The Structural Relationship between Exercise Passion, Sports Confidence, and Exercise Continuation Intention for Taekwondo Players: Moderating the Effect of the Coach's Support.

This study examined the relationship between "exercise passion", sports confidence, exercise continuation intention, and the moderating effect of the coach's support to provide basic data for Taekwondo players and instructors. A total of 428 data items were obtained using purposive sampling. Data were analyzed using frequency analysis, reliability analysis, correlation analysis, confirmatory factor analysis, structural equation model analysis, and moderating effect analysis via SPSS and AMOS version 24.0. It was found that "harmony passion" had a positive effect on all variables of sports confidence. Additionally, two variables of exercise passion had a positive effect on exercise continuation intention. Furthermore, sports confidence was identified as a variable that increased the intention to continue exercising. The coach's support played a partial role as a moderating variable for exercise passion, sports confidence, and exercise continuation intention. It was concluded that the athlete's passion for sports and sports confidence were important variables that increased Taekwondo athletes' exercise continuation intention. Moreover, the active support and interest of a coach who is able to meet the athlete's needs and exercise situation are also required.

Design of Lightweight CFRP Automotive Part as an Alternative for Steel Part by Thickness and Lay-Up Optimization.

Mechanical properties, such as strength and stiffness, of laminated carbon fiber reinforced plastic (CFRP) are generally affected by the lay-up method. However, no precise design rules to replace steel products with CFRP have been established that satisfy these properties. Therefore, this study proposes a set of rules to design automotive parts with equivalent bending stiffness through structural analysis and genetic algorithms (GAs). First, the thickness of the CFRP product was determined by comparing the bending deformation of steel products by structural analysis. To minimize the orthotropic characteristics of CFRP, the quasi-isotropic lay-up method was implemented to determine the thickness. Next, the lay-up angle was determined using GAs. The optimized lay-up angle of the CFRP product with minimum bending deformation was determined by population generation, cross-over, mutation, and fitness evaluation. CFRP B-pillar reinforcement was fabricated using the determined conditions and the bending deformation of the single component was evaluated. Finally, the B-pillar assembled with CFRP reinforcement was investigated by the drop tower test.

Stress generation during self-adjusting file movement: minimally invasive instrumentation.

INTRODUCTION: Although nickel-titanium (NiTi) rotary instruments may produce a well- tapered root canal with a low tendency of aberrations, these are generally perceived to have a high fracture risk during use and may produce significant forces on root dentin during instrumentation, which may induce a dentinal defect or crack in the apical part of the root. This study compared mathematically the stress generated by the Self-Adjusting File (ReDent-Nova, Ra'anana, Israel) with conventional rotary instruments during the movement of 3 NiTi endodontic file designs in a curved root canal. METHODS: Stresses were calculated using finite element analysis. Three file designs with tip size ISO #20 were used in this study. Finite element models of ProFile #20/.06 (Dentsply Maillefer, Ballaigues, Switzerland) (a constant tapered shaft), ProTaper Universal F1 (Dentsply Maillefer) (a progressively changing taper shaft), and SAF 1.5 mm (a mesh shaft) were activated within a curved root canal model. The stress generations resulting from the simulated shaping movement were evaluated in the apical root dentin area. RESULTS: The SAF induced the lowest von Mises stress concentration and the lowest tensile principal stress component in root dentin. The calculated stress values from ProTaper Universal F1 and ProFile #20/.06 were approximately 8 to 10 times bigger than that of the SAF. CONCLUSIONS: Stress levels during shaping and the susceptibility to apical root cracks after shaping vary with instrument design. The design of the SAF may produce minimal stress concentrations in the apical root dentin during shaping of the curved canal, which may increase the chance of preservation of root dentin integrity with a reduced risk of dentinal defects and apical root cracking.

Flexural stiffness and stresses in nickel-titanium rotary files for various pitch and cross-sectional geometries.

