• Archives of Pharmacal Research
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• 제19권4호
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• pp.280-285
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• 1996

The sustained release dosage form which delivers melatonin (MT) in a circadian fashion over 8 h is of clinical value for those who have disordered circadian rhythms because of its short halflife. The purpose of this study was to evaluate the gelling properties and release characteristics of alginate beads varying multivalent cationic species $(Al^{+++}, \; Ba^{++}, \; Ca^{++}, \; Mg^{++}, \; Fe^{+++}, \; Zn^{++})$. The surface morphologies of Ca- and Ba-alginate beads were also studied using scanning electron microscope (SEM). MT, an indole amide pineal hormone was used as a model drug. The $Ca^{++}, \; Ba^{++}, \; Zn^{++}, \; Al^{++}\; and\; Fe^{+++}\; ions\; except\; Mg^{++}$ induced gelling of sodium alginate. The strength of multivalent cationic alginate beads was as follows: $Al^{+++}\llFe^{+++} the induced hydrogel beads were very fragile and less spherical. Fe-alginate beads were also fragile but stronger compared to Al-alginate beads. Ba-alginate beads had a similar gelling strength but was less spherical when compared to Ca-alginate beads. Zn-alginate beads were weaker than Ca- and Ba-alginate beads. Very crude and rough crystals of Ba- and Ca-alginate beads at higher magnifications were observed. However, the type and shape of rough crystals of Ba- and Ca-alginate beads were quite different. No significant differences in release profiles from MT-loaded multivalent cationic alginate beads were observed in the gastric fluid. Most drugs were continuously released upto 80% for 5 h, mainly governed by the passive diffusion without swelling and disintegrating the alginate beads. In the intestinal fluid, there was a significant difference iq the release profiles of MT-loaded multivalent cationic alginate beads. The release rate of Ca-alginate beads was faster when compared to other multivalent cationic alginate beads and was completed for 3 h. Ba-alginate beads had a very long lag time (7 h) and then rapidly released thereafter. MT was continuously released from Feand Zn-alginate beads with initial burstout release. It is assumed that the different release rofiles of multivalent cationic alginate beads resulted from forces of swelling and disintegration of alginate beads in addition to passive diffusion, depending on types of multivalent ions, gelling strength and drug solubility. It was estimated that 0.2M $CaCl_2$ concentration was optimal in terms of trapping efficiency of MT and gelling strength of Ca-alginate beads. In the gastric fluid, Ca-alginate beads gelled at 0.2 M $CaCl_2$ concentration had higher bead strength, resulting in the most retarded release when compared to other concentrations. In the intestinal fluid, the decreased release of Ca-alginate beads prepared at 0.2 M $CaCl_2$ concentration was also observed. However, release profiles of Ca-alginate beads were quite similar regardless of $CaCl_2$ concentration. Either too low or high $CaCl_2$ concentrations may not be useful for gelling and curing of alginate beads. Optimal $CaCl_2$ concentrations must be decided in terms of trapping efficiency and release and profiles of drug followed by curing time and gelling strength of alginate beads.

• 한국식품영양과학회지
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• 제30권1호
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• pp.43-47
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• 2001

Electron spin resonance (ESR) spectroscopy was used to investigate the effect of irradiation dose on the ESR signal intensity and to identify the stability of radicals after 9 weeks of storage in order to detect irradiated shellfishes. The irradiated shellfishes (short-necked clam, purplish washington clam, freshwater clam, jackknifed clam, scallop and hard-shell mussel) presented an asymmetric absorption in shape at $g_{1}$=2.002~2.003 and $g_{2}$=1.998. The strength of the ESR signal increased linearly with the applied doses (1~7 kGy). A highly positive correlation coefficients ($R^{2}$=0.9136~0.9896) were obtained between the irradiation dose and corresponding ESR signal intensity. The intensity of the signals after irradiation was stable even after 9 weeks of storage at 5$\pm$1$^{\circ}C$.

• 동력기계공학회지
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• 제6권4호
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• pp.49-55
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• 2002

In this paper, the elevated temperature tensile properties and short-time creep rupture characteristics were investigated for the friction welded joints of dissimilar materials, Cu-1%Cr-0.5%Zr and STS316L. The joining tests on Cu-1%Cr-0.5%Zr/STS316L by friction welding were performed, and optimum joining conditions of the friction welded joints were determined. The characteristics of the elevated temperature tensile strength, hardness, fractographs were examined, and the creep rupture characteristics for the optimum welded joints were investigated under uniaxal static load at 300, 400 and $500^{\circ}C$.

