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BackgroundAcute variceal bleeding (AVB) is a severe complication of portal hypertension that is caused by rupture of the esophageal or gastric varix. Scoring system for risk stratification of AVB is difficult to use because various variables must be entered, and it is difficult to apply early in the emergency department (ED). We compared and analyzed the usefulness of the D-dimer to albumin ratio (DAR) for risk stratification of AVB.MethodsIn this retrospective observational study, medical records of patients with AVB Between January 2019 and December 2020 were assessed. The primary endpoint was to evaluate whether DAR was a predictor of clinical outcomes for AVB. Receiver operating characteristic (ROC) curves were constructed using cut-off values determined by the Youden Index. Univariate and multivariate logistic regression analyses were performed to assess the factors contributing to the development of outcomes.ResultsOverall, 67 patients required intensive care. The cut-off value of DAR for patients requiring intensive care was 400. A DAR > 400 (adjusted HR: 5.636 [95% CI: 2.216–14.332]) independently predicted the need for ICU admission in these patients. Overall, 13 patients required long-term hospitalization. The cut-off value of DAR for patients requiring long-term hospitalization was 403. A DAR > 403 (adjusted HR: 9.899 [95% CI: 2.012–48.694]) independently predicted the need for long-term hospitalization. Overall, 95 patients required transfusion. The cut-off value of DAR for patients requiring transfusion was 121. A DAR > 121 (adjusted HR: 4.680 [95% CI: 1.703–12.862]) independently predicted the need for transfusion. Overall, 11 patients died during study period. The cut-off value of DAR for mortality was 450. A DAR > 450 (adjusted HR: 26.261 [95% CI: 3.054–225.827]) independently predicted mortality.ConclusionsThe DAR can be used for outcome assessment in patients with AVB with various scoring systems, but its explanatory power is not high.

Objective Early defibrillation is crucial for the survival of patients with out-of-hospital cardiac arrest. This study aimed to examine the trends and associated factors regarding public awareness and willingness to use automated external defibrillators (AEDs) through citywide surveys. Methods Three-round surveys were conducted in February 2012 (n=1,000), December 2016 (n=1,141), and December 2018 (n=1,001) among citizens in Daegu, South Korea, who were aged ≥19 years. The subjects were selected through a three-stage quota sampling. Awareness and willingness to use an AED were assessed in the three groups. The primary outcome was willingness to use AEDs. Results Of 3,142 respondents, 3,069 were eligible for analysis. The proportion of respondents who knew how to use AEDs increased from 4.7% in 2012 to 20.8% in 2018. Of the respondents in 2012, 2016, and 2018, 39.7%, 50.0%, and 43.2%, respectively, were willing to use an AED. Factors associated with willingness to use AEDs were male sex (adjusted odds ratio [AOR], 1.39; 95% confidence interval [CI], 1.10-1.75), cardiopulmonary resuscitation training experience in the previous 2 years (AOR, 1.80; 95% CI, 1.43-2.28), recognition of the Good Samaritan law (AOR, 1.45; 95% CI, 1.13-1.86), and awareness of how to use an AED (AOR, 4.40; 95% CI, 3.26-5.93). Conclusion To increase willingness to use AEDs, education in AED use and the Good Samaritan law, along with re-education to maintain knowledge of AED use, should be considered.

Background: Thoracic acute aortic syndrome (AAS) and non-ST elevation myocardial infarction (NSTEMI) have similar clinical presentations, making them difficult to differentiate. This study aimed to identify useful biomarkers for the differential diagnosis of thoracic AAS and NSTEMI. Methods: This was a retrospective observational study. Participants: consecutive adult patients who visited the emergency department for acute chest pain between January 2015 and December 2021 diagnosed with thoracic AAS or NSTEMI. Clinical variables, including D-dimer (μg/mL) and high-sensitivity troponin T (ng/mL, hs-TnT) levels, were compared between the groups. Results: A total of 52 (30.1%) and 121 (69.9%) patients were enrolled in the thoracic AAS and NSTEMI groups, respectively. Logistic regression analysis revealed that the D-dimer to hs-TnT (D/T) ratio (odds ratio (OR), 1.038; 95% confidence interval (CI), 1.020–1.056; p < 0.001) and the thrombolysis in myocardial infarction (TIMI) score (OR, 0.184; 95% CI, 0.054–0.621; p = 0.006) were associated with thoracic AAS. The D/T ratio had an area under the receiver operating characteristic curve (AUC) of 0.973 (95% CI, 0.930–0.998), and the optimal cutoff value was 81.3 with 91.4% sensitivity and 96.2% specificity. The TIMI score had an AUC of 0.769 (95% CI, 0.644–0.812), and the optimal cutoff value was 1.5 with 96.7% sensitivity and 38.5% specificity. Conclusion: the D/T ratio may be a simple and useful parameter for differentiating thoracic AAS from NSTEMI.

