• Steel and Composite Structures
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• v.36 no.2
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• pp.213-228
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• 2020

Shape Memory Alloys (SMAs) are new materials used in various fields of science and engineering, one of which is civil engineering. Owing to their distinguished capabilities such as super elasticity, energy dissipation, and tolerating cyclic deformations, these materials have been of interest to engineers. On the other hand, the connections of a steel structure are of paramount importance because of their vulnerabilities during an earthquake. Therefore, it is indispensable to find approaches to augment the efficiency and safety of the connection. This research investigates the behavior of steel connections with extended end plates equipped hybridly with 8 rows of high strength bolts as well as Nitinol superelastic SMA bolts. The connections are studied using component method in dual form. In this method, the components affecting the connections behavior, such as beam flange, beam web, column web, extended end plate, and bolts are considered as parallel and series springs according to the Euro-Code3. Then, the nonlinear force- displacement response of the connection is presented in the form of moment-rotation curve. The results obtained from this survey demonstrate that the connection has ductility, in addition to its high strength, due to high ductility of SMA bolts.

• The korean journal of orthodontics
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• v.48 no.3
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• pp.153-162
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• 2018

Objective: The aim of this trial was to compare the alignment efficiency and intermaxillary arch dimension changes of nickel-titanium (NiTi) or copper-nickel-titanium (CuNiTi) round archwires with increasing diameters applied sequentially to the mandibular arch. Methods: The initial alignment phase of fixed orthodontic treatment with NiTi or CuNiTi round archwires was studied in a randomly allocated sample of 66 patients. The NiTi group comprised 26 women, 10 men, and the CuNiTi ($27^{\circ}C$) group comprised 20 women, 10 men. The eligibility criteria were as follows: anterior mandibular crowding of minimum 6 mm according to Little's Irregularity Index (LII), treatment requiring no extraction of premolars, 12 to 18 years of age, permanent dentition, skeletal and dental Class I malocclusion. The main outcome measure was the alignment of the mandibular anterior dentition; the secondary outcome measure was the change in mandibular dental arch dimensions during 12 weeks. Simple randomization (allocation ratio 1:1) was used in this single-blind study. LII and mandibular arch dimensions were measured on three-dimensional digital dental models at 2-week intervals. Results: No statistically significant difference was observed between NiTi and CuNiTi according to LII (p > 0.05). Intercanine and intermolar arch perimeters increased in the CuNiTi group (p < 0.001). Inter-first premolar width showed a statistically significant interaction in week ${\times}$ diameter ${\times}$ application (p < 0.05). Conclusions: The effects of NiTi and CuNiTi round archwires were similar in terms of their alignment efficiency. However, the intercanine and intermolar arch perimeters, and the inter-first premolar width changes differed between groups.

• International Journal of Computer Science & Network Security
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• v.23 no.2
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• pp.183-192
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• 2023

Radiofrequency ablation (RFA) is an alternative treatment for liver cancer to the surgical intervention preferred by surgeons. However, the main challenge remains the use of RF for the ablation of large tumours (i.e., tumours with a diameter of >3 cm). For large tumours, RFA takes a large duration in the ablation process compared with surgery, which increases patient pain. Therefore, RFA for large tumours is not preferred by surgeons. The currently materials used in RF electrodes, such as the nickeltitanium alloy (nitinol), are characterized by low thermal and electrical conductivities. On the other hand, the use of materials that have high thermal and electrical conductivities, such as titanium aluminide alloy (gamma titanium), produces more thermal energy for tumours. In this paper, we developed a cool-tip RF electrode model that uses nickel-titanium alloy and replaced it with titanium aluminide alloy by using the finite element model (FEM). The aim of this paper is to study the effect of the thermal and electrical conductivities of gamma titanium on the ablation volume. Results showed that the proposed design of the electrode increased the ablation rate by 1 cm³ /minute and 6.3 cm³/10 minutes, with a decrease in the required time ablation. Finally, the proposed model reduces the ablation time and damages healthy tissue while increasing the ablation volume from 22.5% cm³ to 62.5% cm³ in ten minutes compared to recent studies.