• 열처리공학회지
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• 제6권3호
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• pp.127-137
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• 1993

The changes of lamellar(${\alpha}_2+{\gamma}$) structure of TiAl intermetallic compound which is a high potential, high temperature aerospace material was investigated by heat treatment. The lamellar structure was short and made subgrain in prior a grains after homogenizing at 1523 K. It became longer and finer, and the subgrain went out during subsequent isothermal heatteating at 1273 K. The yield, fracture strength and strain to fracture if the heat treated specimens was increased and the hardness of them was decreased a little in the finer lamellar structure, because fine lamellar interface, sugrain boundary and grain boundary may block initiation and propagation of crack.

• Advances in materials Research
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• 제3권3호
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• pp.163-174
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• 2014

In this study, fatigue properties and crack growth characteristics of a polycarbonate (PC) were examined during cyclic loading at various mean stress (${\sigma}_{amp}$) and stress amplitude (${\sigma}_{mean}$) conditions. Different S vs. N and da/dN vs. ${\Delta}K$ relations were obtained depending on the loading condition. The higher fatigue strength and the higher resistance of crack growth are seen for the PC samples cyclically loaded at the higher mean stress and lower stress amplitude due to the low crack driving force. Non-linear S - N relationship was detected in the examination of the fatigue properties with changing the mean stress. This is attributed to the different crack growth rate (longer fatigue life): the sample loaded at the high mean stress with lower stress amplitude. Even if the higher stress amplitude, the low fatigue properties are obtained for the sample loaded at the higher mean stress. This was due to the accumulated strain energy to the sample, where severe plastic deformation occurs instead of crack growth (plasticity-induced crack closure). Shear bands and discontinuous crack growth band (DGB) are observed clearly on the fracture surfaces of the sample cyclically loaded at the high stress amplitude, where the lower the ${\sigma}_{mean}$, the narrower the shear band and DGB. On the other hand, final fracture occurred instantly immediately after the short crack growth occurs in the PC sample loaded at the high mean with the low ${\sigma}_{amp}$, i.e., tear fracture, in which the shear bands and DGB are not seen clearly.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2000년도 춘계학술발표대회 논문집
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• pp.67-70
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• 2000

Mechanical properties of (10%$AI_20_3{\cdot}SiO_2$+5%Ni)/Al hybrid composites fabricated by the reaction squeeze casting were compared with those of (15%$AI_20_3{\cdot}SiO_2$)/Al composites. Intermetallic compound formed by reaction between molten aluminum and reinforcing powder was uniformly distributed in the Al matrix. These intermetallic compounds were identified as $Al_3$NI using EDS and X-ray diffraction analysis. Microhardness and flexural strength of hybrid composites were higher than that of (15%$AI_20_3{\cdot}SiO_2$)/Al Composite. In-Situ fracture tests were Conducted on (15%$AI_20_3{\cdot}SiO_2$)/Al Composites and (10%$AI_20_3{\cdot}SiO_2$+5%Ni)/Al hybrid composites to identify the microfracture process. It was identified from the in-situ fracture test of (10%$AI_20_3{\cdot}SiO_2$+5%Ni)/Al composites, microcracks were initiated mainly at the short fiber / matrix interfaces. As the loading was continued, the crack propagated mainly along the separated interfacial regions and the well developed shear bands. It was identified from the in-situ fracture test of (10%$AI_20_3{\cdot}SiO_2$+5%Ni)/Al hybrid composites, microcracks were initiated mainly by the short fiber/matrix interfacial debonding. The crack proceeded mainly through the intermetallic compound clusters

• International Journal of Automotive Technology
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• 제8권4호
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• pp.483-491
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• 2007

