Clustering Application for Condition-based Maintenance in Time-varying Processes: A Review

In the field of industrial process monitoring, more and more interest is being shown in specific process categories. These include time-varying processes, that is, those processes whereby the response one receives as output from the system depends on when the input signal is sent into it. There are many reasons for this process variability and such contexts are not always analyzed with this operational characteristic at their core. At the same time, interest in certain categories of techniques is also becoming more prominent, to meet certain application needs. Among these, clustering and unsupervised techniques in general are gaining ground. This is largely due to the difficulty of finding fault data with which to train, for example, supervised models. On the other hand, the clustering technique, on which this contribution focuses, also makes it possible to compensate for the lack of complete knowledge of the structure of the process itself. With these two considerations in mind, this contribution proposes a literature review on the topic of clustering applied in time-varying contexts, in the maintenance field. The aim is to present an overview of the main fields of study, the role of clustering in this context and the main clustering techniques used.

Process Variability Analysis in Interconnect, Logic, and Arithmetic Blocks of 16-nm FinFET FPGAs

In the current work, we study the process variability of logic, interconnect, and arithmetic/DSP resources in commercial 16-nm FPGAs. We create multiple, soft-macro sensors for each distinct resource under evaluation, and we deploy them across the FPGA fabric to measure intra-die variation, as well as across multiple FPGAs to measure inter-die variation. The derived results are used to create device-signature variability maps characterizing the distribution of variability across the die. Our study includes decoupling of variability to systematic and stochastic parts, exploration of variability under various voltage and temperature conditions and correlation analysis between the variability maps of the different resources. Furthermore, we scrutinize the impact of variability on the performance of actual test circuits and correlate the retrieved results with the sensor-based maps. Our experimental results on four Zynq XCZU7EV FPGAs showed significant intra- and inter-die variability, up to 7.8% and 8.9%, respectively, with a small increase under certain operating conditions. The correlation analysis demonstrated a strong correlation between the logic and arithmetic resources, whereas the interconnects showed a slightly weaker correlation in specific devices. Finally, a relatively moderate correlation was calculated between the variability maps and performance of test circuits due their dissimilar operating behavior versus our sensors.

FinFET Inverter Designs: Behavior and Challenges of Process Variability

Abstract— Technology scaling alongside the increasing process variability impact in modern technology nodes are themain reasons to control deviations over metrics in IC nanome-ter designs. Schmitt Triggers are traditionally used for noise immunity enhancement, and have been recently applied to mitigate radiation effects and process variability impact. The main contribution of this work is to trace the relationship between transistor sizing, supply voltage, and process variability to get a low energy consumption circuit while still keeping low levels of deviations due to the impact of process-induced variability. It is shown that a cost-benefit analysis can highlight sets of sizing and supply voltage where it can provide a 37.51% decrease in energy consumption while only increasing its sensibility by 7.42%. Furthermore, it is presented that the dependence of supply voltage and sensibility to process variability is not directly related, with slight decreases in the supply volt-ages bringing better results. Overall, the traditional CMOS inverter is still the fastest and most energy-efficient circuit, although, when comparing noise immunity characteristics, the 6-Transistor Schmitt Trigger presents higher noise margins, slopes, gains, and hysteresis ratios. The improvements,although, may increase propagation times, energy consumption, and area.

Synthesis of Nanoporous Gold by Chemical Dealloying of Co-Sputtered Gold-Silver Thin Films and Study of Its Variability

In the past two decades, nanoporous metals have attracted wide attention in the areas of energy storage, biomedicine and catalysis. Compared to other metals, nanoporous gold exhibits superior chemical stability, high catalytic activity, and its synthesis is facile and well documented. While many studies elaborate on the dealloying kinetics to understand process-structure relationships, its process variability is known to be large and yet not well documented. In this study, nanoporous gold was synthesized by chemical dealloying of co-sputtered gold-silver thin film. By controlling temperature and time during dealloying, its porosity characteristics, such as ligament diameter and solid area fraction, were controlled. Further, the time evolution of structural and elemental characteristics of nanoporous gold were examined including its correlation to silver residual content. It is found that mean diameters grow as a function of etch time from 25 to 60 nm. The large standard deviation (18.6 nm) of multiple dealloying attempts at any given temperature and dealloying time points to the lack of control in the kinetics of the dealloying reaction and variability in its substrate preparation and processing protocols. A comprehensive analysis of these parameters might provoke a better understanding of nanoporous gold synthesis in terms of the structure evolution kinetics.

Complying with the Guideline for Quality and Equivalence for Topical Semisolid Products: The Case of Clotrimazole Cream

Semisolids constitute a significant proportion of topical pharmaceutical dosage forms available on the market, with creams being considered profitable systems for releasing active substances into the skin. This work aimed at the development of a generic Clotrimazole topical cream, based on the assumptions that assist the development of such formulations. First, the critical parameters to obtain a final formulation as similar as possible to the reference product were defined. Then, the percentages of cetyl palmitate and octyldodecanol were identified as critical variables and chosen for optimization in further studies. A “quality by design” approach was then used to identify the effect of process variability on the structural and functional similarity (Q3) of the generic product qualitatively (Q1) and quantitatively (Q2). A two-factor central composite orthogonal design was applied and eleven different formulations were developed and subjected to physicochemical characterization and product performance studies. The results were used to estimate the influence of the two variables in the variation of the responses, and to determine the optimum point of the tested factors, using a design space approach. Finally, an optimized formulation was obtained and analysed in parallel with the reference. The obtained results agreed with the prediction of the chemometric analysis, validating the reliability of the developed multivariate models. The in vitro release and permeation results were similar for the reference and the generic formulations, supporting the importance of interplaying microstructure properties with product performance and stability. Lastly, based on quality targets and response constraints, optimal working conditions were successfully achieved.