Brain‒machine interface (BMI) is a promising technology that looks set to contribute to the development of artificial limbs and new input devices by integrating various recent technological advances, ...including neural electrodes, wireless communication, signal analysis, and robot control. Neural electrodes are a key technological component of BMI, as they can record the rapid and numerous signals emitted by neurons. To receive stable, consistent, and accurate signals, electrodes are designed in accordance with various templates using diverse materials. With the development of microelectromechanical systems (MEMS) technology, electrodes have become more integrated, and their performance has gradually evolved through surface modification and advances in biotechnology. In this paper, we review the development of the extracellular/intracellular type of in vitro microelectrode array (MEA) to investigate neural interface technology and the penetrating/surface (non-penetrating) type of in vivo electrodes. We briefly examine the history and study the recently developed shapes and various uses of the electrode. Also, electrode materials and surface modification techniques are reviewed to measure high-quality neural signals that can be used in BMI.
Janus drops are thermodynamically stable when a high-viscosity fluid is imposed on a low-viscosity fluid. To understand physical mechanisms in Janus drop impact on macrotextured surfaces, several ...challenges in finding parameters or strategies still remain. Here, this study investigates the asymmetric bounce and separation of impinging Janus drops on non-wettable surfaces decorated with a macroridge to explore the effect of the drop size, viscosity ratio, and ridge size on the dynamics. Through numerical simulations, we determine the threshold Weber number, above which separation occurs, by varying drop diameters and viscosity ratios of the Janus drops. We investigate the initial bouncing directions of separated drops as a function of the impact velocity and viscosity ratio. We also predict how the separation efficiency is affected by the ridge’s height and width. The asymmetric impact dynamics of Janus drops on macrotextured surfaces can provide new strategies to control drop bouncing in applications, such as liquid separation and purification.
Controlling the residence time of drops on the solid surface is related to a wide spectrum of engineering applications, such as self-cleaning and anti-icing. The symmetry-breaking dynamics induced by ...the initial drop shape can promote drop bouncing. Here, we study the bouncing features of spherical and ellipsoidal drops on elliptical surfaces that continuously change curvatures inspired by natural succulent leaves. The bounce characteristics highly depend on the geometric relations between the ellipsoidal drops and curved surfaces. Numerical results show that ellipsoidal shapes of the drops amplify asymmetries of the mass and momentum in synergy with an influence of the surface curvature during the impact, which is verified by experiments. Effects of the surface anisotropy and drops’ ellipticity on the residence time are investigated under various surface morphologies and Weber numbers. The residence time is closely associated with an initial surface curvature at the apex. The underlying principle of modifying the residence time via the drops’ ellipticity and initial surface curvature is elucidated based on momentum asymmetry. The understanding of the bouncing features on curved surfaces will offer practical implications for enhanced heat transfer performances and controlled water repellency, etc.
In this paper, we examine the corporate governance role of banks by investigating the effect of bank monitoring on the borrowers’ earnings management behavior. Our analyses suggest that a borrowing ...firm’s earnings management behavior generally decreases as the strength of bank monitoring increases. The strength of bank monitoring is measured as (1) the magnitude of a bank loan, (2) the reputation (rank) of a lead bank, (3) the length of a bank loan, and (4) the number of lenders. These results imply that bank monitoring plays an important role in the corporate governance of bank-dependent firms. We further examine other bank loan characteristics (collateral, refinancing, loan types, and loan purposes) and their effects on borrowers’ earnings management behavior. Our analyses show that collateral and loan types are significantly associated with borrowers’ earnings management behavior while refinancing and loan purposes have no association.
Microneedles are extensively used in the field of drug deliveries and disease treatment. Cellulose porous microneedles were fabricated using the cellulose acetate phase separation method followed by ...a deacetylation process. The developed cellulose microneedles were tested for porosity, mechanical strength, penetration, and surface hydrophobicity. The porosity of cellulose microneedles increased by approximately 15%, while the Young’s modulus, indicative of mechanical strength, increased by approximately 30% compared with cellulose acetate microneedles before the deacetylation process. The cellulose microneedles easily penetrated the sample skin, making it a potential tool for transdermal drug delivery. The developed cellulose microneedles exhibited enhanced hydrophilicity in comparison to cellulose acetate microneedles. The increased hydrophilicity of the developed microneedles positions them as promising tools for efficient interstitial fluid extraction. These characteristics not only make them suitable for drug delivery but also highlights their potential as biosensors.
