Junhyung Lee

Ni-based bulk amorphous alloys in the Ni–Ti–Zr–Si system

Abstract We report on the fabrication and properties of the new Ni-based bulk amorphous alloys in the Ni–Ti–Zr–Si system that have high glass forming ability (GFA) and large undercooled region (ΔTX), which corresponds to the temperature difference between glass transition temperature and the onset temperature of a first crystallization event. The compositional range for the formation of the amorphous alloys that have large ΔTX (>30 K ) is defined in the pseudo-ternary phase diagram Ni–(Ti,Zr)–Si. Some alloys can be fabricated as fully amorphous rods 2 mm diameter through an injection casting method. Si effects on the crystallization behavior of these new Ni-based amorphous alloys are also investigated and related to the GFA and the ΔTX.

Formation of icosahedral phase from amorphous Zr65Al7.5Cu12.5Ni10Ag5 alloys

The kinetic behavior of quasicrystalline phase formation in amorphous Zr65Al7.5Cu12.5Ni10Ag5 alloys has been studied by using differential scanning calorimetry (DSC), x-ray diffractometry, and transmission electron microscopy. DSC trace obtained during continuous heating from 473 to 873 K shows two distinct exotherms with peak temperatures of 727 and 776 K. The first and second exothermic reactions, respectively, correspond to the formation of quasicrystalline phase from the amorphous matrix and the formation of tetragonal CuZr2 and hexagonal Zr6NiAl2 phases from the previously formed quasicrystalline phase. Partial replacement of Cu by Ag enhanced the formation of quasicrystalline phase from the amorphous structure. Johnson–Mehl–Avrami analysis of isothermal transformation data suggests that the formation of quasicrystalline phase is not entirely polymorphic in nature and may involve partitioning of solute at a later stage.

The 12 September 2016 ML5.8 midcrustal earthquake in the Korean Peninsula and its seismic implications

The seismicity in the Korean Peninsula has increased since the 2011 Mw9.0 Tohoku-Oki megathrust earthquake. Two strike-slip earthquakes with magnitudes of ML5.1 and 5.8 occurred in the southeastern Korean Peninsula on September 12, 2016. The two events occurred within 48 minutes. The ML5.8 earthquake was the largest event in the Korean Peninsula since 1978 when national seismic monitoring began. Both events produced strong high-frequency ground motions. More than 500 aftershocks with local magnitudes greater than or equal to 1.5 followed the events for two months. An unreported subsurface strike-slip fault with a dip of 65∘ to the east and a strike of N27∘ E was responsible for the earthquakes. The fault ruptured at depths of 11-16 km, resulting in a rupture plane of ∼26 km2. The aftershock distribution displayed horizontal streaks at a depth of ∼14 km, which was consistent with the focal mechanism solutions from long-period waveform inversion. The number of aftershocks decreased exponentially with time. The two ML5.1 and 5.8 earthquakes produced regional Coulomb stress changes of -4.9 to 2.5 bar. The spatial distribution of the aftershocks correlated with the Coulomb stress changes. The peak dynamic stress induced by strong ground motions reached 14.2 bar. The groundwater levels changed coseismically in some regions of decreased static stresses. The earthquakes on previously unidentified faults raised attention for the potential seismic hazards by earthquakes with long recurrence intervals.

Time-advanced occurrence of moderate-size earthquakes in a stable intraplate region after a megathrust earthquake and their seismic properties

The distance-dependent coseismic and postseismic displacements produced by the 2011 MW9.0 Tohoku-Oki megathrust earthquake caused medium weakening and stress perturbation in the crust around the Korean Peninsula, increasing the seismicity with successive ML5-level earthquakes at the outskirts of high seismicity regions. The average ML5-level occurrence rate prior to the megathrust earthquake was 0.15 yr−1 (0.05–0.35 yr−1 at a 95% confidence level), and the rate has increased to 0.71 yr−1 (0.23–1.67 yr−1 at a 95% confidence level) since the megathrust earthquake. The 2016 ML5-level midcrustal earthquakes additionally changed the stress field in adjacent regions, inducing the 15 November 2017 ML5.4 earthquake. The successive 2016 and 2017 moderate-size earthquakes built complex stress fields in the southeastern Korean Peninsula, increasing the seismic hazard risks in the regions of long-term stress accumulation. The increased seismic risks may continue until the medium properties and stress field are recovered.