Acute poisoning may necessitate identification of the toxic agent; however, several acutely poisoned patients are treated with minimal laboratory assistance. We investigated whether focused referen...

Objective To investigate the effect of parental involvement in the manual reduction of pulled elbow in children. Methods We conducted a prospective case-control study from January to December 2018. The patients were under 6 years old with suspected radial head subluxation and were randomly assigned to two groups (an intervention group with a physician's and a parent's finger placed on the patient's radial head and a control group with the physician's finger only placed on the patient's radial head) according to the method of reduction. The results of a questionnaire given to the parent and physician were analyzed. Results A total of 150 patients were included in the study: 75 in the intervention group and 75 in the control group. There were no significant differences between the groups. The average number of attempts at manual reduction was 1.29 ± 0.73 in the intervention group and 1.31 ± 0.72 in the control group (P = 0.91) and the success rate of manual reduction was 96.0 and 94.7% (P = 0.70), respectively. The ease of conducting the procedure by the doctors did not show a significant difference between the two groups. However, the parents' understanding and satisfaction was significantly higher in the intervention group. Conclusion Parental involvement did not affect the procedure of physician, but it improved the understanding and satisfaction of the parents.

Objective The point-of-care ultrasound of the airway (POCUS-A) is a useful examination method but there are currently no educational programs for medical students regarding it. We designed a POCUS-A training curriculum for medical students to improve three cognitive and psychomotor learning domains: knowledge of POCUS-A, image acquisition, and image interpretation. Methods Two hours of training were provided to 52 medical students in their emergency medicine (EM) rotation. Students were evaluated for cognitive and psychomotor skills before and immediately after the training. The validity measures were established with the help of six specialists and eight EM residents. A survey was administered following the curriculum. Results Cognitive skill significantly improved after the training (38.7±12.4 vs. 91.2±7.7) and there was no significant difference between medical students and EM residents in posttest scores (91.2±7.7 vs. 90.8±4.6). The success rate of overall POCUS-A performance was 95.8%. The students were confident to perform POCUS-A on an actual patient and strongly agreed to incorporate POCUS-A training in their medical school curriculum. Conclusion Cognitive and psychomotor skills of POCUS-A among medical students can be improved via a limited curriculum on EM rotation.

Delta neutrophil index (DNI), which reflects the fraction of immature granulocytes, is used to detect infection and sepsis from noninfectious conditions, but few studies have evaluated in the early stage of acute poisoning. This retrospective observational study was performed on acute poisoning patients who visited to the emergency department (ED) and were consecutively admitted in intensive care units over 18-month period. The serial DNI, conventional inflammatory biomarkers, and culture results were obtained in the ED and after admission. The outcomes were the identification of sepsis, bacteremia, and 30-day mortality. Of 166 patients (mean age, 56.0 years) in this cohort, 59 (35.5%) had sepsis and 29 (17.5%) had bacteremia. Initial and peak DNI fractions 24 h after ED admission were strong independent predictors of sepsis development. Analysis of the area under the curve according to multiple receiver operating characteristics showed that DNI had a higher capability to predict sepsis than other parameters (0.815 for DNI, 0.700 for procalcitonin, 0.681 for C-reactive protein, and 0.741 for white blood cell). Using multivariable logistic regression analysis, it was found that DNI was an independent predictor of sepsis (95% confidence interval (CI) of odds: 1.03–1.18) and bacteremia (95% CI: 1.01–1.14). Therefore, initial and serial measurement of DNI may serve as useful risk predictor for development of sepsis or bacteremia in acute poisoning.

