• Geomechanics and Engineering
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• 제14권4호
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• pp.307-314
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• 2018

Strength of loess that experienced cyclic freeze and thaw is of great significance for evaluating stability of slopes and foundations in loess regions. This paper takes the frequently encountered loess in the Northwestern China as the study object and carried out three kinds of laboratory tests including freeze-thaw test, direct shear test and SEM test to investigate the strength behaviors of loess after cyclic freeze and thaw, and the correlation with meso-level changes in soil structure. Results show that for loess specimens at four dry densities, the cohesion decreases with freeze-thaw cycles until a residual value is reached and thus an exponential equation is proposed. Besides, little change in the angle of internal friction was observed as freeze-thaw proceeds. This may depend on the varying of soil structure, based on which a clue can be found from the surface morphology and mesoscopic scanning of loess specimens. Clearly we observed significant changes in surface morphology of loess and it tends to aggravate at higher water contents or more cycles of freeze and thaw. Moreover, freeze-thaw cycling leads to obvious changes in the meso-structure of loess including lowering the particle aggregates and increasing both the proportion of fine particles and porosity area ratio. A damage variable dependent on the ratio of porosity area is introduced based on the continuum damage mechanics and its correlation with cohesion is discussed.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.1323-1328
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• 2004

This paper shows the study on the design of the spray-freeze dryer for the production of the pulmonary inhalation powders. Powder production and handling has been an integral part of pharmaceutical processing because of the wide use of oral dosage forms. There are a few commonly used powder preparation methods including mechanical milling, precipitaion, spray drying, freeze drying, and so on. In general, methods available for preparing inhalation powders are limited due to certain inhalation powder's sensitive nature to the processing environments. This is particularly true for preparing dry powder aerosols where the aerodynamic particle size$(<5{\mu}m)$ and the size distribution are pivotal. Supercritical fluid antisolvent and spray freeze drying have recently emerged as promising techniques for producing powders for use in microcapsulation. However, the aerosol applications of these powders are yet to be explored. The purpose of this study is to test the feasibility of using spray freeze-dried pulmonary inhalation powders for aerosolization.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2004년도 학술대회지
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• pp.1-6
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• 2004

This paper shows the study on the design and another applications of the spray-freeze dryer for the production of valuable material powders. Powder production and handling has been an integral part of material extracting processing and pharmaceutical processing because of the wide use of oral dosage forms. There are a few commonly used powder preparation methods including mechanical milling, precipitaion, spray drying, freeze drying, and so on. In general, methods available for preparing inhalation powders are limited due to certain inhalation powder's sensitive nature to the processing environments. This is particularly true for preparing dry powder aerosols where the aerodynamic particle size($<5{\mu}m$) and the size distribution are pivotal. Supercritical fluid antisolvent and spray freeze drying have recently emerged as promising techniques for producing powders for use in microcapsulation. However, the aerosol applications of these powders are yet to be explored. The purpose of this study is to test the feasibility of using spray freeze-dried valuable material powders for aerosolization.

• 한국구조물진단유지관리공학회 논문집
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• 제12권2호
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• pp.67-74
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• 2008

본 연구에서는 탄소섬유접착보강공법의 박리와 연관한 부착특성에 대하여 검토하였다. 그 결과를 요약하면, 온도변화에 따른 변형 특성에서는 바탕 콘크리트의 강도에 관계없이 온도 변화에 따라서 각 재료들의 변형 폭도 커지는 것을 알 수 있었다. 초음파 전파 속도도 온도변화에 따라 작아지는 것으로 나타나 계면에서 박리가 발생하였음을 알 수 있었다. 부착강도는 온도 변화가 클수록 부착강도의 값은 작아지는 것으로 나타났는데, 파괴형태는 계면파괴와 모재파괴 형태로 나타났다. 건습 변화에 따라서는 4사이클까지 각 재료의 변형 및 초음파 전파 속도에서 큰 변화를 나타내지 않아 건습 자체의 반복에는 큰 영향이 없는 것으로 판단된다. 단, 부착강도는 40%정도 저하하는 것으로 나타났지만 비교적 양호한 강도를 나타내었다. 동결융해 시험결과는 온도변화 요인과 유사한 경향으로서 동결융해 작용을 받을 경우 4사이클 이내에 박리가 일어날 수 있는 것으로 분석되었다.