Transcatheter arterial embolisation for acute lower gastrointestinal haemorrhage: a single-centre study

ObjectiveTo investigate the safety and efficacy of transcatheter arterial embolisation (TAE) in the management of lower gastrointestinal bleeding (LGIB) and to identify predictors of clinical outcomes.MethodsBetween December 2005 and April 2017, 274 patients underwent diagnostic angiography for signs and symptoms of LGIB; 134 patients with positive angiographic findings were retrospectively analysed. The technical success of TAE and clinical outcomes, including recurrent bleeding, major complications, and in-hospital mortality were evaluated. The associations of various clinical and technical factors with clinical outcomes were analysed. Predictors for clinical outcomes were evaluated using univariate and multivariate logistic regression analyses.ResultsA total of 134 patients (mean age, 59.7 years; range, 14–82 years) underwent TAE for LGIB. The bleeding foci were in the small bowel in 74 patients (55.2%), colon in 35 (26.1%), and rectum in 25 (18.7%). Technical success was achieved in 127 patients (94.8%). The clinical success rate was 63% (80/127). The rates of recurrent bleeding, major complications, and in-hospital mortality were 27.9% (31/111), 18.5% (23/124), and 23.6% (33/127), respectively. Superselective embolisation and the use of N-butyl cyanoacrylate (NBCA) were significant prognostic factors associated with reduced recurrent bleeding (OR, 0.258; p = 0.004 for superselective embolisation, OR, 0.313; p = 0.01 for NBCA) and fewer major complications (OR, 0.087; p ˂ 0.001 for superselective embolisation, OR, 0.272; p = 0.007 for NBCA).ConclusionsTAE is an effective treatment modality for LGIB. Superselective embolisation is essential to reduce recurrent bleeding and avoid major complications. NBCA appears to be a preferred embolic agent.Key Points• Transcatheter arterial Embolisation (TAE) is a safe and effective treatment for lower gastrointestinal tract haemorrhage.• Superselective embolisation is essential to improve outcomes.• N-butyl cyanoacrylate (NBCA) appears to be a preferred embolic agent with better clinical outcomes.

Safety and effectiveness of transarterial embolization for splenic artery hemorrhage in patients undergoing radical gastrectomy

Background Perigastric lymph nodes are dissected during gastrectomy, potentially resulting in life-threatening postoperative bleeding. Purpose To evaluate the safety and effectiveness of transarterial embolization (TAE) for bleeding from the splenic artery in patients who underwent gastrectomy. Material and Methods Between January 2004 and December 2016, 14,523 patients underwent gastrectomy at our institution, and ten patients (nine men; mean age = 64.7 years; age range = 51–80 years) underwent TAE for postoperative bleeding from the splenic artery. The location of bleeding was classified as either: (i) the main splenic artery (MSA) or (ii) the parenchymal splenic artery (PSA). The clinical outcomes of TAE were explored. Results Bleeding occurred at a median of 13.5 days (range = 4–34 days) after gastrectomy. The onset of bleeding was late in all patients and clinically manifested as abdominal bleeding in seven patients and luminal bleeding in three patients. Technical and clinical success rates were 100% and 70%, respectively. The three major complications occurred only in patients with MSA bleeding, resulting in two 30-day mortality cases and one splenic abscess with fistula formation to the jejunum. The causes of death were infarctions in the spleen and/or remnant stomach and sepsis. Conclusion TAE seems to be effective in stabilizing patients with bleeding from the splenic artery. Moreover, TAE with curative intent may be performed for bleeding from the PSA; however, further resection of the remnant stomach and/or spleen seems to be required to avoid sepsis and mortality in case of bleeding from the MSA.

Variable Speed Limits Model to Minimize Confliction without Change in Total Travel Time Using Queuing Theory

Variable Speed Limits can affect safety and congestion. To estimate the effects of variable speed limits, the operation value should be calculated with queuing theory. In this model after ts minutes since congestion occurred, the queue length is checked and variable speed limits operation would be started. Under this condition, cars pass the modeling area without congestion within the same travel time with non-controlled condition. The confliction under VSL and that under non-controlled condition were compared using SSAM.