• 한국정밀공학회지
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• 제18권5호
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• pp.98-104
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• 2001

A dynamic fracture toughness test method with a chevron notched ceramic specimens is proposed. The notch angles of the chevron specimens were 90, 100$^{\circ}$and 110$^{\circ}$. Finite element analysis(FEA) were done to determine the geometrical properties of chevron-notch specimens according to notch angles. The static fracture toughness of the chevron notched alumina specimen was 3.8MP$\alpha$√m similar to that of the general fracture specimen with a precrack. Dynamic fracture toughness was 4.5 MP$\alpha$√m slightly higher than the static one. These research showed the possibility of the split Hopkinson pressure bar test method using the newly proposed chevron notched specimens to get the dynamic fracture toughness of extremely brittle materials such as ceramics.

• 한국중재학회지:중재연구
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• 제25권4호
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• pp.3-23
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• 2015

The Chevron saga including Chevron/TexPet v. Ecuador, PCA Case No. 34877(hereinafter referred to as "Chevron I") and Chevron/TexPet v. Ecuador, PCA Case No. 2009-23(hereinafter referred to as "Chevron II") started out of domestic litigations between TexPet and Ecuador in the early 1990s. In Chevron I, the Tribunal decided that Article 2(7) of the U.S.-Ecuador BIT on effective means of provision was breached because of undue delays in the seven legal proceedings TexPet had brought against Ecuador in respect to contractual obligations. In Chevron II, it was contended that through the actions and inactions of the judiciary and the executive, Ecuador breached her several obligations under the BIT. Ecuador objected to the jurisdiction of the Tribunal because TexPet's investment was terminated in 1992, and because Chevron is not a party to the 1995 Settlement Agreement and 1998 Final Release. In its Interim Award on Jurisdiction and Admissibility, the Tribunal applied a prima facie standard to the facts alleged by the Claimants but denied by the Respondent, and decided that questions in respect of the Respondent's jurisdictional objections should be joined to the merits under Article 21(4) of the UNCITRAL Arbitration Rules. In the merits phase of Chevron II, the Tribunal divided the merits of the Parties' dispute into two parts, entitled "Track 1" and "Track 2". In its Partial Award on Track 1, the Tribunal decided that Chevron is a "Releasee" under the 1995 Settlement Agreement. In a decision on "Track 1B", the Tribunal decided that the Lago Agrio complaint cannot be read as pleading "exclusively" or "only" diffuse claims, and that, to this extent, the Claimants' reliance on the 1995 Settlement Agreement as a complete bar to the Lago Agrio complaint must fail, as a matter of Ecuadorian law. The Tribunal maintained the position that the Parties' disputes on both merit and jurisdiction should be reserved for Track 2. It remains to be seen how the Tribunal addresses the Claimants' allegations of multiple denials of justice under international law against the judgments of the Respondent's Courts, together with the Respondent's jurisdictional objections in Track 2 of the arbitration.

• 설비공학논문집
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• 제30권4호
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• pp.175-185
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• 2018

This research investigates the internal flow and heat transfer in a plate heat exchanger with chevron shape by utilizing the computational fluid dynamics (CFD) software. The basic unit of the plate heat exchanger is generally composed of a hot channel, an intermediate chevron plate, and a cold channel. Several studies have reported experimental and numerical simulation of heat transfer and pressure drop. This study focused on the detailed numerical simulation of flow and heat transfer in the complicated chevron shape channel. The long chevron plate was designed to include 16 chevron patterns. For proper mesh resolution, the number of cells was determined after the grid sensitivity test. The working fluid is water, and its properties are defined as a function of temperature. The Reynolds number ranges from 900 to 9,000 in the simulation. A realizable $k-{\varepsilon}$ model and non-equilibrium wall function are properly considered for the turbulent flow. The friction factors and heat transfer coefficient are validated by comparing them with existing empirical correlations, and other patterned flow phenomena are also investigated.

• 대한족부족관절학회지
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• 제10권2호
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• pp.230-233
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• 2006

Purpose: The distal chevron osteotomy has gained popularity for the mild to moderate hallux valgus, but necessity of fixation is controversy. No fixation of distal chevron osteotomy cause instability, but fixation has problem which has pin site infection and irritability, extension of operation time, discomfort of rehabilitation. So, the author was going to analyse and compare with and without in the fixation of distal chevron osteotomy. Materials and Methods: Between 2004 and 2005, a total 18 patients (20 feet) following with and without in fixation of distal chevron osteotomies. The fixation group (A) was performed for the treatment of 10 patients (10 feet) and no fixation group (B) was done to 8 patients (10 feet). Results: On group A, the mean first MTP (metatarsophalangeal) angle corrected $17^{\circ}$ pre-operatively to average $29^{\circ}$ (range; $20-37^{\circ}$) and the mean first IM (intermetatarsal) angle corrected $10^{\circ}$ pre-operatively to average $15^{\circ}$ (range; $9-18^{\circ}$). On Group B, the mean first MTP angle corrected $16^{\circ}$ pre-operatively to average $29^{\circ}$ (range; $18-33^{\circ}$) and the mean first IM angle corrected $7^{\circ}$ pre-operatively to average $13^{\circ}$ (range; $9-16^{\circ}$) (P>0.05). Clinical results, based on AOFAS score showed an improvement in the overall results. Conclusions: Comparing the clinical and radiographic results of the distal chevron osteotomies no difference in with and without fixation of distal chevron osteotomies.