We prepared three new compounds [3,6-di(9H-carbazol-9-yl)phenanthrene (3,6-DCP), 2,9-di(9H-carbazol-9-yl)benzo[f]quinoline (2,9-DCBQ), and 3,9-di(9H-carbazol-9-yl)benzo[f]-quinoline (3,9-DCBQ)] containing phenanthrene or benzo[f]quinoline as an electron-withdrawing moiety and a carbazole as electron-donating moiety, respectively, as bipolar hosts for green phosphorescent organic light emitting diodes (PHOLEDs). We intentionally substituted nitrogen atom to the C-3 position of phenanthrene moiety to prepare benzo[f]quinolinegroup. And, we found that it allowed better electron transporting behavior than the phenanthrene moiety. Meanwhile, the benzo[f]quinoline/phenanthrene core moieties significantly improved the thermal stability of those host materials, which exhibited glass transition and decomposition temperatures of 132–139 and 395–427 °C, respectively. The green PHOLEDs which were fabricated with those host materials showed the lowest operating voltage of 4.7 V at 1000 cd/m2 when we used 3,9-DCBQ. Very interestingly, it has an asymmetric structure with completely separated HOMO and LUMO in space. In contrast, 3,6-DCP having phenanthrene and carbazole moieties showed much higher operating voltage of 6.1 V which imply that replacing nitrogen at the C-3 position of phenanthrene improves carrier transport, that is, electron transporting behavior. As a result, the 3,9-DCBQ-based PHOLED showed the best overall performance, exhibiting current and power efficiencies of 48.5 cd/A and 20.6 lm/W, respectively.

New bipolar host materials with the different number of benzo[f]quinoline and carbazole groups were synthesized for green phosphorescent organic light-emitting diodes (PHOLEDs). We controlled the number of the electron transporting benzo[f]quinoline moieties and the hole transporting carbazole moieties to adjust charge balance at the emitting layer (EML) with those bipolar host materials. In addition, we found that they give relatively high triplet energy level (T1 > 2.50 eV) which is suitable for green host materials. As a result, the green PHOLEDs employing those materials together with bis(2-phenylpyridine)(acetylacetonato) iridium (III) [Ir(ppy)2(acac)] as a dopant showed moderately high current efficiency up to 42.85 cd/A.

Objectives: This study aimed to use gastric point of care ultrasound (POCUS) to estimate the prevalence of an “empty stomach” among patients undergoing procedural sedation and analgesia (PSA) in the emergency department (ED) after observing the requisite fasting time at home. Methods: A prospective observational study was conducted with children with facial lacerations who made a scheduled revisit to the ED after completion of the recommended fasting time. Their stomach contents were assessed with a sagittal view of the gastric antrum by POCUS in the right lateral decubitus position. The characteristics of gastric contents were described as empty, solid, and liquid with an estimated gastric volume. “Empty stomach” was defined as a collapsed gastric antrum or calculated a gastric fluid volume of less than or equal to 1.25 mL/kg on POCUS. Results: Gastric POCUS was performed in 125 patients, and the final analysis included 122 patients. For 95 patients who had followed the recommended fasting time, the median fasting time was 7 hours for solids and 6 hours for liquids, and 78 (82%) patients had an empty stomach. Conversely, seven of 27 patients (26%) who did not have an adequate fasting time had an empty stomach. The optimal cut-off value of fasting time to predict an empty stomach was 6.5 hours based on a receiver operating characteristic (ROC) analysis (sensitivity = 0.767, specificity = 0.811). Conclusions: Most scheduled revisiting children had an “empty stomach” at the time of sedation after the recommended fasting. However, providers should be aware that one in five children still had stomach residue, although they had more than 6 hours of fasting.

Background. Clinical presentations of acute appendicitis (AA) and acute right-sided colonic diverticulitis (ARCD) are similar. However, the usual treatment for each disease differs between surgical and conservative management. The aim of this study was to identify clinical differences between AA and ARCD. Method. We performed a single-center retrospective study on adult patients, with uncomplicated AA and ARCD confirmed by computed tomography, who visited an emergency department between March 2018 and August 2019. Clinical variables including past medical history, presented symptoms and signs, and laboratory findings were compared between the two groups. A logistic regression analysis was subsequently performed to differentiate ARCD from AA based on results of univariate analyses. Results. A total of 212 (79.1%) and 56 (20.9%) patients were enrolled in AA and ARSD groups, respectively. Logistic regression analysis revealed that a past history of diverticulitis [OR: 102.679 (95% CI: 9.964–1058.055), p<0.001] was associated with ARCD, while ketonuria [OR: 2.907 (95% CI: 1.091–7.745), p=0.033], anorexia [OR: 21.544 (95% CI: 3.905–118.868), p<0.001], and neutrophilia [OR: 3.406 (95% CI: 1.243–9.336), p=0.017] were associated with AA. Conclusion. Anorexia, neutrophilia, and ketonuria were predictors of AA while a history of diverticulitis was a predictor of ARCD.

