• Title/Summary/Keyword: 성능감소

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Natural Frequency Analysis of Sleeper Floating Track System using Modal Test Technique (모달시험기법을 이용한 침목플로팅궤도의 고유진동수 분석)

  • Jung-Youl Choi
    • The Journal of the Convergence on Culture Technology
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    • v.10 no.3
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    • pp.833-838
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    • 2024
  • The urban railway sleeper floating track(STEDEF) is a structure that structurally separates the sleepers and the concrete bed using sleeper boots and resilience pads to reduce vibration transmitted to the concrete bed. Recently, the resilience pads of sleeper floating tracks that have been in use for more than 20 years are deteriorating. Accordingly, in order to evaluate the performance of the resilience pad, a static spring stiffness test is being performed after extracting the resilience pad. This evaluation technique is performed after replacing the resilience pad in use. However, the track natural frequency can change depending on the resilience pad spring stiffness and the uplift and subsidence of the concrete bed. In this study, modal testing technique was used to evaluate the track natural frequency. For this purpose, the sleeper boots material, resilience pad spring stiffness, and track natural frequency according to concrete bed uplift and subsidence were measured using modal tests at a laboratory scale. It was analyzed that the natural frequency of the sleeper floating track was directly affected by changes in the spring stiffness of the resilience pad. In addition, the change in natural frequency due to the uplift and subsidence of the concrete bed was also found to be large. Therefore, it is believed that the modal test technique presented in this study can be used to evaluate the resilience pad deterioration and voided sleepers.

Diagnostic Performance of Cardiac CT and Transthoracic Echocardiography for Detection of Surgically Confirmed Bicuspid Aortic Valve: Effect of Calcium Extent and Valve Subtypes (외과적으로 확진된 이첨 대동맥 판막의 진단을 위한 심장 CT 및 경흉부 심초음파의 진단적 성능: 판막 아형 및 칼슘의 양이 미치는 효과)

  • Jeongju Kim;Sung Mok Kim;Joonghyun Ahn;Jihoon Kim;Yeon Hyeon Choe
    • Journal of the Korean Society of Radiology
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    • v.84 no.6
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    • pp.1324-1336
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    • 2023
  • Purpose This study aimed to compare the diagnostic performance of cardiac CT and transthoracic echocardiogram (TTE) depending on the degree of valvular calcification and bicuspid aortic valve (BAV) subtype. Materials and Methods This retrospective study included 266 consecutive patients (106 with BAV and 160 with tricuspid aortic valve) who underwent cardiac CT and TTE before aortic valve replacement. Cardiac CT was used to evaluate the morphology of the aortic valve, and a calcium scoring scan was used to quantify valve calcium. The aortic valves were classified into fused and two-sinus types. The diagnostic accuracy of cardiac CT and TTE was calculated using a reference standard for intraoperative inspection. Results CT demonstrated significantly higher sensitivity, negative predictive value, and accuracy than TTE in detecting BAV (p < 0.001, p < 0.001, and p = 0.003, respectively). The TTE sensitivity tended to decrease as valvular calcification increased. The error rate of TTE for CT was 10.9% for the twosinus type of BAV and 28.3% for the fused type (p = 0.044). Conclusion Cardiac CT had a higher diagnostic performance in detecting BAV than TTE and may help diagnose BAV, particularly in patients with severe valvular calcification.

A Service Life Prediction for Unsound Concrete Under Carbonation Through Probability of Durable Failure (탄산화에 노출된 콘크리트 취약부의 확률론적 내구수명 평가)

