Younchang Choi

Magnetic properties of amorphous Sm-Fe and Sm-Fe-B thin films fabricated by radio-frequency magnetron sputtering

Magnetic properties of giant magnetostrictive Sm–Fe and Sm–Fe–B thin films are systematically investigated over a wide composition range from 14.1 to 71.7 at. % Sm. The amount of B added ranges from 0.3 to 0.8 at. %. The microstructure mainly consists of an amorphous phase in the intermediate Sm content range from 20 to 45 at. %. Together with an amorphous phase, crystalline phases of Fe and Sm also exist at low and high ends of the Sm content, respectively. Well-developed in-plane anisotropy is formed over the whole composition range, except for the low Sm content below 15 at. % and the high Sm content above 55 at. %. As the Sm content increases, the saturation magnetization decreases linearly and the coercive force tends to increase, with the exception of the low Sm content where very large magnitudes of the saturation magnetization and the coercive force are observed due to the existence of the crystalline α-Fe phase. The coercive force is affected rather substantially by the B addition, resulting in l...

The magnetic properties of Tb-Fe-(B) thin films fabricated by rf magnetron sputtering

Abstract The magnetic properties of giant magnetostrictive TbFe and TbFeB thin films are systematically investigated. The films were fabricated by rf magnetron sputtering using a composite target which consists of an Fe plate and Tb chips. The introduction of B to the films was done by using an Fe plate containing B. The microstructure, examined by X-ray diffraction, mainly consists of an amorphous phase and, at high Tb contents, a pure Tb phase also exists. A progressive change in the direction of anisotropy from the perpendicular to in-plane occurs as the Tb content increases from 35 to 68 at.% for the B-free TbFe films and from 44 to 67 at.% for the TbFeB thin films. The boundary at which the anisotropy change occurs shifts significantly towards to higher Tb contents when B is introduced to the films. The saturation magnetization exhibits a maximum at the Tb contents of 42 and 48 at.% and the values are about 5800 and 5100 G for the TbFe and TbFeB thin films, respectively. The coercive force, measured in the easy direction, decreases monotonically with the Tb content and ranges from 7.5 to 100 Oe when the films with in-plane anisotropy are considered. The magnetic softness of the present film which exhibits the coercive force of below 10 Oe and a typical squared-loop shape, and saturates at a low field of 1 kOe, is considered to be the best, to our knowledge, among this kind of thin films.

Molecular Characteristics of Subterranean Termites of the genus Reticulitermes (Isoptera: Rhinotermitidae) From Korea

ABSTRACT Molecular and taxonomic studies of subterranean termites in the genus Reticulitermes (Isoptera: Rhinotermitidae) have suggested that Reticulitermes speratus kyushuensis Morimoto is the only species that occurs in Korea. However, the specimens studied to date were collected from a limited number of locations, and basic information about the distribution, taxonomy, and molecular characteristics of this genus in Korea is still lacking. In this study, we collected Reticulitermes specimens from 50 sampling sites distributed throughout the country. By comparing the cytochrome oxidase subunit II gene of mitochondrial DNA sequences, we conclude that Reticulitermes speratus is represented by two haplotypes in Korea. In addition, we report the first occurrence of another Reticulitermes species in this country.

Depth-Based Detection of Standing-Pigs in Moving Noise Environments

In a surveillance camera environment, the detection of standing-pigs in real-time is an important issue towards the final goal of 24-h tracking of individual pigs. In this study, we focus on depth-based detection of standing-pigs with “moving noises”, which appear every night in a commercial pig farm, but have not been reported yet. We first apply a spatiotemporal interpolation technique to remove the moving noises occurring in the depth images. Then, we detect the standing-pigs by utilizing the undefined depth values around them. Our experimental results show that this method is effective for detecting standing-pigs at night, in terms of both cost-effectiveness (using a low-cost Kinect depth sensor) and accuracy (i.e., 94.47%), even with severe moving noises occluding up to half of an input depth image. Furthermore, without any time-consuming technique, the proposed method can be executed in real-time.

Replacement Condition Detection of Railway Point Machines Using an Electric Current Sensor

Detecting replacement conditions of railway point machines is important to simultaneously satisfy the budget-limit and train-safety requirements. In this study, we consider classification of the subtle differences in the aging effect—using electric current shape analysis—for the purpose of replacement condition detection of railway point machines. After analyzing the shapes of after-replacement data and then labeling the shapes of each before-replacement data, we can derive the criteria that can handle the subtle differences between “does-not-need-to-be-replaced” and “needs-to-be-replaced” shapes. On the basis of the experimental results with in-field replacement data, we confirmed that the proposed method could detect the replacement conditions with acceptable accuracy, as well as provide visual interpretability of the criteria used for the time-series classification.

