Chemical effect on the Van Hove singularity in superconducting kagome metal AV3Sb5 (A = K, Rb, and Cs).

To understand the alkali-metal-dependent material properties of recently discovered AV3Sb5 (A = K, Rb, and Cs), we conducted a detailed electronic structure analysis based on first-principles density functional theory calculations. Contrary to the case of A = K and Rb, the energetic positions of the low-lying Van Hove singularities are reversed in CsV3Sb5, and the characteristic higher-order Van Hove point gets closer to the Fermi level. We found that this notable difference can be attributed to the chemical effect, apart from structural differences. Due to their different orbital compositions, Van Hove points show qualitatively different responses to the structure changes. A previously unnoticed highest lying point can be lowered, locating close to or even below the other ones in response to a reasonable range of bi- and uni-axial strain. Our results can be useful in better understanding the material-dependent features reported in this family and in realizing experimental control of exotic quantum phases.

High-Temperature-Operable Electromechanical Computing Units Enabled by Aligned Carbon Nanotube Arrays.

Nano/micro-electromechanical (NEM/MEM) contact switches have great potential as energy-efficient and high-temperature-operable computing units to surmount those limitations of transistors. However, despite recent advances, the high-temperature operation of the mechanical switch is not fully stable nor repetitive due to the melting and softening of the contact material in the mechanical switch. Herein, MEM switches with carbon nanotube (CNT) arrays capable of operating at high temperatures are presented. In addition to the excellent thermal stability of CNT arrays, the absence of a melting point of CNTs allows the proposed switches to operate successfully at up to 550 °C, surpassing the maximum operating temperatures of state-of-the-art mechanical switches. The switches with CNTs also show a highly reliable contact lifetime of over 1 million cycles, even at a high temperature of 550 °C. Moreover, symmetrical pairs of normally open and normally closed MEM switches, whose interfaces are initially in contact and separated, respectively, are introduced. Consequently, the complementary inverters and logic gates operating at high temperatures can be easily configured such as NOT, NOR, and NAND gates. These switches and logic gates reveal the possibility for developing low-power, high-performance integrated circuits for high-temperature operations.

Formation of sub-100-nm suspended nanowires with various materials using thermally adjusted electrospun nanofibers as templates.

The air suspension and location specification properties of nanowires are crucial factors for optimizing nanowires in electronic devices and suppressing undesirable interactions with substrates. Although various strategies have been proposed to fabricate suspended nanowires, placing a nanowire in desired microstructures without material constraints or high-temperature processes remains a challenge. In this study, suspended nanowires were formed using a thermally aggregated electrospun polymer as a template. An elaborately designed microstructure enables an electrospun fiber template to be formed at the desired location during thermal treatment. Moreover, the desired thickness of the nanowires is easily controlled with the electrospun fiber templates, resulting in the parallel formation of suspended nanowires that are less than 100 nm thick. Furthermore, this approach facilitates the formation of suspended nanowires with various materials. This is accomplished by evaporating various materials onto the electrospun fiber template and by removing the template. Palladium, copper, tungsten oxide (WO3), and tin oxide nanowires are formed as examples to demonstrate the advantage of this approach in terms of nanowire material selection. Hydrogen (H2) and nitrogen dioxide (NO2) gas sensors comprising palladium and tungsten oxide, respectively, are demonstrated as exemplary devices of the proposed method.

Dual-Scale Porous Composite for Tactile Sensor with High Sensitivity over an Ultrawide Sensing Range.

Porous structures have been utilized in tactile sensors to improve sensitivity owing to their excellent deformability. Recently, tactile sensors using porous structures have been used in practical applications, such as bio-signal monitoring. However, highly sensitive responses are limited to the low-pressure range, and their sensitivity significantly decreases in a higher-pressure range. Several approaches for developing tactile sensors with high sensitivity overing a wide pressure range have been proposed; however, achieving high sensitivity and wide sensing range remains a crucial challenge. This report presents a carbon nanotube (CNT)-coated CNT-polydimethylsiloxane (PDMS) composite having dual-scale pores for tactile sensors with high sensitivity over a wide pressure range. The porous polymer frame formed with dense pores of dual sizes facilitates the closure of large and small pores at low and high pressures, respectively. This results in an apparent increase in the number of contact points between the CNT-CNT at the pores even under a wide pressure range. Furthermore, the piezoresistivity of the CNT-PDMS composite contributes to achieving a high sensitivity of the tactile sensor over a wide pressure range. Based on these mechanisms, various human movements over a broad pressure spectrum are monitored to investigate the practical usefulness of the sensor.

