Experimental Investigation of ECDM for Fabricating Micro Structures of Quartz

Khac-Ha Nguyen,이평안,김보현 한국정밀공학회 2015 International Journal of Precision Engineering and Vol. No.

Recently, the utilization of electrochemical discharge machining (ECDM) has proved to have potential for enhancing the machiningefficiency and accuracy of micro-drilling and milling for glass. However, there is a lack of information about the machining conditionsfor milling in quartz materials, which have different characteristics than glass. In ECDM, gas film and sparks are generated on atool when voltage is applied between the tool and a counter electrode. Workpiece materials are removed mainly by the heat of thesparks. The spark generation is affected by both the voltage and electrolyte conditions. This study investigated the ECDMcharacteristics according to machining parameters, such as electrolyte level, electrolyte concentration, pulse voltage, offset pulsevoltage, pulse on-time, pulse off-time, and tool feedrate. Surface roughness and sharpness of the rims and edges were observed underdifferent machining conditions. Based on the investigation of the machining conditions, micro structures, including micro grooves andcolumns, were machined on quartz material.

Remote Monitoring of Discharge Current in Micro ECDM

Khac-Ha Nguyen(응웬하),Pyeong An Lee(이평안),Bo Hyun Kim(김보현),Byungjick Kim(김병직) 대한기계학회 2013 대한기계학회 춘추학술대회 Vol.2013 No.5

A Study on the Effects of Specimen Geometry on Measurement Accuracy of Dynamic Constitutive Properties of Metals Using SHTB

Khac-Ha Nguyen,Chang-Whan Lee,Hyunho Shin,Joo Hyoung Lee,Jong-Bong Kim 한국정밀공학회 2020 International Journal of Precision Engineering and Vol.21 No.9

Determination of dynamic tensile response of materials has been a challenge because of experimental difficulty. The split Hopkinson tensile bar (SHTB) is one of the most widely used devices for characterization of various materials under dynamic-tensile loading conditions. Since one-dimensional wave propagation in bars is disturbed by specimens and grips, however, SHTB measurement accuracy may not be guaranteed. This means that the stress–strain curve of the specimen that is calculated using strains at bars may not indicate the real stress–strain relation of the specimen. In this study, simulations for the SHTB test were carried out to investigate the effects of thread pitch, specimen length, specimen diameter, and thread inner diameter of the specimen on the measurement accuracy for two types of metals with medium and high yield strengths. Finally, specimen shapes are recommended for accurate measurement of the stress–strain relation of tantalum and tungsten carbide.

Numerical investigation into the stress wave transmitting characteristics of threads in the split Hopkinson tensile bar test

Nguyen, Khac-Ha,Kim, Hee Cheol,Shin, Hyunho,Yoo, Yo-Han,Kim, Jong-Bong Elsevier 2017 International journal of impact engineering Vol.109 No.-

<P><B>Abstract</B></P> <P>The Split Hopkinson tensile Bar (SHTB) is one of the most widely used methods to study various material behaviors under tensile loading and high nominal strain rate. Since the specimens and grips with thread may disturb the wave propagation between bars and specimen, the stress-strain relation of the specimen, which is calculated from the strains of the incident and transmitter bars, may not match with the stress-strain relation measured directly from the specimen. In order to ensure a high accuracy of SHTB system, specimen calibration is usually carried out. To ensure the no wave distortion in the thread region, the stress wave should be entirely transmitted from the incident bar to the transmitter bar in tests using the calibration specimen (not the real specimen) of the same material and the same diameter with the transmitter and incident bars. Therefore, the strain signals at the incident and transmitter bars need to be the same. This study investigated the wave transmit characteristics through threads in SHTB test. To investigate the effect of the thread on the wave transmission, a specimen with the same diameter of the incident and the transmitter bars is used in the SHTB test. The effects of the thread inner diameter, yield stress, thread type, and strike velocity on the wave propagation characteristics are investigated. Based on the analysis results for various conditions, a proper design guide for a thread shape to secure the measurement accuracy in the SHTB test is proposed.</P> <P><B>Highlights</B></P> <P> <UL> <LI> In SHTB test, wave transmit characteristics through thread region is investigated by 3 dimensional finite element analysis. </LI> <LI> The main cause of error and proper design guide of grips are proposed in this study. </LI> <LI> The effects of the thread inner diameter, yield stress, thread type, and strike velocity on the wave transmit characteristics are investigated. </LI> <LI> It was shown that the wave transmit error is highly dependent on the maximum plastic strain in the thread region. </LI> </UL> </P>