We report a simple rinsing process to enhance the conductivity of printed carbon nanotube (CNT) electrodes. Polystyrene sulfonate(PSS)-wrapped CNTs were well dispersed in ethanol for printing via electrohydrodynamic (EHD) jet printing. PSS as a surfactant reduces the conductivity of CNT electrodes, restricting their applications in electronic devices. Even though the PSS rinsing process is necessary, it promotes delamination of CNTs. The challenges associated with the rinsing process and the delamination of CNTs were overcome in this study by introducing a polymer, poly(vinyl butyral-co-vinyl alcohol-co-vinyl acetate) (P(VB-co-VA-co-VAc)) as an adhesion layer. The use of P(VB-co-VA-co-VAc) increased the adhesion between the CNTs printed by the EHD jet technique and the underlying substrate during the CNT rinsing process. The rinsing process led to a significant enhancement in the conductivity of the CNT electrodes, and these electrodes were applied to organic field-effect transistor devices based on TIPS-pentacene. The device exhibited a high field-effect mobility of 0.25 cm2/(V·s).

Purpose: Sonongraphic examinations such as extended Focused Assessment with Sonography in Trauma (eFAST) are widely used in Emergency Departments. This study is designed to determine student achievement by teaching medical college students through short training. Methods: 38 participants in their 3rd year of medical school were enrolled in this study. An Emergency Medicine physician trained the students to 2 hours of theoretical training followed by 2 hours of hands on training. Results: The average age of students was 28.1±3.4, with 21 male students. The average of pre-educational test results were 60.4±8.9 and post-educational exam results were 80.1±14.5 (p

With the growth of financial industry with smartphone, interest on user authentication using smartphone has been arisen in these days. There are various type of biometric user authentication techniques, but gait recognition using accelerometer sensor in smartphone does not seem to develop remarkably. This paper suggests the method of user authentication using accelerometer sensor embedded in smartphone. Specifically, calibrate the sensor data from smartphone with 3D-transformation, extract features from transformed data and do principle component analysis, and learn model with using gaussian mixture model. Next, authenticate user data with confidence interval of GMM model. As result, proposed method is capable of user authentication with accelerometer sensor on smartphone as a high degree of accuracy(about 96%) even in the situation that environment control and limitation are minimum on the research.

This paper reviews the 6-Month Challenge Platform Program, a short-term intensive start-up supporting program in Korea, which will be launched late 2015 to promote economic growth by taking new ideas and transforming them into new products and start-ups in connection with the Creative Economy Town and the Creative Economy Innovation Centers under the Creative Economy Policy.

Acute kidney injury (AKI) is a serious complication in intoxicated patients. Recently, a new biomarker - neutrophil gelatinase-associated lipocalin (NGAL) - was used to predict AKI in patients who were critically ill or had sepsis.To evaluate the utility of plasma NGAL as an early predictor of AKI in adults with acute poisoning.This retrospective, observational, cohort study was conducted between December 2013 and November 2014. A total of 157 consecutive adult patients who presented to the emergency department (Level 1 regional center) of Kyungpook National University Hospital, a tertiary teaching hospital in Daegu, Korea, within 24 h of poisoning were included. Initial plasma NGAL levels and laboratory parameters were concurrently measured upon hospital arrival. AKI was defined according to Acute Kidney Injury Network criteria. Development of AKI was predicted using plasma NGAL levels and by analyzing the area under the receiver operating characteristic curve (AUC).The overall rate of AKI was 14.6% (n = 23). Plasma NGAL levels in the AKI group were higher than those in the non-AKI group (median, 310 vs. 86 ng/mL; p0.001). Additionally, baseline NGAL levels allowed for better prediction of AKI than initial creatinine levels. The AUC of plasma NGAL was 0.895 (95% confidence interval [CI]: 0.832-0.941), with a cut-off value of 227 ng/mL (sensitivity, 76.2%; specificity, 95.8%). Plasma NGAL had a higher predictive capacity for AKI than serum creatinine (AUC 0.741, 95% CI: 0.662-0.810), base deficit (AUC 0.795, 95% CI: 0.701-0.870), lactate (AUC 0.781, 95% CI: 0.690-0.856), and anion gap (AUC 0.636, 95% CI: 0.535-0.730).Plasma NGAL may serve as a good predictor of AKI in cases of adult poisoning.

