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Biomechanical investigation of the type and configuration of screws used in high tibial osteotomy with titanium locking plate and screw fixation
http://ir.lib.ncku.edu.tw/handle/987654321/188531
title: Biomechanical investigation of the type and configuration of screws used in high tibial osteotomy with titanium locking plate and screw fixation abstract: Background
To maintain the corrected alignment after high tibial osteotomy (HTO), fixation with titanium locking plate and screws is widely used in current practice; however, screw breakage is a common complication. Thus, this study was to investigate the mechanical stability of HTO with locking plate and various screw fixations, including the length as well as the type.
Methods
A finite element (FE) model involving a distal femur, meniscus, and a proximal tibia with HTO fixed with a titanium locking plate and screws was created. The angle of the medial open wedge was 12°, and bone graft was not used. Two types of screws, namely conventional locking and far-cortical locking screws, with various lengths and configurations were used. At the proximal tibia, conventional locking screws with different lengths, 30 and 55 mm, were used; at the tibia shaft, different screw fixations including one-cortical, two-cortical, and far-cortical locking screws were used.
Results
The use of far-cortical locking screw generated the highest equivalent stress on the screws, which was four times (from 137.3 to 541 MPa) higher than that of the one-cortical screw. Also, it led to the maximum deformation of the tibia and a greater gap deformation at the osteotomy site, which was twice (from 0.222 to 0.442 mm) larger than that of the one-cortical screw. The effect of different locking screw length on tibia deformation and implant stress was minor.
Conclusion
Thus, far-cortical locking screws and plates increase interfragmentary movement but the screw stress is relatively high. Increasing the protection time (partial weight duration) is suggested to decrease the risk of screw breakage in HTO through fixation with titanium far-cortical locking screws and plates.
<br>Thu, 30 Jan 2020 08:15:16 GMTAdvanced Geometrical Optics
http://ir.lib.ncku.edu.tw/handle/987654321/188518
title: Advanced Geometrical Optics description: This book employs homogeneous coordinate notation to compute the first- and second-order derivative matrices of various optical quantities. It will be one of the important mathematical tools for automatic optical design. The traditional geometrical optics is based on raytracing only. It is very difficult, if possible, to compute the first- and second-order derivatives of a ray and optical path length with respect to system variables, since they are recursive functions. Consequently, current commercial software packages use a finite difference approximation methodology to estimate these derivatives for use in optical design and analysis. Furthermore, previous publications of geometrical optics use vector notation, which is comparatively awkward for computations for non-axially symmetrical systems.
This book computes the first- and second-order derivative matrices of skew ray and optical path length, while also providing an important mathematical tool for automatic optical design. This book consists of three parts. Part One reviews the basic theories of skew-ray tracing, paraxial optics and primary aberrations – essential reading that lays the foundation for the modeling work presented in the rest of this book. Part Two derives the Jacobian matrices of a ray and its optical path length. Although this issue is also addressed in other publications, they generally fail to consider all of the variables of a non-axially symmetrical system. The modeling work thus provides a more robust framework for the analysis and design of non-axially symmetrical systems such as prisms and head-up displays. Lastly, Part Three proposes a computational scheme for deriving the Hessian matrices of a ray and its optical path length, offering an effective means of determining an appropriate search direction when tuning the system variables in the system design process.
<br>Fri, 10 Jan 2020 06:35:00 GMTNew computation methods for geometrical optics
http://ir.lib.ncku.edu.tw/handle/987654321/188517
title: New computation methods for geometrical optics description: This book employs homogeneous coordinate notation to compute the first- and second-order derivative matrices of various optical quantities. It will be one of the important mathematical tools for automatic optical design. The traditional geometrical optics is based on raytracing only. It is very difficult, if possible, to compute the first- and second-order derivatives of a ray and optical path length with respect to system variables, since they are recursive functions. Consequently, current commercial software packages use a finite difference approximation methodology to estimate these derivatives for use in optical design and analysis. Furthermore, previous publications of geometrical optics use vector notation, which is comparatively awkward for computations for non-axially symmetrical systems.
<br>Fri, 10 Jan 2020 06:34:56 GMT非線性系統與控制. I, 系統分析
http://ir.lib.ncku.edu.tw/handle/987654321/188516
title: 非線性系統與控制. I, 系統分析 description: 國內有關自動控制的教學大多著重於線性系統，一般讀者若是對非線性系統與控制有興趣，就必須直接閱讀專業的原文書籍。但是國外關於非線性系統與控制的書籍大部分是以定理證明為導向，周全了數學的嚴謹性，卻增加了閱讀與應用的困難度。本書希望能提供初學非線性系統
<br>Fri, 10 Jan 2020 06:34:37 GMT