Impact of Preparation of Titanium Alloys on Their Abrasive Water Jet Machining

Several titanium alloys, i.e., grade 2 Ti, Ti6Al4V and NiTi alloy, prepared by selected deformation procedures were subjected to abrasive water jet (AWJ) cutting and subsequently analysed. The study describes samples’ preparations and respective material structures. The impact of deformation processing of the selected alloys on the declination angle during cutting, and the results of measurements of surface wall quality performed for the selected samples at the Department of Physics of Faculty of Electrical Engineering and Computer Science at VŠB–Technical University of Ostrava, are presented and discussed, as are also the influences of structural features of the processed titanium alloys on surface qualities of the investigated samples. The results showed that the highest resistance to AWJ machining exhibited the Ti6Al4V alloy prepared by forward extrusion. Its declination angle (recalculated to the thickness 10 mm to compare all the studied samples) was 12.33° at the traverse speed of 100 mm/min, pumping pressure of 380 MPa, and abrasive mass flow rate of 250 g/min.

Is There a Borderline Value in the Radiological Findings of Patients With Calcaneal Malunion That May Help to Select an Appropriate Treatment Option?

Background: Despite the constant evolution of technological support, operative techniques, and rehabilitation techniques after conservative treatment and operative treatment, a considerable number of patients with calcaneal fractures have constant pain, frequently resulting in loss of occupation. There are numerous options for the operative treatment of painful calcaneal malunion; however, very few publications suggest specific radiological measurements for pre- and postoperative planning—even fewer have statistically analyzed how these radiological measurements affect clinical outcomes. Methods: We performed a retrospective study of 100 patients after operative treatment of calcaneal malunion to determine the correlation between radiological measurements and clinical outcomes. Data were used to create an algorithm that would help to choose between in situ subtalar arthrodesis and complex reconstructive operations. The algorithm was then used to treat 27 prospective patients. The American Orthopaedic Foot & Ankle Society (AOFAS) hindfoot score and visual analog scale (VAS) were used for clinical assessment, whereas standard weightbearing anteroposterior (AP), lateral (LAT) ankle x-rays, and long axial hindfoot view were used for radiological assessment. Results: The talar declination angle was positively correlated with clinical outcome. Patients with talar declination angles less than 6.5 degrees showed worse results in AOFAS score than patients with a greater angle did (57.3 ± 15.3 and 81 ± 15.6, respectively). Conclusion: The combination of subtalar arthrodesis with distraction bone block or calcaneal osteotomy in patients with calcaneal malunion and a talar declination angle less than 6.5 degrees showed better results than isolated in situ arthrodesis. Level of Evidence Level III, retrospective cohort study, case series.

Method and algorithm for determining the geographic coordinates of ground objects from an unmanned aerial vehicle

Introduction: As practice shows, the accuracy of determining the coordinates of objects is influenced by many factors associated with the presence of errors in measuring the angular coordinates of the optical system, the distance to the object and the presence of an inhomogeneous terrain. Purpose: Improving the accuracy of determining the geographic coordinates of ground objects from an unmanned aerial vehicle. Results: A method and an algorithm for determining geographic coordinates based on the use of a digital terrain model and optimization methods have been developed. The accuracy of calculating the coordinates of the object is increased by minimizing the error in measuring the declination angle, azimuth to the target and slant range. To confirm the analytical calculations, a field experiment was carried out with a car on the ground. At a considerable distance, at which the slant range was 900 m, several data freeze frames were taken. As a result of calculations, the geographical coordinates of the car were obtained in two ways (traditional and developed). Ultimately, the accuracy of calculating coordinates using the developed method is 4.8 times higher. Practical relevance: The method and algorithms for information processing proposed in the work will make it possible to create a number of hardware and software solutions for guidance and target designation systems.

