• Structural Engineering and Mechanics
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• 제60권6호
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• pp.939-952
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• 2016

A compression to tensile load transforming (CTT) device was developed to determine indirect tensile strength of concrete material. Before CTT test, Particle flow code was used for the determination of the standard dimension of physical samples. Four numerical models with different dimensions were made and were subjected to tensile loading. The geometry of the model with ideal failure pattern was selected for physical sample preparation. A concrete slab with dimensions of $15{\times}19{\times}6cm$ and a hole at its center was prepared and subjected to tensile loading using this special loading device. The ratio of hole diameter to sample width was 0.5. The samples were made from a mixture of water, fine sand and cement with a ratio of 1-0.5-1, respectively. A 30-ton hydraulic jack with a load cell applied compressive loading to CTT with the compressive pressure rate of 0.02 MPa per second. The compressive loading was converted to tensile stress on the sample because of the overall test design. A numerical modeling was also done to analyze the effect of the hole diameter on stress concentrations of the hole side along its horizontal axis to provide a suitable criterion for determining the real tensile strength of concrete. Concurrent with indirect tensile test, the Brazilian test was performed to compare the results from two methods and also to perform numerical calibration. The numerical modeling shows that the models have tensile failure in the sides of the hole along the horizontal axis before any failure under shear loading. Also the stress concentration at the edge of the hole was 1.4 times more than the applied stress registered by the machine. Experimental Results showed that, the indirect tensile strength was clearly lower than the Brazilian test strength.

• 분석과학
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• 제34권5호
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• pp.212-224
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• 2021

The intent of the present work was to develop a simple, sensitive, accurate, precise, rapid and economical UV- spectrophotometric and reverse phase high pressure liquid chromatographic method for the simultaneous estimation of Spironolactone and Furosemide in bulk and combined tablet dosage forms. UV-Spectrophotometry was carried out by simultaneous equation method using 0.02 M potassium dihydrogen phosphate buffer pH 3.5: Acetonitrile (50:50) v/v as a solvent. The linearity range was 2-14 ㎍ mL^-1 for Spironolactone and Furosemide with a correlation coefficient > 0.99. The chromatographic separation was achieved on 250 mm × 4.6 mm, hypersil BDS C18 column with particle size 5 ㎛, by using an isocratic mixture of 0.02 M potassium dihydrogen phosphate buffer pH 3.5: Acetonitrile: tert butyl methyl ether (49:50:1) v/v/v as a solvent at a flow rate of 1 mL min^-1 and UV detection was carried out at 254 nm. The retention time were observed to be 3.666 and 6.661 minutes for Furosemide and Spironolactone respectively. The two developed methods were validated according to the ICH guidelines for accuracy, precision, linearity, LOD, LOQ and were found to be within the limits. It can be concluded that these two methods could be successfully used for the simultaneous estimation of Spironolactone and Furosemide in bulk and combined tablet dosage forms.

• 농업과학연구
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• 제46권1호
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• pp.33-44
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• 2019

This study was conducted to examine the components of phytoncide from a pine forest in the southern temperate zone. Recent studies have found that a large amount of phytoncide is released not only from cypress trees but also from pine trees. Because the amount released is the highest during summer, we selected a warm climate region in the southern temperate zone and measured the concentration in the month of August. To capture the phytoncide from the forest atmosphere, we used the adsorption tube method with a mini pump and successfully gathered 9 L of forest air at a flow rate of 150 mL/min. We performed duplicate sampling from two different tubes installed at the same location and derived the mean value. A gas chromatography/mass spectrometer detector with thermal desorption spectroscopy was utilized to perform quantitative and qualitative analyses of the captured material. The results showed that the average phytoncide particle of the pine forest in the southern temperate zone contained a number of components as follows in descending order: ${\alpha}$-Pinene (39%, $0.28ng/m^3$), followed by ${\beta}$-Pinene (16%, $0.11ng/m^3$), D-Limonene (8%, $0.06ng/m^3$), camphor (6%, $0.04ng/m^3$), camphene (6%, $0.04ng/m^3$), and p-Cymene (5%, $0.04ng/m^3$). There were also 13 additional phytoncide components in trace amounts. The results of this study are expected to provide a useful dataset for building a "Healing-forest".

