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Self-assembled artificial cilia actuator
Get PDFDepartment of Mechanical EngineeringSlender hair-like cilia are observed in many living organisms. Cilia carry out important roles, such as locomotion, fluid control, fluid diffusion, and cleaning, owing to their high aspect ratio structure. Inspired by cilia in nature, artificial cilia actuators are being extensively developed. An artificial cilia actuator can generate shape morphing and actuation under external stimuli, such as pneumatic, electric-field, light, thermal, and chemical stimuli as well as a magnetic field. Pneumatic cilia actuators have a large driving force compared to their weight and are easy to manufacture. However, they cannot be miniaturized to a microscale, like cilia in nature, because additional components such as pumps and cables are essential. Electric cilia can be manufactured on a microscale and can actuate dynamicallyhowever, their applications are limited owing to their high voltage requirements. Light, chemical, and thermal stimuli-based cilia actuators can also be miniaturized on a microscale, but they have slow response times and do not easily generate the desired actuation. On the other hand, magnetic actuators can be miniaturized, controlled precisely, are non-invasive, and can be driven immediately. Owing to these advantages, cilia actuators based on magnetic fields have been intensively investigated.
Magnetic cilia actuators are mainly constructed using a top-down approach. In this approach, a template mold with a lithographically defined hole array is replicated with a magnetic-particle mixture solution, which enables the reliable fabrication of magnetic cilia with controlled geometry. However, with this technique, synthetic cilia with nanoscopic diameters that are nearly the size of biological cilia are difficult to access owing to the limited pattern resolution of the lithographically prepared template and high viscosity of the composite solution. In addition, the aspect ratio of cilia is limited because the cilia may structurally collapse during a demolding step of the molding process.
The self-assembly approach has emerged as a solution to the limitations of the top-down approach. This approach fabricates a desired structure by manipulating a driving force that moves particles, and it has strong potential for constructing a cilia array with a nanoscale size and high aspect ratio structure. The Langmuir???Blodgett conventional self-assembly technique can precisely control particles. However, this technique typically produces close-packed two-dimensional monolayer or three-dimensional lattice structures. Recently, spray-based and DNA-based self-assembly techniques were conducted to construct a vertical structure. However, spray-based self-assembly has random spatial distributions without controllability of the array geometry. DNA-based self-assembly has a complex processtherefore, obtaining a high aspect ratio is challenging.
We propose a programmable self-assembly strategy that can direct magnetic particles into a highly ordered responsive artificial cilia actuator. The resulting cilia display several structural features, such as diameters of single-particle resolution, controllable diameters and lengths spanning from nanometers to micrometers, and accurate positioning. The proposed strategy is based on the vapor state, which minimizes intermolecular interaction, and precise magnetic-field control using a Ni island. The self-assembled artificial cilia can maintain their structural integrity through interparticle interactions. Interestingly, the cilia can exhibit a field-responsive actuation motion through ???rolling and sliding??? between assembled particles instead of bending the entire ciliary beam. We demonstrate that oleic acid used to coat the particles acts as a lubricating bearing and enables the rolling/sliding-based actuation of the cilia. We further demonstrate that both magnetic nanocilia and microcilia can dynamically and immediately actuate in response to modulated magnetic fields while providing different stroke ranges and actuation torques.ope
Semi-Supervised Learning for Low Signal-to-Noise Ratio NMR Spectra
Get PDFGraduate School of Artificial IntelligenceNuclear magnetic resonance (NMR) spectroscopy has been widely employed for quantitative characterization in chemistry and related fields. However, it suffers from weak signal responses, i.e., a low signal-to-noise ratio (SNR), due to the intrinsic low sensitivity and resolution of the NMR spectrometer. Researchers have reported on previous noise reduction methods, but the processed signals still require the supervision of NMR experts. The area-quantification of the spectra is also troublesome due to entanglement of the noise and the signal. In this work, we introduce L-SNRNet (low signal-to-noise ratio network) consisting of an autoencoder to reduce the dimension of input spectra and a clustering part to differentiate the signal from low SNR spectra. L-SNRNet is developed through three regularization steps: First, in the initial step of data pre-processing, each NMR spectrum is normalized to make the network focus exclusively on its shape information. Secondly, batch normalization layers are added to the autoencoder to enhance the representation capacity of latent variables. Lastly, the mean integration values of the NMR spectra are multiplied to the normalized spectra to compensate for the intensity information, because the quantification of NMR spectra is estimated based on the integrated areas of the peaks. The results show that the latent encoding vectors are separated well by Gaussian mixture
model. We used L-SNRNet to conduct an impurity analysis of the metal precursor, which needs to be extremely pure for reliable semiconductor manufacturing. L-SNRNet corrected 11.4%of NMR expert???s decisions on the impurity determination. L-SNRNet can be applied to the analysis of weak or low SNR signal, which follows the combination of Gaussian and Lorentzian distribution???the Voigt profile???in any measurements.ope
Suppression of Halide Migration for High-Performance Blue Perovskite Light-Emitting Diodes
