• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.2A
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• pp.185-191
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• 2010

Because the concrete crack that is the reason of the serviceability and durability degradation of concrete structure can be arisen from either the stress magnitude and gradient or other structural and material defects, the crack strength of concrete is hard to accurately evaluate. Especially, stress-state in concrete plate components such as rigid pavement and long span slab is biaxial flexure stress, and the flexural strength of those component may be different than the traditional rupture modulus of concrete subjected to uniaxial stress. In this study, an experimental investigation to assess of mechanical behavior under uniaxial and biaxial flexure stress is conducted and the proposed optimum specimen configuration is adopted. From the test, the modulus of rupture under uniaxial and biaxial stress are decreased as the size of aggregate or specimen is larger. And biaxial flexure strength of concrete specimens is varied from 39.5 to 99.2% as compared with that of uniaxial strength, and the biaxial strength of specimen with 20mm aggregate size is only 76% of uniaxial strength.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2022.10a
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• pp.164-167
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• 2022

In table Machine comprehension, the knowledge required for language models or the structural form of tables changes depending on the domain, showing a greater performance degradation compared to text data. In this paper, we propose a pre-learning data construction method and an adversarial learning method through meaningful tabular data selection for constructing a pre-learning table language model robust to these domain changes in table machine reading. In order to detect tabular data sed for decoration of web documents without structural information from the extracted table data, a rule through heuristic was defined to identify head data and select table data was applied. An adversarial learning method between tabular data and infobax data with knowledge information about entities was applied. When the data was refined compared to when it was trained with the existing unrefined data, F1 3.45 and EM 4.14 increased in the KorQuAD table data, and F1 19.38, EM 4.22 compared to when the data was not refined in the Spec table QA data showed increased performance.

• Structural Engineering and Mechanics
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• v.88 no.5
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• pp.481-492
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• 2023

The past earthquakes revealed the importance of the design of moment-resisting reinforced concrete framed structures with ductile behavior. Due to seismic activity, failures in framed structures are widespread in beam-column joints. Hence, the joints must be designed to possess sufficient strength and stiffness. This paper investigates the effects of fibers on the ductility of hybrid fiber reinforced self-compacting concrete (HFRSCC) when subjected to seismic actions; overcoming bottlenecks at the beam-column joints has been studied by adding low modulus sisal fiber and high modulus steel fiber. For this, the optimized dose of hooked end steel fiber content (1.5%) was kept constant, and the sisal fiber content was varied at the rate of 0.1%, up to 0.3%. The seismic performance parameters, such as load-displacement behavior, ductility, energy absorption capacity, stiffness degradation, and energy dissipation capacity, were studied. The ductility factor and the cumulative energy dissipation capacity of the hybrid fiber (steel fiber, 1.5% and sisal fiber, 0.2%) added beam-column joint specimen is 100% and 121% greater than the control specimen, respectively. And also the stiffness of the hybrid fiber reinforced specimen is 100% higher than the control specimen. Thus, the test results showed that adding hybrid fibers instead of mono fibers could significantly enhance the seismic performance parameters. Therefore, the hybrid fiber reinforced concrete with 1.5% steel and 0.2% sisal fiber can be effectively used to design structures in seismic-prone areas.

• The Journal of the Acoustical Society of Korea
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• v.29 no.4
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• pp.270-277
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• 2010

In this paper, we proposed an algorithm that improves tone quality of noisy audio signals by using ICA(Independent Component Analysis) algorithm and perceptual filters. Many algorithms have been proposed to eliminate the noise from the audio signals, such as spectral subtraction method, perceptual filter, etc. The perceptual filter uses a noise that is acquired from silent ranges in the input signal. In this case, the improvement rate of tone quality decreases if the noise energy is changed by the environmental variation in a signal frame. But the proposed method estimates a noise that is changed at each frame using ICA algorithm. The estimated noise is applied to perceptual filter. To show the performance of the proposed algorithm, several tests are performed to various input signals. With the proposed algorithm, we could confirm the enhancement of tone quality in terms of segmental SNR (SSNR), noise-to-mask ratio (NMR) and Degradation Category Rating (DCR) test.

