The interface area of the face sheet and core of the sandwich composite is seen as a weakness due to its low de-bonding toughness. To overcome this concern, it is critical to develop a suitable modification strategy to enhance the de-bonding toughness of the face sheet/core interface. In the present study, the corrugated core reinforced sandwich composite was prepared through co-curing and secondary bonding approaches. The MWCNTs reinforced adhesive was induced in the face sheet/core interface in different weight concentrations. The MWCNT-reinforced adhesive was prepared using the sonication technique, and its dispersion was examined using atomic force microscopy (AFM). The three-point bending test revealed that sandwich composite prepared using the co-cure method has higher flexural strength than secondary bonded samples due to better bonding face sheet and corrugated core. Compared with MWCNT-free corrugated core reinforced co-cured sandwich composites (CCSC), the flexural strength of 1 wt.% MWWCNT-induced sandwich composite was increased by 101.28%. The microstructural study showed that secondary bonded samples had extensive fibre breakage at the face plate due to early de-bonding of the face sheet and corrugated core. Furthermore, the free vibrational analysis was performed to evaluate the natural frequency and damping values of the corrugated core reinforced sandwich composite. The modal test results indicated that inducing 1wt.% MWCNTs in the face sheet/core interface had enhanced the natural frequencies of co-cured sandwich composites. The present study provides a suitable method to address the weaker de-bonding toughness concerns of face sheet/core interface region of sandwich structures.

PURPOSES : To enhance the accuracy of predicting the compressive strength of practical concrete mixtures, this study aimed to develop a machine learning model by utilizing the most commonly employed curing age, specifically, the 28-day curing period. The training dataset consisted of concrete mixture sample data at this curing age, along with samples subjected to a total load not exceeding 2,350 kg. The objective was to train a machine learning model to create a more practical predictive model suitable for real-world applications. METHODS : Three machine learning models—random forest, gradient boosting, and AdaBoost—were selected. Subsequently, the prepared dataset was used to train the selected models. Model 1 was trained using concrete sample data from the 28th curing day, followed by a comprehensive analysis of the results. For Model 2, training was conducted using data from the 28th day of curing, focusing specifically on instances where the total load was 2,350 kg or less. The results were systematically analyzed to determine the most suitable machine learning model for predicting the compressive strength of concrete. RESULTS : The machine learning model trained on concrete sample data from the 28th day of curing with a total weight of 2,350 kg or less exhibited higher accuracy than the model trained on weight-unrestricted data from the 28th day of curing. The models were evaluated in terms of accuracy, with the gradient boosting, AdaBoost, and random forest models demonstrating high accuracy, in that order. CONCLUSIONS : Machine learning models trained using concrete mix data based on practical and real-world scenarios demonstrated a higher accuracy than models trained on impractical concrete mix data. This case illustrates the significance of not only the quantity but also the quality of the data during the machine learning training process. Excluding outliers from the data appears to result in better accuracy for machine learning models. This underscores the importance of using high-quality and practical mixed concrete data for reliable and accurate model training.

본 논문은 하수관 보강 방법 중 보강튜브경화공법(CIPP)의 종점부 미경화 문제를 해결하기 위해 설계된 증기이송튜브 시스템에 대한 유동해석 결과를 보고한다. 설계된 증기이송튜브의 유동해석을 위해 SolidWorks Flow Simulation을 이용하여 해석을 수행하였다. 100mm, 150mm, 200mm의 직경을 갖는 증기이송튜브에 대한 유동 흐름 및 온도 분포가 유동을 해석을 통해 검토되었다. 해석 결과를 통해 증기이송튜브의 직경이 증가함에 따라 경화온도를 만족하는 CIPP 내부 길이가 증가하는 것이 확인되었다. 또한, 직경 200mm를 제외한 모든 직경의 증기이송튜브의 입구에서 증기 역류 현상이 나타남을 확인하였다. 이에 증기이송튜브의 최적 직경은 200mm로 결정되었으며, 이에 대한 유동해석을 통해 증기주입을 시작하고 350초 경과 이후에 CIPP 내 모든 길이에서 경화온도를 만족하는 것을 확인하였다.

