Conditional mean- and median-based cumulative sum control charts for Weibull data

This article deals with the monitoring of censored data using the cumulative sum (CUSUM) control charts for Weibull lifetimes under type-I censoring. To develop an efficient CUSUM structure for censored data, we use the conditional expected value (CEV) and conditional median (CM) approaches. In particular, we focus on the detection of shifts in the mean of Weibull lifetimes assuming censored data. In addition to fixed/known parameter values, the effect of estimation is assessed on the detection power of control charts. The performance of the proposed charts is evaluated by the average run length (ARL). Furthermore, the ARL performance of CUSUM charts is compared with CEV- and CM-based exponentially weighted moving average (EWMA) control charts. Besides an extensive simulation study, the significance of the current work is illustrated by a data set on the response time of a thermostat experiment.     

Hierarchically Branched Siloxane Brushes for Efficient Harvesting of Atmospheric Water

Atmospheric water harvesting is considered a viable source of freshwater to alleviate water scarcity in an arid climate. Water condensation tends to be more efficient on superhydrophobic surfaces as the spontaneous coalescence-induced droplet jumping on superhydrophobic surfaces enables faster condensate removal. However, poor water nucleation on these surfaces leads to meager water harvest. A conventional approach to the problem is to fabricate micro- and nanoscale biphilic structures. Nonetheless, the process is complex, expensive, and difficult to scale. Here, the authors present an inexpensive and scalable method based on manipulating the water-repellent coatings of superhydrophobic surfaces. Flexible siloxane can facilitate water nucleation, while a branched structure promotes efficient droplet jumping. Moreover, ToF-SIMS analysis indicated that branched siloxane provides a better water-repellent coating coverage than linear siloxane and the siloxanes comprise hydrophilic and hydrophobic molecular segments. Thus, the as-prepared superhydrophobic surface, TiO₂ nanorods coated with branched siloxanes harvested eight times more water than a typical fluoroalkylsilane (FAS)-coated surface under a low 30% relative humidity and performed better than most reported biphasic materials.     

Carbide phases on iron-based Fischer-Tropsch synthesis catalysts part II: Some reaction studies

In Part I we have examined some aspects of the characterization and specific reactivity of iron catalysts for synthesis applications, with particular attention to the role of the iron carbide phases that are formed. In this part we continue this examination, but with more attention to reactivity and selectivity than to characterization, and with more attention to iron alloy formulations. However, the role of carbide formation is still an important overall factor in looking at results obtained.     

Generation of electrical energy using lead zirconate titanate (PZT-5A) piezoelectric material: Analytical,numerical and experimental verifications

Energy harvesting is the process of attaining energy from the external sources and transforming it into usable electrical energy. An analytical model of piezoelectric energy harvester has been developed to determine the output voltage across an electrical circuit when it is forced to undergo a base excitation. This model gives an easy approach to design and investigate the behavior of piezoelectric material. Numerical simulations have been carried out to determine the effect of frequency and loading on a Lead zirconate titanate (PZT-5A) piezoelectric material. It has been observed that the output voltage from the harvester increases when loading increases whereas its resonance frequency decreases. The analytical results were found to be in good agreement with the experimental and numerical simulation results.     

Endothermic Reactions between Mullite and Silicon Carbide in an Argon Plasma Environment

Reactions between SiC and mullite in an Ar plasma were investigated using a model composite in which a free-standing CVD SiC coupon was imbedded in mullite cement. After treatment in a radio frequency (RF) plasma, the Si content of the mullite in contact with SiC was found to be less than that in the starting material, and deposits were found on the walls of the plasma chamber due to the reaction of mullite with SiC as follows: Al₆Si₂O₁₃( s )+ SiC( s )= 3Al₂O₃( s )+ 3SiO( g )+ CO( g ). This reaction, which is endothermic (1405 kJ/mol at 1500 K), absorbs thermal energy and consequently prevents the rapid sintering which is observed for single-phase mullite in similar environments. As a consequence, it is suggested that RF plasma sintering probably cannot be used to densify SiC-reinforced mullite-matrix composites because of the resulting energy consumption and damage to the SiC phase.     

Ultrasmall microlens array based on vertically aligned carbon nanofibers

An ultrasmall tunable microlens with a diameter of 1.5 μm is fabricated using nematic liquid crystals (electrically tunable medium) and vertically aligned carbon nanofibers (CNFs, electrodes). Individual CNFs are grown at the center of circular dielectric regions. This allows the CNFs to produce a more Gaussian electric field profile and hence more uniformity in lens array switching.