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- 검색키워드
- 발행기관 : Ulsan National Institute of Science and Technology (검색결과 1,434 건)
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Effective and Efficient Patch Validation via Differential Fuzzing
Eui Bin Bae Ulsan National Institute of Science and Technology 2022 국내석사
Developments in APR(automatic program repair) technology have made it possible to automate the creation of patches. However, due to the loose precision(the current technology only recognizes a patch if it passed a test), it is still left up to the developer to determine whether the generated patch is correct. Accordingly, techniques for determining whether a generated patch is correct are being studied these days. Existing methods mainly score how likely a patch is correct. The calculated score is compared with a predetermined threshold to determine whether the patch is correct. However, it is difficult to improve both recall and precision no matter how the threshold is set. For example, in the case of ODS, it shows a problem that filters out many bad patches, but also filters out many correct patches. In this study, we try to solve this problem through an evidence-based method. We take different results before and after the patch as the minimum condition for determining that the patch is wrong. In this condition, if the input that derives different results represents the passing test, the different test results can be the evidence for showing that the patch is incorrect. We use Differential Fuzzing technology to find program inputs that have different results before and after patching. Also, in order to figure out whether the found input represents a passing test, we use the TEST-SIM+ heuristic, which is an improved version of the existing TEST-SIM heuristic. Finally, we develop a purging technology specialized for TEST-SIM+ technology.
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Hyori Lee Ulsan National Institute of Science and Technology 2023 국내석사
As museums and cultural institutions have responded to the environmental challenges posed by the climate crisis, they have become critical arenas in driving sustainable design practices. Designers can contribute to those communities for sustainability transitions on multiple scales of society and various timelines by using their creative and decisive agency. However, there needs to be more practical knowl- edge of the design approaches for operationalizing sustainability transitions of such institutions. This thesis presents a multi-layered account of the development process of a policy design experiment for sustainability transitions at the National Museum of Modern and Contemporary Art in South Korea. The author retrospectively traced the entire process, conducted interviews with the project team members, including the director and student designers, and performed a thematic analysis to identify how the pro- cess could evolve. The findings suggest that the process of a policy design experiment for sustainability transitions of a public art museum follows a non-linear and complex process intertwined with multiple design activities. This research’s insights can inspire design researchers, practitioners, museums, and cultural institutions seeking systemic and long-term innovation for sustainability.
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Na Gyeong An Ulsan National Institute of Science and Technology 2021 국내박사
Organic photovoltaics (OPVs) have witnessed in next generation energy source due to their outstanding potentials such as light-weight, flexibility, semi-transparency, color-tunability and roll-to-roll (R2R) processability. In addition, OPVs have recently achieved great progress in power conversion efficiency (PCE) of >18%. One key breakthrough is an emergence of non-fullerene acceptors (NFAs), which allows easy tuning of energy level compared fullerene counterparts, give opportunity to explore high open-circuit voltages. A development of ternary system is further contributed to high performance of NFA-based OPVs, which enhances short-circuit current density from complementary absorption of two different donors or acceptors absorption region. Despite of such great advantages and achievements, current manufacturing technology known as one variable at a time experimentation (Edonesian) still has remained far behind the expectations in terms of time consuming and human resource. Therefore, high-throughput experimentation approach is highly in demand. This thesis covers NFA-based ternary OPVs and their applications with a new experimental approach; Firstly, a ternary combination consists of PTB7-Th, IEICO-4F and two simple NFAs based on a bithiophene core with rhodanine end-groups (T2-ORH and T2-OEHRH) were explored and their photovoltaic properties were systematically investigated. PTB7-Th and IEICO-4F are generally known as narrow band gap donor and acceptor and two NFAs retain ultra-wide ban gap, hence, the ternary systems were further utilized to achieve controllable device coloration. We successfully demonstrated blend films with tunable colors including cyan → blue → purple → reddish purple colors, which were controlled by the ratios of IEICO-4F:T2-ORH or IEICO-4F:T2-OEHRH with PTB7-Th. Additionally, optical properties of blend films were studied via absorption and transmission measurements, while the range of colors achieved was quantified using CIE chromaticity and CIELAB color space then represented as RGB color models. Next, we introduced a new research approach to develop OPVs via industrial R2R slot die coating in conjunction with in-situ formulation technique and machine learning (ML) technology. Various PM6:Y6:IT-4F ternary blends, one of the highest performing ternary systems to date, are formulated in-situ and deposited on continuously moving substrates resulting in high-throughput fabrication of OPV with various compositions. The system is used to produce training data of ML technology. Composition/deposition parameters, referred as deposition densities, and efficiencies of 2218 devices are used to screen ML algorithms and to train an ML model based on Random Forest regression algorithm. Generated model is used to predict high-performance formulations and the prediction is experimentally validated resulting in 10.2% efficiency, the highest efficiency from R2R processed OPVs to date.