A closed form solution of a composite mechanics system is performed for the investigation of elastic-plastic behavior in order to predict fiber stresses, fiber/matrix interfacial shear stresses, and matrix yielding behavior in short fiber reinforced metal matrix composites. The model is based on a theoretical development that considers the stress concentration between fiber ends and the propagation of matrix plasticity and is compared with the results of a conventional shear lag model as well as a modified shear lag model. For the region of matrix plasticity, slip mechanisms between the fiber and matrix which normally occur at the interface are taken into account for the derivation. Results of predicted stresses for the small-scale yielding as well as the large-scale yielding in the matrix are compared with other theories. The effects of fiber aspect ratio are also evaluated for the internal elastic-plastic stress field. It is found that the incorporation of strong fibers results in substantial improvements in composite strength relative to the fiber/matrix interfacial shear stresses, but can produce earlier matrix yielding because of intensified stress concentration effects. It is also found that the present model can be applied to investigate the stress transfer mechanism between the elastic fiber and the elastic-plastic matrix, such as in short fiber reinforced metal matrix composites.

• 공업화학
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• 제9권5호
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• pp.715-718
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• 1998

본 연구에서는 수직섬유의 길이가 서로 다른 삼차원 유리직물을 보강재로 사용하고, 매트릭스 수지로 비스페놀 타입 비닐 에스테르 (bisphenol type vinyl ester)를 사용하여 hand lay-up을 이용해 복합재료 (3D composites)를 제조하였다. 삼차원 유리직물의 수직섬유의 길이가 복합재료의 기계적 물성에 미치는 영향을 three-point bending test, flatwise compression test를 통해 조사하였다. Short-beam test법 통하여 복합재료에서의 섬유와 매트릭스 수지간의 계면접착강도를 나타내는 층간 전단강도를 구하였다. 시험 결과를 통하여 수직섬유의 길이가 복합재료의 기계적 물성 및 층간 전단강도에 많은 영향을 미침을 알 수 있었다.

• 콘크리트학회논문집
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• 제23권5호
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• pp.637-645
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• 2011

압축강도 50 MPa이 넘는 고강도 콘크리트가 화재에 취약하다는 것은 널리 알려진 사실이다. 그러나 화재 피해를 입은 고강도 콘크리트 구조 부재의 구조 성능 저감 정도를 정확하게 파악하기 위해서는 단순히 열역학적 거동만으로 파악하는 것이 아니라, 구조 거동에 대한 연구가 필요하다. 따라서 이 연구에서는 비재하 상태에서 고온에 일정시간 노출시킨 고강도 콘크리트 단주를 대상으로 하중 재하 실험을 수행하였다. 실험 변수로는 콘크리트 압축강도, 가열시간, 그리고 폴리프로필렌 섬유 혼입을 통한 폭렬 저감 공법 사용 유무가 있었으며, 실험의 결과로는 콘크리트 강도 및 가열 시간이 증가할수록 구조 성능은 저감되는 것으로 나타났다. 특히 폴리프로필렌 섬유를 혼입하여 폭렬이 저감 된 경우에도 구조 성능에는 변화가 없거나 오히려 감소하는 것으로 나타났다. 이 연구를 통하여 알아낸 바를 토대로 보다 안전하고 경제적인 내화 설계를 할 수 있으며, 또한 화재로 인한 고강도 콘크리트 구조물의 구조성능 저감 정도를 예측하는데 유용하게 활용될 수 있을 것이라고 사료된다.

• 근관절건강학회지
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• 제27권2호
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• pp.71-80
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• 2020

Purpose: This thesis study aimed to examine the effects of elastic-band resistance exercise on physical fitness, activities of daily living (ADLs), falls efficacy, and quality of life among older women receiving home nursing care under long-term care insurance. Methods: We used an equivalent control group pre-test/post-test design. We assigned older women at the nursing care center J to the experimental group (n=21), and older adult women at the nursing care center H to the control group (n=21). The experimental group engaged in an elastic band resistance exercise twice per week from February 18 to April 12, 2019. Results: There were significant differences in the Short Physical Performance Battery score (t=4.15 p<.001), left grip strength (t=0.57, p<.569), right grip strength (t=1.38 p<.177), flexibility test scores (t=2.34, p<.024), ADLs (t=6.86, p<.001), falls efficacy (t=5.16, p<.001), and quality of life (t=3.87, p<.001). Grip strength was increased slightly in the experimental group, but the increase was not significant. Conclusion: Elastic band resistance exercise is an effective nursing intervention to enhance physical fitness, flexibility, ADLs, falls efficacy, and quality of life among older women receiving home nursing care under long term care insurance.