Search

We consider manifolds of tunable all-band flat (ABF) lattices in dimensions d = 1, 2, parametrized by a manifold angle parameter {\theta}. We study localization properties of eigenstates in the presence of weak magnetic flux disorder and weak spin-orbit disorder. We demonstrate that weakly disordered ABF lattices are described by effective scale-free models where the disorder strength is scaled out. For weak magnetic flux disorder we observe sub-exponential localization at flatband energies in d = 1, which differs from the usual Anderson localization. We also find diverging localisation length at flatband energies for weak flux values in d = 2, however the character of the eigenstates at these energies is less clear. For weak spin-orbit coupling disorder in d = 2 we identify a tunable metal-insulator transition with mobility edges. We also consider the case of mixed spin-orbit and diagonal disorder and obtain the metal-insulator transition driven by the manifold parameter {\theta}.

Thin, sensitive skin electronics The properties of the human sense of touch, including high sensitivity to differences in temperature, pressure, or surface roughness, are challenging to replicate in robotics because skin materials must be highly conductive, stretchable, and thin. Jung et al . developed a process to assemble nanomaterials as a monolayer that is partially embedded in an ultrathin elastomer. The process works by depositing a mixed solvent containing nanostructured silver and/or gold, along with elastomer, onto deionized water. This results in a layer of nanoparticles residing at the interface coating with elastomer, which is further densified by the addition of surfactant. The process is scalable, and the resulting elastomer membranes can be transferred to other substrates. —MSL

An electrospun nanofiber membrane significantly improves the electrical performances of triboelectric nanogenerators (TENGs) due to its high surface area. In recent years, composite nanofibers were applied to a TENG using various electrospinning system types to further enhance the performance of TENGs; however, the effects of the systems on the energy harvesting capability of TENGs have not been investigated thoroughly. This study aims to fabricate polyimide/poly(vinylidene fluoride-co-trifluoroethylene) composite nanofiber-based TENGs with three different nozzle systems: single nozzle, conjugated nozzle, and multinozzles, and two different collectors: plate collector and drum collector. A TENG with multinozzle-drum system-based nanofibers produced an output voltage of 364 V, a short-circuit current of 17.2 μA, a transferred charge of 29.72 nC, and a power density of 2.56 W/m2 at a load resistance of 100 MΩ, which were ∼7 times higher than those of other system-based nanofibers. Under the 10,000 cycles of loading, the TENG stably harvested electric energy. The TENG could also harvest energy from the human body motions, and it is sufficient to illuminate 117 light-emitting diodes and drive several electronic devices. The proposed TENG exhibits excellent electric performances as a wearable energy harvester.

The causative factor of COVID-19, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is continuously mutating. Interestingly, identified mutations mainly occur in the spike (S) protein which interacts with the ACE2 receptor and is cleaved via serine protease TMPRSS2. Some mutated strains are becoming dominant in various parts of the globe because of increased transmissibility as well as cell entry efficacy. Remarkably, the neutralizing activity of monoclonal antibodies, convalescent sera, and vaccines against the variants has been reported to be significantly reduced. Therefore, the efficacy of various monoclonal antibodies therapy and vaccines against these variants is becoming a great global concern. We herein summarize the current status of SARS-CoV-2 with gears shifted towards the recent and most common genetic variants in relation to transmission, neutralizing activity, and vaccine efficacy.

In this paper, we develop a privacy-preserving UAV system that does not infringe on the privacy of people in the videos taken by UAVs. Instead of blurring or masking the face parts of the videos, we want to exquisitely modify only the face parts so that the people in the modified videos still look like humans, but they become anonymous. Doing so, the semantic information of the videos can be preserved even with the anonymization. Specifically, based on the latest generative adversarial network architecture, we propose a deep learning-based face-anonymization scheme so that each modified face part looks like the face of a person who does not actually exist. The trained face-anonymizer is then mounted on the UAV system we have implemented. Through experiments, we confirm that the developed privacy-preserving UAV system anonymizes UAV’s first-person videos so that the people in the video are not recognized as anyone in the dataset used. In addition, we show that even with such anonymized videos, the perception performance required for performing UAV’s essential functions such as simultaneous localization and mapping is not degraded.