Get PDFSchool of Energy and Chemical Engineering (Energy Engineering)Cs-based perovskite nanocrystals (PeNCs) have been considered to be excellent emitters for perovskite light-emitting diodes (PeLEDs) due to their remarkable optoelectronic properties such as easily tunable bandgap, narrow full width half maximum (FWHM), inexpensive precursor, solution processability and high photoluminescence quantum yield (PLQY). Contrary to green and red-emitting PeNCs, poor optical properties of blue PeNCs are mainly attributed to the deeper defect states induced by the chlorine content, which has hampered the realization of the full potential of blue PeLEDs. Herein, we propose a surface passivation strategy by employing potassium thiocyanate (KSCN), which is an immobile passivating material (IPM) that considerably improved the structure of the PeNCs by filling halide vacancies and uncoordinated halide sites. IPM which are activated by butanol solvent were added to the as-synthesized blue PeNCs. Indeed, the photoluminescence quantum yield of the IPM-introduced PeNCs was significantly enhanced to 74.1% compared to that of the reference PeNCs (34.0%). Besides, K+ seized the halide ions in the PeNCs, thereby resulting in excellent colloidal stability. Overall, by using the IPM-introduced PeNCs as an emissive layer, the PeLEDs achieved an external quantum efficiency of 2.04% compared to the 0.60% reference device and an elongated operating lifetime. Our strategy provides a simple way for breaking down the hurdles limiting the practicability of PeLEDs in display applications.ope
Tapered and hollowed flexural metamaterial beam for low frequency vibration manipulation
Get PDFDepartment of Mechanical EngineeringIn this thesis, the tapered and hollowed flexural metamaterial for manipulating the vibration beam is proposed. Based on the theoretical analysis of the flexural wave, the flexural metamaterial consisting of the tapered spring and hollowed cylindric mass is designed to suppress the vibration in low-frequency and broadband frequency ranges. In addition, the highly tunable metamaterial cavity for improving the efficiency of elastic energy harvesting is also proposed as a possible application of the proposed metamaterial. The theoretical analysis should be preceded to achieve these vibration manipulations. For the analysis, the equivalent mass-spring method is used. The flexural metamaterial is converted into the equivalent mass-spring system for theoretical investigation. Since the flexural wave has two motions, vertical shear motion and bending motion, the mass-spring system consisting of two kinds of springs, shear spring and bending spring, is adopted to fully describe the flexural wave motion. The analytic condition for achieving broad and low-frequency bandgap is found based on the analysis of flexural wave in the metamaterial. It is revealed that the low-frequency broad bandgap can be achieved with a high shear stiffness, low bending stiffness, high rotational inertia, and low mass. The flexural metamaterial composed of the spring part having the tapered shape and the mass part having the hollowed shape is proposed to achieve the desired stiffness and inertia. The spring of the tapered shape is for low bending stiffness and high shear stiffness. The mass of the hollowed cylindric shape is for high rotational inertia and low mass. Consequently, the tapered and hollowed metamaterial beam having a broad bandgap in a low-frequency range is successfully designed and validated by numerical simulation and experiment. Based on this broadband low-frequency bandgap, the vibration localization is also studied as an application of the proposed metamaterial beam. When the cavity which breaks the periodicity of the metamaterial is introduced into the metamaterial, the cavity mode occurs inside the bandgap. This cavity mode can focus the wave or vibration of the cavity mode frequency into the cavity. Due to this phenomenon, the cavity can be used to improve the efficiency of elastic energy harvesting. Since elastic energy harvesting aims to harvest the wasted ambient vibration, the metamaterial is demanded to have a low-frequency bandgap. Thus, our proposed metamaterial is utilized for the metamaterial cavity for elastic energy harvesting. In addition, our broadband low-frequency bandgap can provide high tunability to the cavity mode frequency since the tunable frequency range of the cavity mode is restricted by the width of the bandgap. Furthermore, the performance of the cavity mode at various frequencies is obtained by adopting the side beam, which pumps the vibration energy into the cavity across the bandgap. Consequently, the metamaterial cavity for localizing the vibration having high tunability in its frequency is achieved and validated through numerical simulations and experiments.ope
The Repeat Library of Unmapped Scaffolds of The Korean Reference Genome
Get PDFDepartment of Biomedical EngineeringSince DNA was discovered as the genetic material of bacteriophages in 1952, genes or genomes have become an area that must be researched thoroughly to understand life. With high-throughput whole-genome sequencing technologies, large-scale population genomics studies have become standard not only for biology scientists in deciphering the code of life, but also for the general public to cope with global crises such as the COVID-19 pandemic. The genomic data from diverse ethnic groups are, therefore, critical resources for investigating into ethnicity-specific genomic variants associated with phenotypic traits including susceptibility and severity of diseases.
In the first chapter, I present my analysis of the satellite DNA regions of the Korean reference genome. The satellite DNA which accounts for 5~10 percent of the human genome is missing in the current Korean reference genome. Although KOREF has been improved and updated since its first publication in 2016, until now, the research on KOREF's repeats has revealed only rudimentary information. Here, in this chapter, I present the methods to improve the contiguity of KOREF and build its repeat library from unplaced scaffolds for further updates.