Validation of the anatomically complex configurations of the Lumbar Puncture Simulator II (KYOTO KAGAKU CO., LTD., 15 Kitanekoya-cho Fushimi-ku Kyoto, Japan 612-8388) have not been reported. Previous validation of the normal anatomic configuration has been reported. This study aims to evaluate evidence for construct and content validity of 4 interchangeable lumbar puncture (LP) complex anatomic configurations of this simulator.We performed a cross-sectional study between April 2018 and May 2019. Novice volunteer medical students and expert physicians who had performed over 30 LP procedures performed sequential LP procedures on each of 4 simulated interchangeable anatomic LP puncture blocks (normal, obesity, geriatric, combined geriatric/obesity). Primary outcome measures compared between groups for each LP procedure were return of cerebrospinal fluid within 5 minutes and a calculated performance score. Subjective face validity and content validity 5-point Likert questionnaires were completed by participants.35 novice (n = 19) and expert (n = 16) subjects completed 140 procedures. Significant differences were found between novice and expert groups for both cerebrospinal fluid success rates and performance scores for normal (P = .001/P = .001) geriatric (P = .005/P = .002) and obesity (P = .003/P = < .001) configurations. There were no differences for the geriatric/obesity configuration. Expert median score of simulator realism (face validity) was 4 (range 3-4); median score of utility as a training tool (content validity) was 4 (range 4-5).We provide evidence for construct validity for each of the complex LP configurations, except combined geriatric/obesity. Expert physicians found the simulator sufficiently realistic to effectively teach LP skills.

Background Bicycling is an increasingly popular recreation and mode of transportation in korea. Improved understanding of sex and gender-specific differences in epidemiologic features and clinical outcomes in bicycling injuries could help to understand bicycle-related injuries and develop preventative strategies. Aims This study aimed to investigate sex and gender-specific differences in epidemiologic features and clinical outcomes in bicycling injuries. Methods This is a cross-sessional study based on the Emergency Department(ED)–based Injury In-depth Surveillance(EDIIS) database from 23 EDs in Korea. All of injured bicyclists between January 1, 2011. and December 31, 2016. were eligible, excluding cases with unknown outcomes. The primary outcome was intracranial injury and the secondary outcomes were in-hospital mortality and clinical important injury (admission or in-hospital death). We calculated adjusted odds ratios (AORs) of gender(male) for study outcomes after adjusting for potential confounders. Results Among 24 306 eligible patients, 19 286 (79.3%) patients were male and 5 020 (20.7%) were female. The rate of helmets use was no diferrence(10.6% in male and 10.2% in female, respectively). Bicycling injuries of male occurred more in child and adolescent, evening and night(all p Discussion and conclusions There were gender-specific differences in epidemiologic features and clinical outcomes in bicycling injuries. Bicycling injuries of male occurred more in child and adolescent and had more severe outcomes than female. Preventative strategies to reduce the bicycling injuries targeting male (esp, child and adolescent male) are needed.

The effects of titanium content on the weld microstructure, mechanical properties, and inclusion characteristics were investigated in the as-deposited bainitic GMA weld metals having nearly constant level of oxygen content. It was found that titanium addition enhanced the formation of acicular ferrite with the maximum proportion being obtained at ∼0.07 wt% Ti. The resultant change in weld microstructure with titanium content was well reflected in the Charpy impact toughness showing the lowest ductile-brittle transition temperature at 0.07 wt% Ti. Detailed TEM and STEM analysis preformed on weld metal inclusions demonstrated that the maximum acicular ferrite recorded in this weld is mainly attributable to the formation of manganese-depleted zone (MDZ) associating with the formation of nonmetallic inclusions dominant with Ti2O3 phase.

A policy is a set of ideas or plans that is used as a basis for making decisions, especially in politics, economics, or business, and it serves as a reference for the organization's activities or specific individual. In this sense, it is important to strengthen the capability of security performance. When it comes to Industrial Control Systems (ICS) which considerably affect the national security, policy compliance with consideration of ICS's characteristic is crucial. This paper is based on data from evaluating the degree of compliance of specific country's infrastructure with survey. Method used in this paper consists of four steps. First, an employee of specific company participates as a subject and evaluates the compliance of his/her organization with personal discretion. Second, determine criteria for further analysis. Third, analyze data for existence and compliance of policy. Fourth, calculate 'Policy- Domain-System (P-D-S)' index from data processed in the previous step. PDS and ISMS data can be used at the same time. This paper will contribute the efficiency of existing ISMS standard.