Experimental Investigation of ECDM for Fabricating Micro Structures of Quartz

Nguyen, Khac-Ha,Lee, Pyeong An,Kim, Bo Hyun Korean Society for Precision Engineering 2015 International Journal of Precision Engineering and Vol.16 No.1

Recently, the utilization of electrochemical discharge machining (ECDM) has proved to have potential for enhancing the machining efficiency and accuracy of micro-drilling and milling for glass. However, there is a lack of information about the machining conditions for milling in quartz materials, which have different characteristics than glass. In ECDM, gas film and sparks are generated on a tool when voltage is applied between the tool and a counter electrode. Workpiece materials are removed mainly by the heat of the sparks. The spark generation is affected by both the voltage and electrolyte conditions. This study investigated the ECDM characteristics according to machining parameters, such as electrolyte level, electrolyte concentration, pulse voltage, offset pulse voltage, pulse on-time, pulse off-time, and tool feedrate. Surface roughness and sharpness of the rims and edges were observed under different machining conditions. Based on the investigation of the machining conditions, micro structures, including micro grooves and columns, were machined on quartz material.

Spatial Interpolation and Assimilation Methods for Satellite and Ground Meteorological Data in Vietnam

( Khac Phong Do ),( Ba Tung Nguyen ),( Xuan Thanh Nguyen ),( Quang Hung Bui ),( Nguyen Le Tran ),( Thi Nhat Thanh Nguyen ),( Van Quynh Vuong ),( Huy Lai Nguyen ),( Thanh Ha Le ) 한국정보처리학회 2015 Journal of information processing systems Vol.11 No.4

This paper presents the applications of spatial interpolation and assimilation methods for satellite and ground meteorological data, including temperature, relative humidity, and precipitation in regions of Vietnam. In this work, Universal Kriging is used for spatially interpolating ground data and its interpolated results are assimilated with corresponding satellite data to anticipate better gridded data. The input meteorological data was collected from 98 ground weather stations located all over Vietnam; whereas, the satellite data consists of the MODIS Atmospheric Profiles product (MOD07), the ASTER Global Digital Elevation Map (ASTER DEM), and the Tropical Rainfall Measuring Mission (TRMM) in six years. The outputs are gridded fields of temperature, relative humidity, and precipitation. The empirical results were evaluated by using the Root mean square error (RMSE) and the mean percent error (MPE), which illustrate that Universal Kriging interpolation obtains higher accuracy than other forms of Kriging; whereas, the assimilation for precipitation gradually reduces RMSE and significantly MPE. It also reveals that the accuracy of temperature and humidity when employing assimilation that is not significantly improved because of low MODIS retrieval due to cloud contamination.

Study on Fibrosis Change with Transient Elastography in Chronic Hepatitis B Virus Treatment with Tenofovir

( Ha Phuong Linh ),( Hoang Van Tiep ),( Dinh Cong Dang ),( Nguyen Khac Hung Manh ) 대한간학회 2020 춘·추계 학술대회 (KASL) Vol.2020 No.1

