[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

A scheme is developed for classifying the types of motion perceived by a humanlike robot. It is assumed that the robot receives visual images of the scene using a perspective system model. Equations, theorems, concepts, clues, etc., relating the objects, their positions, and their motion to their images on the focal plane are presented. >

http://ieeexplore.ieee.org/iel2/815/3148/00100651.pdf

Robot vision

/pdf/remote-sensing-of-the-environment-4yfxjaaswe.pdf

Remote sensing of the environment

This paper provides a comprehensive review of the domain of physical layer security in multiuser wireless networks. The essential premise of physical layer security is to enable the exchange of confidential messages over a wireless medium in the presence of unauthorized eavesdroppers, without relying on higher-layer encryption. This can be achieved primarily in two ways: without the need for a secret key by intelligently designing transmit coding strategies, or by exploiting the wireless communication medium to develop secret keys over public channels. The survey begins with an overview of the foundations dating back to the pioneering work of Shannon and Wyner on information-theoretic security. We then describe the evolution of secure transmission strategies from point-to-point channels to multiple-antenna systems, followed by generalizations to multiuser broadcast, multiple-access, interference, and relay networks. Secret-key generation and establishment protocols based on physical layer mechanisms are subsequently covered. Approaches for secrecy based on channel coding design are then examined, along with a description of inter-disciplinary approaches based on game theory and stochastic geometry. The associated problem of physical layer message authentication is also briefly introduced. The survey concludes with observations on potential research directions in this area.

/pdf/principles-of-physical-layer-security-in-multiuser-wireless-3w4jvwpgy4.pdf

Principles of Physical Layer Security in Multiuser Wireless Networks: A Survey

In this paper, we propose a unified framework to generate a pleasant and high-quality street-view panorama by stitching multiple panoramic images captured from the cameras mounted on the mobile platform. Our proposed framework is comprised of four major steps: image warping, color correction, optimal seam line detection and image blending. Since the input images are captured without a precisely common projection center from the scenes with the depth differences with respect to the cameras to different extents, such images cannot be precisely aligned in geometry. Therefore, an efficient image warping method based on the dense optical flow field is proposed to greatly suppress the influence of large geometric misalignment at first. Then, to lessen the influence of photometric inconsistencies caused by the illumination variations and different exposure settings, we propose an efficient color correction algorithm via matching extreme points of histograms to greatly decrease color differences between warped images. After that, the optimal seam lines between adjacent input images are detected via the graph cut energy minimization framework. At last, the Laplacian pyramid blending algorithm is applied to further eliminate the stitching artifacts along the optimal seam lines. Experimental results on a large set of challenging street-view panoramic images captured form the real world illustrate that the proposed system is capable of creating high-quality panoramas.

A Unified Framework for Street-View Panorama Stitching.

Concentrated stresses and residual ones are critical for the metal structures’ health, because they can cause microcracks that require emergency maintenance or can result in potential accidents. Therefore, an accurate approach to the measurement of stresses is key for ensuring the health of metal structures. The eddy current technique is an effective approach to detect the stress according to the piezoresistive effect. However, it is limited to detect the surface stress due to the skin effect. In engineering, the stress distribution is inhomogeneous; therefore, to predict the inhomogeneous stress distribution, this paper proposes a nondestructive approach which combines the eddy current technique and finite element (FE) method. The experimental data achieved through the eddy current technique determines the relationship between the applied force and the magnetic flux density, while numerical simulations through the FE method bridge the relationship between the magnetic flux density and the stress distribution in different directions. Therefore, we can predict the inhomogeneous stress nondestructively. As a case study, the applied stress in a three-point-bending simply supported beam was evaluated, and the relative error is less than 8% in the whole beam. This approach can be expected to predict the residual stress in metal structures, such as rail and vehicle structures, if the stress distribution pattern is known.

/pdf/prediction-of-inhomogeneous-stress-in-metal-structures-a-1feszrhuto.pdf

Prediction of Inhomogeneous Stress in Metal Structures: A Hybrid Approach Combining Eddy Current Technique and Finite Element Method

Ultrasonic guided waves propagating in bounded elastic media called waveguide are used extensively nowadays for rapid screening and long distance inspection of defect-prone structures. Various types of transducers are available for guided wave generation, including piezoelectric transducers and electromagnetic acoustic transducers (EMATs) etc.. EMAT is based on Lorentz force and/or magnetostrictive effect, and advantageous sometimes because of its non-contact nature. An alternating winding magnetostrictive type EMAT for torsional mode ultrasonic guided wave generation in a steel pipe is introduced in this paper. This new transducer design is composed of a pre-magnetized Nickel strip with circumferential static magnetic field and a coaxial coil in an alternating winding pattern. Theoretically this transducer design could be viewed as an extension of existing magnetostrictive type EMAT for SH guided wave generation in a steel plate. The alternating winding pattern enables accurate and easy control of guided wave mode. Results of experiments done on a steel pipe were shown to verify this transducer design.