Cured-in-place-pipe(CIPP) is the most adopted trenchless application for sewer rehabilitation to extend the life of the existing sewer without compromising both direct construction and indirect social costs especially applied in the congested urban area. This technology is globally and domestically known to be the most suitable for partial and full deteriorated pipe structure rehabilitation in a sewer system. The typical design of CIPP requires a significant thickness of lining to support loading causing sewage flow interruption and increasing material cost. This paper presents development of a high strength glass fiber composite lining material for the CIPP application and structural test results. The test results exhibit that the new glass fiber composite lining material has 12 times of flexural strength, 6.2 times of flexural modulus, and 0.5 Creep Retention Factor. These test results can reduce lining design thickness 35% at minimum. Even though taking into consideration extra materials such as outer and inner films for actual field applications, the structural capacity of the composite material significantly increases and it reduces 20 percent or more line thickness as compared to the conventional CIPP. We expect that the newly developed CIPP lining material lowers material costs and minimizes flow capacity reduction, and fully replaceable to the conventional CIPP lining materials.

This study was conducted to evaluate the acceptability of cured cooked boneless chicken drumettes as a raw material for Chuncheon Dakgalbi and to observe its effect on pH, lipid oxidation, volatile basic nitrogen (VBN) content and total viable count (TVC) during refrigerated storage under vacuum. Boneless chicken drumettes were dry cured with a mixed curing agent (0.20% w/w) consisting of sodium chloride (93.1%), sodium nitrite (5.9%) and sodium bicarbonate (1.0%) for 24 h at 2±2℃. Cured samples were cooked using an oven at 150℃ for 20 min and stored at 5.5±0.5℃ for 60 days under vacuum. Non-cured cooked sample was used as a control. Sensory evaluation was performed on day 2 of storage using 22 untrained panelists and samples were mixed with Dakgalbi sauce and reheated using a microwave for 2 min. There were no significant differences between control and treatment group on appearance, flavor, texture, juiciness and overall acceptability. Cured cooked boneless chicken drumettes had significantly (p<0.05) higher pH, lower lipid oxidation, VBN and TVC consistently during storage in comparison with control. These results suggest that dry curing could be applied to boneless chicken drumettes as raw material for Chuncheon Dakgalbi and could extend its shelf life during refrigerated storage under vacuum.

고등 복합재료 구조물 제작에 적용되는 고온경화용 에폭시 수지 시스템 경화물의 물리적 특성을 연구하였다. 고온경화용 에폭시 수지 경화물의 표면 몰폴로지는 저온경화용 수지 시편의 표면과는 달리 균일한 몰폴로지를 보여주었다. 이 수지 경화물의 열중량분석 결과 300 oC까지는 무게감소가 거의 없는, 즉 열적으로 매우 안정한 것으로 나타났는데, 이는 높은 가교화밀도에 기인한 것이다. 300-500 oC 영역에 서 급격한 무게감도는 매트릭스 수지의 본격적인 열분해에 기인한 것이다. 시편의 인장 및 압축 특성, 열 변형온도, 밀도, 부피수축 등의 특성을 측정하고 평가하였다.

고성능 복합재료 제조에 사용되는 고온경화용 에폭시 수지 시스템의 성형성을 연구하였다. 테트라글리시딜 메틸렌 디아닐린계 에폭시 수지 시스템의 조성과 화학구조를 여러 가지 분석장비를 이용하여 분석하고 확인하였다. 이 수지 시스템은 보통의 작업온도 조건에서 시간 경과에 따른 점도 상승이 미미한 것으로 나타났다. 유전 경화 모니 터링 방법을 이용하여 선정한 수지 시스템의 경화거동을 연구하였다.

This study was performed to evaluate changes of microbiological and hygienic quality characteristics of dry-cured ham during manufacturing process. The water activity(Aw) of dry-cured ham decreased significantly during the period(P<0.05). The salt contents increased from at 0 day to 60 days and decreased slightly at 60 days of post-curing(P<0.05). The contents increased after 120 days again. As the curing, drying and aging progressed, the VBN and TBA of dry-cured ham increased(P<0.05). The dry-cured ham samples showed significantly higher VBN at 120 and 180 days and higher TBA at 180 days. Regarding microbiological analysis, the total aerobic counts and lactic acid bacteria counts increased significantly during the stage(P<0.05). The total aerobic counts closely paralleled the lactic acid bacteria counts. In general, this research can be used as fundamental information for the mass production of a hygienic dry-cured ham.