• Applied Biological Chemistry
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• 제32권3호
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• pp.278-285
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• 1989

가열처리 및 건조방법이 새우의 맛성분과 미세구조에 미치는 영향을 밝히고자 하였다. 생새우의 핵산관련물질은 ATP,ADP,AMP,IMP, inosine 및 hypoxanthine이 검출되었는데 이 중 AMP는 흔적량 검출되었으나, 가열 및 건조방법에 따라서 AMP 함량은 100g당 $23.5{\sim}45.7{\mu}mole$로 증가하였는데 이는 열처리 및 건조에 의하여 ATP 및 ADP가 AMP로 분해된 것으로 판단되었다. 생새우 중의 유리아미노산은 arginine의 함량이 가장 많았고 다음으로 glycine, lysine, proline, alanine등으로 이들 주요 아미노산 함량이 전체 유리아미노산 함량의 70%를 차지하였다. 총유리아미노산 함량은 생새우에서 건물 100g당 1,198mg이던 것이 끓인후 열풍 및 동결건조한 것은 각각 342mg 및 503mg으로 감소하였는데, 이는 가열처리시 수용성 아미노산이 용출된 것으로 판단되었다. 생새우를 가열처리 없이 열풍 및 동결건조한 것은 가열처리나 마이크로파 처리후 열풍 및 동결건조한 것보다 견고성 및 부서짐성이 높았으나 응집성과 검성은 낮았다. 동결건조한 것은 열풍건조한 것에 비하여 근육섬유질의 조직이 부드러웠고 마이크로파 처리후 열풍 및 동결건조한 것은 각각 조밀한 망상조직과 다공질의 망상조직을 형성하였다.

• 한국지반환경공학회 논문집
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• 제11권5호
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• pp.15-23
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• 2010

한강, 낙동강, 영산강, 금강의 하천 및 호소퇴적물을 대상으로 건식체질법, 습식체질법, 광산란법(PSA) 등의 입도분석법을 비교연구 하였다. 건식체질법의 경우 건조과정에서 발생하는 엉김현상에 의해 오차가 크게 발생하며 이러한 현상은 호소시료의 경우 두드러지게 나타났다. 습식체질법은 건식체질법에 비해 복잡하고 노동력이 보다 많이 필요하지만 정확한 분석이 가능하며 PSA의 경우에도 습식체질과 유사한 경향을 나타내었다. 엉김현상을 방지하기 위한 동결건조 및 과산화수소수에 의한 유기물의 산화/동결건조의 경우 엉김현상을 일부 개선할 수 있었으나 여전히 습식체질에 비하여 미세입자의 분율이 적게 나타났다. 입도별 중금속의 용출량 및 함유량이 조사되었으며 예상된 바와 같이 호소 및 하천시료 모두 미세입자에서 높은 농도의 중금속이 용출되었다. 퇴적물의 관리에 있어서 정확한 입도분석법의 사용과 미세입자에 대한 관리가 보다 중요하다.

• 한국세라믹학회지
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• 제40권8호
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• pp.798-803
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• 2003

In synthesis of nano powders, the hard agglomeration for the synthesized powders occurred during the drying processing. In order to avoid hard agglomeration in particles the freeze drying process was used in this experiment. e fabricated the Yttira-Doped Ceria(YDC) nano powder by co-precipitation. Starting materials used in experiments were the cerium(III) nitrate and yttrium(III) nitrate solution with 야-water, which two solutions were mixed and then the precipitated hydroxides were prepared for adding sodium hydroxide. The co-precipitated powders were dried by the thermal drying at 8$0^{\circ}C$ for 24 h and by freeze drying at -4$0^{\circ}C$, 30 mtorr for 72 h. The lattice parameter and crystallite size as a function of calcination temperature was characterized by XRD analysis. The lattice parameter of YDC was decreased with addition amount of yttrium and was estimated as 5.401683 $\AA$ at $700^{\circ}C$. Crystallite size were calculated by XRD-LB method, and morphologies were confirmed with the observation of TEM and SEM. The freeze dried YDC powders had medium diameter of 17 nm with more uniform size distribution than the thermal dried YDC posers, which were mainly ascribed to the difference of agglomerates formation during drying stage.

