CTU Open Journal Systems (Czech Technical University, Prague / České vysoké učení technické v Praze)
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QCT/FEA analyses of palateless splinted and unsplinted maxillary all-on-4 systems
Get PDFThe goal of the presented study was to determine the viability of using splinted and unsplinted maxillary implant-supported overdentures. The main physical quantity used to evaluate their differences was compressive stress in bone and equivalent (von Mises) stress in the implant and overdenture components. We took a 3D X-ray scan of the maxilla and imported the data into a QCT/FEA (Quantitative Computed Tomography-based Finite Element Analysis) software. The loading was done in three load cases. We designed both models of the overdentures in CAD, included the polyetheretherketone (PEEK) overdenture and analyzed the whole model of the reconstructed maxilla with implants. The results show worse (more concentrated) compressive stress distributions for the unsplinted locator variant. The splinted, bar-retained variant shows lower values of stress in all load cases. These findings and their potential for real-time selection of the optimal variant are then further discussed
Image-based random fields in numerical modeling of heterogeneous materials
Get PDFModeling of spatial variability using random fields is nowadays standard in computational modeling of heterogeneous materials. The only difficulty remains in determining the input parameters of the random field in order to represent the modeled material morphology as accurately as possible. The most frequent method of constructing a random field relies on various covariance kernels that primarily use as input the values of the correlation lengths, which are typically estimated ad-hoc. However, another possibility is to extract input parameters from the modeled material morphology. Moreover, this approach enables to calculate the covariance kernel itself. The performance of the image-based procedure is compared with standard methods of random field construction on the response of the two-phase elastic material
Formulation and implementation of nonlinear elasticity in advanced constitutive models in geomechanics
Get PDFSeveral formulations of a nonlinear elastic behavior within the yield surface of the selected advanced constitutive models are described and compared. Since concentrating on geotechnical applications the accompanied numerical simulations are limited to basic laboratory tests such as isotropic compression, oedometer, and drained triaxial compression. The results show a significant influence of the size of the initial load step on final predictions particularly when starting from a very low initial stiffness associated with the assumed zero initial stress. Differences in the predicted response arising from different formulations are also discussed. These might be quite significant and the design engineer should be aware of that when choosing a particular computational software
Parametric analysis for interphase shear stress in MoS2/PET nanocomposite under thermo-mechanical loading
Get PDFIn this study, a parametric analysis on the factors, that influence the value of theoretical interphase shear stress (ISS) in nanocomposite MoS2/PET, subjected to thermo-mechanical loading has been performed. The theoretical value of ISS is calculated based on obtained analytical solutions for the interfacial shear stress. The sensitivity of following parameters on the ISS in the considered nanostructure is investigated: the thicknesses of the nanocomposite layers, the length of the nanocomposite, the magnitude of the applied mechanical load, the applied temperature difference. It is found that the interface thickness does not affect the ISS value. The magnitude of the applied mechanical load has a strong influence on the magnitude of the ISS. The temperature difference (pure thermal loading) also affects the ISS value, but to a lesser extent. It should be noted, that in the case of combined loading (thermo-mechanical) the overall effect is additive. The thicknesses of MoS2 and PET mostly affect ISS, especially the substrate thickness. The obtained results are graphically illustrated and can be used for the fast prediction of ISS in micro scale in similar nanocomposite devices or parts thereof such as sensors, nano- and optical electronic devices, energy devices, etc
Research on the combined damping technology of shallow buried large-section loess tunnel
Get PDFDue to the uniqueness of loess structures and properties and the higher seismic technical requirements for tunnel engineering, it is imperative to study the seismic response of damping loess tunnels. Based on the Xichengshan tunnel project, a three-dimensional numerical model is established by finite element software to analyze the stress and strain response of the structure under different spacing of shock absorption joints and different stiffness lining. The combined damping measures of " rigid lining+ shock absorption joint " are proposed, and the damping effect of the combined damping measures is further analyzed. The results show that the setting of the shock absorption joint can effectively reduce the dynamic response of the loess tunnel under earthquake, and the recommended value of shock absorption spacing of the loess tunnel is 10 m. The dynamic response of the structure is different with different lining stiffness. The greater the stiffness, the greater the structural stress and the smaller the deformation. The combined damping measures of " rigid lining + shock absorption joint " can give full play to the advantages of single damping measures and effectively reduce the damage of earthquake to loess tunnel