  • Kwon, Seung Jun;Park, Sang Soon;Nam, Sang Hyeok;Lho, Byeong Cheol
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.12 no.2
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    • pp.49-58
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    • 2008
  • Generally, steel corrosion occurs in concrete structures due to carbonation in down-town area and underground site and it propagates to degradation of structural performance. In general diagnosis and inspection, only carbonation depth in sound concrete is evaluated but unsound concrete such as joint and cracked area may occur easily in a concrete member due to construction process. In this study, field survey of carbonation for RC columns in down-town area is performed and carbonation depth in joint and cracked concrete including sound area is measured. Probability of durable failure with time is calculated through probability variables such as concrete cover depth and carbonation depth which are obtained from field survey. In addition, service life of the structures is predicted based on the intended probability of durable failure in domestic concrete specification. It is evaluated that in a RC column, various service life is predicted due to local condition and it is rapidly decreased with insufficient cover depth and growth of crack width. It is also evaluated that obtaining cover depth and quality of concrete is very important because the probability of durable failure is closely related with C.O.V. of cover depth.

Study on The Effect of Electrode Drying Temperature on The Silicon Electrode Characteristics of Lithium Secondary Batteries (전극 건조 온도가 리튬이차전지의 실리콘 전극 특성에 미치는 영향 연구)

  • Dong-Wan Ham;Myeong-Hui Jeong;Jeong-Tae Kim;Beom-Hui Lee;Hyeon-Mo Moon;Sun-Yul Ryou
    • Journal of the Korean Electrochemical Society
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    • v.27 no.3
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    • pp.97-104
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    • 2024
  • The electrodes of commercialized lithium secondary batteries are manufactured through a wet coating process, and the drying process (DC) is a very important factor as to electrode production speed and process cost. In this study, silicon anodes were manufactured under high-temperature (180 ℃) and low-temperature (50 ℃) DC to investigate the quality and the electrochemical performance of Si-electrodes according to DC. High-temperature DC can quickly evaporate the solvent in the Si-electrode slurry, improving the electrode production rate. However, this also causes the electrode composite to peel off from the current collector. As a result, the Si-electrode's adhesion weakened, and the electrode coating's quality deteriorated. In addition, the Si-electrode manufactured under high-temperature was found to have a thicker composite material than the Si-electrode manufactured under low-temperature. Si-electrodes manufactured under high-temperature had higher sheet resistance and lower electrical conductivity than those manufactured under low-temperature. Consequently, the Si-electrode manufactured under low-temperature showed 152.5% superior cycle performance compared to the Si-electrode manufactured under high-temperature. (Discharge capacities of Si-electrodes manufactured under high-temperature and low-temperature DC were 844 and 1287 mAh g-1, respectively, after 300 cycles). Establishing the DC of Si-electrodes can easily provide new perspectives to improve the quality and stability of Si-electrodes.

A Study of Recycling Lithium-ion Battery Graphite by Eco-friendly Citric Acid Treatment Method (친환경 구연산처리를 통한 폐흑연 재활용 연구)

  • Dong-kyu Son;Won Jin Park;Jun Young Kim;Ji Hui Yun;Jung Eun Hyun
    • Korean Chemical Engineering Research
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    • v.62 no.3
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    • pp.246-252
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    • 2024
  • In this study, impurities such as Li and F were removed from waste graphite through citric acid treatment, and changes in structural properties, capacity, and cycle stability of regenerated graphite were observed accordingly. Regenerated graphite pretreated in a nitrogen atmosphere was treated with citric acid, and its structure and characteristics were analyzed through SEM (Scanning Electron Microscope), FT-IR (Fourier Transform Infrared spectroscopy), XRD (X-ray Diffraction), and XPS (X-ray Photoelectron Spectroscopy). Waste graphite that was not treated with acid had a rapid decrease in capacity before 70 cycles, but graphite that had been treated with citric acid showed a capacity of 302.9 mAh g-1 and a capacity retention rate of 93.1% at 100 cycles. In addition, despite changes in current density in rate performance, samples treated with citric acid showed 340.2 mAh g-1 performance at 1.0C without change in capacity. As a result, it was confirmed that citric acid treatment not only effectively removed impurities and showed a high capacity retention rate, but also showed stability even at high current densities.

