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In the present research, the influence of tool axis offset on the microstructural and mechanical characteristics of dissimilar friction stir butt welded AA5083-H111 and AA7050-T7651 alloys is investigated. The experiments were conducted with the softer AA5083 alloy on the advancing side (AS) of the joint by varying the tool axis offset from zero to 1 mm, both towards the AS and retreating side (RS) of the joint with a 0.25 mm interval. The tool rotational speed, tool traverse speed, axial pressure and tool tilt angle, fixed by systematic preliminary trials, were held constant. The friction stir welded joints were subjected to microstructural (optical microscopy and EBSD analysis) and mechanical (microhardness and tensile properties) characterizations. The research outputs show that the position of tool axis has significant influence on the microstructure evolution and mechanical properties of the joints. The joint fabricated at 0.25 mm tool axis offset to the RS has exhibited the highest joint strength of 291 MPa (joint efficiency of 94.5%) and the joint efficiency is very sensitive to the change in tool axis offset. With this positional configuration of the alloys, the stir zone (SZ) is dominated by the dynamically recrystallized, strain free AA5083 alloy. The softening of the HAZ of the weaker AA5083 alloy (for higher tool axis offset to AA7050 alloy) and the weakening of the of SZ bottom (for low tool offset to AA7050 alloy and tool axis offset to AA5083 alloy) are the main factors which determine the location of fracture and the strength of the joints. In FSW of dissimilar 7xxx and 5xxx alloys, for better joint efficiency, positional configuration of alloys and appropriate selection of tool axis offset are very important.

The accuracy and stability of Very Long Baseline Interferometry (VLBI) systems are essential for maintaining global geodetic reference frames such as the International Terrestrial Reference Frame (ITRF). This study focuses on the precise determination of the VLBI Invariant Point (IVP) and the detection of antenna axis offset. Ground-based surveys were conducted at the Sejong Space Geodetic Observatory using high-precision instruments, including total station, to measure slant distances, as well as horizontal and vertical angles from fixed pillars to reflectors attached to the VLBI instrument. The reflectors comprised both prisms and reflective sheets to enhance redundancy and data reliability. A detailed stochastic model incorporating variance component estimation was employed to manage the varying precision of the observations. The analysis revealed significant measurement variability, particularly in slant distance measurements involving prisms. Iterative refinement of the variance components improved the reliability of the IVP and antenna axis offset estimates. The study identified an antenna axis offset of 5.6 mm, which was statistically validated through hypothesis testing, confirming its significance at a 0.01 significance level. This is a significance level corresponding to approximately a 2.576 sigma threshold, which represents a 99% confidence level. This study highlights the importance of accurate stochastic modeling in ensuring the precision and reliability of the estimated VLBI IVP and antenna axis offset. Additionally, the results can serve as a priori information for VLBI data analysis.

AbstractThe axis-offset collision of two vortex rings with their various circulation ratios was numerically investigated using the vortex-in-cell method combined with the large-eddy simulation model. For the ratio of 0.1, the robust ring, moving through the weak ring, remains unchanged in its shape and deforms the weak ring. The small-scale vortices are not generated at this ratio. For the ratio of 0.2, the robust ring is still maintained after collision, while parts of the weak ring near the collision regions are entrained by the robust ring. The interaction of these entrained parts with the robust ring produces many small-scale vortices. For the ratio of 0.5, the robust ring is broken into smaller-scale vortices, and the interaction of these vortices with the entrained parts of the weak ring results in many other small-scale vortices. The reconnection takes place at the unity ratio, at which half the first ring links another half the second one to form elliptical vortex rings and produce various vortices including small rings in the collision regions. These rings are rapidly distorted and interact with small vortices surrounding them to establish clusters of various-scale vortices. The energy spectrum of induced flow at high wavenumbers approaches the k−5/3 slope of Kolmogorov’s theorem after the collision, and mixing two vortex rings is the best at the ratio of 0.5. It is stated that the vortex reconnection and formation, as well as the turbulent energy cascade and mixing efficiency, significantly depend on the initial circulation ratio of two vortex rings.

