• 한국추진공학회:학술대회논문집
• /
• 한국추진공학회 2008년 영문 학술대회
• /
• pp.218-225
• /
• 2008

When the heat release and acoustic pressure fluctuations are generated in the combustor by irregular combustion, these fluctuations affect the mass flow rate of the propellants injected through the injectors. Also, the variations of the mass flow rate by these fluctuations again bring about irregular combustion and furthermore that is related with combustion instability. Therefore, it is very important to identify the mass variation for the pressure fluctuation on the injector and to investigate its transfer function. So, we first have studied quantifying the variation of mass flow rate generated in simplex swirl injector by injection pressure fluctuation. To acquire the transient mass flow rate in orifice with time, we have tried to measure of the flow axial velocity and liquid film thickness in orifice. The axial velocity is acquired through theoretical approach after measuring the pressure in orifice and the flow area in the orifice is measured by electric conductance method. As results, mass flow rate calculated by axial velocity and liquid film thickness measuring in orifice accorded with mass flow rate acquired by direct measuring method in the small error range within 1 percents in steady state and within 6 percents as average mass flow rate in pulsated state. Hence this method can be used to measure the mass flow rate not only in steady state but also in unsteady state because the mass flow rate in the orifice can acquire with time and this method shows very high accuracy based on the experimental results.

• Computers and Concrete
• /
• 제21권6호
• /
• pp.623-635
• /
• 2018

In order to research the influence of different recycled aggregate contents on the mechanical properties of pervious concrete, the experimental study and numerical simulation analysis of the mechanical properties of pervious concrete with five kinds of recycled aggregates contents (0%, 25%, 50%, 75% and 100%) are carried out in this paper. The experimental test were first performed on concrete specimens of different sizes in order to determine the influence of recycled aggregate on the compressive strength and splitting tensile strength, direct tension strength and bending strength. Then, the development of the internal cracks of pervious concrete under different working conditions is studied more intuitively by $PFC^{3D}$. The experimental results show that the concrete compressive strength, tensile strength and bending strength decrease with the increase of the recycled aggregate contents. This trend of reduction is not only related to the brittleness of recycled aggregate concrete, but also to the weak viscosity of recycled aggregate and cement paste. It is found that the fracture surface of pervious concrete with recycled aggregate is smoother than that of natural aggregate pervious concrete by $PFC^{3D}$, which means that the bridging effect is weakened in the stress transfer between the left and right sides of the crack. Through the analysis of the development of the internal cracks, the recycled aggregate concrete generated more cracks than the natural aggregate concrete, which means that the recycled aggregate concrete is easier to form a coalescence fracture surface and eventually break.

• Tuberculosis and Respiratory Diseases
• /
• 제84권4호
• /
• pp.299-316
• /
• 2021

Background: The lack of effective medications for coronavirus disease 2019 (COVID-19) has led to a trend of drug repurposing such as the case of azithromycin which shows immunomodulatory and anti-viral effect. Several clinical trials have shown conflicting results. It is currently unclear whether the available evidence is in favor or against the use of azithromycin in COVID-19 patients. Thus, the aim of this study was to investigate the efficacy and safety of azithromycin in COVID-19 patients. Methods: Four independent reviewers selected relevant studies from PubMed, ScienceDirect, EBSCO, and ProQuest published prior to March 2021. The protocol used in this study has been registered in PROSPERO (CRD42020224967). Results: We included 17 studies and found that the mortality rate (odds ratio [OR], 0.95; 95% confidence interval [CI], 0.76-1.19), need of respiratory support (OR, 1.30; 95% CI, 0.98-1.73), hospitalization rate (standardized mean difference, 0.12; 95% CI, -0.02 to 0.27), and intensive care unit transfer (OR, 1.21; 95% CI, 0.79-1.86) of azithromycin-treated group did not differ significantly (p>0.05) from those of the control group. Azithromycin treatment did not significantly increase the risk of getting secondary infection (OR, 1.23; 95% CI, 0.83-1.82), hypoglycemia (OR, 0.73; 95% CI, 0.38-1.40), gastrointestinal problems (OR, 1.03; 95% CI, 0.73-1.45) or electrocardiogram abnormalities (OR, 1.16; 95% CI, 0.94-1.42). The overall quality of evidence ranged from low to very low. Conclusion: Azithromycin did not result in a superior clinical improvement in COVID-19 patients, although it was well-tolerated and safe to use.

