• Journal of Astronomy and Space Sciences
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• v.23 no.1
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• pp.19-28
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• 2006

The noise temperature of existing millimeter-wave receivers is already within two or three times quantum noise limit. One of practical ways to increase the observation speed of single dish radio telescope without longer integration time is use of multi-beam focal plane array receiver as demonstrated in several large single dish radio telescopes. In this context the TRAO (Taeduk Radio Astronomy Observatory), which operates a 143n Cassegrain radio telescope, is planning to develop a 4 x 4 beams focal plane array SIS receiver system for 86-115 GHz band. Even though millimeter-wave HEMT LNA-based receivers approach the noise temperature comparable to the SIS receiver at W-band, it is believed that the receiver based on SIS mixer seems to offer a bit more advantages. The critical part of the multi-beam array receiver will be sideband separating SIS mixers. Employing such a type of SIS mixer makes it possible to simplify the quasi-optics of receiver. Otherwise, an SSB filter should be used in front of the mixer or some sophisticated post-processing of observation data is needed. In this paper we will present a preliminary design concept and components needed for the development of a new 3 mm band multi-beam focal plane array receiver.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.1
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• pp.34-41
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• 2003

A Green's function approach is adopted for analyzing the thermoelastic deformation and stress analysis of a plate made of functionally graded materials (FGMs). The solution to the 3-dimensional steady temperature is obtained by using the laminate theory. The fundamental equations for thermoelastic problems are derived in terms of out-plane deformation and in-plane force, separately. The thermoelastic deformation and the stress distributions due to the bending and in-plane forces are analyzed by using a Green’Às function based on the Galerkin method. The eigenfunctions of the Galerkin Green's function for the thermoelastic deformation and the stress distributions are approximated in terms of a series of admissible functions that satisfy the homogeneous boundary conditions of the rectangular plate. Numerical examples are carried out and effects of material properties on thermoelastic behaviors are discussed.

• Communications of the Korean Mathematical Society
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• v.34 no.4
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• pp.1135-1143
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• 2019

The matrix representation of the Toeplitz operator on the Hardy space with respect to a generalized orthonormal basis for the space of square integrable functions associated to a bounded simply connected region in the complex plane is completely computed in terms of only the Szegő kernel and the Garabedian kernels.

• Journal of Astronomy and Space Sciences
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• v.22 no.4
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• pp.451-462
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• 2005

Optimal Trajectory Correction Maneuver (TCM) design algorithm has been developed using the B-plane targeting method for future Korean Mars missions. For every-mission phase, trajectory informations can also be obtained using this developed algorithms which are essential to design optimal TCM strategy. The information were computed under minimum requiring perturbations to design Mars missions. Spacecraft can not be reached at designed aim point because of unexpected trajectory errors, caused by many perturbations and errors due to operating impulsive maneuvers during the cruising phase of missions. To maintain spacecraft's appropriate trajectory and deliver it to the designed aim point, B-plane targeting techniques are needed. A software NPSOL is used to solve this optimization problem, with the performance index of minimizing total amount of TCM's magnitude. And also executing time of maneuvers on be controlled for the user defined maneuver number $(1\~5)$ of TCMs. The constraints, the Mars arrival B-plane boundary conditions, are formulated for the problem. Results of this work show the ability to design and analyze overall Mars missions, from the Earth launch phase to Mars arrival phase including capture orbit status for future Korean Mars missions

• Architectural research
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• v.13 no.3
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• pp.19-29
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• 2011

Visibility of a space have been defined in several different ways: such as the axial line covering a convex space, a convex space defining the fattest shape in a space and an Isovist field formed by a field of vision at a given vantage point. Isovist fields are referred to as a descriptive medium to describe a movement by reviewing and analyzing geometric properties in them. Many descriptive methods for analysis of three-dimensional isovist are applied to analyzing the morphological properties in a 3D space more realistically. Although these models are regarded as a more advanced method for describing spatial properties, they have pros and cons such as complex mathematical calculations and somewhat arbitrary calibration in addition to huge consumption of memory space. These difficulties lead to the development of a three-dimensional visual accessibility model that explores the implication of building shape on the calculation of isovist fields drawn on a 2D plane. We propose a conceptual framework of how to measure the isovist field not as a 3D volume but as a combination of 2D plane on the ground with the 3D building shape of it's facade.