Hardware neural network (HNN) based on analog synapse array excels in accelerating parallel computations. To implement an energy-efficient HNN with high accuracy, high-precision synaptic devices and ...fully-parallel array operations are essential. However, existing resistive memory (RRAM) devices can represent only a finite number of conductance states. Recently, there have been attempts to compensate device nonidealities using multiple devices per weight. While there is a benefit, it is difficult to apply the existing parallel updating scheme to the synaptic units, which significantly increases updating process’s cost in terms of computation speed, energy, and complexity. Here, we propose an RRAM-based hybrid synaptic unit consisting of a “big” synapse and a “small” synapse, and a related training method. Unlike previous attempts, array-wise fully-parallel learning is possible with our proposed architecture with a simple array selection logic. To experimentally verify the hybrid synapse, we exploit Mo/TiO
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RRAM, which shows promising synaptic properties and areal dependency of conductance precision. By realizing the intrinsic gain via proportionally scaled device area, we show that the big and small synapse can be implemented at the device-level without modifications to the operational scheme. Through neural network simulations, we confirm that RRAM-based hybrid synapse with the proposed learning method achieves maximum accuracy of 97 %, comparable to floating-point implementation (97.92%) of the software even with only 50 conductance states in each device. Our results promise training efficiency and inference accuracy by using existing RRAM devices.
The estimation of bloodstain age is an important factor in forensic analysis. Previously, we have reported a smartphone-based colorimetric system for age estimation of bloodstain, in which Whole ...blood and EDTA whole blood were dropped on 4 different materials (700 μL) and captured using a smartphone for 72 h. In order to enhance sensitivity and accuracy of the previous system, the current work is dedicated towards the application of pattern recognition and classification of bloodstain images based on a smartphone. Three detection methods (blood pool, crack ratio, and colorimetric analysis) in terms of 6 steps of drying process of the bloodstain (coagulation, gelation, edge desiccation, center desiccation, crack propagation, and final desiccation) were applied to estimate age of the bloodstain accurately. Three parameters from the bloodstain images were then classified as comparing to those of stored reference images with similar trends in database. The bloodstain age was successfully determined by 9 h, 18 h, and 48 h with respect to the three detection methods mentioned above, respectively. The differences in bloodstain images were clearly distinguished every hour by using smartphone-based pattern recognition analysis. Therefore, our system is expected to shed a light on the field of forensic science by estimating bloodstain age in real time.
•A smartphone-based pattern recognition was introduced to estimate bloodstain age.•Blood pool, crack ratio, and brightness values of the images were successfully measured.•The proposed methods was designed for enhancing accuracy in the early time zone.•A low detection limit of 1 h toward age estimation of bloodstains could be achieved.
Electroosmotic flow (EOF) is one of the most important techniques in a microfluidic system. Many microfluidic devices are made from a combination of different materials, and thus asymmetric ...electrochemical boundary conditions should be applied for the reasonable analysis of the EOF. In this study, the EOF of power-law fluids in a slit microchannel with different zeta potentials at the top and bottom walls are studied analytically. The flow is assumed to be steady, fully developed, and unidirectional with no applied pressure. The continuity equation, the Cauchy momentum equation, and the linearized Poisson-Boltzmann equation are solved for the velocity field. The exact solutions of the velocity distribution are obtained in terms of the Appell's first hypergeometric functions. The velocity distributions are investigated and discussed as a function of the fluid behavior index, Debye length, and the difference in the zeta potential between the top and bottom.
We report a simple method for electrospinning polymers onto flexible, insulating substrates by controlling the wettability of the substrate surface. Water molecules were adsorbed onto the surface of ...a hydrophilic polymer substrate by increasing the local humidity around the substrate. The adsorbed water was used as the ground electrode for electrospinning. The electrospun fibers were deposited only onto hydrophilic areas of the substrate, allowing for patterning through wettability control. Direct writing of polymer fiber was also possible through near-field electrospinning onto a hydrophilic surface.
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