본 연구는 돈육 뒷다리를 이용하여 한국형 자연발효육제품을 개발할 목적으로 생햄 제조과정 중 품질 변화를 살펴보았다. 발효생햄 제조과정 중 일반성분 분석결과, 수분과 단백질 함량은 제조기간이 경과 함에 따라 유의적으로 감소하는 경향을 나타내었고, 반면 지방함량은 증가하였다(P<0.05). 중량감소율 은 제조기간이 경과할수록 유의적으로 증가하였다(P<0.05). pH 결과는 제조기간 중 0 일에서 가장 낮 은 값을 나타내었고, 점차 증가하여 120 일에서 가장 높은 값을 나타내었다(P<0.05). 반면 보수력 (WHC)은 제조기간 중 0 일에서 가장 높은 값을 나타내었고, 120 일에서 가장 낮은 값을 나타내었다 (P<0.05). 육색에서 명도(L*)를 분석한 결과 0 일에서 가장 높은 값을 나타내었고, 60 일과 180 일에서 가장 낮은 값을 나타내었다(P<0.05). 적색도(a*)는 0 일에서 가장 낮은 값을 나타내었고, 60 일에서 가 장 높은 값을 나타낸 후 감소하였다(P<0.05). 황색도(b*)는 60(+1)일까지 증가한 뒤 그 이후에는 급격히 감소하는 경향을 보였다(P<0.05). 조직감에서 경도(hardness), 검성(gumminess), 씹힘성(chewiness), 전단력가(shear force values)는 제조기간 중 증가하는 경향을 보였다(P<0.05). 본 연구 결과를 통해 발효생햄 대량생산을 위한 기초 자료를 제공할 수 있을 것으로 생각된다.

The aim of the present study was to evaluate the effect of ultimate pH of semimembranosus muscle on quality characteristics of dry-cured ham. The sample selection was determined based on ultimate pH of semimembranosus muscle, and samples were then classified into three groups: A (pH 5.61±0.09), B (pH 5.86±0.06) and C (pH 6.13±0.09). Our results depicted that the ultimate pH had a significant effect on the quality characteristics of dry-cured ham. Particularly, as the ultimate pH increased, the pH values of the dry-cured hams significantly (p<0.05) increased while weight loss decreased. Significantly (p<0.05) higher CIE a*, b* and chroma values were observed in the dry-cure hams from the samples with lower ultimate pH. Additionally, the values of some texture characteristics (e.g., hardness and chewiness) significantly (p<0.05) decreased as the ultimate pH increased. However, no significant differences among the three pH groups were observed for water activity, salinity, volatile basic nitrogen (VBN), calorie as well as sensory properties of dry-cure hams (p>0.05). These results clearly demonstrate that the ultimate pH of semimembranosus muscle is more related to quality characteristics than sensory attributes of dry-cured ham.

진공포장 한 건조발효햄에 감마선을 조사 (0, 2.5, 5, 7.5, 10 kGy)하여 저장 3개월 동안 이화학적 품질 (육색, 지방산패도, 염기태 질소화합물, pH) 및 미생물 (총균, 유산균) 생육특성을 평가하였다. 감 마선 조사는 선량이 높을수록 시료의 표면 육색인 적색도 (a*)와 관능적 육색 및 기호도를 저하시켰다. 반면에 pH, 지방산패도, 염기태 질소화합물, 수분활성도에 큰 영향을 미치지 않은 것으로 나타났다. 미 생물적 측면에서는 감마선 조사 수준이 높을수록 미생물학적 품질이 개선되었다. 관능적 측면인 풍미에 서는 저장기간 및 처리구간에 유의적 차이는 나타나지 않았지만 육색 측면에서는 5 kGy 이상에서는 낮 은 평점을 나타내었다. 따라서 건조발효햄의 저장기간을 고려할 때 미생물학적 및 이화학적 품질은 5 kGy 수준의 감마선 조사에 의해 개선되는 것으로 나타났다.