• Earthquakes and Structures
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• 제19권4호
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• pp.303-313
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• 2020

Spacious experimental and numerical investigation has been conducted by researchers to increase the ductility and energy dissipation of concentrically braced frames. One of the most widely used strategies for increasing ductility and energy dissiption, is the use of energy-absorbing systems. In this regard, the cyclic behavior of a chevron bracing frame system equipped with multi-pipe dampers (CBF-MPD) was investigated through finite element method. The purpose of this study was to evaluate and improve the behavior of the CBF using MPDs. Three-dimensional models of the chevron brace frame were developed via nonlinear finite element method using ABAQUS software. Finite element models included the chevron brace frame and the chevron brace frame equipped with multi-pipe dampers. The chevron brace frame model was selected as the base model for comparing and evaluating the effects of multi-tube dampers. Finite element models were then analyzed under cyclic loading and nonlinear static methods. Validation of the results of the finite element method was performed against the test results. In parametric studies, the influence of the diameter parameter to the thickness (D/t) ratio of the pipe dampers was investigated. The results indicated that the shear capacity of the pipe damper has a significant influence on determining the bracing behavior. Also, the results show that the corresponding displacement with the maximum force in the CBF-MPD compared to the CBF, increased by an average of 2.72 equal. Also, the proper choice for the dimensions of the pipe dampers increased the ductility and energy absorption of the chevron brace frame.

• 한국공간구조학회논문집
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• 제20권3호
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• pp.53-61
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• 2020

This paper presents a systematic numerical analysis to obtain the re-centering and energy dissipation capacities of Chevron braced steel frames subjected to seismic loadings. In order to develop a recentering seismic resistance system excluding a residual deformation, the chevron braced steel frames are assembled using super-elastic SMA (Shape Memory Alloy) braces. The three-dimensional nonlinear finite element models are constructed to investigate the horizontal stiffness, hysteretic behaviors, and failure modes of the re-centering Chevron bracing system.

• 대한족부족관절학회지
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• 제8권1호
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• pp.64-70
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• 2004

Purpose: We compared the result of a proximal metatarsal closed wedge osteotomy and soft tissue procedure with a modified chevron osteotomy and soft tissue procedure in the treatment of hallux valgus. Materials and Methods: Between March 1999 and February 2003, we performed proximal metatarsal closed wedge osteotomy and soft tissue procedure on 17 feet (12 patients), and modified chevron osteotomy and soft tissue procedure on 12 feet (9 patients). Results: According to Mayo clinic forefoot scoring system (FFSS), group 1, with proximal metatarsal closed wedge osteotomy, shows 67.2 points postoperatively and group 2, with modified chevron osteotomy, shows 68.5 points postoperatively. In group 1, the average correction of hallux valgus angle and intermetatarsal angle was 20.8 degrees and 4.8 degrees, respectively. In group 2, the average correction of hallux valgus angle and intermetatarsal angle was 19.9 degrees and 4.7 degrees, respectively. The average shortening was 3.15 mm in group 1 and 1.38 mm in group 2. Conclusion: We obtained relatively good clinical and radiographic result in this study. The effect on shortening of the first metatarsal was greater in the proximal metatarsal closed wedge osteotomy than modified chevron osteotomy, but the metatarsal shortening did not related with metatarsalgia. So, both techniques seems optimal surgical treatment for hallux valgus deformity.

• 대한족부족관절학회지
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• 제18권2호
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• pp.56-61
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• 2014

Purpose: This study was conducted among patients with moderate to severe hallux valgus who underwent distal chevron osteotomy and groups of patients with or without Akin osteotomy were compared for evaluation of the relationship between their radiological and clinical outcomes. Materials and Methods: From January 2009 to January 2012, among patients with moderate to severe hallux valgus who underwent distal chevron osteotomy at our institution, 28 cases with additional Akin osteotomy and 35 cases without Akin osteotomy available to follow up of more than one year were included in this study. For radiologic evaluation, hallux valgus angle, 1, 2 intermetatarsal angle, and hallux interphalangeal angle were measured before and after surgery. For clinical assessment, visual analogue scale score, American Orthopaedic Foot and Ankle Society score, subjective satisfaction of the patients, and passive range of motion of the first metatarsophalangeal joints were evaluated. Results: At the final follow up, correction of valgus hallux angle and 1, 2 intermetatarsal angle was obtained from radiation results of both groups and it was found that patients who underwent Akin osteotomy showed radiographically larger angle correction but less subjective satisfaction. Conclusion: Patients with moderate to severe hallux valgus who underwent distal chevron osteotomy showed not only functional but also radiographically satisfactory results, and patients who underwent additional Akin osteotomy showed decreased subjective satisfaction. Therefore, if an incongruent first metatarsophalangeal joint is not observed, distal chevron osteotomy without Akin osteotomy seems preferable.