Highly conductive and stretchable nanocomposites are promising material candidates for skin electronics. However, the resistance of stretchable metallic nanocomposites highly depends on external strains, often deteriorating the performance of fabricated electronic devices. Here, a material strategy for the highly conductive and stretchable nanocomposites comprising metal nanomaterials of various dimensions and a viscoelastic block-copolymer matrix is presented. The resistance of the nanocomposites can be well retained under skin deformations (50% strain). It is demonstrated that silver nanomaterials can self-organize inside the viscoelastic media in response to external strain when their surface is conjugated with 1-decanethiol. Distinct self-organization behaviors associated with nanomaterial dimensions and strain conditions are found. Adopting the optimum composition of 0D/1D/2D silver nanomaterials can render the resistance of the nanocomposites insensitive to uniaxial or biaxial strains. As a result, the resistance can be maintained with a variance of 1% during 1000 stretching cycles under uniaxial and biaxial strains of50% while a high conductivity of ≈31 000 S cm

Information and communication technology (ICT) companies strive for ceaseless innovation to remain competitive while facing the challenge of maximizing firm value (FV) with limited resources, and increasing the interests of shareholders. However, capital structures have a considerable effect on FV, and the literature still disagrees with the optimum structure in specific industries and countries. Therefore, this study evaluates the FV of ICT companies in terms of profitability efficiency using data envelopment analysis. In addition, this study applies a Tobit regression and Kruskal-Wallis one-way ANOVA to identify the impact of leverage, liquidity, and firm size, which are major capital structure factors influencing FV. The analysis yields three main results. First, in the ICT industry, small and medium companies tend to have better profitability efficiency than companies of other sizes. Second, only small and medium ICT manufacturing companies’ profitability efficiency is positively impacted by the current ratio. Third, only mid-sized service companies’ profitability efficiency is positively impacted by the debt-equity ratio. The results have policy and practical implications for improving the FV of ICT companies.

We study the effect of infinitesimal onsite disorder on d-dimensional all bands flat lattices. The lattices are generated from diagonal Hamiltonians by a sequence of (d + 1) local unitary transformations parametrized by angles ${\theta}_i$. Without loss of generality, we consider the case of two flat bands separated by a finite gap $\Delta$. The perturbed states originating from the flat bands are described by an effective tight binding network with finite on- and off-diagonal disorder strength which depends on the manifold angles ${\theta}_i$. The original infinitesimal onsite disorder strength W is only affecting the overall scale of the effective Hamiltonian. Upon variation of the manifold angles for d = 1 and d = 2 we find that localization persists for any choice of local unitaries, and the localization length can be maximized for specific values of ${\theta}_i$. Instead, in d = 3 we identify a non-perturbative metal-insulator transition upon varying the all bands flat manifold angles., Comment: 5 pages, 3 figures

In this study, the effects of various fabrication parameters on the electrical performance of an electrospun nanofiber-based triboelectric nanogenerator (EN-TENG) are systematically investigated through the design of experiments. We selected four fabrication parameters to examine, namely: (i) working distance (needle to collector distance), (ii) needle gauge, (iii) electrospinning time, and (iv) counter materials. A mixed orthogonal array of L18 experiments was designed with respect to the one factor having two level values and three factors having three level values. The open circuit voltage of the EN-TENG was varied from 86.1 to 576.7 V with the aforementioned fabrication parameters. A longer working distance, a larger needle gauge, and a longer electrospinning time increased the open circuit voltage. The power density of the optimized EN-TENG was approximately 2.39 W/m2 at a 100 MΩ load resistance and was sufficient to illuminate a total of 200 LEDs.

Due to safety issues in the construction industry, interest in research on occupational safety and health (OSH) regulations remains high. Previous studies indicated that OSH regulations not only affect performance in and of themselves, but also indirectly by increasing awareness of such regulations. Studies also demonstrated that OSH regulation can affect innovation and corporate safety. However, the effect of OSH regulation on innovation remains unclear, as the relationship between the perception of OSH regulation and innovation is not fully understood. This study measures the innovation efficiency of companies in the Korean construction industry using data envelopment analysis (DEA), and investigates the relationship between innovation efficiency and companies’ perceptions of OSH regulations. Results indicate that companies that positively recognize OSH regulations tend to be more innovative than those that do not. This study also validates differences in innovation efficiency depending on the perception of OSH regulations by bootstrap DEA. The results of this study suggest appropriate strategies to promote innovation in the construction industry from the perspectives of both government and practitioners in firms.

This study aims to improve the sensitivity of sensors using porous structures and cone-shaped patterns in the composition of a capacitive pressure sensor. A simple and rapid fabrication method for the production of porous structures and cone-shaped patterns using microwave irradiation of emulsions containing polydimethylsiloxane (PDMS) and a sacrificial solvent is introduced in this study. Through this method, a porous PDMS dielectric layer could be simply fabricated within a few minutes. The sensitivity was greatly improved by both enhancing deformability and increasing the dielectric constant under the external pressure. The effect of pattern distance was investigated, and the sensor with the pattern distance of 600 μm showed a remarkably high sensitivity of approximately 5 kPa−1. Moreover, the effect of aspect ratio and sharpness of the patterns were also studied through a finite element analysis. Finally, we demonstrated the performance of the sensor using a sensor array and finger attached sensors, and they showed sufficient performance for use in wearable devices applicable to artificial skin, surgical robots, and pressure monitoring systems, among others.