The surface treatment effects of reinforcement filler were investigated based on the dynamic mechanical properties of mutiwalled carbon nanotubes (MWCNTs)/epoxy composites. The as-received MWCNTs(R-MWCNTs) were chemically modified by direct oxyfluorination method to improve the dispersibility and adhesiveness with epoxy resins in composite system. In order to investigate the induced functional groups on MWCNTs during oxyfluorination, X-ray photoelectron spectroscopy was used. The thermo-mechanical property of MWCNTs/epoxy composite was also measured based on effects of oxyfluorination treatment of MWCNTs. The storage modulus of MWCNTs/epoxy composite was enhanced about 1.27 times through oxyfluorination of MWCNTs fillers at 25℃. The storage modulus of oxyfluorinated MWCNTs (OF73-MWCNTs) reinforced epoxy composite was much higher than that of R-MWCNTs/epoxy composite. It revealed that oxygen content led to the efficient carbon-fluorine covalent bonding during oxyfluorination. These functional groups on surface modified MWCNTs induced by oxyfluorination strikingly made an important role for the reinforced epoxy composite.

Representive cured products such as ham and sausage produced in Korea were purchased at retail and cooked using heating tools such as a gas range (GR), an electric range (ER) and electric range after boiled (BE). Changes of N-nitrosamine (NA), nitrate and nitrite in the cured meats containing$lt;2.0 ug/kg of N-nitrosodimethylamine (NDMA) were checked and analyzed during their cooking process. Contents of nitrate and nitrite in ham products prior to cooking were 2.0 and 1.8 mg/kg, respectively; their contents in regular hams were slightly increased, but those of nitrate in press hams were decreased while those of nitrite were increased during its cooking process. Their contents in sausage products were 1.8 and 0.9 mg/kg; those of nitrate were decreased, while nitrite were slightly increased during its cooking process. NDMA detected only NA in all the collected cured products. Changes of NDMA, regardless of cooking methods, tend to drastically increase in all samples after their cooking; Its contents were increased by average 6.0-70.7 times in the GR samples, by average 2.4-39.2 times in the ER samples and by average 7.0-56.3 times in the BE samples. Virtually, the fact that all of this nitrosamine appeared to arise by the action of precursor such as NO_x was produced during the cooking of cured products.

This experiment was conducted to study occurrence of N-nitrosamine (NA) and its precursors such as nitrate and nitrite. For the experimental samples, 26 kinds of commercial hams and 30 kinds of sausages produced in Korea were purchased. The nitrate and nitrite were positive in all of the collected samples; nitrate levels were by average 4.4-9.2 mg/kg and nitrite ones were by average 1.3-3.6 mg/kg. The contents of nitrate and nitrite were detected higher in sausage than in ham. Especially, nitrate contents were contained higher in lyoner sausage prepared with the mixture of meat and fish, while nitrite contents were contained higher in the meat only mixture. N-nitrosodimethylamine (NDMA) among the analyzed 7 kinds of NA was detected only in ham and sausage; its contents were outstanding in lyoner sausage which was prepared with only meat and pork sausage, and then regular ham was the next one in its order, but its contants were detected by average $lt;0.5 ug/kg in press hams added vegetable.

[ 1982-1983 ]년 사이에 한국인삼연초연구소 음성시험장의 세균성마름병 상습발병포지에서 이 병의 방제체계 확립을 위해 시험한 결과 1. 세균성마름병은 세균증식에 적합한 온도와 토양습도가 주어진 7월하순8월하순에 가장 큰 피해를 나타냈으며 토양훈증제처리구 및 저항성품종재배구에서는 병발생이 적고 느리게 나타낮다. 2. 세균성마름병의 방제효과는 감수성품종인 NC23 26에 비하여 저항성품종인 NC82의 무처리재배의 경우 의 방제효과를 보았으며 토양훈증제처리에 저항성품종인 NC82를 재배 할 경우 의 방제효과를 보았다. 경종적처리에서는 무처리재배에 비하여 로 낮게 나타났으며 저항성품종이나 토양훈증제를 함께 사용 할 경우 그 상승효과는 거의 인정되지 않았다. 3. 세균성마름병의 종합적인 방제체계확립은 경종적처리(춘추경, 잔간근제거, 조기이식, 피복물제거)에 토양훈증(Cylon)를 10a당 40l 토양관주한 후 저항성 품종(NC82)을 재배할 때 이상의 방제효과를 거둘 수 있었다.

