25th Anniversary Article: The Evolution of Electronic Skin (E‐Skin): A Brief History,Design Considerations,and Recent Progress

Human skin is a remarkable organ. It consists of an integrated, stretchable network of sensors that relay information about tactile and thermal stimuli to the brain, allowing us to maneuver within our environment safely and effectively. Interest in large‐area networks of electronic devices inspired by human skin is motivated by the promise of creating autonomous intelligent robots and biomimetic prosthetics, among other applications. The development of electronic networks comprised of flexible, stretchable, and robust devices that are compatible with large‐area implementation and integrated with multiple functionalities is a testament to the progress in developing an electronic skin (e‐skin) akin to human skin. E‐skins are already capable of providing augmented performance over their organic counterpart, both in superior spatial resolution and thermal sensitivity. They could be further improved through the incorporation of additional functionalities (e.g., chemical and biological sensing) and desired properties (e.g., biodegradability and self‐powering). Continued rapid progress in this area is promising for the development of a fully integrated e‐skin in the near future.     

Kinetics and mechanisms of H2S adsorption by alkaline activated carbon

Activated carbon adsorption is widely used to remove hydrogen sulfide (H2S), one of the major odorous compounds, from gas streams. In this study, the mechanisms of H2S adsorption by alkaline activated carbon were systematically studied. Two brands of commercial activated carbons were used as H2S adsorbents. A series of designed experiments were carried outto understand on a fundamental basis the differences in H2S removal capacity observed for the two types of carbons and samples for the same carbon obtained from different batches. The physicochemical and structural characteristics of the original and exhausted activated carbons were identified using several analytical approaches (i.e., XRF, SEM, XRD, and BET). The relationships between the adsorption performances of activated carbon for H2S and its physicochemical characteristics were discussed. The kinetics of the H2S adsorption was also studied using TGA/DSC system. Both physical adsorption and chemisorption played an important role in the H2S adsorption mechanisms with the studied carbons. Chemisorption was rapid and occurred mostly at the carbon surface whereas physical adsorption was relatively slow and mostly took place at the inner pores of carbon. Carbon II demonstrated the best performance of H2S removal due to its high capacity of both physical adsorption and chemisorption. Catalytic effects of transition metals might also contribute to enhancing the H2S oxidation.     

Design of robust envelope-constrained filter with orthonormal bases

In the continuous-time envelope-constrained (EC) filtering problem using an orthonormal filter structure, the aim is to synthesize an orthonormal filter such that the noise enhancement is minimized while the noiseless output response of the filter with respect to a specified input signal stays within the upper and lower bounds of the envelope. The noiseless output response of the optimum filter to the prescribed input signal touches the output boundaries at some points. Consequently, any disturbance in the prescribed input signal or error in the implementation of the optimal filter will result in the output constraints being violated. In this paper, we review a semi-infinite envelope-constrained filtering problem in which the constraint robustness margin of the filter is maximized, subject to a specified allowable increase in the optimal noisy power gain. Using a smoothing technique, it is shown that the solution of the optimization problem can be obtained by solving a sequence of strictly convex optimization problems with integral cost. An efficient optimization algorithm is developed based on a combination of the golden section search method and the quasi-Newton method     

Comparison of lipase-transesterified blend with some commercial solid frying shortenings in Malaysia

A transesterified experimental solid frying shortening was prepared from a palm stearin/palm kernel olein blend at 1∶1 ratio (by weight) by using Rhizomucor miehei lipase at 60°C for 6 h. The fatty acid (FA) and triacylglycerol compositions, polymorphic forms, melting and cooling characteristics, slip melting point (SMP), and solid fat content (SFC) of the transesterified blend were then compared with five commercial solid frying shortenings (three domestic and two imported) found in Malaysia. All the domestic shortenings contained nonhydrogenated palm oil or palm olein and palm stearin as the hard stock, whereas the imported frying shortenings were formulated from soybean oil and cottonseed oil and contained high level of β′ crystals. Trans FA were also found in these samples. The lipase-transesterified blend was found to be more β′-tending than the domestic samples. The SMP of the transesterified blend (47.0°C) fell within the range of the domestic samples (37.8–49.7°C) but was higher than the imported ones (42.3–43.0°C). All samples exhibited similar differential scanning calorimetry cooling profiles, with a narrow peak at the higher temperatures and a broad peak at the lower temperatures, even though their heating thermograms were quite different. Imported samples had flatter SFC curves than both the experimental and domestic samples. The domestic samples were found to have better workability or plasticity at higher temperatures than the imported ones, probably because they were formulated for a tropical climate.     

