• The Journal of the Acoustical Society of Korea
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• v.30 no.8
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• pp.436-445
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• 2011

In this paper, equivalent properties of 2-2 mode piezocomposites were studied. Variation of the properties of 2-2 mode piezocomposites was analyzed by the finite element method, and the result was compared with experimental measurement data to confirm the validity of the analysis. The equivalent properties of a single phase material to represent the piezocomposite composed of PZT-5H and polymer were derived by the asymptotic averaging method. Accuracy of the derived equivalent properties was enhanced by minimizing the discrepancy between the impedance spectra of full 2-2 piezocomposite and equivalent single phase material resonators of various vibration modes by the least square method. The equivalent properties of 2-2 piezocomposites derived in this study can be utilized to the design of diverse acoustic sensors.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.691-698
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• 2017

In this study, the injector transfer function (ITF) of a gas-gas coaxial jet-swirl injector is measured by applying excitation to jet or swirl flow using a loudspeaker. As a result of measuring the ITF according to the variation of feed system length, the ITF peak occurs at the resonance frequency of the space where the perturbed flow passes. When applying the excitation to the jet flow, as the jet flow increases up to 56 slpm, the magnitude of ITF decreases, and ITF increases thereafter. Therefore the larger the velocity difference between the jet and the swirl flow, the larger the ITF. In the case of the swirl excitation, the ITF decreases as the jet flow increases because of the decrease of the energy with respect to the constant flow at the downstream. This difference is caused by the location of the hot wire anemometer on the downstream of the injector center axis.

• Clinics in Shoulder and Elbow
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• v.21 no.1
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• pp.22-29
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• 2018

Background: This study is performed to evaluate anchor-related outcomes and complications after arthroscopic rotator cuff repair using 30% ${\beta}$-tricalcium phosphate (${\beta}$-TCP) with 70% poly lactic-co-glycolic acid (PLGA) biocomposite suture anchors. Methods: A total of 78 patients (mean age, $61.3{\pm}6.9years$) who underwent arthroscopic medium-to-large full-thickness rotator cuff tear repair were enrolled. The technique employed 30% ${\beta}$-TCP with 70% PLGA biocomposite suture anchors at the medial row (38 patients, Healix $BR^{TM}$ anchor [Healix group]; 40 patients, Fixone anchor B [Fixone group]). The radiologic outcomes (including perianchor cyst formation or bone substitution) and anatomical outcomes of the healing failure rate were evaluated using magnetic resonance imaging at least 6 months after surgery, the pain visual analogue scale at 3, 6 months, and final follow-up visit, and American Shoulder and Elbow Surgeons scores at least 1 year postoperatively. Anchor-related complications were also evaluated. Results: The perianchor cyst formation incidence was similar for both groups (60.5%, Healix group; 60.0%, Fixone group; p=0.967), although severe perianchor cyst incidence was slightly lower in the Fixone group (15.0%) than in the Healix group (21.1%). There was no occurrence of anchor absorption and bone substitution. No differences were observed in the healing failure rate (13.2%, Healix group; 15.0%, Fixone group; p=0.815) and functional outcome between groups (all p>0.05). Anchor breakage occurred in 5 patients (2 Healix anchors and 3 Fixone anchors); however, there were no major anchor-related complications in either group. Conclusions: No differences were observed in the clinical outcomes of the Healix and Fixone groups, neither were there any accompanying major anchor-related complications.

• Journal of Korean Neurosurgical Society
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• v.61 no.6
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• pp.767-773
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• 2018

Three male patients diagnosed with surfer's myelopathy (19-30 years) were admitted to our hospital. All three patients were novice surfers showing a typical clinical course of rapid progression of paraplegia following the onset of back pain. Typical history and magnetic resonance imaging features indicated the diagnosis of surfer's myelopathy. Two patients received high-dose steroid therapy and the other was treated with induced hypertension. One patient treated with induced hypertension showed almost full recovery; however, two patients who received high-dose steroid therapy remained completely paraplegic and required catheterization for bladder and bowel dysfunction despite months of rehabilitation. Our case series demonstrates the potentially devastating neurological outcome of surfer's myelopathy; however, early recovery in the initial 24-72 hours of presentation can occur in some patients, which is in accordance with previous reports. Ischemic insult to the spinal cord is thought to play a crucial role in the pathophysiology of surfer's myelopathy. Treatment recommendations include hydration, induced hypertension, early spinal angiography with intra-arterial intervention, intravenous tissue plasminogen activator, and high-dose steroid therapy; however, there is no standardized treatment option available. Early recovery appears to be important for long-term neurological outcome. Induced hypertension for initial treatment can be helpful for improving spinal cord perfusion; therefore, it is important for early and long-term neurological recovery. Education and awareness are essential for preventing surfer's myelopathy and avoiding further deterioration of neurological function.