Noncovalent approach for formulating organo-soluble assembly of chemically reduced graphene oxide (rGO) with hydrophobic semiconducting polymer was demonstrated for the first time by utilizing a mi...

판재를 강관으로 제조할 경우 내경의 변형이 없다고 가정하면 외경으로 갈수록 변형량이 증가한다. 본 실험에서는 판재 중심부의 변형량을 기준으로 하였고, 강관제조사에서 19.5mm 판재는 외경이 914mm 강관을, 25mm 판재는 외경이 765mm 강관을 제조함으로 이를 기준으로 변형량을 계산하였다. 내경과 중심부 원길이 변화를 계산하면 19.5mm 판재의 중심부는 2.2%로 변형되며, 25mm는 3.5% 변형된다. 따라서 19.5mm 판재는 각각 2, 4, 6% 변형을 주었으며, 25mm 판재는 각각 3, 5, 7% 변형을 주었다. 변형은 300 ton 인장시험기를 사용하였으며, 소성변형 후 100mm ×20mm×강관두께가 되도록 HIC 시편 3개씩 채취하였고, 무변형의 시편도 채취하였다. 시편 절단시 변형된 표면이 충분히 제거되도록 모든 면을 기계가공하고, 순차적으로 연마한 다음 320번의 연마지로 최종 연마한 후 최종적으로 아세톤으로 탈지하였다. 탈지 후 SAM(scanning acoustic microscope)을 이용하여 2차원 초음파 탐상으로 초기 시편의 결함상태를 관찰하였다.

The morphological and chemical nature of the inclusions in flux cored arc welding (FCAW) weld metal of E71T-1 grade were analyzed in SEM/TEM/scanning transmission electron microscope (STEM) equipped with energy-dispersive X-ray (EDX) to understand the sequence of inclusion formation and to verify the absence of the Mn-depleted region in close proximity to the inclusion surface. Basically, all the inclusions were nearly spherical in shape and chemically a mixture of Ti-rich oxide and (Si,Mn)-rich oxide partly covered with MnS phase. From the morphological features of each phase, the formation sequence of the inclusion can be predicted in the order of Ti-rich solid oxide, (Si,Mn)-rich liquid oxide, and MnS phase. The MnS phase always presented on the surface of the (Si,Mn)-rich liquid oxide and was fully confined within the outer circle of the inclusion implying that it was formed from (Si,Mn)-rich oxide. STEM/EDX analysis performed on the MnS phase and its neighbor did not show any Mn depletion over a distance of about 70 nm from the outer surface of the MnS phase.Based on these results, it could be concluded that as the MnS phase was formed from the liquid (Si,Mn)-rich oxide, the manganese concentration in the steel matrix cannot be varied.

This study evaluated the cold cracking susceptibility of high-strength bainitic steels having a strength level of over 800 MPa and 1.1 GPa according to their respective chemical compositions. For evaluation of cold cracking susceptibility, a modified implant test was employed. Two different shielding gases (100% CO2 gas and 98% CO2 mixed with 2% H2 gas) were used to estimate the effect of diffusible hydrogen on the cold cracking. The diffusible hydrogen contents measuring 100% CO2 and 98% CO2+2% H2 gas were recorded as 0.58 and 9.01 ml/100 g, respectively. In the case of the lower hydrogen content, cold cracking susceptibility was very low in spite of the very high strength of the base steel regardless of chemical composition and rolling condition. However, when the mixed shielding gas was used, cold cracking susceptibility increased due to an increase in the hydrogen content. Most notably, the cold cracking resistance of steels containing higher alloy content deteriorated significantly due to the higher hardness of the coarsegrained heat-affected zone. However, the effect of the rolling condition on the cold cracking susceptibility turned out to be negligible compared to that of the chemical composition.