INTRODUCTION: Shape is the main determinant of mechanical performance for nickel-titanium rotary instruments. This study evaluated how pitch and cross-sectional geometry affected flexural stiffness and stresses. METHODS: Finite element models of rotary instruments with 4 cross-sectional geometries (triangle, slender-rectangle, rectangle, square) and 3 pitches (5-, 10-, 15-threads) were created, featuring superelastic nickel-titanium properties. All models had the same length, taper, and external peripheral radius; cross-sectional area and/or center-core area varied. The clamped shaft was rotated axially, while the tip was deflected 5 mm. Flexural stiffness and maximum von Mises stresses were calculated. RESULTS: Stiffness and maximum stress decreased with decreasing pitch (increasing threads). Doubling or tripling the threads for the triangular or rectangular cross sections decreased the stiffness and stress 6% and 12%, respectively; square cross sections were less affected (1% and 3% decrease, respectively). Square cross sections (higher cross-sectional and center-core areas) had higher stiffness and stresses than other models with same deflection. Rectangular and triangular models with the same center-core areas had similar stresses, but the rectangular model was 30%-40% stiffer. The slender-rectangle had the smallest center-core area and the lowest stiffness and stresses. Both rectangular cross sections caused stiffness and stress variations with rotation angle (13% for slender-rectangle); larger pitch caused more variation. CONCLUSIONS: Under the same tip deflection (simulating canal curvature), flexural stiffness and stress correlated with center-core area. Increasing pitch increased flexural stiffness and stresses.

Comparison of torsional stiffness of nickel-titanium rotary files with different geometric characteristics.

INTRODUCTION: The aim of this study was to evaluate the theoretical effect from pitch and cross-sectional geometry on torsional stiffness of nickel-titanium (NiTi) instruments. METHODS: Finite element models of NiTi rotary instruments with different cross-sectional geometries and different number of threads were made for comparison of torsional stiffness. Four cross-sectional shapes were tested: triangle, slender rectangle, rectangle, and square. Taper and external peripheral radius were the same for all models, whereas cross-sectional area and/or center core area were varied. Three pitch values (5, 10, and 15 threads) were tested for each type of cross-sectional geometry. The torsional stiffness of the 12 resulting finite element models was calculated by twisting the file shanks 20 degrees while holding the file tip at apical 4 mm. RESULTS: The file models with larger pitch (fewer threads) had lower torsional stiffness. The models with the rectangular cross section had higher torsional stiffness than models with the triangular cross section, even when the cross-sectional areas were the same or the center core area was smaller. File models with larger cross-sectional area had higher torsional stiffness. CONCLUSIONS: Torsional deformation and/or fracture of NiTi rotary files might be reduced by reducing the pitch (increasing the number of threads) and increasing the cross-sectional areas rather than the center core area.

Correlation between experimental cyclic fatigue resistance and numerical stress analysis for nickel-titanium rotary files.

INTRODUCTION: The aim of this investigation was to study cyclic fatigue resistance of various nickel-titanium (NiTi) rotary files under various root canal curvatures by correlating cyclic fatigue fracture tests with finite-element analysis (FEA). METHODS: Four NiTi rotary instruments with different cross-sectional geometries but comparable sizes were selected for this study: ProTaper (Dentsply Maillefer, Ballaigues, Switzerland), ProFile (Dentsply Maillefer), HeroShaper (Micromega, Besançon, France), and Mtwo (VDW, Munich, Germany). The ProFile and HeroShaper files were of size 30/.06 taper, the Mtwo was of size 30/.05 taper, and the ProTaper was F3. The cyclic fatigue test was conducted in a custom-made device that simulated canals with 25°, 35°, and 45° curvature. For the FEA, the file models were meshed, and 17-mm long curved canals were modeled to have same curvatures as the cyclic fatigue tests. Numerical analysis was performed to determine the stress distributions in the NiTi instruments while they rotated in the simulated curved canals. RESULTS: ProTaper (the stiffest instrument) showed the least cyclic fatigue resistance and highest stress concentration for all tested curvatures, whereas Mtwo showed the best cyclic fatigue resistance. A comparison between the FEA and fatigue results showed that when stresses increased, the number of instrument rotations to fracture decreased. Maximum stresses in the instruments predicted the approximate location of the fatigue fracture. CONCLUSIONS: The stiffer instrument had the highest stress concentration in FEA and the least number of rotations until fracture in the cyclic fatigue test. Increased curvature of the root canal generated higher stresses and shortened the lifetime of NiTi files. Finite-element stress analysis reflected cyclic fatigue fracture resistance.

