• Structural Engineering and Mechanics
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• 제65권4호
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• pp.491-504
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• 2018

Because of sandwich structures with low weight and high stiffness have much usage in various industries such as civil and aerospace engineering, in this article, buckling and free vibration analyses of coupled micro composite sandwich plates are investigated based on sinusoidal shear deformation (SSDT) and most general strain gradient theories (MGSGT). It is assumed that the sandwich structure rested on an orthotropic elastic foundation and make of four composite face sheets with temperature-dependent material properties that they reinforced by carbon and boron nitride nanotubes and two flexible transversely orthotropic cores. Mathematical formulation is presented using Hamilton's principle and governing equations of motions are derived based on energy approach and applying variation method for simply supported edges under electro-magneto-thermo-mechanical, axial buckling and pre-stresses loadings. In order to predict the effects of various parameters such as material length scale parameter, length to width ratio, length to thickness ratio, thickness of face sheets to core thickness ratio, nanotubes volume fraction, pre-stress load and orthotropic elastic medium on the natural frequencies and critical buckling load of double-bonded micro composite sandwich plates. It is found that orthotropic elastic medium has a special role on the system stability and increasing Winkler and Pasternak constants lead to enhance the natural frequency and critical buckling load of micro plates, while decrease natural frequency and critical buckling load with increasing temperature changes. Also, it is showed that pre-stresses due to help the axial buckling load causes that delay the buckling phenomenon. Moreover, it is concluded that the sandwich structures with orthotropic cores have high stiffness, but because they are not economical, thus it is necessary the sandwich plates reinforce by carbon or boron nitride nanotubes specially, because these nanotubes have important thermal and mechanical properties in comparison of the other reinforcement.

• 한국습지학회지
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• 제12권3호
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• pp.57-65
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• 2010

본 연구는 저수지의 퇴적작용을 이해하는데 필요한, 저수지퇴적토 코어의 물리적 특성 변화에 대한 기초자료를 제공하기 위하여 수행되었다. 준설작업이 시행된 적이 없는 세 곳의 저수지에서 채취한 퇴적토 코어에 대하여 깊이에 따른 가비중, 유기물량, 평균입자크기, 모래의 비율 변화를 연중 일강수량 50mm이상일 때의 강수량을 합산한 연강수량(AP50) 변화 자료와 비교, 분석하였다. 저수지의 퇴적토 코어는 무기질 토양으로서 유기물은 육상식물의 잔재물로부터 기원하였으며, 유기물 함량이 10% 이하인 미사질양토 퇴적토에서 유기물 함량의 변화는 저수지로 유입되는 토양입자크기의 변화와 관계가 있었다. 퇴적토 코어의 입자크기 및 모래 비율의 급격한 변동은 강수량의 증감과 관계가 있었으며, 저수지의 수위 변화와 유속이 저수지의 퇴적토 형성에 영향을 미칠 수도 있다. AP50의 연간 변동 자료를 기초로 추정하였을 때, 10년 이내의 짧은 기간 동안 약 30cm 이상의 퇴적토가 쌓일 수 있는 것으로 나타났다. 저수지에서 짧은 시간 동안 쌓여서 형성된 퇴적토에도 유역에서 발생한 인위적 또는 자연적 사건들이 퇴적토의 물리적 특성들에 반영될 수 있음이 확인되었다.

• Applied Microscopy
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• 제22권1호
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• pp.33-41
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• 1992

To clarify the exocytotic features in adrenal medullary aminergic cells, the authors observed rat adrenal medulla prepared by the TAGO method with transmission electron microscope. Rat adrenal medulla contains two types of aminergic cells, adrenergic and noradrenergic, as described. They were present as a group. In a single group both adrenergic and noradrenergic cells were present, but the same kind of cells showed the tendency forming small groups. Adrenergic cells were characterized with the granules having relatively electroluscent cores. These granules were relatively uniform in size, and the cores filled the granules with only thin halos. Noradrenergic cells were characterized with the granules of various size and forms. Most of the cores of these granules were generally more electron-dense than those of the adrenergic cells and only partly filled the granules without forming the halos. But, some granules were very similar in the shape and electron density as those of the adrenergic cells. Even empty-looking granules were present. Exocytotic figures with the classical omega figures were observed in both types of aminergic cells, but they were more frequent in adrenergic cells. These figures were mainly present along the plasma membranes toward the capillary. The excreted materials could be identified in the cleft of the omega figures. Apocrine-like secretory patterns but without cytoplasmic rims were identified in noradrenergic cells. Some vesicles, possibly formed from the cytoplsmic tubular systems were released. Some irregular lamellar structures of varying sizes were also observed. They looked like membranous structures sneaking through the plasma membranes. We could not, however, found any evidences of their involvement in exocytotic processes. These were present toward the capillaries and found only in the adrenergic cells. The authors conclude that the secretory processes in adrenal chromaffin cells may include not only the classical exocytotic processes but also the unusual direct secretions of granules or parts of cellular organelles. The membranous lamellar structures may indicate the remnants of excreted granules or functionally inactive excess membranes of the organelles removed from the cytoplasm.