The construction disturbance caused by pipe jacking is an index that must be strictly controlled in the project. With the wide application of curved pipe jacking in urban underground construction, predicting its ground surface settlement characteristics has become an increasingly important research topic. Based on finite element numerical simulation, a three-dimensional model of curved pipe jacking was established to simulate the construction stage. Compared with the straight pipe jacking, the normal component of jacking force is set in the outer tunnel of the curved pipe jacking to simulate the extrusion of the outer soil caused by the corner of the pipe joint, and the surface settlement characteristics of the curved pipe jacking are explored by changing the pressure value. The research results show that the surface settlement of the curved pipe jacking conforms to the normal distribution as a whole. Compared with the linear pipe jacking, the surface settlement is not symmetrical about the design axis of the tunnel. With the increase of the pressure outside the tunnel, the maximum settlement value of the surface and the difference between the two sides of the axis increase. Compared with the Peck formula, the width of the settling tank of the curved pipe jacking is larger, the convergence rate outside the width of the settling tank is slower, and the settlement trend is more in line with the Verruijt formula. The calculation formula is modified by axis offset distance and ovalization coefficient and modified formula can better reflect the measured engineering data. The research results can provide guidance and reference for the prediction and control of surface settlement of curved pipe jacking.

The tapping process is one of the most widespread manufacturing processes for internal threads, usually carried out at the end of the value chain. Any non-compliance with required quality standards or even the destruction of the thread due to process uncertainty in the tapping process is therefore subjected to high rework costs. Possible process uncertainties in the tapping process can be triggered by synchronization errors between feed rate and spindle speed, axis offset, faulty core holes and wear of the tapping tool. In order to detect process uncertainties during tapping and thus provide a basis for initiating countermeasures, a sensor-integrated tap holder was developed. This paper presents the realized concept of a rotating telemetry unit for signal processing, data acquisition and wireless data transmitting via WiFi standard on basis of low-cost embedded systems. Furthermore, two unique sensor concepts for measuring close-to-tool vibrations and the axial length compensation of the tapping tool are shown. Based on the sensor data in combination with feature engineering methods, process uncertainty during tapping are detected.

Response surface methodology was adopted to establish the mathematical model between the parameters (overlap ratio, Y -axis lift, and X -axis offset) and responses (non-fusion area, flatness ratio, and width of clad). The results indicated that the non-fusion area reduced at first and increased afterwards as overlap ratio decreased and Y -axis lift increased, while gradually reduced when overlap ratio increased and X -axis offset decreased. The flatness ratio gradually decreased by lowering the overlap ratio and raising the X -axis offset but gradually increased as Y -axis lift and X -axis offset lowered simultaneously. The clad width gradually reduced when overlap ratio or X -axis offset increased. A validation experiment was carried out with the target of minimizing the non-fusion area and maximizing the flatness ratio. The error rate for both responses was 7.7% and 3.6%, respectively. This article provides a theoretical basis for the forming control and prediction of double-layer and multi-track coatings by laser cladding.

T1/T2 parametric mapping may reveal patterns of elevation (“hotspots”) in myocardial diseases, such as rejection in orthotopic heart transplant (OHT) patients. This study aimed to evaluate the diagnostic accuracy of free-breathing (FB) multi-parametric SAturation recovery single-SHot Acquisition (mSASHA) T1/T2 mapping in identifying hotspots present on conventional Breath-held Modified Look-Locker Inversion recovery (BH MOLLI) T1 and T2-prepared balanced steady-state free-precession (BH T2p-bSSFP) maps in pediatric OHT patients. Pediatric OHT patients underwent noncontrast 1.5T CMR with BH MOLLI T1 and T2p-bSSFP and prototype FB mSASHA T1/T2 mapping in 8 short-axis slices. FB and BH T1/T2 hotspots were segmented using semi-automated thresholding (ITK-SNAP) and their 3D coordinate locations were collected (3-Matic, Materialise, Leuven, Belgium). Receiver operator characteristic curve analysis and measures of central tendency were utilized. 40 imaging datasets from 23 pediatric OHT patients were obtained. FB mSASHA yielded a sensitivity of 82.8% for T1 and 80% for T2 maps when compared to the standard BH MOLLI, as well as 100% specificity for both T1 and T2 maps. When identified on both FB and BH maps, hotspots overlapped in all cases, with an average long axis offset between FB and BH hotspot centers of 5.8 mm (IQR 3.5–8.2) on T1 and 5.9 mm (IQR 3.5–8.2) on T2 maps. FB mSASHA T1/T2 maps can identify hotspots present on conventional BH T1/T2 maps in pediatric patients with OHT, with high sensitivity, specificity, and overlap in 3D space. Free-breathing mapping may improve patient comfort and facilitate OHT assessment in younger patient populations.