• The Journal of the Acoustical Society of Korea
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• v.28 no.3
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• pp.279-284
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• 2009

Speaker verification determines whether the claimed speaker is accepted based on the score of the test utterance. In recent years, methods based on Gaussian mixture models and universal background model have been the dominant approaches for text-independent speaker verification. These speaker verification systems based on these methods provide very good performance under laboratory conditions. However, in real situations, the performance of speaker verification system is degraded dramatically. For overcoming this performance degradation, the feature recombination method was proposed, but this method had a drawback that whole sub-band feature vectors are used to compute the likelihood scores. To deal with this drawback, a modified feature recombination method which can use each sub-band likelihood score independently was proposed in our previous research. In this paper, we propose a sub-band weighting method based on sub-band signal-to-noise ratio which is combined with previously proposed modified feature recombination. This proposed method reduces errors by 28% compared with the conventional feature recombination method.

• Advances in concrete construction
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• v.16 no.4
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• pp.205-216
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• 2023

Concrete structures may become vulnerable during their lifetime due to several reasons such as degradation of their material properties; design or construction errors; and environmental damage due to earthquake. These structures should be repaired or strengthened to ensure proper performance for the current service load demands. Several methods have been investigated and applied for the strengthening of reinforced concrete (RC) structures using various materials. Fiber reinforced polymer (FRP) reinforcement is one of the most recent type of material for the strengthening purpose of RC structures. The main objective of the present research is to identify the behavior of reinforced concrete slabs strengthened with FRP bars by using near surface mounted (NSM) technique. Validation study is conducted based on the experimental test available in the literature to investigate the accuracy of finite element models using LS-DYNA to present the behavior of the models. A parametric analysis is conducted on the effect of FRP bar diameters, number of grooves, groove intervals as well as width and height of the grooves on the flexural behavior of strengthened reinforced slabs. Performance of strengthening RC slabs with NSM FRP bars was confirmed by comparing the results of strengthening reinforced slabs with control slab. The numerical results of mid-span deflection and stress time histories were reported. According to the numerical analysis results, the model with three grooves, FRP bar diameter of 10 mm and grooves distances of 100 mm is the most ideal and desirable model in this research. The results demonstrated that strengthening of reinforced concrete slabs using FRP by NSM method will have a significant effect on the performance of the slabs.

• Nanomaterials
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• v.12 no.12
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• pp.1956-1965
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• 2022

The electrode concept of graphite and silicon blending has recently been utilized as the anode in the current lithium-ion batteries (LIBs) industry, accompanying trials of improvement of cycling life in the commercial levels of electrode conditions, such as the areal capacity of approximately 3.3 mAh/cm² and volumetric capacity of approximately 570 mAh/cm³. However, the blending concept has not been widely explored in the academic reports, which focused mainly on how much volume expansion of electrodes could be mitigated. Moreover, the limitations of the blending electrodes have not been studied in detail. Therefore, herein we investigate the graphite blending electrode with micron-sized SiO_x anode material which is one of the most broadly used Si anode materials in the industry, to approach the commercial and practical view. Compared to the silicon micron particle blending electrode, the SiO_x blending electrode showed superior cycling performance in the full cell test. To elucidate the cause of the relatively less degradation of the SiO_x blending electrode as the cycling progressed in full-cell, the electrode level expansion and the solid electrolyte interphase (SEI) thickening were analyzed with various techniques, such as SEM, TEM, XPS, and STEM-EDS. We believe that this work will reveal the electrochemical insight of practical SiO_x-graphite electrodes and offer the key factors to reducing the gap between industry and academic demands for the next anode materials.