Highly Sensitive Flexible Tactile Sensors in Wide Sensing Range Enabled by Hierarchical Topography of Biaxially Strained and Capillary-Densified Carbon Nanotube Bundles.

Flexible tactile sensors with high sensitivity have received considerable attention for their use in wearable electronics, human-machine interfaces, and health-monitoring devices. Although various micro/nanostructured materials are introduced for high-performance tactile sensors, simultaneously obtaining high sensitivity and a wide sensing range remains challenging. Here, a resistive tactile sensor is presented based on the hierarchical topography of carbon nanotubes (CNTs) prepared by a low-cost and straightforward manufacturing process. The 3D hierarchical structure of the CNTs over large areas is formed by transferring vertically aligned CNT bundles to a prestrained elastomer substrate and subsequently densifying them through capillary forming, providing a monotonic increase in the contact area as applied pressure. The deformable and hierarchical structure of CNTs allows the sensor to exhibit a wide sensing range (0-100 kPa), high sensitivity (141.72 kPa-1 ), and low detection limit (10 Pa). Additionally, the capillary-formed CNT structure results in increased durability of the sensor over repeated pressures. Based on these advantages, meaningful applications of tactile sensors, such as object recognition gloves and multidirectional force perceptions, are successfully realized. Given the scalable fabrication method, 3D hierarchically structured CNTs provide an essential step toward next-generation wearable devices.

Recent Progress in Flexible Tactile Sensors for Human-Interactive Systems: From Sensors to Advanced Applications.

Flexible tactile sensors capable of measuring mechanical stimuli via physical contact have attracted significant attention in the field of human-interactive systems. The utilization of tactile information can complement vision and/or sound interaction and provide new functionalities. Recent advancements in micro/nanotechnology, material science, and information technology have resulted in the development of high-performance tactile sensors that reach and even surpass the tactile sensing ability of human skin. Here, important advances in flexible tactile sensors over recent years are summarized, from sensor designs to system-level applications. This review focuses on the representative strategies based on design and material configurations for improving key performance parameters including sensitivity, detection range/linearity, response time/hysteresis, spatial resolution/crosstalk, multidirectional force detection, and insensitivity to other stimuli. System-level integration for practical applications beyond conceptual prototypes and promising applications, such as artificial electronic skin for robotics and prosthetics, wearable controllers for electronics, and bidirectional communication tools, are also discussed. Finally, perspectives on issues regarding further advances are provided.

Microfluidic perfusion bioreactor for optimization of microalgal lipid productivity.

Nutrient deprivation in a batch process induces microbes to produce secondary metabolites while drastically constraining cellular growth. A microfluidic continuous perfusion system was designed and tested to culture microalgae, Chlamydomonas reinhardtii, under constant nutrient concentration slightly lower than normal condition. When cultured in 7.5%/7.5% of NH4+/PO42-, C. reinhardtii showed a 2.4-fold increase in TAG production with a 3.5-fold increase in biomass compared to level obtained under an only NH4+ depleted condition. The microfluidic continuous perfusion bioreactor with steady continuous nutrient flow can be used to optimize conditions for enhancing secondary metabolite production and increasing microbial biomass.

Anti-solvent co-crystallization of carbamazepine and saccharin.