Background: Tenofovir disoproxil fumarate (TDF) is one of the first optimal choices to be used in the treatment of chronic hepatitis B. FibroScan is non-invasive methods to assess liver fibrosis. Aims: To evaluate the therapeutic effect of TDF on fibrosis via FibroScan after treatment. Methods: This study was conducted in 63 chronic hepatitis B patients who had the indication of antiviral therapy at 103 Cam Khe Clinic from March 2019 to March 2020. All patients with chronic hepatitis B treated with TDF during 6 months. Liver fibrosis stages was appreciated using transient hepatic elastography by Fibroscan before and after 6 months treatment. Results: The average age of patients was 46 years, with men accounted for 69% of the total. After treatment, normalization of ALT 71.26%, viral response of 90.23%, HBV DNA below the detection level was 66.3%. Liver fibrosis evaluated by FibroScan before and after 6 months treatment were 7.15 ± 1.56 kPa, and 3.58 ± 1.19 kPa eveluated by FibroScan. Conclusions: TDF was effective for patients after treatment on liver fibrosis assessed by FibroScan in chronic hepatitis B patients.

Study on Correlation between Serum Ferritin Levels and Liver Stiffness Assessed by Fibroscan in Patients with Chronic Hepatitis C

( Ha Phuong Linh ),( Hoang Van Tiep ),( Dinh Cong Dang ),( Nguyen Khac Hung Manh ) 대한간학회 2020 춘·추계 학술대회 (KASL) Vol.2020 No.1

Aims: Chronic hepatitis C is a major infectious disease which is mainly cause of morbidity worldwide in patients with liver disease, and liver transplantation. Raised ferritin levels play an important role of intervening the process which is associated with hepatic injury. Screening with non-invasive strategies can detect the disease at early stage and intervention could be initiated. To determine correlation between serum ferritin levels and liver stiffness values in patients of chronic hepatitis C. Methods: A cross-sectional study was conducted at 103 Cam Khe Clinic from May 2019 to April 2020. 93 patients with chronic hepatitis C fulfilling inclusion criteria were included in this study. Liver fibrosis stages was appreciated using transient hepatic elastography by Fibroscan, the activities of serum liver function biomarker enzymes and serum ferritin levels were determined by automated analyser. Results: The average age of patients was 48 years, with men accounted for 78% of the total. The mean serum ferritin value was 148.19 ng/ml, liver stiffness measurements range from 12.5 to 75.5 kPa, with a median value of 17.39 ± 15.98 kPa. Significantly elevated levels of serum ferritin (P<0.001), were detected in patients with severe fibrosis compared to mild fibrosis. Concentration of serum ferritin was increased with the evolution of fibrosis in all stages from F0 to F4 and this increase was significant (P<0.01) in cirrhotic patients (F4). There was a positive correlation between serum level of ferritin and progression of fibrosis (0.979391) (r = 0.976). Conclusions: There is significant correlation between serum ferritin and liver stiffness. Serum ferritin concentration may be used as liver fibrosis biomarkers.

Effect of Dry and Wet Harvest on Postharvest Longevity, Water Relations, and Gene Expression of Cut Roses

Suong Ha,Minjung Kwon,Saika Anne,Toan Khac Nguyen,Jin-Hee Lim 한국원예학회 2019 한국원예학회 학술발표요지 Vol.2019 No.10

Analysis of chrysanthemum genetic diversity by genotyping-by-sequencing

Toan Khac Nguyen,Suong Tuyet Thi Ha,임진희 한국원예학회 2020 Horticulture, Environment, and Biotechnology Vol.61 No.5

Application of next-generation sequencing to very large genomes, such as chrysanthemum ( Chrysanthemum sp.), faceschallenges including repeated sequences, limited short-reads, and various contigs in massive fragments. Genotyping-bysequencing(GBS) can overcome many of these drawbacks by high-multiplexing, and potential genotyping-sequencingapproaches could have wide-ranging utilizations in chrysanthemum breeding. The study aimed to establish an approach forGBS application and to elucidate a phylogenomic structure in an individual with a large genome. We identifi ed single nucleotidepolymorphism (SNP) for SNP calling (279,189 markers) and SNP fi ltering (7758 markers) that will promote analysisof chrysanthemum population genetics. We conclude that GBS is the best approach for genotyping in chrysanthemum andcan be applied in genetic breeding in various plants.