• Geomechanics and Engineering
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• 제14권3호
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• pp.301-306
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• 2018

Stabilization of clayey soil has been studied from past to present by mixing different additives to the soil to increase its strength and durability. In recent years, there has been an increasing interest in stabilization of soils with natural pozzolans. Despite this, very few studies have investigated the impact of pozzolanic additives under freeze-thaw cycling. This paper presents the results of an experimental research study on the durability behavior of clayey soils treated with lime and perlite. For this purpose, soil was stabilized with 6% lime content by weight of dry soil (optimum lime ratio of the the soil), perlite was mixed with it in 0%, 5%, 10%, 20%, 25% and 30% proportions. Test specimens were compacted in the laboratory and cured for 7, 28 and 84 days, after which they were tested for unconfined compression tests. In addition to this, they were subjected to 12 closed system freeze-thaw cycles after curing for 28 days. The results show that the addition of perlite as a pozzolanic additive to lime stabilized soil improves the strength and durability. Unconfined compressive strength increases with increased perlite content. The findings indicate that using natural pozzolan which is cheaper than lime, has positive effect in strength and durability of soils and can result cost reduction of stabilization.

• Food Science and Biotechnology
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• 제14권5호
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• pp.661-666
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• 2005

The specific objectives of this study were to dry yam chips using microwave vacuum drying, freeze drying and hot air drying, then to coat the dried yam chips with ascorbic acid cocrystallized sucrose, and finally to compare the quality of yam chip snack foods with respect to drying and coating characteristics. The microwave vacuum dried sample showed the highest drying rates and much less surface damage than the hot air dried one did. The shape and color of the microwave vacuum dried/coated sample were allocated between those of the freeze dried/coated sample and the hot air dried/coated sample. The freeze dried/coated sample scored excessively low in organoleptic hardness and chewiness to be suitable as a snack. The hot air dried/coated sample was too deep in color, wrinkled, excessively high in organoleptic hardness and chewiness, and excessively low in mouthfeeling. Therefore, the microwave vacuum dried/coated sample presented the best overall attributes as a snack, with respect to organoleptic characteristics, shape, color, and drying rates.

• 한국식품영양학회지
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• 제17권3호
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• pp.286-293
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• 2004

가시오가피, 구기자, 당귀, 오미자의 열수 추출물이 유산균의 생육과 동결건조시 보호제로서의 역할 및 동결건조된 유산균원료의 저장 시 생존율에 미치는 영향을 조사하였다. MRS 배지에 생약 추출물을 첨가한 경우 유산균주 16종에 대하여 가시오가피, 구기자, 당귀 및 오미자 추출물을 MRS broth에 각각 50%(v/v)씩 첨가한 배지에서의 생육상태를 조사하였다. 가시오가피 추출물을 첨가한 경우 L. acidophilus, L. bulgaricus, L. paracasei, L. casei, L. pentosus 균주가 생육이 양호하였으며 구기자 추출물을 첨가한 경우 L. acidophilus, L. bulgaricu L. paracasei 등이 양호하였고 당귀 추출물에서는 L. acidophilus, L. bulgaricus, L. casei, L. plantarum, L. lactis 등이 잘 생육하였으며 오미자 추출물에서는 L. acidophilus, L. rhamnosus, L. pentosus 등이 양호하였다. 기본 동결보호제로 조성으로 구성된 skim milk 10%(w/v)와 sucrose 5%(w/v)에 생약 추출물 2.5%(v/v)를 첨가한 경우 동결건조 직후 생존율은 L. acidophifus, L. bulgaricus, L. paracasei, L. casei가 평균 각각 81.7%, 63.8%, 73.2%, 78.1%를 나타냈다. 동결건조한 유산균 원료를 온도 4$0^{\circ}C$, 습도 70% 유지하는 항온항습기에서 한달간 방치시킨 후 생존율은 L. acidophilu의 경우 대조군에 비해 약 6%, L. paracasei와 L. bulgaricu의 경우 약3%의 생존율 증가를 보여 가혹조건에서 균의 생존율을 연장시키는데 역할을 하는 것으로 보이며, 구기자 추출물을 2.5% 첨가하여 동결건조 한 균 원료의 경우 L. paracasei에서 약 1.5% 정도 증가를 나타냈으며 L. aoidophilus와 L. bulgariolis에서는 약 1% 정도 감소하는 경향을 보였다. 특히, 구기자 추출물의 경우 L. acidophilus와 L. bulgaricus에서 당귀 추출물의 경우 L. bulgaricu와 L. casei에서 동결 보호제로서 이용할 수 있을 것으로 사료된다.