formation in highspeed orthogonal metal cutting process. A fracture algorithm has been implemented that simulates the separation of the chip from the workpiece and the simultaneous breakage of the chip into multiple segments. The path of chip separation and breakage is not assigned in advance but rather is controlled by the state of stress and strain induced by tool penetration. A special contact algorithm has been developed that automatically updates newly created surfaces as a result of chip separation and breakage and flags them as contact surfaces. This allows for simulation of contact between tool and newly created surfaces as well as contact between simulated chip segments. The work material is modeled as elastic/perfectly plastic, and the entire cutting process from initial tool workpiece contact to final separation of chip from workpiece is simulated. In this paper, the results of the numerical simulation of continuous and segmented chip formation in orthogonal metal cutting of material are presented in the form of chip geometry, stress, and strain contours in the critical regions.     

Issues in porting software from c to c++

This paper describes an experiment in the development of a small piece of software in both the languages C and C++ in a university setting. The C++ codes were found to be more modular than the corresponding C codes. Some of the other effects of C++ on program quality are very briefly discussed. The paper also discusses some of the errors that C programmers may make as novice C++ programmers, and the testing of object-oriented programs. Some of the error types possible in C++, but not in C, include delays in the flushing of output buffers and polymorphism.     

Computation of stress intensity factors (KI, KII) and T-stress for cracks reinforced by composite patching

To increase the operational life of defected structures, a repairing method using composite patches has been used to reinforce cracked components. Due to various advantages of composite materials, this method has received much attention from researchers and engineers. Considerable investigations have been performed to highlight the effect of bonded composite patches on the fracture parameters such as stress intensity factors (SIF) and J-integral. However the effect of composite patches on the T-stress, the constant stress term acting parallel to the crack, has not been investigated in the past. In this paper, the finite element method is carried out to analyze the effect of bonded composite patches for repairing cracks in pure mode I and also mixed mode I/II conditions, by computing the stress intensity factors and the T-stress, as functions of the crack length, the crack inclination angle and the type of composite material. In pure mode I condition, the finite element analysis is carried out for three different specimens: centre crack, double edge crack and single edge crack specimens. For mixed mode I/II condition the analysis is conducted on an inclined central crack of various slant angles. For both pure mode I and mixed mode I/II, the numerical results show that composite patching has considerable effect on the T-stress.     

The single-queue switch: a building block for switches withprogrammable scheduling

We introduce a new approach to ATM switching. We propose an ATM switch architecture which uses only a single shift-register-type buffering element to store and queue cells, and within the same (physical) queue, switches the cells by organizing them in logical queues destined for different output lines. The buffer is also a sequencer which allows flexible ordering of the cells in each logical queue to achieve any appropriate scheduling algorithm. This switch is proposed for use as the building block of large-stale multistage ATM switches because of low hardware complexity and flexibility in providing (per-VC) scheduling among the cells. The switch can also be used as scheduler/controller for RAM-based switches. The single-queue switch implements output queueing and performs full buffer sharing. The hardware complexity is low. The number of input and output lines can vary independently without affecting the switch core. The size of the buffering space can be increased simply by cascading the buffering elements     

Effect of Process Mismatches on Integrated CMOS Phased Arrays Based on Multiphase Tuned Ring Oscillators

Tuned ring oscillators are used to generate multiple phases of a sinusoid for a variety of applications including phased- array transceivers and clock and data recovery circuits. A variable-phase ring oscillator (VPRO) is presented that generates outputs with a controllable phase progression, enabling its use in a compact low-power single-chip phased-array transceiver architecture. The VPRO functionality is shown to be robust with respect to process and layout mismatches. This enables the implementation of integrated phased arrays with acceptable array performance even in the absence of mismatch calibration circuitry, which are essential in other phase-shifterless schemes such as coupled oscillator arrays. A prototype 24-GHz four-channel single-chip phased-array transceiver implemented in a 0.13-mum CMOS process is presented to validate these claims.