본시험은 붕소시용이 잎담배의 생리적특성과 입고병 발생에 미치는 영향을 구명하고자 황색종인 NC2326, Coker 86을 공시하여 입고병포장에서 실시한바 그 결과를 요약하면 다음과 같다. 1. 붕소시용량이 증가할수록 지상부의 생장이 지연되었고 간장은 낮아졌으나 붕우시용구에서 세근발달이 억제되고 뿌리의 부패율과 입고병이병율이 크게 감소 되여 입고병발생에 간접적인 효과가 있었다. 2. 수량은 10a당 붕소 또는 붕산 시용구에서 높았고 붕소시용에 따른 증수경향은 NC2326에서 컸다. 3. 건엽중의 Phenol 화합물은 붕소시용구에서 증가하였고 입고병저항성이 큰 Coker 86에서 더 많았으며 니코친합량은 붕소시용량이 증가할수록 감소하였다.

In this study, to analyze the change of mass of concrete structure subjected to fire damage, cement paste was exposed at high temperature to maintenance time and analyzed mass change characteristics by TGA analysis. As a result of analysis, the mass reduction rate of cement paste decreased with increasing heating time after heating at high temperature.

대표적인 콘크리트 혼화재료 중 하나인 고로슬래그 미분말을 혼입한 콘크리트는 잠재수경성에 의해 콘크리트의 장기 내구성능 및 역학적 성능이 향상된다. 본 연구에서는 3 가지 수준의 물-결합재 비(0.37, 0.42, 0.47) 및 고로슬래그 미분말 혼입률(0 %, 30 %, 50 %)을 고려하여 염해에 대한 내구성능 평가를 수행하였으며, 염화물 확산 거동(촉진 염화물 확산계수, 통과 전하량)을 예측하는 식을 도출하고 촉진 염화물 확산계수와 통과 전하량간의 상관관계를 평가하였다. 2년 양생조건 시 고로슬래그 미분말 혼입 콘크리트에서 OPC 콘크리트 대비 촉진 염화물 확산계수 평가 결과에서는 최대 28 %의 감소율을 통과 전하량 평가에서는 최대 29 %의 감소율을 나타냈다. 또한 물-결합재 비의 증감에 의한 영향을 OPC 콘크리트 보다 GGBFS 미분말 혼입 콘크리트에서 더 적게 받는 것으로 판단된다. 배합 특성 및 실험 결과를 바탕으로 촉진 염화물 확산계수 및 통과 전하량을 예측하는 식을 다중회귀분석을 통해 도출한 결과, 통과 전하량 예측식이 확산계수 예측식보다 높은 결정계수를 나타냈다.

철근콘크리트 구조물의 대표적인 열화현상인 염해를 억제하고자 여러 가지 연구가 진행되었는데, 그 중에서 혼화재료를 콘크리트에 혼입하여 사용하는 방법이 대표적으로 알려져 있다. 본 연구에서는 대표적인 콘크리트 혼화재료인 플라이애시를 혼입한 콘크리트와 OPC 콘크리트에 대하여 3가지 수준의 물-결합재비(37%, 42%, 47%)를 고려해 내구성능 평가를 실시하였다. 각 목표 재령일에서 Tang's method에 준하여 촉진 염화물 확산계수 측정 실험을, ASTM C 1202에 준하여 통과전하량 측정 실험을, KS F 2405에 준하여 압축강도 실험을 실시하였다. 또한, 기존의 연구결과인 재령 28일의 실험결과를 참고하여 확산계수에 대한 시간의존성지수(m)를 도출하여 고찰하였으며, 장기재령의 압축강도와 시간의존성지수 간의 상관관계를 평가하였다. 재령 49일부터 플라이애시 혼입 콘크리트에서 OPC 콘크리트 대비 개선된 염해저항성능을 나타내었으며 이는 포졸란 반응에 의해 생성된 불용성의 수화물이 원인으로 사료된다. 플라이애시 혼입 콘크리트에서 OPC 콘크리트 대비 약 1.5배 높은 시간의존성지수를 나타내었으며, 압축강도와의 상관관계 평가 결과, OPC 콘크리트는 압축강도가 증가할수록 선형적으로 시간의존성지수가 증가하는 경향을, 플라이애시 콘크리트는 압축강도가 증가할수록 선형적으로 시간의존성지수가 약간 감소하는 경향을 나타냈다.