• International Journal of Computer Science & Network Security
• /
• 제21권8호
• /
• pp.353-359
• /
• 2021

Information technology and the need for timely and effective communication during the Covid-19 have made most governments adopt technological approaches to provide their services. E-government services have been adopted by most governments especially in developed countries to quickly and effectively share information. This study discusses the reasons why governments in the Gulf region should develop a new model for information technology knowledge management practices. To achieve this, the author identified possible benefits of adopting information technology knowledge management practices and why most governments in the Gulf find it hard to adopt them. Knowledge management allows for learning, transfer as well as sharing of information between government organizations and citizens and with the development of technology, the effectiveness of electronic services can easily be achieved. Also, effective adoption of information technology can improve knowledge management with the help of techniques that enhance capture, storage, retrieval as well as sharing of information. The author used systematic literature review to select 28 journals and articles published post 2019. IEEE, Google Scholar and Science Direct were used to select potential studies from which 722 journals and articles were selected. Through screening and eligibility assessment, 21 articles were retained while the back and forward search had 7 more articles which were also included in the study. Using information gathered from these articles and journals a new conceptual model was developed to help improve information technology knowledge management for governments in the Gulf region to effectively deliver e-services during Covid-19. This model was developed based on the process of KM, Theory of Planned Behavior and Unified Theory of Acceptance and Use of Technology. Based on the developed model. From UTAUT model, performance expectancy, effort expectancy as well as social influence had a great impact.

• 대기
• /
• 제31권2호
• /
• pp.199-214
• /
• 2021

A record-breaking high surface air temperature of 41.0℃ was observed on 1 August 2018 at Hongcheon, South Korea. In this study, to quantitatively determine the formation mechanism of this extremely high surface air temperature, particularly considering the contributions of the foehn and the foehnlike wind, observational data from Korea Meteorological Administration (KMA) and the Weather Research and Forecasting (WRF) model were utilized. In the backward trajectory analysis, trajectories of 100 air parcels were released from the surface over Hongcheon at 1600 LST on 1 August 2018. Among them, the 47 trajectories (38 trajectories) are tracked back above (below) heights of 1.4 km above mean sea level at 0900 LST 31 July 2018 and are defined as upper (lower) routes. Lagrangian energy budget analysis shows that for the upper routes, adiabatic heating (11.886 × 10³ J kg^-1) accounts for about 77% of the increase in the thermal energy transfer to the air parcels, while the rest (23%) is diabatic heating (3.650 × 10³ J kg^-1). On the other hand, for the lower routes, adiabatic heating (6.111 × 10³ J kg^-1) accounts for about 49% of the increase, the rest (51%) being diabatic heating (6.295 × 10³ J kg^-1). Even though the contribution of the diabatic heating to the increase in the air temperature rather varies according to the routes, the contribution of the diabatic heating should be considered. The diabatic heating is caused by direct heating associated with surface sensible heat flux and heating associated with the turbulent mixing. This mechanism is the Type 4 foehn described in Takane and Kusaka (2011). It is concluded that Type 4 foehn wind occurs and plays an important role in the extreme event on 1 August 2018.

• Journal of Radiation Protection and Research
• /
• 제46권4호
• /
• pp.178-183
• /
• 2021

Background: This study was carried out to provide environmental transfer parameter values to estimate activity concentrations of these radionuclides in agricultural crops when direct contamination occurred. Materials and Methods: Mass interception fractions (F_Bs) and weathering half-lives (T_ws) of ¹³¹I and radiocesium were calculated using openly available monitoring data obtained after the Fukushima Daiichi Nuclear Power Plant accident. F_B is the ratio between the initial radioactivity concentration of a radionuclide retained by the edible part of the plant (Bq·kg^-1 fresh weight [FW]) and the amount of deposited radionuclide in that area (Bq·m^-2). T_w values can be calculated using activity concentrations of crops decreased with time after the initial contamination. Results and Discussion: Calculated F_B and T_w values for ¹³¹I and radiocesium were mostly obtained for leafy vegetables. The analytical results showed that there was no difference of F_Bs between ¹³¹I and radiocesium by t-test; geometric mean values for leafy vegetables cultivated under outdoor conditions were 0.058 and 0.12 m²·kg^-1 FW, respectively. Geometric mean T_w value of ¹³¹I in leafy vegetables grown under outdoor conditions was 8.6 days, and that of radiocesium was 6.6 days; there was no significant difference between T_w values of these radionuclides by Wilcoxon rank sum test. Conclusion: There was no difference between ¹³¹I and radiocesium for F_Bs and T_ws. By using these factors, we would be able to carry out a rough estimation of the activity concentrations of ¹³¹I and radiocesium in the edible part of leafy crops when a nuclear accident occurred.

