Distance In Vertical Direction Research Articles

Rapid Calibration Method for 3D Laser Scanner

Background: The 3D laser scanner is a non-contact active-sensing system, which has a number of applications. Many patents have been filed on the technologies for calibrating 3D laser scanner. A precise calibration method is important for measuring the accuracy of the 3D laser scanner. The system model contains three categories of parameters to be calibrated which include the camera intrinsic parameters, distortion coefficients and the light plane parameters. Typically, the calibration process is completed in two steps. Based on Zhang’s method, the calibration of the camera intrinsic parameters and distortion coefficients can be performed. Then, 3D feature points on the light plane should precisely be formed and extracted. Finally, the points are used to calculate the light plane parameters. Methods: In this paper, a rapid calibration method is presented. Without any high precision auxiliary device, only one coplanar reference target is used. By using a group of captured images of the coplanar reference target placed in the field of view arbitrarily, calibration can be performed in one step. Based on the constraint from the planes formed by the target in different directions and the camera imaging model, a large amount of 3D points on the light plane can easily be obtained. The light plane equation in the camera coordinates system can be gathered by executing plane fitting to the 3D points. Results: During the experimental process, the developed 3D laser scanner was calibrated by the proposed method. Then, the measuring accuracy of the system was verified with known distance in vertical direction of 1mm with sequential shifting motion generated by precision translation stage. The average value of the measured distances was found to be 1.010mm. The standard deviation was 0.008mm. Conclusion: Experimental results prove that the proposed calibration method is simple and reliable.

Effects of stop hole on crack turning, residual fatigue life and crack tip stress field

The aim of this paper is to research the effects of stop hole on crack turning, residual fatigue life and crack tip stress field, in which the location, size and shape of stop hole are considered. The numerical model is established according to M-integral technology, and crack turning angle is determined by maximum hoop stress criterion. The calculation results show that stop hole location has a significant effect on crack turning angle and residual fatigue life, and it should be drilled with a reasonable distance in vertical and horizontal direction around crack tip to achieve a better residual fatigue life retardation effect. The larger the stop hole size is, the wider effect range of stop hole on crack turning and residual fatigue life will be. The effects of elliptical stop hole on crack turning angle and residual fatigue life retardation are greater than that of round hole when the distance in vertical direction increases. Crack tip stress distribution is changed by increasing σy and decreasing σx, and the most dramatical changes occur at the circumferential direction of 90° and 270°.

Quantitative morphometric analysis of the Jama River profile in a tectonically active margin (Northwestern Ecuador)

The longitudinal profile of a river channel can be described in function of mathematical expressions. The logarithmic fit is the most used method to describe the relative equilibrium of a channel elevation profile. Rivers showing zones of high channel gradient and convex-upward profiles can be evaluated in function of the offset distance with respect to the logarithmic curve. The Jama River profile has been constructed using differential GPS data for the downstream reach and 4-m-grid DEM data base for the remaining headward profile. The resulting longitudinal profile shows a prominent knickpoint of about 80 m in elevation characterized by sharp local convexity. The offset distance in vertical direction from the logarithmic plot is interpreted as the successive accumulation of multiple uplift episodes associated with the Jama Fault System activity. The horizontal offset is suggested to represent the remaining retreated distance for the upstream propagation of the Jama knickpoint. The highly resistant Cretaceous rocks outcropping along the Jama knickpoint reach acts as an inflection point between two subprofiles that show well-fitted logarithmic curves, thereby representing a temporary partitioned equilibrium along the Jama River profile.

Application of a pelvic phantom in brachytherapy dosimetry for high-dose-rate (HDR) 192Ir source based on Monte Carlo simulations

In this study, we evaluate how the radial dose function is influenced by the source position as well as the phantom size and shape. A pelvic water phantom similar to the pelvic shape of a human body was designed by averaging dimensions obtained from computed tomography (CT) images of patients treated with brachytherapy for cervical cancer. Furthermore, for the study of the effects of source position on the dose distribution, the position of the source in the water phantom was determined by using the center of mass of the gross target volume (GTV) in the CT images. To obtain the dosimetric parameter of a high-dose-rate (HDR) 192Ir source, we performed Monte Carlo simulations by using the Monte Carlo n-particle extended code (MCNPX). The radial dose functions obtained using the pelvic water phantom were compared with those of spherical phantom with different sizes, including the Monte Carlo (MC) results of Williamson and Li. Differences between the radial dose functions from this study and the data in the literature increased with the radial distances. The largest differences appeared for spherical phantom with the smallest size. In contrast to the published MC results, the radial dose function of the pelvic water phantom significantly decreased with radial distance in the vertical direction because full scattering was not possible. When the source was located in posterior position 2 cm from the center in the pelvic water phantom, the differences between the radial dose functions rapidly decreased with the radial distance in the lower vertical direction. If the International Commission on Radiation Units and Measurements bladder and rectum points are considered, doses to these reference points could be underestimated by up to 1%–2% at a distance of 3 to 6 cm. Our simulation results provide a valid clinical reference data and can used to improve the accuracy of the doses delivered during brachytherapy applied to patients with cervical cancer.

Underwater Continuous Localization Based on Magnetic Dipole Target Using Magnetic Gradient Tensor and Draft Depth

In the area of underwater autonomous localization based on geomagnetic anomaly inversion, it is a challenge to obtain the magnitude of magnetic dipole field from data measured by magnetometers, due to the existence of geomagnetic background field, where geomagnetic anomaly comes from magnetic dipole target. We propose, in this letter, a localization method combined with magnetic gradient tensor and draft depth, where the distance in vertical direction between underwater vehicle and the target can be calculated by measurements at two draft depths. On the other hand, to avoid movement of the underwater vehicle, the magnetic moment of the target is used to form an equation group about position of the vehicle, which is solved to realize continuous underwater localization. The detailed principle and steps of this continuous localization algorithm are described in detail, and its good performances, such as high-precision and fast convergence, are proved by theoretical analysis and numerical simulation.

Numerical Study of the Curve Route Levitation Performance of the HTS Bulk over NdFeB Guideway

The passive levitation has a self-adjust characteristic to adapt to environmental changes. Levitation Height (LH) or Lateral Displacements (LD) of the high-temperature superconducting (HTS) Maglev vehicle, running over Permanent Guideway (PMG), will change respectively or synchronously due to some external reasons, which caused the vehicle move a certain distance in vertical direction (Y direction) or horizontal direction (X direction) according to a line space route curve along Y or X direction, or random route lying in a XY plane which is perpendicular to the vehicle running direction (Z direction) corresponding to a complicated space route curve. In these cases, how are the levitation performances of the HTS bulk? From a simplest space line route, this paper studied computationally the curve route levitation performance of the HTS bulk which is subject to a PMG applied field. Results show that the change of the levitation and guidance force is different when the HTS bulk moved along line space route. This provides important scientific theories for the numerical simulation of HTS Maglev vehicle.