The most recent Wi-Fi standard, IEEE 802.11ax, supports uplink multiuser (MU) multi-input multi-output (MIMO) with the expectation of increased throughput and reduced access delay, compared with the legacy Wi-Fi. Recent studies on cellular mobile networks, such as 3GPP LTE, have shown that MU-MIMO indeed greatly improves the delay and throughput performance, compared to single user (SU)-MIMO. However, there is no study explicitly comparing the 802.11ax and the legacy Wi-Fi in the uplink delay and throughput perspectives. This paper presents numerical comparison of uplink MU- and SU-MIMO on the delay and throughput performance.

In recent years, innovative research has been widely conducted on flexible devices for wearable electronics applications. Many examples of wearable electronics, such as smartwatches and glasses, are already available to consumers. However, strictly speaking, the sensors used in these devices are not flexible. Many studies are underway to address a wider range of wearable electronics and the development of related fields is progressing very rapidly. In particular, there is intense interest in the research field of flexible pressure sensors because they can collect and use information regarding a wide variety of sources. Through the combination of novel materials and fabrication methods, human-machine interfaces, biomedical sensors, and motion detection techniques, it is now possible to produce sensors with a superior level of performance to meet the demands of wearable electronics. In addition, more compact and human-friendly sensors have been invented in recent years, as biodegradable and self-powered sensor systems have been studied. In this review, a comprehensive description of flexible pressure sensors will be covered, and design strategies that meet the needs for applications in wearable electronics will be presented. Moreover, we will cover several fabrication methods to implement these technologies and the corresponding real-world applications.

Surface modification of polyimides (PIs) using electrospinning would significantly improve the performance of TENGs because of the larger surface area of the electrospun friction layer. However, PIs generally have high solvent resistance, so it is complicated to convert them into nanofibers using electrospinning process. This study aims to fabricate PI nanofibers via simple, one-step electrospinning and utilize them as a friction layer of TENGs for better performance. PI nanofibers were directly electrospun from PI ink made of polyimide powder without any additional process. The effect of PI concentration on spinnability was investigated. Uniform and continuous nanofibrous structures were successfully produced at concentrations of 15 wt% and 20 wt%. Electrospun PI nanofibers were then utilized as a friction layer for TENGs. A TENG with 20 wt% produced an open circuit voltage of 753 V and a short circuit current of 10.79 μA and showed a power density of 2.61 W m−2 at a 100 MΩ load resistance. During tapping experiment of 10,000 cycles, the TENG could stably harvest electrical energy. The harvested energy from the proposed TENG is sufficient to illuminate more than 55 LEDs and drive small electronic devices, and the TENGs exhibit excellent performance as a wearable energy harvester.

The objective of this work is to establish a volumetric metal 3-dimensional (3D) printing system based on material extrusion method and to fabricate metal patterns by investigating various process variables. Numerical heat transfer simulation was conducted to design the nozzle system with a minimized heat loss at the nozzle tip. Based on the simulation results, a metal 3D printing system with X, Y, and Z stages was constructed. The effects of lead content in molten metals and printing conditions such as stage speed and flow rate were investigated. The line formation like bulged, uniform, and dashed lines was evaluated using an optical microscope, and the variation in line widths of uniform lines was investigated with the process variables. Various types of 2-dimensional (2D) patterns were fabricated with an optimized process variable. A simple 3D structure was obtained to demonstrate the feasibility of the proposed system and procedure.

The literature has two different perspectives on which innovation types should be implemented to achieve innovation performance, some argue that they should pursue process-oriented innovation, while others maintain that both product- and process-oriented innovation should be performed. Though innovation efficiency should be measured, which takes both input and output variables into account, the research so far has been measured only with the performance of the innovation. Accordingly, this study identifies which innovation type is the most advantageous in terms of innovation efficiency for the chemical firms. We use data of 64 Korean chemical companies from a 2016 Korean innovation survey and perform data envelopment analysis to calculate innovation efficiency. Kruskal&ndash, Wallis one-way ANOVA and bootstrap DEA were also conducted to compare the difference of innovation efficiency among groups, depending on which innovation types are oriented. The result shows that focusing on process innovation rather than both product and process innovation is more appropriate to achieve higher innovation efficiency, and pursuing process innovation rather than product innovation tends to achieving a higher level of innovation efficiency in the Korean chemical industry.