• 우주기술과 응용
• /
• 제1권3호
• /
• pp.356-363
• /
• 2021

중적외선을 이용하여 획득한 영상은 상온 부근의 온도 측정에는 적당하지 않다는 것이 교과서적 상식이었으나, 최근 중적외선 센서를 이용한 위성 영상을 살펴보면 중적외선 센서를 이용하여 측정한 결과물도 상온 부근의 온도를 측정할 수 있다는 가능성을 보여주고 있다. 본 논문에서는 중적외선 센서를 가지는 위성영상의 상온 온도 정보 추출 가능성 및 정확도에 대해 살펴보고자 한다. 논문에서 검토된 중적외선 위성영상은 상온 부분의 온도를 잘 표시하였으며, 측정된 온도의 절대값으로서의 신뢰성에 관해서는, 태양광의 지표면 직접 반사에 의한 열전달량 영향과 대기에서 흡수되는 적외선 대기 흡수량의 영향은 비교적 작거나 일정한 값으로 볼 수 있지만, 비접촉식 온도계의 한계인 물성치의 의한 복사 계수(emissivity)의 불확실성 문제는 여전히 해결해야할 문제로 남아 있게 되었다.

• 한국전기전자재료학회논문지
• /
• 제35권4호
• /
• pp.377-385
• /
• 2022

Thermal batteries are specialized as primary reserve batteries that operate when the internal heat source is ignited and the produced heat (450~550℃) melts the initially insulating salt into highly conductive eutectic electrolyte. The heat source is composed of Fe powder and KClO₄ with different mass ratios and is inserted in-between the cells (stacks) to allow homogeneous heat transfer and ensure complete melting of the electrolyte. An ideal heat source has following criteria to satisfy: sufficient mechanical durability for stacking, appropriate heat calories, ease of combustion by an igniter, stable combustion rate, and modest peak temperature. To satisfy the aforementioned requirements, Fe powder must have high surface area and porosity to increase the reaction rate. Herein, the hydrothermal and spray drying synthesis techniques for Fe powder samples are employed to investigate the physicochemical properties of Fe powder samples and their applicability as a heat source constituent. The direct comparison with the state-of-the-art Fe powder is made to confirm the validity of synthesized products. Finally, the actual batteries were made with the synthesized iron powder samples to examine their performances during the battery operation.

• 기록학연구
• /
• 제74호
• /
• pp.155-186
• /
• 2022

2022년 현재 행정안전부 정부24 웹사이트에 등록된 공공부문 인터넷 웹사이트는 1만 7천여 개이다. 이처럼 많은 웹사이트를 기록으로 관리하기 위해 기록물 생산기관과 기록물관리기관이 상호 간 직접 이관하는 방식은 많은 인적·물적자원을 필요로 한다. 각 웹사이트 구동에 필요한 운영 소프트웨어와 응용소프트웨어 기술을 기록물관리기관이 보유하고 운영하는 것도 현실적으로 어렵다. 이러한 현실적 한계를 극복하기 위해 웹수집 소프트웨어를 이용하여 원격지에서 웹사이트를 자동으로 수집하는 방식이 국내외에서 사용되고 있다. 이 연구는 공공부문 인터넷 웹사이트를 원격으로 수집하여 기록으로 관리할 때 필요한 웹수집기의 성능을 비교하였다. 선행연구 및 문헌조사 등에서 검토한 다수의 웹수집 소프트웨어에 대하여 단계별 검토를 거쳐 가장 적합한 웹수집기를 선정하였다. 성능 평가 과정에는 일부 공공기관 웹사이트를 대상으로 실제 원격 수집 성능을 비교하였다. 이 연구 결과는 웹기록 관리를 위해 웹수집기 선택이 필요한 기관에 실증적이고 구체적인 성능 비교 정보를 제공한다.

• 한국재료학회지
• /
• 제32권11호
• /
• pp.508-514
• /
• 2022

Piezoelectric composite films which are enabled by inorganic piezoelectric nanomaterials-embedded polymer, have attracted enormous attention as a sustainable power source for low powered electronics, because of their ease of fabrication and flexible nature. However, the absorption of applied stress by the soft polymeric matrices is a major issue that must be solved to expand the fields of piezoelectric composite applications. Herein, a flexible and porous piezoelectric composite (piezoelectric sponge) comprised of BaTiO₃ nanoparticles and polydimethylsiloxane was developed using template method to enhance the energy conversion efficiency by minimizing the stress that vanishes into the polymer matrix. In the porous structure, effective stress transfer can occur between the piezoelectric active materials in compression mode due to direct contact between the ceramic particles embedded in the pore-polymer interface. The piezoelectric sponge with 30 wt% of BaTiO₃ particles generated an open-circuit voltage of ~12 V and a short-circuit current of ~150 nA. A finite element method-based simulation was conducted to theoretically back up that the piezoelectric output performance was effectively improved by introducing the sponge structure. Furthermore, to demonstrate the feasibility of pressure detecting applications using the BaTiO₃ particles-embedded piezoelectric sponge, the composite was arranged in a 3 × 3 array and integrated into a single pressure sensor. The fabricated sensor array successfully detected the shape of the applied pressure. This work can provide a cost-effective, biocompatible, and structural strategy for realizing piezoelectric composite-based energy harvesters and self-powered sensors with improved energy conversion efficiency.