Comparative Analysis of Noise Characteristics by Road Pavement Types as Measurement Methods (측정 방법에 따른 도로 포장 종류별 소음 특성 비교 연구)

  • Guk-Gon Song;Seok-Kyeong Bae;Woo-Young Cho;Hyun-Woo Cho
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.28 no.5
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    • pp.47-53
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    • 2024
  • This study investigates the noise reduction effects of various road pavement methods to mitigate traffic noise caused by the increasing proximity between roads and residential areas in urban environments. The noise characteristics of four types of road pavement-Dense Asphalt Concrete (DAC), Double Layer Porous Asphalt Concrete (DLPAC), Transverse Tining Concrete (TTC), and Exposed Aggregate Concrete (EAC)-were evaluated using CPX close-proximity noise and pass-by noise measurements. The CPX measurements showed that noise levels increased logarithmically with vehicle speed for all pavements. Specifically, DLPAC demonstrated higher noise levels in the low-frequency range below 800 Hz and lower noise levels in the high-frequency range, which is attributed to resonance effects within the internal pores of the pavement and the reduction of compression and expansion noise. In pass-by noise measurements, DLPAC exhibited higher low-frequency noise compared to DAC, likely due to pavement durability deterioration and the influence of external environmental noise. The results indicate that the CPX measurement method is more effective in evaluating road noise performance as it better reflects the impact of vehicle speed. However, since the study was conducted under limited site conditions, further research across various sites and conditions is necessary to enhance reliability.

Development and Self-Healing Performance of Epoxy Based on Disulfide (이황화 결합을 기반으로 한 자가치유 에폭시 개발 및 자가치유 성능 평가)

  • Donghyeon Lee;Seong Baek Yang;Jong-Hyun Kim;Mantae Kim;Dong-Jun Kwon
    • Composites Research
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    • v.37 no.4
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    • pp.337-342
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    • 2024
  • Thermosetting composite materials are applied in mobility and structural applications due to their high mechanical strength and thermal properties. Nevertheless, these materials are difficult to recycle or reprocess. Therefore, research is currently underway to introduce vitrimer as a solution to this challenge. In this study, to enable reprocessing and self-healing of structural epoxy, an epoxy containing disulfide bonds was synthesized and added. The addition of disulfide epoxy resulted in a decrease in tensile strength and Young's modulus, but an increase in tensile strain. Analysis of the fracture surface after tensile testing revealed that the addition of disulfide epoxy imparted characteristics of ductile materials. This is attributed to the structure of disulfide epoxy, which primarily involves alkyl chains and bond exchange occurring at the disulfide bonds. It was confirmed that the addition of disulfide epoxy enables self-healing through reprocessing. While reprocessing was not possible with disulfide epoxy content below 17 wt%, it was feasible up to four times with content above 0.25 wt%. This study is expected to contribute to extending the lifespan of structural composites and enhancing recycling possibilities through reprocessing.

Sound Pressure and Vibration Characteristics of Reinforced Concrete Slab with Heavy Weight Mortar for Cross-section Recovery (단면 회복용 중량 모르타르를 사용한 철근콘크리트 슬래브의 음압 및 진동 특성)

  • Jae-Sung Kim;Jin-Man Kim
    • Journal of the Korean Recycled Construction Resources Institute
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    • v.12 no.3
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    • pp.298-305
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    • 2024
  • This paper is a basic study to improve floor impact noise of reinforced concrete slabs. Considering the case where thickness differences occur due to construction, changes in sound insulation characteristics were analyzed when the cross section of a reinforced concrete slab was restored with mortar. The houses subject to analysis were divided into two types, 84 type and 59 type, with different floor plans. When pre-mortaring was done with heavy mortar to restore the cross section on the reinforced concrete slab, the case was when pre-mortaring was done with the reinforced concrete slab alone and with general mortar. Compared with, the difference between vibration acceleration level and sound pressure was measured. As a result of measuring the vibration acceleration level of the slab after pouring the mortar, the CS mortar was 66.4 dB and the ES mortar was 66.1 dB at 84 type 63 Hz, which was more than 2 dB lower than that of regular mortar. In addition, compared to the reinforced concrete slab alone, CS mortar was reduced by 5.5 dB and ES mortar was reduced by 4.6 dB, showing relatively excellent values. As for the floor impact sound pressure, the 84B type was similar at 63 Hz for CS mortar and general mortar at 67.3 dB, and the reduction compared to the reinforced concrete slab alone was 3.6 dB for CS mortar, 2.7 dB for ES mortar, and 2.7 dB for general mortar was reduced by 1.4 dB. By pouring mortar to compensate for the thickness of the reinforced concrete slab, the vibration acceleration level and floor impact noise were reduced, and when a heavy mortar using copper smelting slag fine aggregate was used, relatively excellent performance was found.