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GeunWook Kim Ulsan National Institute of Science and Technology 2022 국내석사
The induction heater directly applies electrical energy to the target and heats it by thermal energy conversion, unlike the conventional heating method. There are advantages of heating performance, high efficiency, and cleanliness through this. Unlike the existing fossil fuel combustion type, a current of AC frequency is generated through a coil to generate a magnetic field. This magnetic field forms an eddy current at the target, and heat is generated in the part where the current inside the target is generated. This operation procedure is different from making carbon gas such as coal and petroleum LPG as by-products. It has the advantage of not making flames and by-products accordingly, and safe heating is possible through electrical control. Application is roughly divided into domestic and industrial applications, and the research directions of the two fields are different. First of all, home applications focus on user convenience technology. For example, various studies have been conducted, such as a technology that enables operation in all-metal containers, a technology that reduces EMC emission caused by high frequency during operation, and estimating the temperature of the load. Among them, measuring the impedance of the load and estimating the temperature based on the impedance has expectations for automatic cooking in the future. Automatic cooking is a technique that informs the user of the recipe for the desired food and helps put the right ingredients at the right time. Estimating load impedance in the domestic cooker IH field to predict the state or temperature of cooking will serve as the basis for automatic cooking technology. In addition, it can be applied to secure safety by creating an alarm that informs water boiling alarm or overheating of the contents. In this thesis, user convenience technology has been studied for home applications by applying the above research direction. In industrial applications, research is being conducted to increase output power and speed up the heating of loads. The industry is demanding a method of increasing the temperature of the load by increasing output power rather than user convenience technology. To achieve a high output IH, an output voltage should be increased, and a device capable of operating at a constant frequency should be used. When a full-bridge inverter is implemented using a MOSFET device, there is a limitation in manufacturing high-power IH due to manufacturing a withstand voltage protection circuit and an increase in the unit price of a switching device. Using more switching elements, it is difficult to reconstruct a system suitable for the output power to expand the output capacity. This thesis proposes a method of stabilizing the system and easily extending the output by manufacturing an induction heating inverter in a modular manner and connecting input-parallel output-series. In this thesis, this study would like to present a design method for analyzing and producing induction heaters used as home cooking containers in the industry. In addition, for home cooking containers, user convenience technology was studied by adding impedance estimation technology. Industrial induction heaters constructed a modular inverter and increased the output voltage to study how to quickly heat and increase the range of operations that can be output. The above study was verified by simulation and experiment through a 2kW class induction heater.