Potential relationship between design of nickel-titanium rotary instruments and vertical root fracture.

INTRODUCTION: Nickel-titanium (NiTi) rotary files can produce cleanly tapered canal shapes with low tendency of transporting the canal lumen. Because NiTi instruments are generally perceived to have high fracture risk during use, new designs have been marketed to lower fracture risks. However, these design variations may also alter the forces on a root during instrumentation and increase dentinal defects that predispose a root to fracture. This study compared the stress conditions during rotary instrumentation in a curved root for three NiTi file designs. METHODS: Stresses were calculated using finite element (FE) analysis. FE models of ProFile (Dentsply Maillefer, Ballaigues, Switzerland; U-shaped cross-section and constant 6% tapered shaft), ProTaper Universal (Dentsply; convex triangular cross-section with notch and progressive taper shaft), and LightSpeed LSX (Lightspeed Technology, Inc, San Antonio, TX; noncutting round shaft) were rotated within a curved root canal. The stress and strain conditions resulting from the simulated shaping action were evaluated in the apical root dentin. RESULTS: ProTaper Universal induced the highest von Mises stress concentration in the root dentin and had the highest tensile and compressive principal strain components at the external root surface. The calculated stress values from ProTaper Universal, which had the biggest taper shaft, approached the strength properties of dentin. LightSpeed generated the lowest stresses. CONCLUSION: The stiffer file designs generated higher stress concentrations in the apical root dentin during shaping of the curved canal, which raises the risk of dentinal defects that may lead to apical root cracking. Thus, stress levels during shaping and fracture susceptibility after shaping vary with instrument design.

Comparison of forces generated during root canal shaping and residual stresses of three nickel-titanium rotary files by using a three-dimensional finite-element analysis.

The study was aimed to compare the stress distribution during simulated root canal shaping and to estimate the residual stress thereafter for some nickel-titanium rotary instruments. Three brands of instruments (ProFile, ProTaper, and ProTaper Universal; Dentsply Maillefer) were scanned with micro-computed tomography to produce a real-size, 3-dimensional model for each. The stresses on the instrument during simulated shaping of a root canal were analyzed numerically by using a 3-dimensional finite-element package, taking into account the nonlinear mechanical behavior of the nickel-titanium material. From the simulation, the original ProTaper design showed the greatest pull in the apical direction and the highest reaction torque from the root canal wall, whereas ProFile showed the least. In ProTaper, stresses were concentrated at the cutting edge, and the residual stress reached a level close to the critical stress for phase transformation of the material. The residual stress was highest in ProTaper followed by ProTaper Universal and ProFile.

Cybernetic modeling of the cephalosporin C fermentation process by Cephalosporium acremonium.

A cybernetic mathematical model has been developed to describe the production of cephalosporin C. In developing the model, diauxic behavior of substrate consumption, morphological differentiation of cells, and catabolite repression of cephalosporin C production by the preferred substrate, glucose, were considered. The proposed model was tested on the experimental data from the literature and could adequately describe the morphological differentiation of cells, the sequential utilization of carbon sources and the production of cephalosporin C. It could be a useful tool to optimize the production of cephalosporin C by Cephalosporium acremonium in batch, fed-batch or continuous operations.