• 한국분말재료학회지
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• 제29권6호
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• pp.459-467
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• 2022

Soft magnetic powder materials are used throughout industries such as motors and power converters. When manufacturing Fe-based soft magnetic composites, the size and shape of the soft magnetic powder and the microstructure in the powder are closely related to the magnetic properties. In this study, Fe-Si-Al-P alloy powders were manufactured using various manufacturing process parameter sets, and the process parameters of the vacuum induction melt gas atomization process were set as melt temperature, atomization gas pressure, and gas flow rate. Process variable data that records are converted into 6 types of data for each powder recovery section. Process variable data that recorded minute changes were converted into 6 types of data and used as input variables. As output variables, a total of 6 types were designated by measuring the particle size, flowability, apparent density, and sphericity of the manufactured powders according to the process variable conditions. The sensitivity of the input and output variables was analyzed through the Pearson correlation coefficient, and a total of 6 powder characteristics were analyzed by artificial neural network model. The prediction results were compared with the results through linear regression analysis and response surface methodology, respectively.

• Computers and Concrete
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• 제31권3호
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• pp.207-221
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• 2023

In this investigation, the interaction between opening space and neighboring joint has been examined by experimental test and Particle flow code in two dimension (PFC2D) simulation. Since, firs of all PFC was calibrated using Brazilian experimental test and uniaxial compression test. Secondly, diverse configurations of opening and neighboring joint were provided and tested by uniaxial test. 12 rectangular sample with dimension of 10 cm*10 cm was prepared from gypsum mixture. One quarter of tunnel and one and or two joint were drilled into the sample. Tunnel diameter was 5.5 cm. The angularities of joint in physical test were 0°, 45° and 90°. The angularities of joint in numerical simulation were 0°, 30°, 60°, -30°, -45°, -60° and its length were 2cm and 4cm. Loading rate was 0.016 m/s. Tensile strength of material was 4.5 MPa. Results shows that dominant type of crack which took place in the model was tensile cracks and or several shear bands develop within the model. The Final stress is minimum in the cases where oriented angle is negative. The failure stress decrease by decreasing the joint angle from 30° to 60°. In addition, the failure stress decrease by incrementing the joint angle from -30° to -60°. The failure stress was incremented by decreasing the number of notches. The failure stress was incremented by decreasing the joint length. The failure stress was incremented by decreasing the number of notches. Comparing experimental results and numerical one, showed that the failure stress is approximately identical in both conditions.

• Structural Engineering and Mechanics
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• 제81권1호
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• pp.81-91
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• 2022

The effects of interaction between concrete-gypsum interface and edge crack on the failure behavior of the specimens in senicircular bend (SCB) test were studied in the laboratory and also simulated numerically using the discrete element method. Some quarter circular specimens of gypsum and concrete with 5 cm radii and hieghts were separately prepared. Then the semicircular testing specimens were made by attaching one gypsum and one concrete sample to one another using a special glue and one edge crack is produced (in the interface) by do not using the glue in that part of the interface. The tensile strengths of concrete and gypsum samples were separately measured as 2.2 MPa and 1.3 MPa, respectively. during all testing performances a constant loading rate of 0.005 mm/s were stablished. The proposed testing method showed that the mechanism of failure and fracture in the brittle materials were mostly governed by the dimensions and number of discontinuities. The fracture toughnesses of the SCB samples were related to the fracture patterns during the failure processes of these specimens. The tensile behaviour of edge notch was related to the number of induced tensile cracks which were increased by decreasing the joint length. The fracture toughness of samples was constant by increasing the joint length. The failure process and fracture pattern in the notched semi-circular bending specimens were similar for both methods used in this study (i.e., the laboratory tests and the simulation procedure using the particle flow code (PFC2D)).

• 자원리싸이클링
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• 제32권2호
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• pp.33-42
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• 2023

금속 에멀젼(metal emulsion)은 제강 공정의 효율성을 높이는 방법으로 수십 년 동안 연구되어 왔습니다. 본 연구는 육안으로 관찰하기 어려운 고온 실험의 단점을 보완하기 위해 상온에서 관찰 가능한 수모델을 이용하여 수행하였다. 슬래그 내 금속 에멀젼의 대신하여 증류수를 실리콘 오일에 적하하여 운동량 균형 방정식에 의한 계산 결과와 비교하는 실험을 하였다. 물방울의 하강 속도는 물방울의 직경과 유체(실리콘 오일)의 점도가 증가함에 따라 감소하였다. 교반 조건에서 실리콘 오일에서 물방울의 하강 속도를 시뮬레이션하기 위해 유체(실리콘 오일)의 유속을 입자 이미지 속도계(PIV) 방법으로 측정하였다. 물방울의 하강 속도 계산은 점성 실리콘 오일을 교반하거나 교반하지 않고 측정된 값과 잘 일치하였다.