Abrasive Waterjet (AWJ) Forces—Potential Indicators of Machining Quality

The necessity of monitoring the abrasive waterjet (AWJ) processes increases with the spreading of this tool into the machining processes. The forces produced on the workpiece during the abrasive waterjet machining can yield some valuable information. Therefore, a special waterjet-force measuring device designed and produced in the past has been used for the presented research. It was tested during the AWJ cutting processes, because they are the most common and the best described up-to-date AWJ applications. Deep studies of both the cutting process and the respective force signals led to the decision that the most appropriate indication factor is the tangential-to-normal force ratio (TNR). Three theorems concerning the TNR were formulated and investigated. The first theorem states that the TNR strongly depends on the actual-to-limit traverse speed ratio. The second theorem claims that the TNR relates to the cutting-to-deformation wear ratio inside the kerf. The third theorem states that the TNR value changes when the cutting head and the respective jet axis are tilted so that a part of the jet velocity vector projects into the traverse speed direction. It is assumed that the cutting-to-deformation wear ratio increases in a certain range of tilting angles of the cutting head. This theorem is supported by measured data and can be utilized in practice for the development of a new method for the monitoring of the abrasive waterjet cutting operations. Comparing the tilted and the non-tilted jet, we detected the increase of the TNR average value from 1.28 ± 0.16 (determined for the declination angle 20° and the respective tilting angle 10°) up to 2.02 ± 0.25 (for the declination angle 30° and the respective tilting angle of 15°). This finding supports the previously predicted and published assumptions that the tilting of the cutting head enables an increase of the cutting wear mode inside the forming kerf, making the process more efficient.

Effects of Receiver Parameters on Solar Flux Distribution for Triangle Cavity Receiver in the Fixed Linear-Focus Fresnel Lens Solar Concentrator

The objective of the study is to investigate and optimize the solar flux uniformity of a fixed linear-focus Fresnel lens solar concentrator using a triangle cavity receiver. The effects of receiver parameters including the vertical distance from the cavity opening plane to the Fresnel lens f, receiver internal surface absorptivity αab, end reflection plane reflectivity ρr, solar declination angle δ and solar angle ω on the uniformity factor (UF) of a triangle cavity receiver were carried out. The effects of receiver parameters are evaluated with a significance test of critical factors. The results showed that the increase in f and δ would result in an increase in the UF. The average UF with f = 600, 625, 650, 675 and 700 mm, respectively, are 0.5030, 0.5858, 0.6337, 0.6576 and 0.6784 for ω in range of 0–60°. Moreover, the UF increases as αab decreases when other receiver parameters are constant for the δ of 0–8°. The ρr has a limited effect on the UF until δ becomes relatively larger and ω becomes relatively smaller. Furthermore, ω effects are most significant on the UF, followed by δ, f and αab. Setting a suitable f is the most economical and effective way to improve the UF.

Error Analysis of Accelerometer- and Magnetometer-Based Stationary Alignment

This paper revisits the stationary attitude initialization problem, i.e., the stationary alignment, of Attitude and Heading Reference Systems (AHRSs). A detailed and comprehensive error analysis is proposed for four of the most representative accelerometer- and magnetometer-based stationary attitude determination methods, namely, the Three-Axis Attitude Determination (TRIAD), the QUaternion ESTimator (QUEST), the Factored Quaternion Algorithm (FQA), and the Arc-TANgent (ATAN). For the purpose of the error analysis, constant biases in the accelerometer and magnetometer measurements are considered (encompassing, hence, the effect of hard-iron magnetism), in addition to systematic errors in the local gravity and Earth magnetic field models (flux density magnitude, declination angle, and inclination angle). The contributions of this paper are novel closed-form formulae for the residual errors (normality, orthogonality, and alignment errors) developed in the computed Direction Cosine Matrices (DCM). As a consequence, analytical insight is provided into the problem, allowing us to properly compare the performance of the investigated alignment formulations (in terms of ultimate accuracy), as well as to remove some misleading conclusions reported in previous works. The adequacy of the proposed error analysis is validated through simulation and experimental results.

