• Journal of Biomedical Engineering Research
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• v.25 no.5
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• pp.421-430
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• 2004

Clinically, it is almost impossible for a physician to distinguish subtle changes of frequency spectrum by using a stethoscope alone especially in the early stage of thrombus formation. Considering that reliability of mechanical valve is paramount because the failure might end up with patient death, early detection of valve thrombus using noninvasive technique is important. Thus the study was designed to provide a tool for early noninvasive detection of valve thrombus by observing shift of frequency spectrum of acoustic signals with computer aid diagnosis system. A thrombus model was constructed on commercialized mechanical valves using polyurethane or silicon. Polyurethane coating was made on the valve surface, and silicon coating on the sewing ring of the valve. To simulate pannus formation, which is fibrous tissue overgrowth obstructing the valve orifice, the degree of silicone coating on the sewing ring varied from 20％, 40％, 60％ of orifice obstruction. In experiment system, acoustic signals from the valve were measured using microphone and amplifier. The microphone was attached to a coupler to remove environmental noise. Acoustic signals were sampled by an AID converter, frequency spectrum was obtained by the algorithm of spectral analysis. To quantitatively distinguish the frequency peak of the normal valve from that of the thrombosed valves, analysis using a neural network was employed. A return map was applied to evaluate continuous monitoring of valve motion cycle. The in-vivo data also obtained from animals with mechanical valves in circulatory devices as well as patients with mechanical valve replacement for 1 year or longer before. Each spectrum wave showed a primary and secondary peak. The secondary peak showed changes according to the thrombus model. In the mock as well as the animal study, both spectral analysis and 3-layer neural network could differentiate the normal valves from thrombosed valves. In the human study, one of 10 patients showed shift of frequency spectrum, however the presence of valve thrombus was yet to be determined. Conclusively, acoustic signal measurement can be of suggestive as a noninvasive diagnostic tool in early detection of mechanical valve thrombosis.

• Journal of Korea Water Resources Association
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• v.52 no.10
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• pp.743-752
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• 2019

The flow in the meandering channel is characterized by the spiral motion of secondary currents that typically cause the erosion along the outer bank. Hydraulic structures, such as spur dike and groyne, are commonly installed on the channel bottom near the outer bank to mitigate the strength of secondary currents. This study is to investigate the effects of submerged vanes installed in a $90^{\circ}$ meandering channel on the development of secondary currents through three-dimensional numerical modeling using the hybrid RANS/LES method for turbulence and the volume of fluid method, based on OpenFOAM open source toolbox, for capturing the free surface at the Froude number of 0.43. We employ the second-order-accurate finite volume methods in the space and time for the numerical modeling and compare numerical results with experimental measurements for evaluating the numerical predictions. Numerical results show that the present simulations well reproduce the experimental measurements, in terms of the time-averaged streamwise velocity and secondary velocity vector fields in the bend with submerged vanes. The computed flow fields reveal that the streamwise velocity near the bed along the outer bank at the end section of bend dramatically decrease by one third of mean velocity after the installation of vanes, which support that submerged vanes mitigate the strength of primary secondary flow and are helpful for the channel stability along the outer bank. The flow between the top of vanes and the free surface accelerates and the maximum velocity of free surface flow near the flow impingement along the outer bank increases about 20% due to the installation of submerged vanes. Numerical solutions show the formations of the horseshoe vortices at the front of vanes and the lee wakes behind the vanes, which are responsible for strong local scour around vanes. Additional study on the shapes and arrangement of vanes is required for mitigate the local scour.

• Journal of the Korean Orthopaedic Association
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• v.56 no.1
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• pp.26-33
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• 2021

Purpose: This study evaluated the results of dual plate fixation for periprosthetic femur fracture after total knee arthroplasty (TKA). Materials and Methods: From October 2007 to February 2013, 23 cases of periprosthetic femur fracture after TKA were treated at the author's hospital. There were 13 cases of fixation using a medial and lateral dual plate when the stability of the fracture site could not be achieved by one side fixation with a follow-up of more than one year. The cases included no loosening of the femoral component in fractures that were categorized as Lewis-Rorabeck classification II and supracondylar comminuted fractures and elongation of the fracture line to the lateral epicondyle of the femur or stem in the medullary canal. The mean age was 72 years (65-82 years), and 11 cases were female. Three cases had a stem due to revision. The mean bone marrow density was -3.2 (-1.7 to -4.4), and the mean period from primary TKA to periprosthetic fractures was 28 months (1-108 months). The mean follow-up period was 23 months (12-65 months). The medial fracture site was first exposed via the subvastus approach. Second, the supplementary plate was fixed on the lateral side of the fracture using a minimally invasive plate osteosynthesis technique. The average union time, complications, and Hospital for Special Surgery Knee Score (HSS) at the last follow-up were evaluated. Results: The mean union time was 17.4 weeks (7-40 weeks). Two cases showed delayed bone union and nonunion occurred in one case, in whom bone union was achieved three months later after re-fixation using a dual plate with an autogenous bone graft. The mean varusvalgus angulation was 1.67 degrees (-1.2-4.9 degrees), and the mean anterior-posterior angulation was 2.86 degrees (0-4.9 degrees) at the last follow-up. The mean knee range of motion was 90 degrees, and the HSS score was 85 points (70-95 points) at the last follow-up. Conclusion: Dual plate fixation for periprosthetic femur fractures that had not achieved stability by one side plate fixation after TKA showed a good clinical result that allowed early rehabilitation.