ENHANCING CLINICAL EFFICIENCY: AUTONOMOUS DETERMINATION OF CARDIAC EFFECTIVE REFRACTORY PERIOD USING ECG SIGNALS
Get PDFElectrophysiological procedures for managing arrhythmias remain time-consuming, causing patients to wait for critical interventions. To address this pressing need, we introduce a revolutionary algorithm that autonomously calculates the effective refractory period (ERP) of cardiac tissue from electrocardiogram (ECG). The algorithm principally comprises signal filtering techniques and the detection of local extrema within the signal waveform. This algorithm underwent rigorous assessment using an in-house database of ECG signals acquired from ten patients who underwent electrophysiological examinations. Fundamental digital signal processing methods, such as linear filtering and thresholding, were employed in the determination of ERP. The algorithm yielded results congruent with the ERP values established by electrophysiologists in nine out of ten cases, with a standard deviation of 18.97 milliseconds. By being accurate and easy to integrate., this algorithm holds promise for real-time deployment in clinical settings, where it could potentially streamline and automate stimulation protocols, thereby expediting the examination process
METHOD COMPARISON FOR BONE DENSITY IN MULTIPLE MYELOMA PATIENTS
Get PDFBone mineral density (BMD) is an important indicator of bone health, particularly in patients with conditions such as multiple myeloma. This study aims to compare three methodologies for quantifying BMD in vertebral regions affected by lytic lesions: two using data from conventional CT with different corrections for tissue composition, and one using data acquired on a dual-energy CT system. Method 1 is based on conventional CT with corrections using reference values for muscle and fat, Method 2 uses conventional CT with corrections based on the measured CT values of paraspinal muscle, and Method 3 is based on dual-energy CT. The Wilcoxon signed-rank test was used for statistical comparison, as the dataset did not follow a normal distribution. The results indicated significant differences between Methods 1 and 2 for BMD in regions of interest (ROIs) within lytic lesions, while no significant differences were found for other comparisons in this group. For vertebrae affected by multiple myeloma, significant differences were found between Methods 1 and 2, and Methods 2 and 3, but not between Methods 1 and 3. In healthy vertebrae, a significant difference was found only between Methods 2 and 3. When all ROIs were combined, significant differences were found between Methods 1 and 2, and Methods 2 and 3, with no difference between Methods 1 and 3. Future research will focus on objectively assessing the accuracy of these methods by comparing their results with a calibration phantom
Gear ratio optimization of single and two-speed transmission for an electric motorcycle
Get PDFMost electric vehicles have a single-speed transmission as the traction characteristic of an electric motor allows operation with sufficient motor torque at low and high speeds. Then, the selection of the single-gear ratio is a trade-off between available torque for acceleration (or gradability) at lower speeds and the designed maximum vehicle speed corresponding to the electric motor’s maximum speed limit. Nevertheless, the multiple-speed transmission can be used, and the vehicle can benefit from improved acceleration at low speeds and higher maximum speeds. In this paper, the gear ratio of a single-speed transmission for an electric racing motorcycle is optimized to achieve a trade-off between acceleration, lap time, and maximum speed. With the same goal, the gear ratios for two-speed transmission are optimized, and the results are compared
Autonomous driving with a focus on HMI for parallel parking maneuvers
Get PDFAutonomous vehicles remain a major topic in the automotive industry today, including assistance systems, cooperative communication, and other aspects that lead to full vehicle autonomy. This paper investigates vehicle autonomy with a focus on parking assistance. Along with a review of parking assistants, the paper presents a prototype parking assistant with an alternative distance display. The parking assistant prototype, compared to parking without an assistant and conventional parking assistant, was tested in a real-world experiment of a within-subjects study design. The user experience of the proposed distance representation was obtained, and the results indicated that the prototype parking assistant with an alternative distance display helps less experienced drivers get a better idea of the distance from the obstacle