• Journal of the Korean Society of Propulsion Engineers
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• v.22 no.4
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• pp.99-107
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• 2018

In this study, the injector transfer function (ITF) of a gas-gas coaxial jet-swirl injector is measured by perturbing jet or swirl flow using a speaker as jet flow increases. As a result of measuring the ITF varying feed system length, a peak occurs at a resonance frequency of space where the perturbed flow passes. With jet excitation, the ITF magnitude decreases, but increases thereafter as increasing the jet flow. Therefore the larger the velocity difference between jet and swirl flow, the larger the ITF. With swirl excitation, ITF decreases as increasing the jet flow because of the energy decrease with respect to the constant downstream flow.

• Clinics in Shoulder and Elbow
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• v.22 no.4
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• pp.203-209
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• 2019

Background: Clinical outcomes and prognosis of large and massive rotator cuff tears are known to be unpredictable not only in degeneration of the rotator cuff, but also due to a high rate of retear. Methods: Totally, 81 patients who had undergone arthroscopic rotator cuff repair from May 2008 to February 2016 were evaluated in our study. Clinical and functional evaluations were performed with the Constant score and the University of California, Los Angeles (UCLA) score, as well as full physical examination of the shoulder. All patients were confirmed to have magnetic resonance imaging (MRI) of tendon healing at least 1 year postoperatively. Results: The average age at the time of surgery was 65 years (range, 47-78 years). The average duration of postoperative time in which a follow-up MRI was performed was 36.1 months (range, 12-110 months). Large tears were present in 48 cases (59.3%) and massive tears in 33 cases (40.7%). Overall, there were 33 retear cases (40.7%). All the average clinical outcome scores were significantly improved at the last follow-up (p<0.001), although repair integrity was not maintained. Compared to type A, types C, and D of the Collin's classification showed significantly higher retear rates (p=0.036). Conclusions: Arthroscopic rotator cuff repair yields improved clinical outcomes and a relatively high degree of patient satisfaction, despite the repair integrity not being maintained. Involvement of the subscapularis muscle or infraspinatus muscle had no effect on the retear rate.

• Clinics in Shoulder and Elbow
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• v.22 no.4
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• pp.183-189
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• 2019

Background: Since the establishment of biological augmentation to improve the treatment of rotator cuff tears, it is imperative to explore newer techniques to reduce the retear rate and improve long-term shoulder function after rotator cuff repair. This study was undertaken to determine the consequences of a gel-type atelocollagen injection during arthroscopic rotator cuff repair on clinical outcomes, and evaluate its effect on structural integrity. Methods: Between January 2014 and June 2015, 121 patients with full thickness rotator cuff tears underwent arthroscopic rotator cuff repair. Of these, 61 patients were subjected to arthroscopic rotator cuff repair in combination with an atelocollagen injection (group I), and 60 patients underwent arthroscopic rotator cuff repair alone (group II). The visual analogue scale (VAS) for pain and the Korean Shoulder Society (KSS) scores were evaluated preoperatively and postoperatively. Magnetic resonance imaging (MRI) was performed at 6 months postoperatively, to assess the integrity of the repair. Results: VAS scores were significantly lower in group I than in group II at 3, 7, and 14 days after surgery. KSS scores showed no significant difference between groups in the 24 months period of follow-up. No significant difference was obtained in the healing rate of the rotator cuff tear at 6 months postoperatively (p=0.529). Conclusions: Although a gel-type atelocollagen injection results in reduced pain in patients at 2 weeks after surgery, our study does not substantiate the administration of atelocollagen during rotator cuff repair to improve the clinical outcomes and healing of the rotator cuff.