To counteract thermal error due to material deformation in multi-axis heavy-duty CNC machining applications, this paper presents an approach based on Autoencoder-Augmented Long Short Term Memory deep learning models. The model predicts the z-axis offset of machine tools, in an idle state, with up to 96% accuracy, from ambient temperature sensor readings. By enabling a Long Short-Term Memory (LSTM) algorithm to learn time dependencies across input features and past output values with a fifth-order lag, a sequence-to-sequence regression problem is formulated. The model objective is to predict the z-axis thermal offset as an output from temperature sensor inputs. To reduce input data redundancy, the algorithm also leverages an Autoencoder to learn a reduced dimension feature representation for the input data. The reduction in input dimensionality achieves a considerable reduction in computation effort, measured in units of time, without compromising the prediction accuracy. The performance of the proposed technique is evaluated on a subset of the recorded data, and the model is benchmarked against several techniques from the literature. The results and qualitative evaluation demonstrate the superiority of the proposed approach at generating accurate predictions of the z-axis error of the system and, consequently, reducing the control error.

Three main effects from general relativity (GR) may change the geometry and orientation of artificial earth satellite orbits, i.e., the Schwarzschild, Lense–Thirring, and De Sitter effects. So far, the verification of GR effects was mainly based on the observations of changes in the orientation of satellite orbital planes. We directly observe changes of the satellite orbit geometry caused by GR represented by the semimajor axis and eccentricity. We measure the variations of orbit size and shape of GPS, GLONASS, and Galileo satellites in circular and eccentric orbits and compare the results to the theoretical effects using three years of real GNSS data. We derive a solution that assumes the GR to be true, and a second solution, in which the post-Newtonian parameters are estimated, thus, allowing satellites to find their best spacetime curvature. For eccentric Galileo, GR changes the orbital shape and size in perigee in such a way that the orbit becomes smaller but more circular. In the apogee, the semimajor axis decreases but eccentricity increases, and thus, the orbit becomes more eccentric. Hence, the orbital size variabilities for eccentric orbits are greatly compensated by the orbital shape changes, and thus the total effect of satellite height change is much smaller than the effects for the size and shape of the orbit, individually. The mean semimajor axis offset based on all GPS, GLONASS, and Galileo satellites is − 17.41 ± 2.90 mm, which gives a relative error of 0.36% with respect to the theoretical value.

In this study, we present an IoT-based robot for wrist rehabilitation with a new protocol for determining the state of injured muscles as well as providing dynamic model parameters. In this model, the torque produced by the robot and the torque provided by the patient are determined and updated taking into consideration the constraints of fatigue. Indeed, in the proposed control architecture based on the EMG signal extraction, a fuzzy classifier was designed and implemented to estimate muscle fatigue. Based on this estimation, the patient’s torque is updated during the rehabilitation session. The first step of this protocol consists of calculating the subject-related parameters. This concerns axis offset, inertial parameters, passive stiffness, and passive damping. The second step is to determine the remaining component of the wrist model, including the interaction torque. The subject must perform the desired movements providing the torque necessary to move the robot in the desired direction. In this case, the robot applies a resistive torque to calculate the torque produced by the patient. After that, the protocol considers the patient and the robot as active and all exercises are performed accordingly. The developed robotics-based solution, including the proposed protocol, was tested on three subjects and showed promising results.