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Seong-Joon Kim Ulsan National Institute of Science and Technology 2021 국내박사
Volatile organic compounds (VOCs) have a critical impact on human health and the environment, and they are commonly emitted from a variety of sources, such as anthropogenic and biogenic sources. Also, VOCs are currently a big headache in the world due to their secondary formation for ozone (O3) and secondary organic aerosol (SOA) in the atmosphere. Seoul, one of the largest cities in Northeast Asia, is the capital city of South Korea with 9.8 million inhabitants and 3.1 million vehicles, and Ulsan located in the southeast of the Korean Peninsula with 1.1 million inhabitants is the largest industrial city, including automobile, heavy-shipbuilding, petrochemical, and non-ferrous industrial complexes in South Korea. Therefore, Seoul and Ulsan could have a significant impact on the VOC pollution from human (e.g., gasoline/diesel vehicular exhausts and printing/painting solvents) and industrial activities (e.g., solvent usage and production/combustion processes). Nevertheless, studies on the atmospheric VOCs and their potential for the O3 and SOA formation have been rarely conducted from now on. The integrated monitoring of atmospheric VOCs in this study was divided into (1) primary monitoring of VOCs in the urban city using passive air samplers (PASs), (2) subsequent monitoring of VOCs in the urban city using an active air sampler (AAS), and (3) simultaneous monitoring of air pollutants in the industrial city using the PAS. Finally, the implication for the control strategy of VOCs, SOA, and O3 was suggested. In the primary monitoring, PASs were seasonally deployed to measure 50 VOCs at 26 urban, 4 road, and 6 background sites in Seoul. Among the target compounds, toluene (summer: 8.72 μg/m3; winter: 5.47 μg/m3), ethyl acetate (summer: 2.36 μg/m3; winter: 3.51 μg/m3), and ethylbenzene (summer: 1.72 μg/m3; winter: 0.88 μg/m3) exhibited higher mean concentrations than other compounds. Printing offices and industrial facilities seem to have strong influences on the VOC levels in the center and southwest of Seoul, respectively. Diagnostic ratios indicated that the main sources of VOCs were related to local volatilization in summer and vehicular exhaust and transport from other areas in winter. Positive matrix factorization (PMF) suggested four major sources of VOCs: residential/commercial solvents for printing and painting (Factor 1); transport from other areas (Factor 2); industrial solvents for painting, manufacturing, and cleaning (Factor 3); and gasoline/diesel vehicular exhausts (Factor 4). Factors 1 and 3 were dominant in summer, and Factors 2 and 4 were dominant in winter. In conclusion, the seasonal meteorological conditions (e.g., temperature and wind patterns) were found to play an important role in the spatial distribution of VOCs in Seoul, and solvent use was a predominant source. In the subsequent monitoring, a sequential tube sampler (STS-25) was used to automatically collect 24 air samples for a day every month at an urban site in Seoul. The annual mean concentration of toluene (9.08 ± 8.99 μg/m3) was the highest, followed by ethyl acetate (5.55 ± 9.09 μg/m3), m,p-xylenes (2.79 ± 4.57 μg/m3), benzene (2.37 ± 1.55 μg/m3), ethylbenzene (1.81 ± 2.27 μg/m3), and o-xylene (0.91 ± 1.47 μg/m3), indicating that they accounted for 77.8–85.6% in four seasons. The Σ60 VOC concentrations in spring and winter were statistically higher compared to in summer and fall due to the location of sampling sites/periods, wind patterns, and major sources in the surrounding area. Overall, the concentrations of individual VOCs were higher during the time in the presence of sunlight than at late night and dawn due to human activities. From conditional bivariate probability function (CBPF) and concentration weighted trajectory (CWT) analysis, domestic effects, such as vehicular exhaust and solvents in Seoul seemed to be dominant; however, sometimes higher concentration events of VOCs might occur from China, North Korea, and industrial facilities nearby Seoul. Benzene, toluene, ethylbenzene, m,p,o-xylenes (BTEX) were the most abundant compounds for the secondary organic aerosol formation potential (SOAFP), which accounted for 5–29% of the PM2.5 concentration during the four seasons. The cancer and non-cancer risks for targeted VOCs were the safety level below the tolerable level (1 × 10-4) and the acceptable safe level (Hazard quotient: HQ < 1), respectively in this study area. Although the levels of the risk and the SOAFP for individual VOCs were not severe, human activities inner-Seoul were a predominant source and the transported effect was identified. In the simultaneous monitoring, PASs for VOCs, O3, NO2, and SO2 were deployed during four seasons 2019–2020 at 6 industrial and 10 urban sites in Ulsan. During the whole sampling periods, the concentration of toluene (mean: 8.75 μg/m3) was