• 한국분말재료학회지
• /
• 제26권4호
• /
• pp.327-333
• /
• 2019

In this study, a process is developed for 3D printing with alumina ($Al_2O_3$). First, a photocurable slurry made from nanoparticle $Al_2O_3$ powder is mixed with hexanediol diacrylate binder and phenylbis(2,4,6-trimethylbenzoyl) phosphine oxide photoinitiator. The optimum solid content of $Al_2O_3$ is determined by measuring the rheological properties of the slurry. Then, green bodies of $Al_2O_3$ with different photoinitiator contents and UV exposure times are fabricated with a digital light processing (DLP) 3D printer. The dimensional accuracy of the printed $Al_2O_3$ green bodies and the number of defects are evaluated by carefully measuring the samples and imaging them with a scanning electron microscope. The optimum photoinitiator content and exposure time are 0.5 wt% and 0.8 s, respectively. These results show that $Al_2O_3$ products of various sizes and shapes can be fabricated by DLP 3D printing.

• 한국재료학회지
• /
• 제29권1호
• /
• pp.23-29
• /
• 2019

Three-dimensional(3D) printing is a process for producing complex-shaped 3D objects by repeatedly stacking thin layers according to digital information designed in 3D structures. 3D printing can be classified based on the method and material of additive manufacturing process. Among the various 3D printing methods, digital light processing is an additive manufacturing technique which can fabricate complex 3D structures with high accuracy. Recently, there have been many efforts to use ceramic material for an additive manufacturing process. Generally, ceramic material shows low processability due to its high hardness and strength. The introduction of additive manufacturing techniques into the fabrication of ceramics will improve the low processability and enable the fabrication of complex shapes and parts. In this study, we synthesize silica composite material that can be applied to digital light processing. The rheological and photopolymeric properties of the synthesized silica composite are investigated in detail. 3D objects are also successfully produced using the silica composite and digital light processing.

• 한국건축시공학회지
• /
• 제19권3호
• /
• pp.219-228
• /
• 2019

본 연구의 목적은 저점도형 고성능 감수제가 혼화재료를 포함하는 시멘트 계열 재료의 유동성 및 레올로지 특성에 미치는 영향을 분석하여 기초적인 정보를 제공하는 것이다. 이에 플라이애시, 고로슬래그, 실리카흄을 치환한 시멘트 페이스트와 모르타르에 대하여 일반적인 고성능 감수제와 저점도형 고성능 감수제를 사용하여 실험을 실시하였다. 실험 결과 저점도형 고성능 감수제는 소성점도에 있어서 일반형 고성능 감수제보다 크게 저감시키는 것으로 나타났다. 이러한 결과를 바탕으로 본 연구가 향후 저점도형 고성능 감수제를 사용하는 데에 기초적인 데이터를 제공할 것으로 기대한다.

• Earthquakes and Structures
• /
• 제23권6호
• /
• pp.493-502
• /
• 2022

In recent decades, infrastructural development has exploded, particularly in the coastal region of Saudi Arabia. The rising demand of most consumed aggregate in construction can be effectively compensated by the alternative material like scoria which lavishly exists in the western region. Scoria is characterized as lightweight aggregate beneficially used to develop lightweight concrete (LWC) - a potential alternative of normal weight concrete (NWC) ensuring reduction in the structural element's size, increase in building height, comparatively lighter foundation, etc. Hence, the goal of this study is to incorporate scoria-based structural lightweight concrete and evaluate its impact on superstructure and foundation design beside contributing to the economy of construction. Fresh, mechanical, and rheological properties of the novel LWC have been investigated. The structural analyses employ the NWC as well as LWC based structures under seismic and wind loadings. The commercial finite element package - ETABS was employed to find out the change in structural responses and foundations. The cost estimation and SWOT analysis for superstructure and foundation have also been carried out. It was revealed that the developed LWC enabled a more flexible structural design. Notable reduction in the steel and concrete prices of LWC might be possible in the low-rise building. It is postulated that the cost-effective and eco-friendly LWC will promote the usage of scoria as an effective alternative in Saudi Arabia and GCC countries for structurally viable LWC construction.