Alternating winding magnetostrictive electromagnetic acoustic transducer for pipe torsional guided wave generation

Emissivity variations are one of the most critical challenges in thermography technologies; this is due to the temperature calculation strongly depending on emissivity settings for infrared signal extraction and evaluation. This paper describes an emissivity correction and thermal pattern reconstruction technique based on physical process modelling and thermal feature extraction, for eddy current pulsed thermography. An emissivity correction algorithm is proposed to address the pattern observation issues of thermography in both spatial and time domains. The main novelty of this method is that the thermal pattern can be corrected based on the averaged normalization of thermal features. In practice, the proposed method brings benefits in enhancing the detectability of the faults and characterization of the materials without the interference of the emissivity variation problem at the object’s surfaces. The proposed technique is verified in several experimental studies, such as the case-depth evaluation of heat-treatment steels, failures, and fatigues of gears made of the heat-treated steels that are used for rolling stock applications. The proposed technique can improve the detectability of the thermography-based inspection methods and would improve the inspection efficiency for high-speed NDT&E applications, such as rolling stock applications.

/pdf/emissivity-correction-and-thermal-pattern-reconstruction-in-2vplohwd.pdf

Emissivity Correction and Thermal Pattern Reconstruction in Eddy Current Pulsed Thermography

Deep insights into microstructures and domain wall behaviors in the evaluation of different material statuses under elastic and plastic stress ranges have essential implications for magnetic sensing and nondestructive testing and evaluation (NDT&E). This paper investigates the repeatability and stability of residual magnetic field (RMF) signals using a magneto-optical Kerr effect microscope for the stress characterization of silicon steel sheets beyond their elastic limit. Real-time domain motion is used for RMF characterization, while both the repeatability under plastic ranges after the cyclic stress rounds and stability during relaxation time are studied in detail. The distinction between elastic and plastic materials is discussed in terms of their spatio-temporal properties for further residual stress measurement since both ranges are mixed. During the relaxation time, the RMF of the plastic material shows a two-stage change with apparent recovery, which is contrasted with the one-stage change in the elastic material. Results show that the grain boundary affects the temporal recovery of the RMF. These findings concerning the spatio-temporal properties of different RMFs in plastic and elastic materials can be applied to the design and development of magnetic NDT&E for (residual) stress measurement and material status estimation.

/pdf/comparison-of-repeatability-and-stability-of-residual-tzvvqmye.pdf

Comparison of Repeatability and Stability of Residual Magnetic Field for Stress Characterization in Elastic and Plastic Ranges of Silicon Steels

In NDT it is important to have a high probability of detection and reliable sizing of defects in a sample. This can be gained by using several techniques, which leads to an increase in cost and time for testing. Another option is to use several techniques combined into a single probe, in which case data fusion for the techniques is possible. We report measurements using a dual probe containing a pair of electro-magnetic acoustic transducers generating and detecting low frequency broadband ultrasonic surface waves, combined with a pulsed eddy current probe. These two techniques are complementary but can be combined to work as competitive or cooperative sensors depending on the type of defect being investigated. Our work gives the depth of surface breaking defects by performing data fusion on certain features of data from each technique in a competitive sense, with data fusion by mathematical algorithm. Further analysis of the results using cooperative data fusion can give details of the depth and type of defect, for example surface breaking or near surface. The dual probe has been demonstrated on several samples, including aluminium and steel samples with several simulated defects on each side.

Gui Yun Tian

Papers

Prediction of Inhomogeneous Stress in Metal Structures: A Hybrid Approach Combining Eddy Current Technique and Finite Element Method

Alternating winding magnetostrictive electromagnetic acoustic transducer for pipe torsional guided wave generation

Emissivity Correction and Thermal Pattern Reconstruction in Eddy Current Pulsed Thermography

Comparison of Repeatability and Stability of Residual Magnetic Field for Stress Characterization in Elastic and Plastic Ranges of Silicon Steels

Data Fusion for Combining Techniques to Detect and Size Surface and Near‐Surface Defects