The co-crystal approach has been investigated extensively over the past decade as one of the most promising methods to enhance the dissolution properties of insoluble drug substances. Co-crystal powders are typically produced by mechanical grinding (neat or wet) or a solution method (evaporation or cooling). In this study, high-purity carbamazepine-saccharin (CBZ-SAC) co-crystals were manufactured by a novel method, anti-solvent addition. Among various solvents, methanol was found to perform well with water as the anti-solvent for the co-crystallization of CBZ and SAC. When water was added to the methanol solution of CBZ and SAC at room temperature under agitation, nucleation of CBZ-SAC co-crystals occurred within 2-3 min. Co-crystallization was complete after 30 min, giving a solid yield as high as 84.5% on a CBZ basis. The effects of initial concentrations, focusing on the SAC/CBZ ratio, were examined to establish optimal conditions. The whole anti-solvent co-crystallization process was monitored at-line via ATR-FTIR analysis of regularly sampled solutions. The nucleation and crystal growth of CBZ-SAC co-crystals were detected by a significant increase in absorption in the range of 2400-2260 cm(-1), associated with the formation of hydrogen bonds between the carbonyl group in CBZ and the N-H of SAC. When CBZ hydrates were formed as impurities during anti-solvent co-crystallization, the hydrogen bonding between methanol and water was reduced greatly, primarily due to the incorporation of water molecules into the CBZ crystal lattice. In conclusion, an anti-solvent approach can be used to produce highly pure CBZ-SAC co-crystal powders with a high solid yield.

An in vitro study of the antifungal effect of silver nanoparticles on oak wilt pathogen Raffaelea sp.

In this study, we investigated the antifungal activity of three different forms of silver nanoparticles against the unidentified ambrosia fungus Raffaelea sp., which has been responsible for the mortality of a large number of oak trees in Korea. Growth of fungi in the presence of silver nanoparticles was significantly inhibited in a dosedependent manner. We also assessed the effectiveness of combining the different forms of nanoparticles. Microscopic observation revealed that silver nanoparticles caused detrimental effects not only on fungal hyphae but also on conidial germination.

Development of surface plasmon resonance immunosensor through metal ion affinity and mixed self-assembled monolayer.

An immunosensor based on surface plasmon resonance (SPR) with enhanced performance was developed through a mixed self-assembled monolayer. A mixture of 16- mercaptohexadecanic acid (16-MHA) and 1-undecanethiol with various molar ratios was self-assembled on gold (Au) surface and the carboxylic acid groups of 16-MHA were then coordinated to Zn ions by exposing the substrate to an ethanolic solution of Zn(NO(3))(2)d6H2O. The antibody was immobilized on the SPR surface by exposing the functionalized substrate to the desired solution of antibody in phosphatebuffered saline (PBS) molecules. The film formation in series was confirmed by SPR and atomic force microscopy (AFM). The functionalized surface was applied to develop an SPR immunosensor for detecting human serum albumin (HSA) and the estimated detection limit (DL) was 4.27 nM. The limit value concentration can be well measured between ill and healthy conditions.

Solubility enhancement of aggregation-prone heterologous proteins by fusion expression using stress-responsive Escherichia coli protein, RpoS.

BACKGROUND: The most efficient method for enhancing solubility of recombinant proteins appears to use the fusion expression partners. Although commercial fusion partners including maltose binding protein and glutathione-S-transferase have shown good performance in enhancing the solubility, they cannot be used for the proprietory production of commercially value-added proteins and likely cannot serve as universal helpers to solve all protein solubility and folding issues. Thus, novel fusion partners will continue to be developed through systematic investigations including proteome mining presented in this study. RESULTS: We analyzed the Escherichia coli proteome response to the exogenous stress of guanidine hydrochloride using 2-dimensional gel electrophoresis and found that RpoS (RNA polymerase sigma factor) was significantly stress responsive. While under the stress condition the total number of soluble proteins decreased by about 7 %, but a 6-fold increase in the level of RpoS was observed, indicating that RpoS is a stress-induced protein. As an N-terminus fusion expression partner, RpoS increased significantly the solubility of many aggregation-prone heterologous proteins in E. coli cytoplasm, indicating that RpoS is a very effective solubility enhancer for the synthesis of many recombinant proteins. RpoS was also well suited for the production of a biologically active fusion mutant of Pseudomonas putida cutinase. CONCLUSION: RpoS is highly effective as a strong solubility enhancer for aggregation-prone heterologous proteins when it is used as a fusion expression partner in an E. coli expression system. The results of these findings may, therefore, be useful in the production of other biologically active industrial enzymes, as successfully demonstrated by cutinase.