Influence of Device Geometry on Transport Properties of Topological Insulator Microflakes

In the transport studies of topological insulators, microflakes exfoliated from bulk single crystals are often used because of the convenience in sample preparation and the accessibility to high carrier mobilities. Here, based on finite element analysis, we show that for the non-Hall-bar shaped topological insulator samples, the measured four-point resistances can be substantially modified by the sample geometry, bulk and surface resistivities, and magnetic field. Geometry correction factors must be introduced for accurately converting the four-point resistances to the longitudinal resistivity and Hall resistivity. The magnetic field dependence of inhomogeneous current density distribution can lead to pronounced positive magnetoresistance and nonlinear Hall effect that would not exist in the samples of ideal Hall bar geometry.

Geometric Correction Method Applying the Holographic Ray Direction Control Technology

In recent years, there has been an increasing need for larger screens and higher definition displays, while projectors are becoming smaller and cheaper. Furthermore, an ultra-short-throw projector that can display on a large screen while significantly reducing the distance between the projector and screen is being developed. However, ultra-short-throw projectors are required to be precisely aligned with the screen, and if the screen is not flat, the projected image becomes distorted. Therefore, geometric correction projection technology is attracting attention for projection on curtains and the walls of living rooms instead of screens for realizing the correction of distortion during projection with ultra-short-throw projectors, projection mapping, signage, etc. We focused on developing a hologram with perfect command of the ray. Conventional geometry-correction systems are expensive systems that require a personal computer and a camera. In this study, we developed a geometric correction method applying holographic ray direction control technology to control a holographic ray at a low cost and in real time. In this paper, we studied the exposure technology and proposed a ray-direction control technology that combines a scanning laser projector that uses a hologram and a micro electro mechanical systems mirror. We also proposed and demonstrated the basic principle of a holographic surface projector (HSP), which uses hologram geometry correction technology. Finally, we constructed a geometrically corrected hologram exposure system using a depth camera and conducted geometrically corrected projection experiments.

Improving Accuracy of Checkshot Time-Depth by Applying Advanced Model-Based Correction for Rig-Source Survey on a Highly Inclined Well

In seismic exploration, checkshot survey is an important method to obtain accurate time-depth profile for depth-to-time or time-to-depth conversion. However, the standard geometry correction for a rig-source survey in a high-inclination well will not provide a reliable time-depth result due to ray-bending effect. The objective of this study was to enhance the accuracy of the time-depth velocity by utilizing an advanced technique called model-based correction or pseudo walk-above simulation. To obtain model-based vertical times, a flat-layered velocity model was built by using the checkshot velocities as initial guess. The model was then inverted to match the observed checkshot travel times, which were the actual measurement of travel path from source to receivers. The model was iterated to minimize the residual between the observed and modeled travel times in a least-square sense. A pseudo walk-above checkshot simulation was run on the inverted model by positioning the sources exactly on top of the receivers to get the vertical times, which were used for the final time-depth relationship and further image processing. The residual times of less than 1 millisecond (ms) were observed between the actual measured transit times and modeled travel times from a fixed source to the receivers in the inverted model. This demonstrated the inverted model was realiable to use for obtaining more accurate vertical time-depth through pseudo walk-above checkshot simulation. This optimal inverted model was considered as the best estimation of the true earth model in this case. A comparison of modeled vertical times estimated through the pseudo walk-above simulation and calculated vertical times using standard geometry correction were done. The difference between the two scenarios was 6 ms one-way time (OWT) demonstrated the reduction of 6 ms uncertainty of using the advanced model-based correction versus the standard geometry correction. In short, the advanced technique delivered more reliable time-depth velocity information to reduce depth uncertainties for drilling operation. The walk-above or vertical incidence checkshot survey, which required boat and navigation system, was unable to acquire in a highly deviated well due to very bad weather conditions. The rig-source survey was carried out instead of employing the walk-above survey in this project. The standard geometry correction using simple trigonometry was not able to provide the correct vertical times. The advanced model-based correction was the optimal solution to improve the accuracy of checkshot time-depth velocity data.