• 천문학회보
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• 제41권1호
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• pp.73.1-73.1
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• 2016

We present preliminary results of the submillimeter continuum observations of 14 Planck Galactic Cold Clumps (PGCCs), located in the ${\lambda}$ Orionis Complex. This region is the nearest large HII region, which is an ideal site for a study of the stellar feedback to its surroundings. We observed 14 PGCCs with JCMT/SCUBA-2 and used J=1-0 transitions of CO isotopologues from the PMO mapping observation. Several sub-clumps toward three PGCCs were detected at $850{\mu}m$. In order to examine whether these clumps can be candidates for pre-stellar cores, we compared each clump mass calculated from the $850{\mu}m$ continuum map to its Virial mass and Jeans mass calculated from the $^{12}CO$ and $C^{18}O$ (1-0) spectra, respectively. All clumps have masses smaller than their Virial and Jeans masses, indicating that none of them are gravitational bound and thus in the pre-stellar core stage. Also, the CO depletion factor, which has been derived from the dust continuum and the $C^{18}O$(1-0) line and can be an indicator of core evolution, toward the clumps is in the range of 1 to 5, suggesting that they are not very evolved dense pre-stellar cores. In addition, within individual PGCCs, we found clear gradients of velocity (${\sim}1km\;s^{-1}\;pc^{-1}$) and temperature (${\sim}10K\;pc^{-1}$) in the $^{13}CO$ (1-0) first moment map and the $^{12}CO$(1-0) excitation temperature map, respectively. This can be attributed to the compression and external heating by the HII region, which may prevent clumps from forming gravitationally bound structures and eventually disperse clumps. These results could be a hint about the negative effect of stellar feedback on core formation.

• 한국컴퓨터정보학회논문지
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• 제18권2호
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• pp.31-39
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• 2013

본 논문에서는 멀티코어 프로세서에서 단일 실시간 병렬 작업의 데드라인을 만족하면서 전력 소모량의 확률적 기대 값을 최소화하는 스케쥴링 기법을 제안하였다. 제안된 기법에서는 단일 작업을 여러 개의 코어들 상에서 동시에 수행하는 병렬 처리 기법을 적용하였고, 전체 코어들 중에서 일부의 코어들만을 사용하고 나머지 코어들의 전원을 소등하여 전력 소모량을 줄였다. 또한 한정된 개수의 이산적 클락 주파수 값들을 가지는 DVFS 기반 멀티코어 프로세서에 대해서, 확률적 계산량 모델을 가진 실시간 병렬 작업의 데드라인을 만족하면서 전력 소모량의 확률적 기대 값을 최소화함을 수학적으로 증명하였다. 성능평가 실험에서, 제안된 기법이 기존 방법의 전력소모량을 최대 81%까지 감소시킴을 확인하였다.

• 디지털콘텐츠학회 논문지
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• 제9권3호
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• pp.471-481
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• 2008

전력소모를 고려한 테스트 스케줄링은 회로의 복잡도가 높은 SoC 시스템을 테스트할 경우 제한된 전력 소모량 내에서 고장 검출율을 높일 수 있고 테스트 시간을 단축 할 수 있는 효과적인 방법이다. 본 논문에서는 제한된 전력소모량 내에서 효율적으로 테스트를 수행하기 위한 테스트 자원의 모델링 방법 및 테스트 스케줄링 알고리듬을 제안하고 그 유효성을 검증한다. 테스트 자원의 모델링 방법으로는 전력사용량의 최고점과 차고점을 이용한 방법 및 소모 전력의 변화량에 따라 테스트 자원을 분할하는 방법을 제시한다. 또한 테스트 자원과 코어의 상관관계를 이용하여 동시 사용가능한 최대 코어 수를 생성하는 확장나무성장 그래프 생성 알고리듬 및 전력의 최적화가 가능한 전력 소모량 변이 그래프 생성 알고리듬으로 구성된 휴리스틱(heuristic) 테스트 스케줄링 알고리듬을 제안하고 이전의 알고리듬과 비교한다.

• The Journal of Advanced Prosthodontics
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• 제7권2호
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• pp.108-114
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• 2015

PURPOSE. The aim of this study was to evaluate effect of different surface treatment methods on the bond strength between aged composite-resin core and luting agent. MATERIALS AND METHODS. Seventy-five resin composites and also seventy-five zirconia ceramic discs were prepared. 60 composite samples were exposed to thermal aging (10,000 cycles, 5 to $55^{\circ}C$) and different surface treatment. All specimens were separated into 5 groups (n=15): 1) Intact specimens 2) Thermal aging-air polishing 3) Thermal aging- Er:YAG laser irradiation 4) Thermal aging- acid etching 5) Thermal-aging. All specimens were bonded to the zirconia discs with resin cement and fixed to universal testing machine and bond strength testing loaded to failure with a crosshead speed of 0.5 mm/min. The fractured surface was classified as adhesive failure, cohesive failure and adhesive-cohesive failure. The bond strength data was statistically compared by the Kruskal-Wallis method complemented by the Bonferroni correction Mann-Whitney U test. The probability level for statistical significance was set at ${\alpha}$=.05. RESULTS. Thermal aging and different surface treatment methods have significant effect on the bond strength between composite-resin cores and luting-agent (P<.05). The mean baseline bond strength values ranged between $7.07{\pm}2.11$ and $26.05{\pm}6.53$ N. The highest bond strength of $26.05{\pm}6.53$ N was obtained with Group 3. Group 5 showed the lowest value of bond strength. CONCLUSION. Appropriate surface treatment method should be applied to aged composite resin cores or aged-composites restorations should be replaced for the optimal bond strength and the clinical success.