Pressure sensors for wearable electronics are mounted on irregular surfaces and exposed to various external stimuli. Therefore, the sensor should have a flexible structure and wide pressure measurement range along with high sensitivity. In this study, we fabricated hierarchically porous structured polydimethylsiloxane (PDMS) composites with a simple and cost-effective method using sugar particles and a water-in-oil emulsion. Hierarchically porous PDMS composites were employed as the dielectric layers of flexible capacitive pressure sensors. The capacitive pressure sensor presents a sensitivity 22.5 times higher (0.18 kPa−1) than the sensors using bulk PDMS with a wide measurement range (0–400 kPa). The finite element analysis was implemented to analyze the non-linearity of sensors by observing the compressive behavior of the PDMS composites. For the practical applications, finger attached-sensor, respiration monitoring system, and sensor array were tested, and the proposed sensors showed sufficient potential for application in wearable electronics.

This paper proposes a method for seamless interaction between students and their professor using Twitter, one of the typical social network service (SNS) platforms, in large lectures. During the lecture, the professor poses surprise questions in the form of a quiz on an overhead screen at unexpected moments, and students submit their answers through a smartphone response system using Twitter. Since points are awarded on a first-come–first-served basis to only a limited number of the students who submit correct answers, students are required to concentrate on the lecture if they want to score. The proposed method solves both the problem of decreased concentration arising from frequent use of smartphones for nonlearning purposes in lectures and of inefficient interaction that occurs in large university classrooms. Evaluation through analysis of exam results and a post-course survey confirm that the proposed solution produces better results in terms of both students' academic achievement and their concentration during lectures.

We present an all-optical packet buffer system that enables variable delay of the incoming packets in the optical domain based on the controllable-delay recirculating loop. It consists of two optical logic gate stages based on cross gain modulation nonlinear effect of semiconductor optical amplifiers to control the amount of delay. Incoming optical packets were either stored in the recirculating loop or routed to the system output by an optical control signal. The validity of the system has been experimentally verified using the optical bit sequences operating at 1 Gbps. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:2058–2061, 2014

This work aims to present a flexible, highly sensitive, capacitive pressure sensor based on an elastomeric dielectric layer with uniformly distributed micro-pores. The porous dielectric layer was simply produced by microwave treatment of polydimethylsiloxane (PDMS) mixed with a sacrificial solvent within a few minutes. The pressure sensor using a porous PDMS dielectric layer fabricated with 40 wt% sacrificial solvent had a sensitivity of 0.813 kPa−1, which is 11 times higher than that of the sensor using a non-porous dielectric layer. To further improve the sensitivity, low-cost commercial glass was used as a mold to form microstructures on the surface of the porous dielectric layer. Due to the enhanced deformability, high sensitivity of 1.43 kPa−1 and a fast response time of 70 ms was achieved. The performances of a sensor array as well as finger sensors were also demonstrated by placing light-weight objects on the array and holding a plastic cup. It would be expected that the proposed sensors could be utilized in the application of artificial skins or soft robotics.

The ZnO nano-particles were made in the polyimide dielectric matrix by using the chemical reaction between the zinc metal film and polyamic acid. The concentration of the ZnO particle is about 1.5×1012 cm−2, with average size below 10 nm, and its shapes are almost spherical. Then, the polyimide layer is a stable dielectric material with a dielectric constant of 2.9. To investigate the electrical properties of ZnO particles in the polyimide insulator film, we fabricated a metal-insulator-semiconductor (MIS) structure and measured capacitance-voltage (C-V) with temperature modulation. At room temperature, C-V hysteresis with a voltage gap of 2.8 V appeared in the MIS structure using SiO2/Si substrate. As the measuring temperature decreased, the C-V curves were shifted slightly to the accumulation region with gate bias. It was considered that the electrical charging may occur dominantly in nanoparticles, having only a few defects at the interface of the polyimide/SiO2 and the polyimide/ZnO.