Impact of Antarctic Sudden Stratospheric Warming on Mid-Latitude Thermosphere and Ionosphere over USA and Europe

<p>Limited observational evidence indicates that ionospheric changes caused by Arctic SSWs propagate to at least the middle latitudes in the Southern Hemisphere. However, it is not known if similar ionospheric anomalies are produced by Antarctic SSWs, mostly because Antarctic SSWs occur less often than the Arctic events. The sudden stratospheric warming of September 2019 has provided a perfect opportunity to investigate whether SSW are linked to upper atmospheric anomalies at middle latitudes of the opposite hemisphere. In this study we provide an overview of thermospheric and ionospheric anomalies observed in September 2019 at middle latitudes in the Northern Hemisphere. Our results indicate persistent and strong positive anomalies in total electron content and thermospheric O/N2 ratio observed in the western region of USA. Central and eastern regions of USA do not experience similar positive perturbations and show mostly moderate suppression of TEC reaching 20-40% of the baseline. Both positive and negative anomalies are observed over the central Europe. We discuss potential mechanisms that could be responsible for the observed features and suggest that regional differences in TEC response could be related to modulation of thermospheric winds by SSW and large declination angle over Western US.</p>

Association between Proximal Tibiofibular Joint Morphology and Knee Alignment in Osteoarthritis Patients

This study aimed to determine whether proximal tibiofibular joint (PTFJ) morphology was related to knee alignment in osteoarthritis (OA) patients. Methods: 67 OA patients were enrolled in this study. The morphology of the PTFJ including articular shape type, articular surface area, joint inclination, relative articular height, and joint declination were measured from 3D models. The knee alignment of each subject was characterized as varus, normal, or valgus according to the femorotibial angle (FTA). The FTA was measured on weight-bearing X-rays. Multinomial logistic regression analysis was used to evaluate the association between PTFJ morphology and knee alignment. Results: there were significant differences between varus, valgus, and normal FTA groups in terms of shape type (p = 0.021), inclination of the PTFJ (p = 0.025), relative articular height (p = 0.019), and PTFJ declination angle (p = 0.011). A higher relative articular height (OR: 0.608, 95% CI: 0.205–0.998, and p = 0.017) and lower declination angle (OR: 0.632, 95% CI: 0.601–0.887, and p =0.019) were found to be associated with an increased likelihood of having a valgus FTA rather than a varus FTA. Conclusion: our results indicate that PTFJ morphology is associated with knee alignment.

Characterization of Machined Surface Topography Based on the Normal Declination Angle of Microfacets

It is important to characterize surface topography in order to study machined surface characteristics. Due to the features of periodicity and randomness of machined surface topography, the existing topographical parameters may not describe its features accurately. A novel characterization method called the normal declination angle of microfacet-based surface topography is thus proposed for this task. The topography of machined surfaces is measured and the data on the normal declination angle are obtained. Then, surface topography is analyzed via the distribution of the normal declination angle. The lognormal distribution characterization model of machined surface topography is established, and the accuracy of the model is verified by error analysis. The results show that the calculated results of the present characterization model are generally consistent with the distribution of the normal declination angle, where the maximal root mean square errors (RMSE) is 4.5%. Therefore, this study may serve as an effective and novel way to describe the characteristics of the machined surface topography.

Association Between the Morphology of Proximal Tibiofibular Joint and the Presence of Knee OA

Objective: The aim of this study was to evaluate the association between the morphology of the proximal tibiofibular joint (PTFJ) and the presence of knee osteoarthritis (OA).Methods: Twenty-eight OA subjects and 30 healthy subjects were enrolled in this study. A 3D model of the lower limb of each subject was constructed from CT scans and used to measure the characteristics of the PTFJ, including the shape of the articular facets, articular surface area, joint inclination, relative articular height, and joint declination. The association between the characteristics of the PTFJ and presence of knee OA was assessed using binomial logistic regression analysis.Results: There was a significant difference between the OA and healthy groups in terms of the inclination (p = 0.028) and declination (p = 0.020) of the PTFJ and relative articular height (p = 0.011). A greater inclination angle (OR: 1.463, 95% CI: 1.124–1.582, p = 0.021), greater declination angle (OR: 1.832, 95% CI: 1.691–2.187, p = 0.009), and lower relative articular height (OR: 0.951, 95% CI: 0.826–0.992, p = 0.008) were found to be associated with an increased likelihood of knee OA being present.Conclusion: The results of this study suggest that abnormal PTFJ morphology is associated with the presence of knee OA.