Enhanced in-plane anisotropy of Tb–Fe thin films by Sm addition

Effects of Sm on the magnetic and magnetostrictive properties of Tb–Fe thin films are investigated. Four alloy systems, RxFe100−x (R=Tb+Sm) with x=39.8, 41.9, 43.7, and 45.8, are examined with Sm content varied from 0 (Sm free) to 2.2 at. %. In-plane anisotropy is found to be enhanced by the addition of Sm and the strongest in-plane anisotropy occurs in the Sm content range of 1 to 2 at. % depending on R content. At low magnetic fields of 1000 Oe and below, magnetostriction increases significantly with increasing Sm content, and reaches a maximum at an intermediate Sm content where well-developed in-plane anisotropy is observed. At higher magnetic fields of 3000–5000 Oe, however, no substantial improvement of magnetostriction occurs with the addition of Sm. The Sm content dependences of magnetization and coercive force are also examined.

A Kinect-Based Segmentation of Touching-Pigs for Real-Time Monitoring

Segmenting touching-pigs in real-time is an important issue for surveillance cameras intended for the 24-h tracking of individual pigs. However, methods to do so have not yet been reported. We particularly focus on the segmentation of touching-pigs in a crowded pig room with low-contrast images obtained using a Kinect depth sensor. We reduce the execution time by combining object detection techniques based on a convolutional neural network (CNN) with image processing techniques instead of applying time-consuming operations, such as optimization-based segmentation. We first apply the fastest CNN-based object detection technique (i.e., You Only Look Once, YOLO) to solve the separation problem for touching-pigs. If the quality of the YOLO output is not satisfied, then we try to find the possible boundary line between the touching-pigs by analyzing the shape. Our experimental results show that this method is effective to separate touching-pigs in terms of both accuracy (i.e., 91.96%) and execution time (i.e., real-time execution), even with low-contrast images obtained using a Kinect depth sensor.

Aging Detection of Electrical Point Machines Based on Support Vector Data Description

Electrical point machines (EPM) must be replaced at an appropriate time to prevent the occurrence of operational safety or stability problems in trains resulting from aging or budget constraints. However, it is difficult to replace EPMs effectively because the aging conditions of EPMs depend on the operating environments, and thus, a guideline is typically not be suitable for replacing EPMs at the most timely moment. In this study, we propose a method of classification for the detection of an aging effect to facilitate the timely replacement of EPMs. We employ support vector data description to segregate data of “aged” and “not-yet-aged” equipment by analyzing the subtle differences in normalized electrical signals resulting from aging. Based on the before and after-replacement data that was obtained from experimental studies that were conducted on EPMs, we confirmed that the proposed method was capable of classifying machines based on exhibited aging effects with adequate accuracy.

CPU-GPU Heterogeneous Implementations of Depth-based Foreground Detection

Video sensor data has been widely used in automatic surveillance applications. In this study, we present a method that automatically detects the foreground by using depth information. For real-time implementation, we propose a means of reducing the execution time by applying parallel processing techniques. In general, most parallel processing techniques have been used to parallelize each specific task efficiently. In this study, we consider a practical method to parallelize an entire system consisting of several tasks (i.e., low-level and intermediate-level computer vision tasks with different computational characteristics) by balancing the total workload between CPU and GPU. Experimental results with a pig monitoring application reveal that the proposed method can automatically detect the foreground using CPU-GPU heterogeneous computing platforms in real time, regardless of the relative performance between the CPU and GPU.

Heterogeneous computing for a real-time pig monitoring system

Video sensor data has been widely used in automatic surveillance applications. In this study, we present a method that automatically detects pigs in a pig room by using depth information obtained from a Kinect sensor. For a real-time implementation, we propose a means of reducing the execution time by applying parallel processing techniques. In general, most parallel processing techniques have been used to parallelize a specific task. In this study, we consider parallelization of an entire system that consists of several tasks. By applying a scheduling strategy to identify a computing device for each task and implementing it with OpenCL, we can reduce the total execution time efficiently. Experimental results reveal that the proposed method can automatically detect pigs using a CPU-GPU hybrid system in real time, regardless of the relative performance between the CPU and GPU.