Development of Prediction Model for XRD Mineral Composition Using Machine Learning (기계학습을 활용한 XRD 광물 조성 예측 모델 개발)

  • Park Sun Young;Lee Kyungbook;Choi Jiyoung;Park Ju Young
    • Korean Journal of Mineralogy and Petrology
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    • v.37 no.2
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    • pp.23-34
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    • 2024
  • It is essential to know the mineral composition of core samples to assess the possibility of gas hydrate (GH) in sediments. During the exploration of gas hydrates (GH), mineral composition values were obtained from each core sample collected in the Ulleung Basin using X-ray diffraction (XRD). Based on this data, machine learning was performed with 3100 input values representing XRD peak intensities and 12 output values representing mineral compositions. The 488 data points were divided into 307 training samples, 132 validation samples, and 49 test samples. The random forest (RF) algorithm was utilized to obtain results. The machine learning results, compared with expert-predicted mineral compositions, revealed a Mean Absolute Error (MAE) of 1.35%. To enhance the performance of the developed model, principal component analysis (PCA) was employed to extract the key features of XRD peaks, reducing the dimensionality of input data. Subsequent machine learning with the refined data resulted in a decreased MAE, reaching a maximum of 1.23%. Additionally, the efficiency of the learning process improved over time, as confirmed from a temporal perspective.

The Effect of Corporate Association on the Perceived Risk of the Product (소비자의 제품 지각 위험에 대한 기업연상과 효과: 지식과 관여의 조절적 역활을 중심으로)