• The Journal of Advanced Prosthodontics
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• 제4권4호
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• pp.187-191
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• 2012

PURPOSE. The aim of the present study was to assess the effect of ascorbic acid, ethanol and acetone on microtensile bond strength between fiber posts pre-treated with hydrogen peroxide and composite resin cores. MATERIALS AND METHODS. Twenty four fiber posts were pre-treated with 24% hydrogen peroxide and divided into 4 groups as follows: G1: no treatment, as control group; G2: treatment with10% ascorbic acid solution for 5 minutes; G3: treatment with 70% ethanol solution for 5 minutes; and G4: treatment with 70% acetone solution for 5 minutes. Each fiber post was surrounded by a cylinder-shaped polyglass matrix which was subsequently filled with composite resin. Two sections from each sample were selected for microtensile test at a crosshead with speed of 0.5 mm/min. Statistical analyses were performed using one-way ANOVA and a post hoc Tukey HSD test. Fractured surfaces were observed under a stereomicroscope at ${\times}20$ magnification. The fractured surfaces of the specimens were observed and evaluated under a SEM. RESULTS. Means of microtensile bond strength values (MPa) and standard deviations in the groups were as follows: G1: $9.70{\pm}0.81$; G2: $12.62{\pm}1.80$; G3: $16.60{\pm}1.93$; and G4: $21.24{\pm}1.95$. G4 and G1 had the highest and the lowest bond strength values, respectively. A greater bond strength value was seen in G3 compared to G2. There were significant differences between all the groups (P<.001). All the failures were of the adhesive mode. CONCLUSION. Application of antioxidant agents may increase microtensile bond strength between fiber posts treated with hydrogen peroxide and composite cores. Acetone increased bond strength more than ascorbic acid and ethanol.

• The Journal of Advanced Prosthodontics
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• 제5권2호
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• pp.179-186
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• 2013

PURPOSE. One of the most important factors in evaluating the quality of fixed dental prostheses (FDPs) is their gap. The purpose of this study was to compare the marginal and internal gap of two different metal-ceramic crowns, casting and selective laser sintering (SLS), before and after porcelain firing. Furthermore, this study evaluated whether metal-ceramic crowns made using the SLS have the same clinical acceptability as crowns made by the traditional casting. MATERIALS AND METHODS. The 10 study models were produced using stone. The 20 specimens were produced using the casting and the SLS methods; 10 samples were made in each group. After the core gap measurements, 10 metal-ceramic crowns in each group were finished using the conventional technique of firing porcelain. The gap of the metal-ceramic crowns was measured. The marginal and internal gaps were measured by two-dimensional and three-dimensional replica techniques, respectively. The Wilcoxon signed-rank test, the Wilcoxon rank-sum test and nonparametric ANCOVA were used for statistical analysis (${\alpha}$=.05). RESULTS. In both groups, the gap increased after completion of the metal-ceramic crown compared to the core. In all measured areas, the gap of the metal cores and metal-ceramic crowns produced by the SLS was greater than that of the metal cores and metal-ceramic crowns produced using the casting. Statistically significant differences were found between cast and SLS (metal cores and metal-ceramic crown). CONCLUSION. Although the gap of the FDPs produced by the SLS was greater than that of the FDPs produced by the conventional casting in all measured areas, none exceeded the clinically acceptable range.

• 한국통신학회논문지
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• 제30권2A호
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• pp.129-136
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• 2005

지정된 비트 크기를 갖는 승산기 코어의 Verilog-HDL 모델을 생성하는 가변 정밀도 승산기 생성기 (VPM_Gen; Variable-Precision Multiplier Generator)에 대해 기술한다. 사용자의 필요에 따라 승수와 피승수의 비트 수를 8-비트${\sim}32$-비트 범위에서 1-비트 단위로 선택할 수 있으며, 승산결과는 $8-b{\sim}64-b$ 범위에서 2-비트 단위로 절사할 수 있도록 함으로써 총 3,455 가지 승산기 코어를 생성할 수 있다. 승산결과가 절사되는 경우, 절사되는 부분의 회로를 제거함으로써 게이트 수와 전력소모가 각각 최대 40%와 30% 감소되도록 하였으며, 이를 통해 효율적인 저전력 승산기 코어가 구현되도록 하였다. 또한, 절사 비트 수에 따른 적응 오차보상 방법을 적용함으로써 절사오차가 최소화되도록 하였다. VPM_Gen에 의해 생성되는 승산기 코어는 Xilinx FPGA 보드와 논리분석기를 통하여 그 기능을 검증하였다.