• 대한족부족관절학회지
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• 제9권2호
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• pp.146-150
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• 2005

Purpose: We made a radiological comparison between $60^{\circ}$ distal Chevron osteotomy with short armed two parts and $40^{\circ}$ distal Chevron osteotomy with long armed one part performing operation in cases of hallux valgus angle of less than $40^{\circ}$, intermetatarsal angle of less than $15^{\circ}$. Materials and Methods: 12 cases with $60^{\circ}$ distal Chevron osteotomy and 12 cases with $40^{\circ}$ distal Chevron osteotomy were selected from October 2000 to March 2005. We have analysed the hallux valgus angle, 1-2 intermetatarsal angle, metatarsal length, distal metartarsal articular angle and angulation at osteotomy site on lateral view in each radiological films taken at preoperative, postoperative and 3 months after operation presuming bone union. All cases were women, both sides were 9 cases and average age was 52.3 years old. Results: Data taken at preoperative, postoperative and 3 months follow up films in $60^{\circ}$ distal Chevron osteotomy were as follows; the hallux valgus angles were $32.1^{\circ}$, $10.9^{\circ}$, $13.8^{\circ}$, the 1-2 intermetatarsal angles were $13.6^{\circ}$, $8.5^{\circ}$, $8.4^{\circ}$, the metatarsal length were 60.6 mm, 58.8 mm, 58 mm, the distal metartarsal articular angles were $13^{\circ}$, $6^{\circ}$, $6.6^{\circ}$ and 3 cases were over $3^{\circ}$ angulation at lateral view. In $40^{\circ}$ distal Chevron osteotomy, the hallux valgus angles were $34.5^{\circ}$, $11.6^{\circ}$, $15.3^{\circ}$, the 1-2 intermetatarsal angles were $12.7^{\circ}$, $8.2^{\circ}$, $7.8^{\circ}$, the metatarsal length were 59.2 mm, 56.9 mm, 55.9 mm, the distal metartarsal articular angles were $12^{\circ}$, $7.3^{\circ}$, $7.3^{\circ}$ and there were no case with angulation over $3^{\circ}$ at lateral view. Conclusion: In comparison between $60^{\circ}$ distal Chevron osteotomy and $40^{\circ}$ distal Chevron osteotomy measuring at postoperative and follow up, most of all data were similar, but 3 cases over $3^{\circ}$ angulation at lateral view happened in $60^{\circ}$ Chevron osteotomy. This result showed that $40^{\circ}$ distal Chevron osteotomy fixing with screws through long armed one part may have benefit than $60^{\circ}$ distal Chevron osteotomy fixing with K-wires through short armed two parts in making rigid fixation, even though there is a personal difference of technigue.

• 대한족부족관절학회지
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• 제12권1호
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• pp.20-25
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• 2008

Purpose: The purpose of this study is comparison of radiological and clinical outcomes between proximal metatarsal osteotomy and distal chevron osteotomy for the correction of hallux valgus. Materials and Methods: In this retrospective study, we included subjects who underwent the correction of hallux valgus in our institution between March 2001 and August 2006, with a minimum follow-up of 12 months. The group of proximal metatarsal osteotomy was 23 patients (34 feet); the group of distal chevron osteotomy was 20 patients (26 feet). The group of proximal metatarsal osteotomy was composed of 26 severe cases (76.5%) and 8 moderate cases (23.5%); the group of distal chevron osteotomy was composed of 13 severe cases (50.0%) and 13 moderate cases (50.0%). Results: Compared to preoperative values, the hallux valgus angle, the first-second intermetatarsal angle and the distance of first-fifth metatarsal head were significantly decreased in two groups (p<0.05). In each parameter, the hallux valgus angle was decreased 66.3% (proximal metatarsal osteotomy) versus 49.6% (distal chevron osteotomy), which were significant (p=0.037). The first-second intermetatarsal angle and the distance of first-fifth metatarsal head were not significant. Mayo clinic forefoot scoring system (FFSS) score was significantly improved in two groups (p<0.05). The ratio of improvement was not significant (p=0.762). In severe group, hallux valgus angle and the first-second intermetatarsal angle was significantly decreased in proximal metatarsal osteotomy group compared to distal chevron osteotomy group (p<0.05), but the difference of the distance of first-fifth metatarsal head and FFSS score was not significant in both groups. In moderate group, the difference of all parameters was not significant in both groups. Conclusion: Although both proximal metatarsal osteotomy and distal chevron osteotomy showed satisfactory result in FFSS, proximal metatarsal osteotomy was more proper operative technique than distal chevron osteotomy in severe group, because of superiority of correction in radiological parameters.