An electrohydrodynamic (EHD) patterning method was utilized to obtain high-resolution line patterns in a low electric field regime without an additional mechanical drawing process. Molecular weight and weight percent of a polymer were selected as key parameters to reduce the voltage. EHD patterning was performed using polyethylene oxide (PEO) solutions. The threshold voltages (V th) to initiate jet ejection are almost the same for all solutions. A method verified in this study, reducing the driving voltage (V d) just after the initiation of the jet at the threshold voltage, can make a very thin, continuous jet, while increasing molecular weight and weight percent were enabled to further reduce the input voltage. As the voltage reduction ratio (V d/V th) is decreased, the jet behaves like a solid rather than a liquid due to its fast solidification. The line width of the resultant line pattern could be tuned from 50 nm to 10 μm depending on the substrate moving speed. Contour maps were also developed that show the pattern mode variation as a function of the voltage reduction ratio and key parameters. The results show that well-defined PEO line and grid patterns can be fabricated via the proposed EHD direct patterning under appropriate conditions.

Highly sensitive capacitive pressure sensors with poly(vinylidenefluoride-co-trifluoroethylene) (P(VDF-TrFE)) dielectric layers were prepared. The dielectric layers were directly produced by electrospinning P(VDF-TrFE) nanofibers for various spinning times. A longer spinning time enhanced the deformability of the electrospun P(VDF-TrFE) layers, resulting in higher sensitivity owing to larger changes in the deformation of the dielectric layer. One of the capacitive pressure sensors showed a high sensitivity of 2.81 kPa−1 at a pressure ≤ 0.12 kPa, a good response time of 42 ms, and small hysteresis. The sensitivity of the sensor was five times higher than that of a typical capacitive pressure sensor. The fabricated pressure sensor could detect a tiny water droplet as light as 7 mg. It is expected that the electrospun P(VDF-TrFE) nanofibers can be used as sensing materials for highly sensitive pressure sensors in wearable electronics applications.

In this study, a honeycomb-like nanofiber based triboelectric nanogenerator (HN-TENG) is presented. In order to fabricate the honeycomb-like nanofiber, we utilized self-assembly of electrospun poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) nanofibers. The honeycomb-like P(VDF-TrFE) nanofiber network was directly produced via electrospinning without any additional processing. The HN-TENG showed a maximum voltage, current, and power density of 160 V, 17 μA, and 1.6 W/m2, respectively. The power density was enhanced more than twofold as compared with a typical flat nanofiber network based TENG due to the large surface area and high surface roughness of the honeycomb structure. Finally, we verified that HN-TENG has the potential to be used for practical applications by driving 100 light emitting diodes and charging capacitors.

The effect of the needle shape on electrohydrodynamic (EHD) printing was investigated by comparing flat outlet needles and hypodermic needles. Line fabrication was performed to confirm the tendency of jetting stability and the printed line width with various driving voltage and stage speed by using Ag nanoparticle ink as a jetting solution on a hydrophobic surface. We verified that the hypodermic needle greatly improves the resolution in EHD printing. The ink slips down the inner wall of the hypodermic needle, and a very small meniscus is generated at the tip of the needle. Due to this phenomenon, high-resolution printing can be accomplished. The narrowest line that was fabricated using a hypodermic needle has a line width of 0.7 μm, and it is smaller than 1% of the needle inner diameter.

Purpose: To assess the inter-device agreement of peripapillary retinal nerve fiber layer (RNFL) thickness measurements by 2 spectral domain Cirrus HD optical coherence tomography (OCT) devices in healthy Korean subjects. Methods: Eleven eyes of 11 healthy volunteers were enrolled in the present study. Each eye was scanned with the Optic Disc Cube 200 × 200 scan of 2 Cirrus HD OCT devices for peripapillary RNFL thickness calculation. The inter-device agreements of the 2 Cirrus HD OCTs for average, quadrant, and clock-hour RNFL thickness values were determined with Wilcoxon signed rank test, Friedman test, Cronbach’s alpha (α), intraclass correlation coefficient (ICC), coefficient of variation (COV), and Bland-Altman plot. Results: The mean age of the participants was 25.82 ± 3.28 years and all had a 0.00 logarithm of the minimum angle of resolution of best-corrected visual acuity. The signal strengths of scans from the 2 Cirrus HD OCT were not significantly different (p = 0.317). The inter-device agreement of average RNFL thickness was excellent (α, 0.940; ICC, 0.945; COV, 2.45 ± 1.52%). However, the agreement of nasal quadrant RNFL thickness was not very good (α, 0.715; ICC, 0.716; COV, 5.72 ± 4.64%). Additionally, on the Bland-Atman plot, the extent of agreement of the 2 Cirrus HD OCTs for RNFL thickness was variable according to scanned sectors. Conclusions: The inter-device agreement of 2 spectral domain Cirrus HD OCT devices for peripapillary RNFL thickness measurements was generally excellent but variable according to the scanned area. Thus, physicians should consider this fact before judging a change of RNFL thicknesses if they were measured by different OCT devices.