• Structural Engineering and Mechanics
• /
• 제81권5호
• /
• pp.617-631
• /
• 2022

In this paper the viscoelastic responses of four experimental steel-concrete composite beams subjected to highly variable environmental conditions are investigated by means of a finite element (FE) model. Concrete specimens submitted to stepped stress changes are also evaluated to validate the current formulations. Here, two well-known approaches commonly used to solve the viscoelastic constitutive relationship for concrete are employed. The first approach directly solves the integral-type form of the constitutive equation at the macroscopic level, in which aging is included by updating material properties. The second approach is postulated from a rate-type law based on an age-independent Generalized Kelvin rheological model together with Solidification Theory, using a micromechanical based approach. Thus, conceptually both approaches include concrete hardening in two different manners. The aim of this work is to compare and analyze the numerical prediction in terms of long-term deflections of the studied specimens according to both approaches. To accomplish this goal, the performance of several well-known model codes for concrete creep and shrinkage such as ACI 209, CEB-MC90, CEB-MC99, B3, GL 2000 and FIB-2010 are evaluated by means of statistical bias indicators. It is shown that both approaches with minor differences acceptably match the long-term experimental deflection and are able to capture complex oscillatory responses due to variable temperature and relative humidity. Nevertheless, the use of an age-independent scheme as proposed by Solidification Theory may be computationally more advantageous.

• 한국식생활문화학회지
• /
• 제21권3호
• /
• pp.311-318
• /
• 2006

This study aims to investigate the quality characteristics of breads with the addition of sweet pumpkin powder. Farinogram showed that the absorption rate of the dough decreased, the development time and stability became shortened, and the degree of attenuation tended to be grown along with increasing the amount of pumpkin powder. From the amylogram, it was found that the gelatinization starting temperature and the maximum viscosity of pumpkin powder added dough seemed to be decreased as the amount of pumpkin powder was increased. Extensogram showed that there was a decrease in the degree of extension of the dough added with increasing the amount of pumpkin powder, while an increase in the degree of resistance and resistance/extensibility. The lightness (L value) and redness (a value) of bread was found to be decreased with increasing the amount of pumpkin powder, while the yellowness (b value) increased. In terms of the dough texture, for which the hardness, cohesiveness and gumminess of the dough were measured, there were no significant differences between groups, while the dough added with 8.0% pumpkin powder showed a significant decrease in the elasticity. The results of sensory evaluation showed that the highest score of color (p<0.05) and taste (p<0.05) were obtained from the bread added with 6.0% and 8.0% pumpkin powder, while the highest score of texture in control and 3.0% pumpkin bread. In addition, the highest score of flavor (p<0.05) and overall acceptance (p<0.05) were observed in bread added with 6.0% pumpkin powder. Upon the results of this study, it was assumed that the development of food products using pumpkin are prospective in response to health-oriented consumers.

• 공업화학
• /
• 제34권5호
• /
• pp.501-506
• /
• 2023

수크로스 에스터와 세라마이드를 혼합하여 겔레이터로 사용한 해바라기 오일의 올레오겔과 올레오겔 에멀전을 제조하였다. 올레오겔과 올레오겔 에멀젼 제형 내에서 겔레이터의 결정 구조는 편광현미경으로 관찰하고 물의 분산형태는 공초점 현미경으로 확인하였다. DSC 열차트 분석을 통해, 수크로스 에스터와 세라마이드를 혼합하면 세라마이드의 결정구조는 사라지고 제형에 물이 첨가되면 혼합된 겔레이터의 결정성이 더욱 상승함을 확인하였다. 제형에서의 수크로스 에스터, 세라마이드, 물의 비율에 따른 점도와 점탄성 등의 유변학적 특성의 변화를 살펴보았다. 세라마이드와 물의 함량이 증가할수록 점도 및 저장탄성률, 손실 탄성률 등이 모두 증가하고, 또한 제형의 안정성도 높아지는 경향을 보였다.

• Steel and Composite Structures
• /
• 제51권1호
• /
• pp.73-91
• /
• 2024

This paper has focused on presenting vibration analysis of trapezoidal sandwich plates with a damaged core and FG wavy CNT-reinforced face sheets. A damage model is introduced to provide an analytical description of an irreversible rheological process that causes the decay of the mechanical properties, in terms of engineering constants. An isotropic damage is considered for the core of the sandwich structure. The classical theory concerning the mechanical efficiency of a matrix embedding finite length fibers has been modified by introducing the tube-to-tube random contact, which explicitly accounts for the progressive reduction of the tubes' effective aspect ratio as the filler content increases. The First-order shear deformation theory of plate is utilized to establish governing partial differential equations and boundary conditions for the trapezoidal plate. The governing equations together with related boundary conditions are discretized using a mapping-generalized differential quadrature (GDQ) method in spatial domain. Then natural frequencies of the trapezoidal sandwich plates are obtained using GDQ method. Validity of the current study is evaluated by comparing its numerical results with those available in the literature. After demonstrating the convergence and accuracy of the method, different parametric studies for laminated trapezoidal structure including carbon nanotubes waviness (0≤w≤1), CNT aspect ratio (0≤AR≤4000), face sheet to core thickness ratio (0.1 ≤ ${\frac{h_f}{h_c}}$ ≤ 0.5), trapezoidal side angles (30° ≤ α, β ≤ 90°) and damaged parameter (0 ≤ D < 1) are carried out. It is explicated that the damaged core and weight fraction, carbon nanotubes (CNTs) waviness and CNT aspect ratio can significantly affect the vibrational behavior of the sandwich structure. Results show that by increasing the values of waviness index (w), normalized natural frequency of the structure decreases, and the straight CNT (w=0) gives the highest frequency. For an overall comprehension on vibration of laminated trapezoidal plates, some selected vibration mode shapes were graphically represented in this study.

