An improved auto-tuning scheme for PI controllers

Ziegler-Nichols tuned PI and PID controllers are usually found to provide poor performances for high-order and nonlinear systems. In this study, an improved auto-tuning scheme is presented for Ziegler-Nichols tuned PI controllers (ZNPICs). With a view to improving the transient response, the proportional and integral gains of the proposed controller are continuously modified based on the current process trend. The proposed controller is tested for a number of high-order linear and nonlinear dead-time processes under both set-point change and load disturbance. It exhibits significantly improved performance compared to ZNPIC, and Refined Ziegler-Nichols tuned PI controller (RZNPIC). Robustness of the proposed scheme is established by varying the controller parameters as well as the dead-time of the process under control.     

Thermal stability of CeO<Subscript>2</Subscript>/ZrO<Subscript>2</Subscript> multilayer thin films prepared by pulsed laser deposition

Multilayers of CeO₂/ZrO₂ thin films were deposited on Si (100) substrates using pulsed laser deposition at an optimized oxygen partial pressure of 3×10⁻² mbar and at room temperature. The CeO₂ layer thickness was 10 nm, while the ZrO₂ layer thickness was varied as 10, 20 and 30 nm. CeO₂ and ZrO₂ layers were deposited alternately to obtain 25 bilayers. High temperature x-ray diffraction (HTXRD) results showed that the multilayer films had cubic ceria and tetragonal ZrO₂. Thermal expansion coefficients were calculated for CeO₂ and t-ZrO₂ and found to increase with the decrease of ZrO₂ layer thickness. The cross sectional transmission electron microscopy (XTEM) of CeO₂/ZrO₂ multilayer also indicated that ceria was found to be in cubic phase while zirconia contained predominantly tetragonal phase along with cubic phase in thermally annealed specimen.     

Is cloned code really stable?

Clone has emerged as a controversial term in software engineering research and practice. The impact of clones is of great importance from software maintenance perspectives. Stability is a well investigated term in assessing the impacts of clones on software maintenance. If code clones appear to exhibit a higher instability (i.e., higher change-proneness) than non-cloned code, then we can expect that code clones require higher maintenance effort and cost than non-cloned code. A number of studies have been done on the comparative stability of cloned and non-cloned code. However, these studies could not come to a consensus. While some studies show that code clones are more stable than non-cloned code, the other studies provide empirical evidence of higher instability of code clones. The possible reasons behind these contradictory findings are that different studies investigated different aspects of stability using different clone detection tools on different subject systems using different experimental setups. Also, the subject systems were not of wide varieties. Emphasizing these issues (with several others mentioned in the motivation) we have conducted a comprehensive empirical study where we have - (i) implemented and investigated seven existing methodologies that explored different aspects of stability, (ii) used two clone detection tools (NiCad and CCFinderX) to implement each of these seven methodologies, and (iii) investigated the stability of three types (Type-1, Type-2, Type-3) of clones. Our investigation on 12 diverse subject systems covering three programming languages (Java, C, C#) with a list of 8 stability assessment metrics suggest that (i) cloned code is often more unstable (change-prone) than non-cloned code in the maintenance phase, (ii) both Type 1 and Type 3 clones appear to exhibit higher instability than Type 2 clones, (iii) clones in Java and C programming languages are more change-prone than the clones in C#, and (iv) changes to the clones in procedural programming languages seem to be more dispersed than the changes to the clones in object oriented languages. We also systematically replicated the original studies with their original settings and found mostly equivalent results as of the original studies. We believe that our findings are important for prioritizing code clones from management perspectives.     

Factorial Design Approach to Investigate the Effects of Groundwater Cooccurring Solutes on Arsenic Removal by Electrocoagulation

Effects of groundwater cooccurring solutes such as phosphate (PO4), silicate (SiO3), bicarbonate (HCO3), calcium (Ca), and iron (Fe) on arsenic removal were investigated in this study. Investigation by two-level full-factorial designed experiments revealed that PO4 and SiO3 have negative effect on arsenic removal, whereas HCO3 has negligible positive effect. The effects of Ca and Fe present in groundwater have positive effect on arsenic removal by electrocoagulation (EC). Hypothesis testing at 5% significance level suggests that alkalinity (HCO3) is not an important parameter in arsenic removal by EC in naturally occurring pH range of water.     

