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Rustamov, Sardorbek,Kim, Sangwoo,Kwon, Minho,Kim, Jinsup Techno-Press 2021 Advances in concrete construction Vol.12 No.1
The main goal of this research is to investigate the effect of polyvinyl alcohol (PVA) fiber and steel fiber on lightweight concrete, in which lightweight aggregate was used as the coarse aggregate. The lightweight aggregate was a kind of expanded clay aggregate made using bottom ash from a thermal power plant located in South Korea. Three types of specimens, lightweight concrete without fibers (LC), lightweight concrete containing polyvinyl alcohol fiber (LCPVA), and lightweight concrete with steel fiber (LCSF) were cast with two different fiber-volume fractions (0.5 and 1.0%). Tests of their compressive strength and splitting tensile strength were performed to evaluate the effectiveness of fiber type and fiber-volume fraction in lightweight concrete at 28 days and after 90 days. The results indicated that using fibers in lightweight concrete improved both the compressive strength and splitting tensile strength. The addition of fibers in lightweight concrete showed a positive effect, and the effectiveness of PVA fiber at 28 and 90 days (regarding compressive strength and splitting tensile strength) was more pronounced than steel fiber. Overall, it can be concluded that the 1.0% PVA fiber-volume fraction showed good performance in the lightweight concrete.
Rustam RUSTAMOV,Chong Woon CHO,Dan Gao,Hyung Min KIM,Jong Seong KANG 한국분석과학회 2021 학술대회논문집 Vol.2021 No.11
In previous study, Black chokeberry (Aronia melanocarpa, Rosacea family) were reported to have various bioactivities such as antioxidants, anti-cancer activity. Many researchers have studied to prepare the enhanced bioactive rich fraction from berry fruits. However, it has been reported that the previously methods are insufficient to effectively evaluate the enhanced bioactive rich fraction. The purpose of this study is to compare the quality of main components between 50% EtOH extracts as original extracts and the enriched bioactive rich fraction of black chokeberry (ABF ex). Contents of two samples were determined by total anthocyanin contents (TAC), total phenolic contents (TPC), total flavonoid contents (TFC), total carbohydrate contents (TCC), and total organic acid contents (TAOC). Additionally, individual concentrations of phenolic acid and sugars in samples were analyzed by HPLC analysis. As a result, the content of anthocyanins in ABF extracts is higher than 50% EtOH extracts. In addition, TAC in ABF extracts (14% in a sample) was 10 times higher than 50% EtOH extracts (1.3% in a sample). Additionally, sugars (fructose, sorbitol and glucose) were detected in 50% EtOH extracts. However, sugars were not detected in ABF extracts. Phenolic acids such as chlorogenic acid and neochlorogenic acid content are 8 ~ 10 times higher in ABF samples than in 50% EtOH extracts. The result indicates that the overall contents of bioactive compounds in ABF extracts are much higher than the contents in 50% EtOH extracts.
Improving the speed of the Lizard implementation
Shakhriddin Rustamov,이윤호 한국인터넷정보학회 2019 인터넷정보학회논문지 Vol.20 No.3
Along with the recent advances in quantum computers, it is anticipated that cryptographic attacks using them will make it insecure to use existing public key algorithms such as RSA and ECC. Currently, a lot of researches are underway to replace them by devising PQC (Post Quantum Cryptography) schemes. In this paper, we propose a performance enhancement method for Lizard implementation which is one of NIST PQC standardization submission. The proposed method is able to improve the performance by 7 ~ 25% for its algorithms compared to the implementation in the submission through the techniques of various implementation aspects. This study hopes that Lizard will become more competitive as a candidate for PQC standardization.
Experimental investigations into fretting wear and damage mechanisms of Inconel X-750 alloy
Ibrohim Rustamov,Fei Guo,Zixi Wang 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.10
Fretting wear characteristics of Inconel X-750 were investigated under the dry test condition. Ball-on-flat contact configuration was subjected to the oscillatory movement at different sliding amplitudes through the different time duration and normal loading. Fretting tests were carried out according to the American Society for Testing and Materials standards (ASTM D6425) by the high frequency linear-oscillation wear test rig SRV 4 at room temperature with ~60 % relative humidity. Worn surface morphologies in the case of stick, partial slip and gross slip regimes were examined by 3D optical profiler, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The aim of this research is to study the tribological characteristics of the Ni-based Inconel X-750 superalloy, which is widely used in the air lubricated gas foil bearing applications where contacting surfaces are subjected to fretting motion. It is found that the displacement amplitude and normal load had strong effect on the fretting mode and damage mechanism. Wear mechanisms were associated with the plastically sheared asperities and crack nucleation and propagation during the stick and partial slip regimes, respectively. As the displacement increased, the wear modes were switched to adhesion, abrasion, debris oxidation, delamination and plastic deformation during the gross slip condition. Fretting time dependence was critical in the higher displacement amplitudes where the wear volume loss progressed significantly. However, test duration was less consistent in the stick and partial slip regimes where the wear properties remains unchanged over time.
동결융해에 노출된 섬유보강 경량콘크리트의 기계적 거동 평가
루스타모브사르도르벡 ( Rustamov Sardorbek ),김진섭 ( Kim Jin-sup ) 한국구조물진단유지관리공학회 2020 한국구조물진단유지관리공학회 학술발표대회 논문집 Vol.24 No.1
This paper deals with the influence of steel fiber and polyvinyl alcohol (PVA) fiber on the mechanical properties of lightweight concrete (LC) containing fly ash (FA) exposed to freezing and thawing cycles. The volume fraction of steel fiber was 0.25% in the Fiber-Reinforced Lightweight Concrete(FRLC) mixture, but PVA was added 1.25%. Moreover, FA was replaced by 15% on the mass basis of the cement. LC and FRLC were subjected to 0; 150 and 300 periodic freezing and thawing cycles. The main goal of the experimental part is to explore the deterioration of LC and FRLC specimens subjected to continuous freezing and thawing cycles through air-dried specimens. The difference between the compressive strength, flexural strength, direct tensile strength was measured by the frozen-thawed and air-dried specimens after selected freeze-thaw cycles. The results have shown that the application of fly ash and fibers increased the compressive, flexural, and direct tensile strength of specimens. Besides, the FRLC was found better to prevent cracking and resistance to freezing-thawing than compared to concrete without fibers. The FRLC produced with 1.25% of PVA fiber showed better strength than steel fiber with 0.25%.