the highest among 50 VOCs, followed by m,p-xylenes (4.52 μg/m3), ethylbenzene (4.48 μg/m3), 3-methylpentane (4.40 μg/m3), n-octane (4.26 μg/m3). The seasonal variation of total VOC concentration was not statistically different, indicating that a large amount of VOCs is emitted to the atmosphere throughout a year as a characteristic of the industrial city. On the other hand, the concentrations of O3, NO2, and SO2 had a seasonal characteristic due to meteorological conditions and different sources. The spatial distributions of total VOCs, NO2, and SO2 showed that industrial complexes were major sources, while higher concentrations of O3 were observed in the outskirts of the sampling sites. From the PMF model, five major sources (Factor 1: production processes in the petrochemical industries and gasoline/diesel vehicular exhausts; Factor 2: solvent usage in automobile and ship manufacturing; Factor 3: production processes in the petrochemical/non-ferrous industries and ship emission; Factor 4: gasoline evaporation and combustion in the petrochemical/non-ferrous industries; and Factor 5: industrial solvent usage and secondary formation) were identified. Finally, aromatic compounds, such as m,p,o-xylenes, toluene, and 1,2,4-trimethylbenzene were determined as the most reactive compounds for the O3 formation; therefore, decreasing in the emission amount of these species can be more effective than reducing in that of NO2 in terms of the O3 reduction in the case of this study area. In conclusion, in comparison with the main sources between Seoul and Ulsan, the mean contribution of the main sources of VOCs was totally different. As expected, the effects from atmospheric VOCs primarily emitted from industrial activities were substantial in Ulsan, while human activities, such as printing/painting solvents and gasoline/diesel vehicular exhausts were dominant in Seoul. Therefore, different types of reduction strategy in the emission amount of VOCs should be applied according to a characteristic of the cities. Furthermore, three steps of the procedure applied in this study are suggested; (1) Measurement & analysis: level of VOCs and spatial-temporal variations are identified using the PAS and AAS, (2) Main sources: the most important thing is to look for the source origin using several advanced tools, such as diagnostic ratio, CBPF, CWT, and PMF, and (3) Secondary formation: the relationship between VOCs, SOA, and O3 should be revealed. In the future, the emission aspect, composition, reactivity, and concentration of precursors for the SOA and O3 formation, such as VOCs will be continuously changed. Therefore, integrated monitoring for air pollutants should be periodically conducted for the control strategy of VOCs, SOA, and O3, and this study will be helpful for the improvement of air quality. Also, this monitoring approach can be explored in the urbanized and industrialized cities in the world.
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E-San Jang Ulsan National Institute of Science and Technology 2021 국내박사
In this dissertation, the Monolithic Trantenna (Transistor + Antenna) as high-performance terahertz(THz) detector; based on Silicon (Si) nano-ring type field-effect transistor (FET) is demonstrated for sub-THz imaging technology. And its operation based on highly localized plasmonic wave in the scalable ring-channel is analyzed by using technology computer-aided design (TCAD) and electromagnetic (EM) wave solver tools. The ring-FET is fabricated by Si-CMOS process and we obtained total 900-fold photoresponse ( u) enhancement in on-chip ground-signal-ground (GSG) probing measurement setup. For the high capacitance asymmetry a = Cgd=Cgs, the inner circle diameter (din) is scaled down to 130 nm under the parasitic resistance limit case. Furthermore, the u asymmetry originated by different ground(gnd) source configuration between (i) gnd-out or (ii) gnd-in of the ring-gate is analyzed for the higher responsivity Rv and lower channel thermal noise. Therefore, by taking (i) gnd-out source, we characterized 5-times additional enhancement followed by the 180-times from din and a scaling. Finally, based on the highly localized plasmonic ring-FET, high performance compact THz detector is demonstrated in free-space by using the compact monolithic Trantenna structure without the external amplifier gain. For a higher THz wave power absorption design, the conductive circular active area of ring-FET is designed as circular patch antenna with resonant frequency and the THz wave is absorbed directly in the ring-channel for the plasmonic rectification without the lossy feeding network. As a result, The record-high RV over 12 kV/W and low noise equivalent power of sub-10 pW/Hz0:5 without external gain are experimentally achieved through free-space 0.12 THz illumination. Moreover, free-space THz imaging experiments shows polarization-independent imaging results due to an isotropic circular antenna characteristic.
