Sanghyuk Kim

Extraction of P300 using constrained independent component analysis

A brain computer interface (BCI) uses electrophysiological activities of the brain such as natural rhythms and evoked potentials to communicate with some external devices. P300 is a positive evoked potential (EP), elicited approximately 300ms after an attended external stimulus. A P300-based BCI uses this evoked potential as a means of communication with the external devices. Until now this P300-based BCI has been rather slow, as it is difficult to detect a P300 response without averaging over a number of trials. Previously, independent component analysis (ICA) has been used in the extraction of P300. However, the drawback of ICA is that it extracts not only P300 but also non-P300 related components requiring a proper selection of P300 ICs by the system. In this study we propose an algorithm based on constrained independent component analysis (cICA) for P300 extraction which can extract only the relevant component by incorporating a priori information. A reference signal is generated as this a priori information of P300 and cICA is applied to extract the P300 related component. Then the extracted P300 IC is segmented, averaged, and classified into target and non-target events by means of a linear classifier. The method is fast, reliable, computationally inexpensive as compared to ICA and achieves an accuracy of 98.3% in the detection of P300.

Finite element simulation of ultrasound propagation in bone for quantitative ultrasound toward the diagnosis of osteoporosis

Osteoporosis is a serious bone disease which leads to the increased risk of bone fractures. For prevention and therapy, early detection of osteoporosis is critical. In general, for diagnosis of osteoporosis, dual-energy X-ray absoptiometry (DXA) or densitometry is most commonly used. However DXA exhibits some disadvantages such as ionizing radiation, relatively expensive cost, and limited information on mineralization and geometry of the bone. As an alternative method of DXA, quantitative ultrasound (QUS) is being investigated. In contrast to DXA, QUS is non-ionizing and relatively inexpensive. It can also provide some bone-related parameters (e.g., quantitative measurements including speed of sound and frequency-dependent attenuation). However the estimation of these parameters is difficult and few analytical solutions exist due to the complex behavior of ultrasound propagation in bone. As an alternative to the analytical methods, in most attempts, finite difference time domain (FDTD) method is used for simulation of ultrasound propagation in bone with a limited capability of modeling complex geometries of the bone. Finite element method (FEM) is a better solution since it can handle the complex geometry, but has been rarely applied due to its computational complexity. In this work, we propose an approach of FEM-based simulation of ultrasound propagation in bone. To validate our approach, we have tested simulated and real bone models from micro-CT using the index of speed-of-sound. Our results achieve an average of 97.54% in the computational accuracy.

PROTO-MODEL OF AN INFRARED WIDE-FIELD OFF-AXIS TELESCOPE

We develop a proto-model of an ofi-axis re∞ective telescope for infrared wide-fleld observations based on the design of Schwarzschild-Chang type telescope. With only two mirrors, this design achieves an entrance pupil diameter of 50 mm and an efiective focal length of 100 mm. We can apply this design to a mid-infrared telescope with a fleld of view of 8 ‐ £ 8 ‐ . In spite of the substantial advantages of ofi-axis telescopes in the infrared compared to refractive or on-axis re∞ective telescopes, it is known to be di‐cult to align the mirrors in ofi-axis systems because of their asymmetric structures. Ofi-axis mirrors of our telescope are manufactured at the Korea Basic Science Institute (KBSI). We analyze the fabricated mirror surfaces by fltting polynomial functions to the measured data. We accomplish alignment of this two-mirror ofi-axis system using a ray tracing method. A simple imaging test is performed to compare a pinhole image with a simulated prediction.

Optical Design of a Reflecting Telescope for CubeSat

Space telescope optics is one of the major parts of any space mission used to observe astronomical targets or the Earth. This kind of space mission typically involves bulky and complex opto-mechanics with a long optical tube, but attempts have been made to observe a target with a small satellite. In this paper, we describe the optical design of a reflecting telescope for use in a CubeSat mission. For this design we adopt the off-axis segmented method for astronomical observation techniques based on a Ritchey-Chr

Fabrication of electroless nickel plated aluminum freeform mirror for an infrared off-axis telescope

\acute{e}

THE INFRARED MEDIUM-DEEP SURVEY. V. A NEW SELECTION STRATEGY FOR QUASARS AT z > 5 BASED ON MEDIUM-BAND OBSERVATIONS WITH SQUEAN

tien type telescope. The primary mirror shape is a rectangle with dimensions of

The Infrared Medium-deep Survey. III. Survey of Luminous Quasars at 4.7 ≤ z ≤ 5.4

8cm{\times}8cm

Development of SED Camera for Quasars in Early Universe (SQUEAN)

, and the secondary mirror has dimensions of

Changes in Distribution of Electrical Field in tDCS with Ring Electrode Due to Tissue Anisotropy: a 3D High Resolution Finite Element Head Model Study

2.4cm{\times}4.1cm

Camera for Quasars in Early Universe

. The focal ratio is 3 which can yield a 0.383 degree diagonal angle in a