  • Cho, Hyun-Chul;Kang, Suk-Hou;Kim, Jin-Yong
    • Journal of Global Scholars of Marketing Science
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    • v.18 no.4
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    • pp.1-32
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    • 2008
  • Brown and Dacin (1997) have investigated the relationship between corporate associations and product evaluations. Their study focused on the effects of associations with a company's corporate ability (CA) and its corporate social responsibility (CSR) on consumers' product evaluations. Their study has found that both of CA and CSR influenced product evaluation but CA association has a stronger effect than CSR associations. Brown and Dacin (1997) have, however, claimed that there are few researches on how corporate association impacts product responses. Accordingly, some of researchers have found the variables to moderate or to mediate the relationship between the corporate association and the product responses. In particular, there has been existed a few of studies that tested the influence of the reputation on the product-relevant perceived risk, but the effects of two types of the corporate association on the product-relevant perceived risk were not identified so far. The primary goal of this article is to identify and empirically examine some variables to moderate the effects of CA association and CSR association on the perceived risk of the product. In this articles, we take the concept of the corporate associations that Brown and Dacin (1997) had proposed. CA association is those association related to the company's expertise in producing and delivering its outputs and CSR association reflected the organization's status and activities with respect to its perceived societal obligations. Also, this study defines the risk, which is the uncertainty or loss of the product and corporate that consumers have taken in a particular purchase decision or after having purchased. The risk is classified into product-relevant performance risk and financial risk. Performance risk is the possibility or the consequence of a product not functioning at some expected level and financial risk is the monetary loss one perceives to be incurring if a product does not function at some expected level. In relation to consumer's knowledge, expert consumers have much of the experiences or knowledge of the product in consumer position and novice consumers does not. The model tested in this article are shown in Figure 1. The model indicates that both of CA association and CSR association influence on performance risk and financial risk. In addition, the effects of CA and CSR are moderated by product category knowledge (product knowledge) and product category involvement (product involvement). In this study, the relationships between the corporate association and product-relevant perceived risk are hypothesized as the following form. For example, Hypothesis 1a($H_{1a}$) is represented that CA association has a positive influence on the performance risk of consumer. Also, the hypotheses that identified some variables to moderate the effects of two types of corporate association on the perceived risk of the product are laid down. One of the hypotheses of the interaction effect is Hypothesis 3a($H_{3a}$), it is described that consumer's knowledges of the product moderates the negative relationship between CA association and product-relevant performance risk. A field experiment was conducted in order to examine our model. The company tested was not real but imagined to meet the internal validity. Water purifiers were used for our study. Four scenarios have been developed and described as the imaginary company: Type A with both of superior CA and CSR, Type B with superior CSR and inferior CA, Type C with superior CA and inferior CSR, and Type D with both inferior of CA and CSR. The respondents of this study were classified into four groups. One type of four scenarios (Type A, B, C, or D) in its questionnaire was given to the respondent who filled out questions. Data were collected by means of a self-administered questionnaire to the respondents, chosen in convenience. A total of 300 respondents filled out the questionnaire but 207 were used for further analysis. Table 1 indicates that the scales in this study are reliable because the range of coefficients of Cronbach's $\alpha$ are from 0.85 to 0.92. The composite reliability is in the range of 0,85 to 0,92 and average variance extracted is in 0.72-0.98 range that is higher than the base level of 0.6. As shown in Table 2, the values for CFI, NNFI, root-mean-square error approximation (RMSEA), and standardized root-mean-square residual (SRMR) are acceptably close to the standards suggested by Hu and Bentler (1999):.95 for CFI and NNFI,.06 for RMSEA, and.08 for SRMR. We also tested discriminant validity provided by Fornell and Larcker (1981). As shown in Table 2, we found strong evidence for discriminant validity between each possible pair of latent constructs in all samples. Given that these batteries of overall goodness-of-fit indices were accurate and that the model was developed on theoretical bases, and given the high level of consistency across samples, this enables us to proceed the previously defined scales. We used the moderated hierarchical regression analysis to test the influence of the corporate association(CA and CSR associations) on product-relevant perceived risk(performance and financial risks) and to identify the variables moderating the relationship between the corporate association and product-relevant performance risk. In this study, dependent variables are performance and financial risk. CA and CSR associations are described the independent variables. The moderating variables are product category knowledge and product category involvement. The results are, as expected, found that CA association has statistically a significant influence on the perceived risk of the product, but CSR association does not. Product category knowledge and involvement moderate the relationship between the CA association and the perceived risk of the product. However, the effect of CSR association on the perceived risk of the product is not moderated by the consumers' knowledge and involvement. For this result, it is necessary for a corporate to inform its customers CA association more than CSR association so that they could be felt to be the reduction of the perceived risk. The important theoretical contribution of this research is the meanings that two types of corporate association that Brown and Dacin(1997), and Brown(1998) have proposed replicated the difference of the effects on product evaluation. According to Hunter(2001), it was an important affair to accomplish the validity of a particular study and we had to take about ten studies to deduce a strict study. Next, there is the contribution of the this study to find that the effects of corporate association on the perceived risk of the product are varied by the moderator variables. In particular, the moderating effect of knowledge on the relationship between corporate association and product-relevant perceived risk has not been tested in Korea. In the managerial implications of this research, we suggest the necessity to stress the ability that corporate manufactures the product well(CA association) than the accomplishment of corporate's social obligation(CSR association). This study suffers from various limitations that imply future research directions. The moderating effects of product category knowledge and involvement on the relationship between corporate association and perceived risk need to be replicated. Next, future research could explore whether the mediated effects of the perceived risk has the relationship between corporate association and consumer's product purchase. In addition, to ensure the external validity of the study will be needed to use realistic company, not artificial.

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