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Bioinspired composite cilia for active and passive droplet control
Sang-Hyeon Lee Ulsan National Institute of Science and Technology 2022 국내박사
Water droplets and wetting phenomena on various surfaces are ubiquitous in nature and pose significant challenges in various fields. Water droplets in contact with surfaces for a long period lead to the formation of biofilms and cause hygiene problems. They also cause surface icing and metal corrosion, which affect social infrastructure. In addition, water droplets on transparent surfaces degrade optical performance, such as light transmission. Various techniques have been used to address these problems, such as mechanical removal, chemical fluid release (de-icing, anti-corrosion, biocidal, etc.), and Joule heating. However, these techniques are ineffective, expensive, and environmentally harmful. Bioinspired droplet control technology has emerged as a fundamental solution to various problems caused by water droplets and the wetting phenomena. Inspired by living organisms, surfaces with nano/micro-scale cilia structures have been proposed as excellent candidates for droplet control. Multiscale cilia structure-based surfaces can solve the existing problems by maximizing the surface wettability to control the wetting / de-wetting behavior of droplets. A superhydrophobic surface, consisting of cilia array and hydrophobic material, removes the droplets from the surfaces and minimizes the contact between them, preventing freezing and corrosion. In contrast, a superhydrophilic surface, made of cilia array and hydrophilic material, spreads the droplets and forms a thin and continuous aqueous film on the surface, preventing settling of impurities and fogging caused by droplet condensation. However, single-strategy droplet control technologies based on such a simple structure still have several limitations. For example, if a typical superhydrophobic surface based on a cilia array is horizontally arranged, the droplets cannot be removed without additional external force. Moreover, superhydrophilic surfaces with cilia arrays are susceptible to fouling by airborne contaminants, such as dust, due to high surface energy of the hydrophilic materials. Recently, research has been conducted on active and passive droplet control technologies using functional materials to solve the problems caused by wetting phenomena and to address the limitations of the existing technology. First, active droplet control techniques based on stimuli-responsive materials can modulate the droplet manipulation and drop bouncing dynamics using various external stimuli. Among the stimuli-responsive materials, a magneto-responsive composite material was chosen as the primary functional material for active droplet control because it has a fast response speed and doesn’t require additional external power source for precise deformation control. The surface morphology of the magneto-responsive composite elastomer can be actively controlled using a magnet, which enables droplet manipulation and easy removal of droplets from the surface. Second, passive droplet control techniques based on anti-fouling materials can prevent a wide range of contamination such as airborne and waterborne pollution by the hydration barrier and weak adhesion. Second, owing to hydration barrier and weak adhesion, passive droplet control techniques based on anti-fouling materials can prevent a wide range of contamination such as airborne and waterborne pollution. An amphiphilic copolymer with both hydrophilic and hydrophobic segments is also being considered as a suitable material for passive droplet spreading. It was found that an amphiphilic copolymer has droplet spreading ability and exhibits “fouling-resistant” property in the hydrophilic segment and the “fouling-release” property in the hydrophobic segment. Therefore, based on their unique properties, amphiphilic material-based surfaces exhibit excellent anti-fogging and anti-biofouling properties. In addition, these surfaces can prevent external contaminants from firmly adhering to the surface and reduce surface contamination. However, single-strategy active and passive droplet control technologies based only on functional materials also have some limitations. Owing to the lack of de-wetting or wetting properties, planar surfaces composed of only functional materials without multiscale cilia structures do not exhibit a sufficiently high capability to remove or spread droplets on the surface. For example, droplets may adhere to a magneto-responsive composite planar surface because of insufficient hydrophobicity. In addition, it is not easy to spread droplets over a wide area on an amphiphilic planar surface because of its insufficient wetting performance. Many previous studies on droplet control focused on single-strategy techniques, such as typical superwetting surfaces based on multiscale structures or planar surfaces based on functional materials. However, such single-strategy approaches to droplet control have many limitations. Therefore, new strategies in multi-approaches, that integrate both strategies in approaches of multiscale architectures and functional composite materials, are needed to overcome the problems of existing technologies. We proposed a bioinspired magneto-responsive cilia array for active droplet control based on a superhydrophobic and hierarchical cilia array composed of a magneto-responsive composite elastomer. In this study, the dynamic cilia array showed robust droplet shedding performance by actively controllable multimodal drop bouncing dynamics and precise droplet manipulation. Furthermore, it exhibited remarkable anti-icing properties compared to conventional technologies. We also presented a bioinspired amphiphilic copolymer nanocilia array for passive droplet spreading. The hybrid of hydrophilic hydrogel, hydrophobic lubricant, and nanostructures showed significantly enhanced spreading ability due to the synergetic integration of the amphiphilic copolymer and nanoscale cilia array. The amphiphilic nanocilia hybrid exhibited a pronounced anti-fogging performance due to its water-spreading properties and retardation of droplet nucleation. It also exhibited notable anti-biofouling performance by integrating fouling-resistant, fouling-release, and foulant-killing mechanisms.
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