Prediction of Arsenic Removal by Electrocoagulation: Model Development by Factorial Design

Model was developed by two-level five-factor full-factorial designed-experiment to predict arsenic removal from contaminated water by electrocoagulation. Five factors, namely arsenic concentration (As), solution volume (V); current (I), electrode area (A), and current processing time (t) were investigated. Among the factors, arsenic concentration (As) and volume (V) have negative effect, and area (A), time (t), and current (I) have positive effect on arsenic removal. Within the studied levels of the factors, variance analysis at 5% significance level indicated that electrode area is not significant in arsenic removal by electrocoagulation. The model predicted reasonably good arsenic removal (error<2%) from low (0.288 mg/L) and high (0.882 mg/L) initial arsenic concentrations in presence of naturally cooccurring solutes in the groundwater. For the range of operating variables studied, optimum removal of arsenic (98.56%) is obtained at higher arsenic concentration (1.18 mg/L), lower volume (1 L), higher current (3 A), and higher current processing time (120 s).     

A 4 bit highly energy and area efficient SC SAR ADC based on a combinational technique with reduced reset energy

A combinational method, based on hybrid and junction splitting techniques, is used to realize a 4 bit high energy efficient SC SAR ADC. The hybrid switching scheme is very energy efficient in which the first three comparison cycles do not consume any energy. In junction split technique, the total value of capacitors does not remain constant. Rather capacitors are appended as bits are being determined successively. The present method combines the features of these two methods to realize an even more energy efficient SC SAR ADC. Reset energy, in some cases, can seriously impact the overall efficiency of a SC SAR ADC. A study has been made about the normal reset energy and two step reset energy for the different cases. A table has been drawn to show the overall energy efficiency for normal conversion, conversion with single step reset and lastly conversion with two step reset for all the architectures.

     

A smart spectrum utilization approach using multiantenna‐based cognitive relays in cognitive radio network

Efficient spectrum utilization is a promising technique for a prolonged unused radio frequency (RF) spectrum in a wireless network. In this paper, an adaptive spectrum sharing cognitive radio (CR) network has been proposed consisting of a primary user (PU) and secondary user transmitter (SU ? Tx) that communicates with secondary user receiver (SU ? Rx) via multiantenna‐based proactive decode‐and‐forward (DF) relay selection scheme. In our model, strategically an adaptable joint venture on underlay/overlay protocol is defined based on channel occupancy using spectrum sensing technique. Here, secondary transmitters (i.e., source transmitter) continuously sense the PU activities by energy detector and can simultaneously transmit to secondary receivers. Depending on sensing result secondary transmitters automatically switches in underlay mode if PU is active otherwise operates in overlay mode. The advantage of this scheme is that the joint mode of transmission allows the SUs to maximize their transmission rate. The outage performance at SU ? Rx and closed‐form expressions of joint underlay/overlay protocol has been evaluated. The power control policies at different transmitter nodes are taken care of. With the same diversity order, a trade‐off between multiantenna and multirelay is shown. This comparison shows improvement in outage behavior when the count in relays surpasses the number of antennas. Finally, the analytical model of smart efficient spectrum utilization without harming license users in CR is validated by MATLAB simulation.     

Performance improvement of PI controllers through dynamic set-point weighting

Responses of high-order systems under Ziegler-Nichols tuned PI controllers (ZNPIs) are characterized by excessive oscillation with a large overshoot. Although, a fixed set-point weighting based PI controller (FSWPI) may decrease the overshoot considerably, it fails to reduce the oscillation in the set-point response. Moreover, both FSWPI and ZNPI exhibit equally poor load regulation. Keeping in mind an overall improved performance, we propose an online dynamic set-point weighting technique for ZNPIs. The dynamic set-point weighting factor (β_d) is heuristically derived from the instantaneous process trend. Performance of the proposed dynamic set-point weighting based PI controller (DSWPI) for various second- and third-order processes including a pH process shows a significant improvement during both the set-point and load disturbance responses over other methods. Stability and robustness of the proposed DSWPI are addressed. Effectiveness of the DSWPI is demonstrated through the real-time implementation on a practical DC position control system.     

Fuzzy tuned model based control for level and temperature processes

Microsystem Technologies - At present, model based controllers are being extensively used in process industries due to their simple tuning strategy. Internal model control (IMC) is one of the...