Investigation of structure and mechanical properties of toughened poly(l‐lactide)/thermoplastic poly(ester urethane) blends

In this study, poly(l ‐lactide) (PLA) is melt‐blended with thermoplastic polyurethane (TPU) to modify the brittleness of PLA. An aliphatic ester‐based TPU was selected in order to have an ester sensitivity for degradation and an inherent biocompatibility. Using this compatible TPU, there was no need to apply problematic compatibilizers, so the main positive properties of PLA such as biocompatibility and degradability were not challenged. The detected microstructure of PLA/TPU blends showed that when the TPU content was lower than 25 wt %, the structure appeared as sea‐islands, but when the TPU content was increased, the morphology was converted to a cocontinuous microstructure. A higher interfacial surface area in the blend with 25 wt % TPU (PLA25) resulted in a higher toughness and abrasion resistance. The various analyses confirmed interactions and successful coupling of two phases and confirmed that melt‐blending of PLA with the aliphatic ester‐based TPU is a convenient, cost‐effective, and efficient method to conquer the brittleness of PLA. The prepared blends are general‐purpose plastics, but PLA25 showed an optimum mechanical strength, toughness, and biocompatibility suitable for a wide range of applications. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43104.     

Continuous-time feedforward SD modulators with robust lowpass STF

Continuous-time sigma-delta modulators are often implemented using the feedforward structure. This type of architecture is prone to large out-of-band peaking and degraded anti-aliasing filtering owing to its sensitivity to process variation. Two alternative continuous-time delta- sigma modulators, which exhibit significantly lower signal transfer function (STF) sensitivity, are described.     

Current-mode class AB design using floating voltage-source

A basis for class AB operation of current-mode CMOS circuits is presented. This has led to a new CMOS class AB current conveyor suitable for VLSI implementation. The CCII has a low input resistance with a variation of only 10% over the whole linear range     

Glitch reduction in second-generation SI circuits

A simple method for reducing the glitches of second-generation SI circuits is presented. For a given SI circuit it is sufficient to apply this technique only to the last stage     

Experimental and finite element analysis of EDM process and investigation of material removal rate by response surface methodology

In this study, thermal modeling and finite element simulation of electrical discharge machining (EDM) has been done, taking into account several important aspects such as temperature-dependent material properties, shape and size of the heated zone (Gaussian heat distribution), energy distribution factor, plasma flushing efficiency, and phase change to predict thermal behavior and material removal mechanism in EDM process. Temperature distribution on the cathode has been calculated using ANSYS finite element code, and the effect of EDM parameters on heat distribution along the radius and depth of the workpiece has been obtained. Temperature profiles have been used to calculate theoretical material removal rate (MRR) from the cathode. Theoretically calculated MRRs are compared with the experimental results, making it possible to precisely determine the portion of energy that enters the cathode for AISI H13 tool steel. Also in this paper, the effect of EDM parameters on MRR has been investigated by using the technique of design of experiments and response surface methodology. Finally, a quadratic polynomial regression model has been proposed for MRR, and the accuracy of this model has been checked by means of analysis of residuals.     

Experimental investigation and 3D finite element prediction of the white layer thickness, heat affected zone, and surface roughness in EDM process

An axisymmetric three-dimensional model for temperature distribution in the electrical discharge machining process has been developed using the finite element method to estimate the surface integrity characteristics of AISI H13 tool steel as workpiece. White layer thickness, depth of heat affected zone, and arithmetical mean roughness consisting of the studied surface integrity features on which the effect of process parameters, including pulse on-time and pulse current were investigated. Additionally, the experiments were carried out under the designed full factorial procedure to validate the numerical results. Both numerical and experimental results show that increasing the pulse on-time leads to a higher white layer thickness, depth of heat affected zone, and the surface roughness. On the other hand, an increase in the pulse current results in a slight decrease of the white layer thickness and depth of heat affected zone, but a coarser surface roughness. Generally, there is a good agreement between the experimental and the numerical results.     

Wide-angle beam steering using coupled-PLLs

A coupled-PLLs network suitable for phased-array systems is presented. The proposed structure uses phase-frequency detectors, instead of analogue multipliers, to achieve up to plusmn180deg phase shift between output signals. This improvement makes it possible to extend the scanning angle from plusmn30deg off the normal achieved through current coupled-oscillators to plusmn90deg.     

Compound current conveyor (CCII+ and CCII-)

A CMOS current conveyor configurable as CCII⁺ and/or CCII^- is proposed. The circuit has the advantages of providing two symmetrical outputs, presenting a low input resistance and giving a high output to input resistance ratio. An input resistance of 28 Ω with a zero at 6 MHz in a 0.5 μm implementation with a supply voltage of 3.3 V have been obtained     

Stochastic resonance in sigma-delta modulators

Occurrence of the stochastic resonance phenomenon in sigma-delta modulators is reported. It is shown that when the internal quantiser of a /spl Sigma//spl Delta/-modulator comprises a multitude of comparators and noise sources, the system exhibits improved performance for a certain amount of added noise.