• The korean journal of orthodontics
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• v.53 no.2
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• pp.89-98
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• 2023

Objective: This study aimed to compare the mechanical and thermal properties in the anterior and posterior segments of new and retrieved specimens of a commercially available multizone superelastic nickel-titanium (NiTi) archwire. Methods: The following groups of 0.016 × 0.022-inch Bioforce NiTi archwires were compared: a) anterior and b) posterior segments of new specimens and c) anterior and d) posterior segments of retrieved specimens. Six specimens were evaluated in each group, by three-point bending and bend and free recovery tests. Bending moduli (Eb) were calculated. Furthermore, the new specimens were evaluated with scanning electron microscopy/energy-dispersive X-ray spectrometry. A multiple linear regression model with a random intercept at the wire level was applied for data analysis. Results: The forces in the posterior segments or new specimens were higher than those recorded in the anterior segments or retrieved specimens, respectively. Accordingly, Eb also varied. Higher austenite start and austenite finish (Af) temperatures were recorded in the anterior segments. No statistically significant differences were found for these temperatures between retrieved and new wires. The mean elemental composition was (weight percentage): Ni, 52.6 ± 0.5; Ti, 47.4 ± 0.5. Conclusions: The existence of multiple force zones was confirmed in new and retrieved Bioforce archwires. The retrieved archwires demonstrated lower forces during the initial stages of deactivation in three-point bending tests, compared with new specimens. The Af temperature of these archwires may lie higher than the regular intraoral temperature. Even at 2 mm deflections, the forces recorded from these archwires may lie beyond biologically safe limits.

• Journal of Hydrogen and New Energy
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• v.34 no.6
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• pp.631-640
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• 2023

This study selected Eco-AZ91 MgH₂, which shows high enthalpy as a material for this purpose, as the basic material, and analyzed the change in characteristics by synthesizing TiNi as a catalyst to control the thermodynamic behavior of MgH₂. In addition, the catalyst dispersion technology using graphene oxide (GO) was studied to improve the high-temperature aggregation phenomenon of Ni catalyst and to secure a source technology that can properly disperse the catalyst. XRD, SEM, and BET analysis were conducted to analyze the metallurgical properties of the material, and TGA and DSC analysis were conducted to analyze the dehydrogenation temperature and calorific value, and the correlation between MgH₂, TiNi catalyst, and GO reforming catalyst was analyzed. As a result, the MgH₂-5 wt% TiNi at GO composite could lower the dehydrogenation temperature to 478-492 K due to the reduction of the catalyst aggregation phenomenon and the increase in the reaction specific surface area, and an experimental result for the catalyst dispersion technology by GO could be ensured.

• Korean Journal of Radiology
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• v.2 no.3
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• pp.145-150
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• 2001

Objective: To investigate the effectiveness of the newly designed Niti-S stent in the management of iliac arterial stenoses and occlusions. Materials and Methods: Stenoses (n=25) or occlusions (n=5) in the iliac arteries of 25 patients (30 limbs) were treated. The site of the lesions was the common (n=15) or external (n=11) iliac artery, or both (n=4). Eight limbs were treated for diffuse disease, six for highly eccentric lesion, five for occlusive lesion, and 11 for failed angioplasty. Results: In all patients, technical success was achieved without major complications. One death, not procedure-related, occurred within 30 days. Ankle-brachial indexes improved from 0.63 0.30 to 0.99 0.21, and ischemic symptoms showed improvement in 22 patients (88%). Fontaine classifications before stenting, namely IIa(n=3), IIb(n=16), III(n=2), and IV(n=4) improved to I(n=17), IIa(n=5), and IV(n=3). Follow-up over a 27 (mean, 19.8 8)-month period showed that cumulative patency rates were 95.8% at 1 year and 86.2% at 2 and 3 years. No significant decrease in the mean ankle-brachial index was observed. Conclusion: The Niti-S stent appears to be a safe and effective device for the treatment of iliac stenoses and occlusions. These preliminary results require confirmation with a larger series.