• Journal of the Korean School Mathematics Society
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• v.13 no.4
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• pp.655-678
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• 2010

In the elementary mathematics, geometric education emphasize spatial sense and understandings of figures through development of intuitions in space. Especially space visualization is one of the factors which try conclusion with geometric problem solving. But studies about space visualization are limited to middle school geometric education, studies in elementary level haven't been done until now. Namely, discussions about elementary students' space visualization process and methods in plane or space figures is deficient in relation to geometric problem solving. This paper examines these aspects, especially in relation to plane and space problem solving in elementary levels. First, we investigate visualization methods for plane problem solving and space problem solving respectively, and analyse in diagram form how progress understanding of figures and visualization process. Next, we derive constituent factor on visualization process, and make a check errors which represented by difficulties in visualization process. Through these analysis, this paper aims at deriving an influence of visualization on geometric problem solving in the elementary mathematics.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.8
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• pp.637-648
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• 2021

This paper aims to propose new reentry guidance for Korean Space plane (KSP). Similar to the Space Shuttle guidance concept, a reference drag profile is first determined to satisfy several flight path constraints and boundary conditions, and the proposed guidance commands are realized in a way to track the predetermined reference drag profile. To this end, the drag dynamics is examined. The investigation uncovers that the dynamics characteristics of the drag and the flight path angle are considerably different. Based on this fact, the proposed guidance commands are determined using the time-scale separation technique and the feedback linearization methodology. The key feature of the proposed guidance lies in its simple structure and a clear working mechanism. Therefore, the proposed method is simple to implement compared to existing methods. Numerical simulations are performed to investigate the performance of the proposed method.

• Bulletin of the Korean Space Science Society
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• 2011.04a
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• pp.28.1-28.1
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• 2011

Radiation-induced displacement damage which has caused the increase of the dark current in the focal plane adopted in the Ozone Monitoring Instrument (OMI) was studied in regards of the primary protons and the secondaries generated by the protons in the orbit. By using the Monte Carlo N-Particle Transport Code System (MCNPX) version 2.4.0 along with the Stopping and Range of Ions in Matter version 2010 (SRIM2010), effects of the primary protons as well as secondary particles including neutron, electron, and photon were investigated. After their doses and fluxes that reached onto the charge-coupled device (CCD) were examined, displacement damage induced by major sources was presented.

• Journal of Astronomy and Space Sciences
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• v.19 no.1
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• pp.19-24
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• 2002

The five space density distribution D(z) wish distance perpendicular to the Galactic plane were combined. The scale heights and the local densities at z = 0 of the thin disk, thick disk, and the halo components were estimated from the nonlinear least square fits of exponential law. The scale heights of the thin disk, thick disk, and the halo components were estimated to be $260{\pm}90$ pc, $660{\pm}220$ pc, and $3.6{\pm}1.4$ kpc, respectively. The density ratio of each components to the thin disk component at the galactic plane, i.e., z = 0.0, were also derived as 1 :0.07:0.002. Our model fit suggests that the thick disk component has a local density of 6.9% relative to the thin disk.

• Journal of Astronomy and Space Sciences
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• v.35 no.3
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• pp.133-141
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• 2018

We report on our Galactic plane searches for magnetars in the archival Chandra X-ray Observatory (CXO) data. We summarize the properties of known magnetars and use them to establish a procedure for magnetar searches. The procedure includes four steps: source finding, spectral characterization, optical counterpart checks, and period searches. We searched 1,282 archival CXO observations, found 32,838 X-ray sources, and selected 25 intriguing candidates using the developed procedure. Although we do not firmly identify a magnetar among them, we significantly reduced the number of targets in future magnetar searches to be done with better X-ray telescopes.