In the second chapter, I present the human COVID-19-related variant study. Large-scale genomic investigation provides the correlations between diverse case fatality rate across ethnic groups and genomic variants. This shows the usefulness of large-scale genomics studies on pandemics.
In conclusion, I present a large-scale genomics study on COVID-19-related variants and an improved Korean reference genome assembly with its repetitive sequence library.ope
Radiological safety evaluation of a recycling facility for dismantled concrete waste
No full textWhen decommissioning a nuclear power plant, a large amount of radioactive waste will be generated. It must be disposed of in a safe and efficient way. Approximately 50% of radioactive waste is concrete waste. The bio-shield is expected to be highly activated compared to concrete structures because of its continuous radiation by neutron flux. Therefore, the spatial dose distribution of the recycling facility and the acquired doses of workers must be determined when recycling or disposing of bio-shield concrete. This study constitutes a preliminary evaluation of radiation safety for a recycling facility for dismantled concrete structures. The radiation dose was simulated using VISIPLAN code to simulate the spatial dose distribution and the external dose of radiation workers. The internal dose of radiation workers was also calculated. The most significant factor in the dose assessment of concrete waste recycling is the radioactivity value of the waste. Thus, this radioactivity value used by cutting the bio-shield is important. It is classified into three cases as follows: the section of the bio-shield that was exposed to the highest radiation levels (case 1), a vertical cut through the section closest to the nuclear reactor (case 2), and where the concrete waste exceeded the allowable concentration for the regulatory clearance (case 3). Case 3 includes parts of cases 1 and 2, as wastes with concentrations higher than the allowable limit for regulatory clearance are classified regardless of the cutting method. The annual effective doses of a worker were 4.40E+01 mSv, 9.07E+00 mSv, and 5.19E+00 mSv for cases 1, 2, and 3, respectively. We determined that the stipulated safety thresholds of 100 mSv over 5 years and no more than 50 mSv in any single year were only exceeded (specifically, the 5-year limit) for case 1, under the assumptions made in our study. We demonstrated that lead shielding is highly effective in reducing doses. Shielding corresponding to thickness of 10 mm and 20 mm, respectively, produced reductions in dose rates of 43.5% and 65.8%, respectively. The workers' annual doses in all cases except case 1 with lead 10 mm when adding lead shielding did not exceed the stipulated annual dose limit of 20 mSv. This dose evaluation of the work processes of a concrete recycling facility is expected to be applied to the actual management of workers??? radiation safety
Effects of cation and anion substitution in KVPO4F for K-ion batteries
No full textThe effects of cation (Ti4+) and anion (O2???) substitution on the electrochemical properties of KVPO4F cathodes are investigated in this work. Both forms of substitution lead to smoothing of the associated voltage profile as well as reduced charging time at high voltage (>4.8 V vs. K/K+). These changes effectively suppress electrolyte decomposition, thereby enhancing the capacity retention in the ion-substituted KV(1 ??? x)TixPO4+yF1???y materials. Ionic substitution also enables the intercalation of excess K ions at a reasonably high voltage (???1.8 V vs. K/K+) relative to that required in pure KVPO4F (<1.0 V vs. K/K+). Finally, this study reveals that detours in the synthesis reaction pathways can be created by using a pre-reacted precursor, VPO4, rather than the conventional precursors V2O3 and NH4H2PO4 to form stoichiometric (or non-substituted) KVPO4F. These results highlight several design criteria that can be used to optimize KVPO4F and related compositions to prepare K-ion batteries with high capacity, good cyclability, and fast rate capability
Editorial: Introducing a Special Issue on Sustainability, Ethics, and ESG Marketing for the New Decade
No full textA Path Planning Study Based on Limited Adaptive Resolution Grid Map
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Large Transconductance of Electrochemical Transistors Based on Fluorinated Donor-Acceptor Conjugated Polymers
No full textOrganic electrochemical transistors (OECTs) have enor-mous potential for use in biosignal amplifiers, analyte sensors, and neuromorphic electronics owing to their exceptionally large trans-conductance. However, it is challenging to simultaneously achieve high charge carrier mobility and volumetric capacitance, the two most important figures of merit in OECTs. Herein, a method of achieving high-performance OECT with donor-acceptor conjugated copolymers by introducing fluorine units is proposed. A series of cyclopentadithiophene- benzothiadiazole (CDT-BT) copolymers for use in high-performance OECTs with enhanced charge carrier mobility (from 0.65 to 1.73 cm2 center dot V-1 center dot s-1) and extended volumetric capacitance (from 44.8 to 57.6 F center dot cm-3) by fluorine substitution is achieved. The increase in the volumetric capacitance of the fluorinated polymers is attributed to either an increase in the volume at which ions can enter the film or a decrease in the effective distance between the ions and polymer backbones. The fluorine substitution increases the backbone planarity of the CDT-BT copolymers, enabling more efficient charge carrier transport. The fluorination strategy of this work suggests the more versatile use of conjugated polymers for high-performance OECTs