• Korean Journal of Agricultural and Forest Meteorology
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• v.22 no.1
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• pp.26-46
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• 2020

An irrigated-maize agroecosystem is viewed as an open thermodynamic system upon which solar radiation impresses a large gradient that moves the system away from equilibrium. Following the imperative of the second law of thermodynamics, such agroecosystem resists and reduces the externally applied gradient by using all means of this nature-human coupled system acting together as a nonequilibrium dissipative process. The ultimate purpose of our study is to test this hypothesis by examining the energetics of agroecosystem growth and development. As a first step toward this test, we employed the eddy covariance flux data from 2003 to 2014 at the AmeriFlux NE1 irrigated-maize site at Mead, Nebraska, USA, and analyzed the energetics of this agroecosystem by scrutinizing its radiation, energy and entropy exchange. Our results showed: (1) more energy capture during growing season than non-growing season, and increasing energy capture through growing season until senescence; (2) more energy flow activity within and through the system, providing greater potential for degradation; (3) higher efficiency in terms of carbon uptake and water use through growing season until senescence; and (4) the resulting energy degradation occurred at the expense of increasing net entropy accumulation within the system as well as net entropy transfer out to the surrounding environment. Under the drought conditions in 2012, the increased entropy production within the system was accompanied by the enhanced entropy transfer out of the system, resulting in insignificant net entropy change. Drought mitigation with more frequent irrigation shifted the main route of entropy transfer from sensible to latent heat fluxes, yielding the production and carbon uptake exceeding the 12-year mean values at the cost of less efficient use of water and light.

• Journal of Korean Tunnelling and Underground Space Association
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• v.25 no.4
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• pp.261-283
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• 2023

This study aimed to review the performance stability of PET (Polyethylene terephthalate) fiber reinforcing materials among the synthetic fiber types for which the application of performance reinforcing materials to fiber-reinforced concrete is being reviewed by examining short-term and long-term performance changes. To this end, the residual performance was analyzed after exposing the PET fiber to an acid/alkali environment, and the flexural strength and equivalent flexural strength of the PET fiber-reinforced concrete mixture by age were analyzed, and the surface of the PET fiber collected from the concrete specimen was examined using a scanning microscope (SEM). The changes in were analyzed. As a result of the acid/alkali environment exposure test of PET fiber, the strength retention rate was 83.4~96.4% in acidic environment and 42.4~97.9% in alkaline environment. It was confirmed that the strength retention rate of the fiber itself significantly decreased when exposed to high-temperature strong alkali conditions, and the strength retention rate increased in the finished yarn coated with epoxy. In the test results of the flexural strength and equivalent flexural strength of the PET fiber-reinforced concrete mixture, no reduction in flexural strength was found, and the equivalent flexural strength result also did not show any degradation in performance as a fiber reinforcement. Even in the SEM analysis results, no surface damage or cross-sectional change of the PET reinforcing fibers was observed. These results mean that no damage or cross-section reduction of PET reinforcing fibers occurs in cement concrete environments even when fiber-reinforced concrete is exposed to high temperatures in the early stage or depending on age, and the strength of PET fibers decreases in cement concrete environments. The impact is judged to be of no concern. As the flexural strength and equivalent flexural strength according to age were also stably expressed, it could be seen that performance degradation due to hydrolysis, which is a concern due to the use of PET fiber reinforcing materials, did not occur, and it was confirmed that stable residual strength retention characteristics were exhibited.

• Applied Chemistry for Engineering
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• v.21 no.6
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• pp.697-701
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• 2010

We investigate the cell performance and characteristics of a direct formic acid fuel cell (DFAFC) using palladium (Pd) as a catalyst for anode. Pd is deposited on the electrolyte using the "direct paint" method. From a continuous three time-test of the polarization curve of the DFAFC, it is found that the catalytic activity of Pd and the cell performance of DFAFC steadily degrade as the tests are proceeded. This behavior may be due to the deactivation of Pd by formate (COOH) and hydroxyl (OH) groups, which are electrochemically dissociated from formic acid solution. Estimations of the degradation, followed by reactivation in activity of Pd catalyst and DFAFC cell performance are implemented by linear voltage sweep tests going in both positive and negative directions. When the maximum voltage of 1.0 V versus DHE is applied to the cell while a linear voltage sweep test going in negative directions, the activity of Pd catalyst and the DFAFC cell performance recover by the rehabilitation in activity of the deactivated Pd.