• Clinical and Experimental Pediatrics
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• v.48 no.5
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• pp.512-517
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• 2005

Purpose : In adults, endoscopic tracheobronchial balloon dilatation and stenting have become valuable methods to establish and maintain an adequate airway lumen when tracheomalacia or neoplastic growth compromise the airways. But in children, only a few cases were reported due to technical problems. We report six children who were treated with stent implantation and describe the use and safety of airway stents. Methods : Six patients with severe airway obstruction were treated. We investigated the underlying medical problems, stenotic site, symptomatic improvement and complications, and the size and location of stent. Results : The median age of the six patients was 21 months. Three of them were mechanically ventilated and one had an endotracheal tube to maintain the patency of airway. Diagnoses were : congenital tracheal stenosis with or without bronchomalacia, granulation tissue formation after right upper lobectomy by bronchial carcinoid or after prolonged intubation, endobronchial tuberculosis, and airway compression by mediastinal undifferentiated sarcoma. Nitinol stents were implanted in the airway guided by bronchoscopy and fluoroscopy simultaneously. Three cases were placed in trachea, the others were in the bronchus. After stent implantation, all patients showed marked improvements of their airway obstructive symptoms. Four patients are doing well, although two expired due to underlying diseases. Four patients had granulation tissue formation around stents, but that was tolerable after removing the stent. Conclusion : We suggest that the use of expandible metallic stent implantation can offer safe therapeutic option even in extremely severe, life threatening and inoperable airway stenosis in children.

• Progress in Medical Physics
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• v.20 no.3
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• pp.139-144
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• 2009

Recently, the mathematical analysis of stent simulation has been improved, with the help of development of various tool which measure mechanical property and location of stent in artery. The most crucial part of the stent modeling is how to design ideal stent and to evaluate the interaction between stent and artery. While there has been great deal of researches on the evaluation of the expansion, stress distribution, deformation of the stent in terms of the various parameters, few verification through computer simulation has been performed about deformation and stress distribution of the stent. In this study, we have produced the corresponding results between experimental test using Universal Testing Machine and computer simulation for the ideal model of stent. Also, we have analyzed and compared stress distribution of stent in the cases of that with membrane and that without membrane. The results of this study would provide minimum change of plan and good quality for ideal stent replacing damaged artery through the analysis using computer simulation in the early stage of stent design.

• Journal of Korean Society of Steel Construction
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• v.27 no.6
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• pp.493-501
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• 2015

Superelastic shape memory alloys (SMAs) are metallic materials that can automatically recover to their original condition without heat treatment only after the removal of the applied load. These smart materials have been wildly applied instead of steel materials to the place where large deformation is likely to concentrate. In spite of many advantages, superelastic SMA materials have been limited to use in the construction filed because there is lack of effort and research involved with the development of the material model, which is required to reproduce the behavior of superelastic SMA materials. Therefore, constitutive material models as well as algorithm codes are mainly treated in this study for the purpose of simulating their hysteretic behavior through numerical analyses. The simulated curves are compared and calibrated to the experimental test results with an aim to verify the adequacy of material modeling. Furthermore, structural analyses incorporating the material property of the superelastic SMAs are conducted on simple and cantilever beam models. It can be shown that constitutive material models presented herein are adequate to reliably predict the behavior of superelastic SMA materials under cyclic loadings.

• Journal of Chest Surgery
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• v.42 no.1
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• pp.53-58
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• 2009

Background: The goal of this study was to compare the patency and complications of femoropopliteal bypass with superficial femoral artery stenting for patients with atherosclerotic superficial femoral artery occlusive disease. Material and Method: Between July 2005 and July 2008, we reviewed 29 femoropopliteal bypass procedures (24 patients) with prosthetic grafts (the bypass group) and 19 superficial femoral artery stentings (15 patients) with nitinol stent (the stent group). There were 35 male patients (89.7%) and the mean age of the patients was 69.2 years (range: 48~84). The number of patients who had DM, hypertension and a smoking history was 25 patients (64.1%), 17 patients (43.6%) and 30 patients (76.9%), respectively. 23 (59.0%) patients had skin ulceration or tissue gangrene at admission. Result: There were 27 cases (93.0%) of TASC C&D lesion in the bypass group and 16 cases (84.2%) of TASC A&B lesion in the stent group. There were significant differences for the indications for a procedure between the two groups (p<0.01). The primary patency rates at 6 months, 12 months and 24 months were 91.9%, 79.7% and 79.7% for the bypass group and 93.3%, 86.2% and 86.2% for the stent group, respectively. There were no statistical difference between the two groups (p=0.48). Conclusion: There were no significant differences in the outcome between two groups. TASC C&D lesion and failed intervention therapy should be treated with femoropopliteal bypass surgery, and TASC A&B lesion and the high-risk patients should be treated with femoral artery stent insertion.