• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.23 no.2
• /
• pp.152-159
• /
• 2013

A structural health monitoring(SHM) technique for locating impact position in a composite plate is presented in this paper. The technique employs a single sensor and spatial focusing properties of time reversal(TR) and inverse filtering(IF). We first examine the focusing effect of back-propagated signal at the impact position and its surroundings through simulation. Impact experiments are then carried out and the localization images are found using the TR and IF signal processing, respectively. Both techniques provide accurate impact location results. Compared to existing techniques for locating impact or acoustic emission source, the proposed methods have the benefits of using a single sensor and not requiring knowledge of material properties and geometry of structures. Furthermore, it does not depend on a particular mode of dispersive Lamb waves that is frequently used in the SHM of plate-like structures.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.25 no.2
• /
• pp.87-94
• /
• 2005

In recent, Lamb wave has been actively studied for non-destructive testing of plate. Among those studios, laser generation method of focused Lamb wave is expected to have high spatial resolution with advantages of non-contact testing. In this method, the laser beam is illuminated on the surface of object by through an arrayed-arc slit, and then the energy of the generated Lamb wave is concentrated at a focus of arc. This focusing effect improves the spatial resolution, which is dependant on the geometries of arrayed-arc slit. In this paper, the relationships between the parameters of arc-shaped slit and the focusing ability of the generated Lamb wave was investigated by the simulation based parametric study The results show that to improve the focusing effect, radius of illuminated laser, angle of arc and number of arcs must be increased, which minimum radius of arc and distance between arcs(=wavelength) must be decreased. These results are expected to be used as a guide to design the proper shape of slit.

• Journal of Korea Game Society
• /
• v.7 no.2
• /
• pp.73-82
• /
• 2007

This study deals with how computer game affects spatial-temporal capability of game users. Focusing on college students, this study shows almost the same results as 'Mozart effect' by Gordon Shaw's previously famous study for music on spatial-temporal capability. Additionally, in comparison to music and animation, on-line racing game has more positive influence on a specific spatial-temporal capability.

• Proceedings of the Korean Association of Geographic Inforamtion Studies Conference
• /
• 2003.04a
• /
• pp.629-636
• /
• 2003

• Education of Primary School Mathematics
• /
• v.9 no.2 s.18
• /
• pp.119-134
• /
• 2005

The goals of this study is to analyze develop the materials which help students develop spatial sense in elementary school and to investigate its effects. To accomplish those goals, the 7th National Curriculum was analyzed to identify the contents of spatial sense. After analyzing the 7th National Curriculum, the principle for developing the teaching aids focusing the realization of the contents in the spatial sense was set up. And then various teaching materials which can enhance students' spatial sense was developed. It is consist of 17 kinds of concretely operating materials, 7 kinds of tangram papers, one web-material. To verify the effect of the materials, surveyed the usability of the materials and two classes was selected and tests were administered before and after the treatment. Through this application, several conclusion were drawn. First, a survey result says that teachers thought materials developed would be effective in developing spatial sense. Second, the materials developed were effective to develop spatial sense. The score gained by the experiment group after the treatment was statistically meaningfully higher than the control group. This means that the materials developed helped children to develop spatial sense.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.32 no.4
• /
• pp.355-361
• /
• 2012

This paper presents an experimental study on the detection and location of nonlinear scattering source due to the presence of fatigue crack in a laboratory specimen. The proposed technique is based on a combination of nonlinear elastic wave spectroscopy(NEWS) and time reversal(TR) focusing approach. In order to focus on the nonlinear scattering position due to the fatigue crack, we employed only one transmitting transducer and one receiving transducer, taking advantage of long duration of reception signal that includes multiple linear scattering such as mode conversion and boundary reflections. NEWS technique was then used as a pre-treatment of TR for spatial focusing of reemitted second harmonic signal. The robustness of this approach was demonstrated on a cracked specimen and the nonlinear TR focusing behavior is observed on the crack interface from which the second harmonic signal was originated.

• Proceedings of the Acoustical Society of Korea Conference
• /
• 1992.06a
• /
• pp.123-126
• /
• 1992

A new class of data transformation matri is introduced for estimation of angles of arrivals by the rank reduction of multiple wideband sources. The proposed unitary focusing matri minimizes the average of the squared norm of focusing error over the angles of interest without a priori knowledge of source locations. The merit that result as a consequence is a lower resolution threshold. These matrices can be applied to the case of the multigroup sources. Simulations and the comparison of statistical performance are compared with the algorithms (especially, spatial resampling method) which does not require the pre-estimation.

• Korean Institute of Interior Design Journal
• /
• no.36
• /
• pp.30-36
• /
• 2003

The purpose of this study is to analyze the contextual cognition of space in architecture focusing on Aldo Rossi and Michael Graves, the representative architects of spatial cognition in contextual architecture. This study on the contextual cognition of architectural space can be connected with linguistics and aesthetics's approaches. The conclusions of the study as per the above mentioned aims and intentions are as follows : The concept of spatial analysis in Aldo Rossi's contextual cognition in architecture is described the Analogical Space of Speculative Aesthetics by Diachronie Restoration That of Michael Graves' contextual cognition Is defined Semiotics Space of Empirical Aesthetics by Synchronie Repeatition.

• Research in Mathematical Education
• /
• v.16 no.2
• /
• pp.107-123
• /
• 2012

A group of twenty-nine high school student-teachers were given a set of mathematical propositions focusing on shape-to-shape transformations. Their task was to determine through hands-on manipulation and use of dynamic software that each shape be transformed into an area equivalent rectangular region. This paper reports on a classroom-based research.

• Journal of Environmental Health Sciences
• /
• v.37 no.1
• /
• pp.1-11
• /
• 2011

Recent advances in Geographic Information Systems and spatial statistical and analytical methods, along with the availability of spatially referenced health and environmental data, have created unique opportunities to investigate spatial associations between environment exposures and health outcomes at multiple spatial scales and resolutions. However, the increased use of spatial data also faces challenges, one of which is to ensure certainty and accuracy of locational data that meets the needs of a study. This article critically reviews the use of spatially referenced data in epidemiologic studies, focusing on the issue of locational uncertainty generated from the process of geocoding health and environmental data. Primarily, major issues involving the use of spatially referenced data are addressed, including completeness and positional accuracy, potential source of bias and exposure misclassification, and implications for epidemiologic studies. The need for critical assessment and caution in designing and conducting spatial epidemiology studies is briefly discussed.