• Journal of Microbiology and Biotechnology
• /
• 제34권5호
• /
• pp.1135-1145
• /
• 2024

When cells are exposed to freezing temperatures, high concentrations of cryoprotective agents (CPA) prevent ice crystal formation, thus enhancing cell survival. However, high concentrations of CPAs can also cause cell toxicity. Exopolysaccharides (EPSs) from polar marine environments exhibit lower toxicity and display effects similar to traditional CPA. In this study, we sought to address these issues by i) selecting strains that produce EPS with novel cryoprotective activity, and ii) optimizing culture conditions for EPS production. Sixty-six bacteria producing mucous substances were isolated from the Ross Sea (Antarctic Ocean) using solid marine agar plates. Among them, Pseudoalteromonas sp. RosPo-2 was ultimately selected based on the rheological properties of the produced EPS (p-CY02). Cryoprotective activity experiments demonstrated that p-CY02 exhibited significantly cryoprotective activity at a concentration of 0.8% (w/v) on mammalian cells (HaCaT). This activity was further improved when combined with various concentrations of dimethyl sulfoxide (DMSO) compared to using DMSO alone. Moreover, the survival rate of HaCaT cells treated with 5% (v/v) DMSO and 0.8% (w/v) p-CY02 was measured at 87.9 ± 2.8% after freezing treatment. This suggests that p-CY02 may be developed as a more effective, less toxic, and novel non-permeating CPA. To enhance the production of EPS with cryoprotective activity, Response Surface Methodology (RSM) was implemented, resulting in a 1.64-fold increase in production of EPS with cryoprotective activity.

• 한국수산과학회지
• /
• 제28권1호
• /
• pp.23-30
• /
• 1995

횟감용 활어의 육질을 향상시키는 새로운 방법을 개발하기 위한 기초연구로서, 전기자극 처리가 사후 조기의 횟감용 어육의 물리화학적 및 물성적 변화에 미치는 영향에 대하여 검토한 결과는 다음과 같다. 전기자극시킨 경우에 사후경직의 진행이 촉진되었으나, 전기자극 시간에 따른 사후경직 진행속도에는 큰 차이가 없었다. 한편, 전기자극 시간이 길어질수록 최고 경직 이후의 저하속도가 빨랐다. 치사직후의 어육 중의 ATP함량은 즉살에서 가장 높았으며, 전기자극 시간이 길어질 수록 ATP분해는 촉진되었다. ATP가 완전히 분해되는 시간은 전기자극 15초에서 16시간, 전기자극 35초에서 11시간, 전기자극 60초에서 5시간, 그리고 즉살에서 32시간이었다. 또, 분해속도 상수는 각각 $0.244hr^{-1},\;0.358hr^{-1},\;0.479hr^{-1},\;0.195hr^{-1}$이었다 어육 중의 유산량도 전기자극시키므로서 그 값이 급격히 증가하였으며, 전기자극시간이 길어질수록 유산 축적량이 최대로 되는 시간이 짧았다. 유산 축적의 반응속도 상수는 15초 전기자극에서 $1.171hr^{-1}$, 35초 전기자극에서 $1.392hr^{-1}$, 60초 전기자극에서는 $1.635hr^{-1}$, 그리고 즉살에서는 $0.534hr^{-1}$이었다. 즉살시킨 경우의 치사직후의 파괴강도는 $1050.30\pm50.23g$이었으며, 파괴강도가 최고 값에 도달하는 시간과 그 값은 각각 15초 전기자극에서 2시간과 $1264.43\pm35.76g$, 35초 전기자극에서 0시간과 $1357.68\pm22.50g$이었다. 한편, 60초 전기자극에서는 치사직후에 $1012.18\pm57.36g$으로 즉살보다 그 값이 낮았다. 그리고, 전기자극시간이 길수록 최고 값에 도달한 후의 파괴강도의 저하속도가 빨랐다.