GMA(gas metal arc) 용접은 높은 생산성, 높은 용접품질, 자동화의 용이성으로 인하여 널리 이용되고 있으며, 또한 탄소강, 저합금강, 스테인리스, 알루미늄, 구리, 티타늄과 니켈합금과 같이 다양한 합금들의 용접이 가능하다. GMA 용접에서의 큰 특징은 소모성전극 끝단의 용융금속이 아크를 통하여 모재로 이행되거나 또는 모재에 접촉하여 이행되는 것이다. 이러한 금속이행은 용입깊이, 비드모양, 흄발생, 공정의 안정성과 스패터에 영향을 주며, 전류, 전압, 극성, 와이어 돌출길이, 보호가스 조성과 전극직경에 의하여 영향을 받는다

In the 21st century, knowledge is an important asset to improve productivity in the business world. In today`s rapidly changing business environment, companies have rigorously brought in knowledge management system in order to secure the sustainable competitiveness and effective knowledge management. Knowledge management has now become mandatory, not optional. Today many companies which have built knowledge management on top of information technology and hardware-based infrastructure are having a difficulty in creating organizational culture in knowledge management. Even though companies have invested substantial time and money in knowledge management, the performances have not met their expectations. To solve this problem, software oriented strategy for knowledge management such as education and networking is more needed rather than hardware oriented strategy such as information technology systems. Though the knowledge management framework suggested in this study is exploratory, this study contributes to the clarification of the critical elements that companies which are about to build knowledge management should take in account.

Morphologically, the acicular ferrite (AF) microstructure developed in ferritic weld metal has been widely described as having an “interlocking structure” or “basket weave structure,” following its fine nature of the optical microstructure revealed by 2 % Nital etching solution. However, the grain or effective grain size of AF, which controls the fracture unit, is not well understood. In this study, we attempted to develop the morphological grain structure of AF by using a newly-developed electro-chemical etching technique and then determined the crystallographic grain structure using EBSD analysis with misorientation angles. Both of these grain structures were then compared to the cleavage facet size measured from the brittle fracture surface. As a result, the morphological grain boundaries revealed by electro-chemical etching were found to match the crystallographic boundaries developed by EBSD. It was also demonstrated that the crystallographic grains with tolerance angles of 15° or higher, i.e., high-angle boundaries, were similar in size to the cleavage facets. From these results, it was concluded that the effective grain size of AF can be determined by EBSD and can be estimated by the electro-chemical etching technique.

Due to the practical limitations of lowering the diffusible hydrogen content of flux-containing welding consumables, it is now felt that modification of the weld microstructure would alleviate the risk of weld metal cracking in multi-pass weld deposits. Thus, this study aimed to identify and evaluate the effect of the weld microstructure on the cold cracking susceptibility of FCAW weld metals and then to provide a basic guideline for designing new welding consumables from a microstructural point of view. In order to identify the parameter(s) that can quantify the microstructural susceptibility of multi-pass weld deposit, two sets of FCAW wires with tensile strength of about 600 MPa were prepared by controlling the Ni content to allow sufficient variation in the weld microstructure, but with little change in weld metal strength. The cold crack susceptibility of those two chemistries was evaluated by a multi-pass weld metal cracking test at various levels of diffusible hydrogen content. All of the cold cracks developed were Chevron-type, and the occurrence of such cracks depended upon the proportion of grain boundary ferrite (%GF) as well as the diffusible hydrogen (HD) content. In fact, at the same level of HD, higher Ni (1.5%Ni) wire showed better resistance to cold cracking than lower Ni (0%Ni) wire even though the latter was stronger and also higher in carbon equivalent. This result could be explained solely by the difference in grain boundary ferrite content between those two welds since Chevron cracking preferentially initiates at and propagates along grain boundary ferrite. Therefore, we propose the use of a value of %GF as a parameter to quantify the microstructural susceptibility of ferritic multipass weld deposit with a strength level of about 600 MPa. It was further suggested that, in addition to the hydrogen control approach, microstructural modification in the form of reducing the %GF can be pursued to develop welding consumables with improved resistance to cold cracking.

Facing the practical difficulties in reducing the diffusible hydrogen content of fluxcontaining welding consumables like flux-cored arc welding (FCAW) wires, the present study investigated the microstructural aspect to improve the hydrogen-induced cold crack (HICC) resistance of multipass weld metal of 600MPa strength. Two FCA welding wires were prepared by controlling the Ni content to give different weld microstructure, but to have similar levels of hardness and diffusible hydrogen content. HICC susceptibility of those two consumables was evaluated by 'G-BOP test' and also by 'multi-pass weld metal cold cracking test'. As a result of this study, it was demonstrated that microstructural modification with decreased proportion of grain boundary ferrite (GF) improved cold crack resistance of weld metal. The detrimental effect of GF against HICC has also been addressed based on the characteristics of weld metal cold cracking.