• Nuclear Engineering and Technology
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• v.54 no.1
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• pp.207-219
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• 2022

The suppression of high-intensity blob structures in the scrape-off layer (SOL) by ion-cyclotron range of frequencies (ICRF) power, leading to a decrease in the turbulent fluctuation level, is observed first in the Experimental Advanced Superconducting Tokamak (EAST) experiment. This suppression effect from ICRF power injection is global in the whole SOL at EAST, i.e. blob structures both in the regions that are magnetically connected to the active ICRF launcher and in the regions that are not connected to the active ICRF launcher could be suppressed by ICRF power. However, more ICRF power is required to reach the full blob structure suppression effect in the regions that are magnetically unconnected to the active launcher than in the regions that are magnetically connected to the active launcher. Studies show that a possible reason for the blob suppression could be the enhanced E_r × B shear flow in the SOL, which is supported by the shaper radial gradient in the floating potential profiles sensed by the divertor probe arrays with increasing ICRF power. The local RF wave power unabsorbed by the core plasma is responsible for the modification of potential profiles in the SOL regions.

• Journal of Sensor Science and Technology
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• v.30 no.4
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• pp.250-254
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• 2021

A highly sensitive and selective non-dispersive infrared (NDIR) carbon dioxide gas sensor requires achieving high transmittance and narrow full width at half maximum (FWHM), which depends on the interface of the optical filter for precise measurement of carbon dioxide concentration. This paper presents the design, simulation, and fabrication of a Fabry-Perot filter based on a distributed Bragg reflector (DBR) for a low-cost NDIR carbon dioxide sensor. The Fabry-Perot filter consists of upper and lower DBR pairs, which comprise multilayered stacks of alternating high- and low-index thin films, and a cavity layer for the resonance of incident light. As the number of DBR pairs inside the reflector increases, the FWHM of the transmitted light becomes narrower, but the transmittance of light decreases substantially. Therefore, it is essential to analyze the relationship between the FWHM and transmittance according to the number of DBR pairs. The DBR is made of silicon and silicon dioxide by RF magnetron sputtering on a glass wafer. After the optimal conditions based on simulation results were realized, the DBR exhibited a light transmittance of 38.5% at 4.26 ㎛ and an FWHM of 158 nm. The improved results substantiate the advantages of the low-cost and minimized process compared to expensive commercial filters.

• Clinics in Shoulder and Elbow
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• v.25 no.4
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• pp.257-264
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• 2022

Background: Chronic subscapularis tendon tear (SBT) is a degenerative disease and a common pathologic cause of shoulder pain. Several potential risk factors for chronic SBT have been reported. Although metabolic abnormalities are common risk factors for degenerative disease, their potential etiological roles in chronic SBT remains unclear. The purpose of this study was to investigate potential risk factors for chronic SBT, with particular attention to metabolic factors. Methods: This study evaluated single shoulders of 939 rural residents. Each subject undertook a questionnaire, physical examinations, blood tests, and simple radiographs and magnetic resonance imaging (MRI) evaluations of bilateral shoulders. Subscapularis tendon integrity was determined by MRI findings based on the thickness of the involved tendons. The association strengths of demographic, physical, social, and radiologic factors, comorbidities, severity of rotator cuff tear (RCT), and serologic parameters for SBT were evaluated using logistic regression analyses. The significance of those analyses was set at p<0.05. Results: The prevalence of SBT was 32.2% (302/939). The prevalence of partial- and full-thickness tears was 23.5% (221/939) and 8.6% (81/939), respectively. The prevalence of isolated SBT was 20.2% (190/939), SBT combined with supraspinatus or infraspinatus tendon tear was 11.9% (112/939). In multivariable logistic regression analysis, dominant side involvement (p<0.001), manual labor (p=0.002), diabetes (p<0.001), metabolic syndrome (p<0.001), retraction degree of Patte tendon (p<0.001), posterosuperior RCT (p=0.010), and biceps tendon injury (p<0.001) were significantly associated with SBT. Conclusions: Metabolic syndrome is a potential risk factor for SBT, as are these factors: overuse activity, diabetes, posterosuperior RCT, increased retraction of posterosuperior rotator cuff tendon, and biceps tendon injury.