Synthesis,characterization and biophysical evaluation of the 2D Ti2CTx MXene using 3D spheroid-type cultures

MXenes are novel 2-D materials which have been extensively investigated for use in advanced biocomposites, water purification, biosensors, bioimaging and antibacterial systems. However, the knowledge associated with the mechanism of cytotoxic response is still limited to lack of verification against 3D spheroid-type cultures. Herein, we present a report on the in vitro cytotoxicity of Ti₂CT_x MXene against cervical cancer cell lines (HeLa) in a form of 3D spheroid with comparison to 2D cell culture system. Ti₂CT_x MXenes can be characterized by their multi-layered structure that is produced by the efficient elimination of Al and appearance of the surface functional groups. The biological results with 2D and 3D HeLa indicated that the Ti₂CT_x MXene was moderately cytotoxic to cells and the cytotoxicity was dose dependent. Our results showed that the toxicity of MXenes is potentially due to direct contact of the Ti₂CT_x MXene with the cell membrane wall. The Raman spectra suggested that the Ti₂CT_x MXenes interfered with the cytoplasmic proteins’ conformation and the surrounding microenvironment. This inherently modified the biochemistry of the cell membrane and caused cell apoptosis. This paper contributes to the pool of knowledge regarding the biocompatibility and biophysical properties of Ti₂CT_x MXene.     

Intensifying Heat Using MOF-Isolated Graphene for Solar-Driven Seawater Desalination at 98% Solar-to-Thermal Efficiency

Photothermal materials are crucial for diverse heating applications, but it remains challenging to achieve high energy conversion efficiency due to the difficulty to concurrently improve light absorbance and suppress heat loss. Herein, a zeolitic imidazolate framework-isolated graphene (G@ZIF) nanohybrid is demonstrated that utilizes ultrathin, heat-insulating ZIF layers, and G@ZIF interfacial nanocavity to synergistically intensify light absorbance and heat localization. Under artificial sunlight illumination (≈1 kW m⁻²), the G@ZIF film attains a maximum temperature of 120 °C in an open environment with a 98% solar-to-thermal conversion efficiency. Importantly, the porous ZIF layer allows small molecules/media to enter and access the embedded hot graphene surface for targeted heat transfer in practical applications. As a proof-of-concept, the G@ZIF-based steam generator realizes 96% energy conversion from light to vapor with near-perfect desalination and water purification efficiencies (>99.9%). This design is generic and can be extended to other photothermal systems for advanced solar-thermal applications, including catalysis, water treatments, sterilization, and mechanical actuation.     

Array interconnection for rearrangeable 2-D MEMS optical switch

Two-dimensional (2-D) microelectromechanical systems (MEMS) optical switches can be constructed by arranging the MEMS-actuated micromirrors as an array. We consider here the switching capability, routing, and optimization of the rectangular array interconnection on which the capability and efficiency of 2-D MEMS switches depend. The switching capability of a rectangular array is proved analytically. Two routing algorithms, namely, the most-bend routing and the least-bend routing, are developed, which, respectively, maximize and minimize the number of 2 /spl times/ 2 switches in the "bend" state. A method of counting the number of permutations realizable with a given number of switches in the "bend" state is proposed to evaluate the performance of both routing schemes. The understanding of the underlying interconnection pattern enables us to study the problem of constructing rearrangeable optical switches of arbitrary size.     

Suboptimal SISO decoding of systematic binary algebraic block codes

Previous work on concatenated single parity-check codes has yielded exceptionally good performance despite, or perhaps because of, their weak algebraic structure. In this article, maximum a posteriori single parity-check decoders are applied to the decoding of systematic binary algebraic block codes. Results for a range of Hamming codes show good performance compared to soft-decision brute force (maximum-likelihood) and algebraic decoding. The decoding complexity of the proposed technique grows only linearly with increasing block length.