• Journal of Applied Biological Chemistry
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• 제55권1호
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• pp.55-59
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• 2012

본 연구에서는 목재로부터 신속한 폼알데하이드 정량분석 시험법을 개발하고자 챔버법을 변형한 방법을 설계하였으며, 톱밥시료는 0.15-2.0 mm 크기의 입자를 사용하였고, 휘발부와 포집부가 분리된 장치에서 휘발온도 및 질소유량별 폼알데하이드 포집률을 측정하였다. 그 결과 질소유량 40 mL/min, $100^{\circ}C$ 조건에서 30분간 포집 할 경우 94.8%의 최대 포집률이 확인되었으며, 본 공정의 농도별 폼알데하이드 포집률은 71.0-94.8% ($r^2$=0.9968)로 확인되었으며, 목재 중 총 폼알데하이드 농도가 증가 할수록 휘발된 폼알데하이드량이 정량적으로 증가함을 확인할 수 있었다($r^2$=0.8234). 목재종류 별 폼알데하이드 평균 함량은 천연톱밥(0.7-4.6 ${\mu}g/g$), 방부목(3.9-5.6 ${\mu}g/g$), 접착제 사용 가공목재(5.9-211.5 ${\mu}g/g$) 순으로 낮은 함량을 확인하였고, 각 그룹별 폼알데하이드 분석결과에 대한 Duncan's multiple range test 수행결과 천연톱밥과 접착제를 사용하지 않는 방부목은 95% 신뢰수준에서 유의적 차이를 나타내지 않았으나, 천연톱밥과 접착제 사용목재간에는 동일 수준에서 유의차가 확인되었다. 이러한 결과로 볼 때, 접착제가 사용된 목재는 본 시험분석을 통해 신속하게 천연목재와 구분이 가능 할 것으로 판단된다.

• Korean Chemical Engineering Research
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• 제48권2호
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• pp.185-192
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• 2010

매체 순환식 연소는 연소 공정 자체에서 질소 산화물 생성이나 부가적인 에너지 소비 없이 이산화탄소 분리가 이루어지는 신공정이다. 이 공정은 금속 산화물 입자가 두 개의 반응기를 순환하며 산화와 환원을 거치는 과정으로 구성되어 있다. 이 연구에서는 bentonite에 담지된 산화철 산소 공여 입자의 반응 속도 식을 shrinking core 모델을 통하여 수립하였다. 반응성 결과를 바탕으로 반응기 설계 기준인 고체 순환량과 입자 충전량을 도출하였다. 매체 순환식 연소 공정의 적용을 위하여 두 가지 형태의 연결된 유동층 즉, 상승관과 기포 유동층이 각각 한 개씩인 형태, 상승관 한 개와 기포 유동층이 두 개로 구성된 형태로 시스템을 설계하였다. 고체 순환량은 loop-seal을 통하여 $30kg/m^2s$ 정도까지 변화시켰다. 고체 순환량은 loop-seal의 기체 주입량이 증가할수록 증가하였으며 보조 기체를 주입하면 그 양이 더 증대되었다. 고체 순환량이 증가함에 따라 상승관 내부의 고체량은 증가하였다. 상승관으로부터 다른 반응기로의 기체 누출량은 1% 미만의 수준이었다.

• 농업생명과학연구
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• 제52권6호
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• pp.1-12
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• 2018

본 연구는 산지계류에 시설되는 사방댐의 투과정도를 파악하고, 이를 바탕으로 재해예방과 생물종 다양성에 대한 적절한 보호 및 관리를 위하여 개방형에 따른 사방댐의 생태적 기능을 분석한 결과를 요약하면 다음과 같다. 투과율이 15% 미만인 불투과형 중력식 댐은 투과형 댐으로 구조개량 하거나 전환할 경우 투과율이 0.72%에서 55.8%로 약 77배 이상 증가하는 것으로 나타났다. 저사 및 저수 등 특별한 목적을 두고 시공하는 불투과형 중력식 사방댐을 제외하고는 하류지역으로 토사의 이동, 어류 및 양서류의 상 하류에의 생태통로 등 다양한 기능을 비교적 양호하게 할 수 있는 투과형으로 개선하여 시공할 필요성이 있다. 사방댐 차단높이에 따른 개방은 유효고, 기초부의 높이 및 하부기초 부분의 매몰정도에 따라 다르므로 현장여건 및 시공목적에 따라 설계할 필요성이 있다. 횡단면의 개방형태에 따른 사방댐의 생태적 기능은 어류소통형, 홍수조절형, 저수형(산불방지취수형), 토석막이형(저사형), 토석막이형(토석형) 및 입도분석형으로 제시하였다.