Three-Dimensional Simulation of Crack Propagation in the Central-Cracked Flat and Stiffened Plates Under Uniform Tension

In this paper, the crack propagation behavior in flat and stiffened plates with central-cracked is studied based on the theory of linear elastic fracture mechanics and 3D finite-element method. The magnitude and distribution of the stress intensity factor in a 3D stiffened plates are affected by the out-of-plane bending and loading modes. Initially, for validating this method, the behavior of crack propagation in a central-cracked flat plate (unstiffened), followed by the propagation behavior and the crack arrest effects on stiffened plates by stiffeners, as well as the out-of-plane bending effect on the geometry correction function distribution are studied; However, the results are compared with the results of the referenced article. In order to analyze the effect of stiffeners in preventing crack expansion, stiffeners with variable thickness and height were used. It should also be noted that the crack propagation behavior in the stiffened plate is analyzed in two methods. In the first analysis, after the crack tip reaches to the stiffeners, they have not fracture and the crack only expands in the stiffened plate (in the stiffened plate type 1 and 2). In the second analysis, with the crack growth in the stiffened plate and the crack tip reaching to the stiffeners, Also they fractured and cracks in the stiffened plate and stiffeners are propagated (only in the stiffened plate type 2). In both analyses, the magnitudes ​​of the geometry correction function in the middle-plane, the crack arrest effect by the stiffeners (Δβs), and the out-of-plane bending effect (Δβ) were obtained. Then, the changes in these magnitudes ​​were investigated. It was observed that the stiffeners thickness had a negligible effect on the distribution of the geometry correction function and, in general, the stiffeners had a significant role in preventing the crack growth compared to the flat plate, and the more the crack tip is closer to the adjoining stiffeners; the stiffeners effect in the crack arrest will increases. Furthermore, with attention to the geometry correction function that is studied for different crack sizes, it was determined that the geometry correction function and stress intensity coefficient with increasing the length of the crack in the plate, increase.

Shoreline Change Dynamics using Digital Shoreline Analysis in Cemara Besar Island

This paper will describe a study to find out the shoreline changes that occurred on Cemara Besar Island along with the accretion and abrasion. Data taken from the images was obtained through google earth as a result of radiometry and geometry correction from Landsat satellites in the last 5 years. Wind data is obtained from ecmwf interm every season for 5 years. Analysis of shoreline changes was carried out using the DSAS (Digital Shoreline Analysis) method and analyzed by wind and sea wave factors in each season. The results of the analysis obtained LRR and EPR values for 5 years, the extent of changes in island land mass, the value of Hs and Ts from the results of wave forecasting using wind data. To simplify the analysis, Cemara Besar Island is divided into 9 segments based on variations in LRR values. The results show that in general Cemara Besar Island have very high accretion in segments A, B and E with an average of 3.61 m and very high abrasion occurred in segment F with an average of -1.01 m. Abrasion occurs with the greatest speed of change in segment A with an average of 4.64 m/year and the largest accretion rate in segment F with an average of -1.21791 m/year. Analysis of oceanographic factors through wave forecasting shows that in the west and transition I season, waves occur with Hs 1.21 m, greater than the eastern season and transition II season with Hs 0.91 m. wind direction from north dominant direction 377.50 in west season and transition I, and from east direction 67,25 in east season and transition I season. Direction of wind blowing influences wave propagation and direction of wave coming towards shore which affects sediment transport which produces accretion and abrasion on the Cemara Besar Island.

Inherent Geometry Correction for Diffusion EPI Using the Reference Echoes as Navigators

Diffusion-weighted EPI has become an indispensable tool in body MRI. Geometric distortions due to field inhomogeneities are more prominent at large field–of–view and require correction for comparison with T2W TSE. Several known correction methods require acquisition of additional lengthy scans, which are difficult to apply in body imaging. We implement and evaluate a geometry correction method based on the already available non phase-encoded EPI reference data used for Nyquist ghost removal. The method is shown to provide accurate and robust global geometry correction in the absence of strong, local phase offsets. It does not require additional time for calibrations and is directly compatible with parallel imaging methods. The resulting images can serve as improved starting point for additional geometry correction methods relying on feature extraction and registration.

Influence of included drill angle on cutting forces during drilling of aluminum alloy

The paper presents the analysis of the influence of the twist drill geometry, in particular the 2κr angle, on the cutting forces during holes drilling in the element made of aluminum alloy for plastic forming EN AW-2024. In addition, the impact of the application of the drill geometry correction on the values of cutting forces was also investigated. During the tests, the values of components Fx, Fy and Fz of the cutting force for tools with different geometry with the set, variable technological parameters, i.e.: feed f and cutting speed vc were measured. The changes in the value of the axial component Fz were analyzed in detail. It was found that the use of drills with an angle of 2κr < 100°, due to the significant value of the axial force Fz and high amplitude is unfavorable. Also, the lack of drill correction translates into an increase in the value of the axial force Fz and its amplitude.