• Communications of the Korean Mathematical Society
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• v.9 no.4
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• pp.917-926
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• 1994

Let ($M, G_M, F$) be a (p+q)-dimensional Riemannian manifold with a foliation F of codimension q and a bundle-like metric $g_M$ with respect to F ([9]). Aside from the Laplacian $\bigtriangleup_g$ associated to the metric g, there is another differnetial operator, the Jacobi operator $J_D$, which is a second order elliptic operator acting on sections of the normal bundle. Its spectrum isdiscrete as a consequence of the compactness of M. The study of the spectrum of $\bigtriangleup_g$ acting on functions or forms has attracted a lot of attention. In this point of view, the present authors [7] have studied the spectrum of the Laplacian and the curvature of a compact orientable cosymplectic manifold. On the other hand, S. Nishikawa, Ph. Tondeur and L. Vanhecke [6] studied the spectral geometry for Riemannian foliations. The purpose of the present paper is to study the relation between two spectra and the transversal geometry of cosymplectic foliations. We shall be in $C^\infty$-category. Manifolds are assumed to be connected.

• Journal of Internet Computing and Services
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• v.18 no.3
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• pp.11-17
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• 2017

To the elderly, sudden falls are one of the most frightening accidents. If an accident occurs, a prompt action has to be taken to deal with the situation. Recently, there have been a number of attempts to detect sudden falls using acceleration sensors embedded in the mobile devices, such as smart phones and wrist-bands. However, using the sensor readings only, the detection rate of the falls is around 65%. Ordinary daily activities such as running or jumping could not be well distinguished from the falls. In this paper, we describe our attempts on improving the fall-detection rate. We implemented a wrist-band fall detection module, using a three-axis acceleration sensor. With the pattern matching on the fall signal-strength frequency spectrum, in addition to the conventional signal strength measurement, we could improve the detection rate by 9% point. Furthermore, by applying two wrist-bands in the experiment, we could further improve the detection rate to 82%.

• Earthquakes and Structures
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• v.13 no.4
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• pp.337-351
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• 2017

In the present study a capacity spectrum method based on constant ductility inelastic spectra to estimate the seismic performance of structures equipped with elastic viscous dampers is presented. As the definition of the structures' effective damping, due to the damping system, is necessary, an alternative method to specify the effective damping ratio ${\xi}eff$ is presented. Moreover, damping reduction factors (B) are introduced to generate high damping elastic demand spectra. Given the elastic spectra for damping ratio ${\xi}eff$, the performance point of the structure can be obtained by relationships that relate the strength demand reduction factor (R) with the ductility demand factor (${\mu}$). As such expressions that link the above quantities, known as R - ${\mu}$ - Τ relationships, for different damping levels are presented. Moreover, corrective factors (Bv) for the pseudo-velocity spectra calculation are reported for different levels of damping and ductility in order to calculate with accuracy the values of the viscous dampers velocities. Finally, to evaluate the results of the proposed method, the whole process is applied to a four-storey reinforced concrete frame structure and to a six-storey steel structure, both equipped with elastic viscous dampers.

• Journal of IKEEE
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• v.17 no.1
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• pp.10-15
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• 2013

This paper, we analyzed that the measured data of the radiated power spectrum of electromagnetic waves of the normal spark ignition system and the spark ignition system with feed through type ceramic condenser. The results show that the strength of power spectrum radiated from the system with feed through type ceramic condenser is weaker than the normal system, and the density of power spectrum radiated from the system with feed through type ceramic condenser is smaller than the normal system. From these results, the feed through type ceramic condenser can reduce the electromagnetic waves radiating from the spark ignition system which is the spurious emission, and it can be concluded that the ignition coil of the spark ignition system generating high voltage pulse is equivalent to the radio frequency oscillator which is oscillating high frequency from a electronic point of view.

• Journal of the Korean earth science society
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• v.28 no.7
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• pp.871-877
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• 2007

The response spectrum was studied using the observed pound motion from the Odaesan Earthquake (2007/01/20), and then the results were compared to the seismic design response spectra (Reg Guide 1.60) applied to the domestic nuclear power plants. For the response spectrum analysis, 21 horizontal and 8 vertical observed Pound motions were used for normalization and statistical analysis. The results showed that the MPOSD (Mean Plus One Sigma Standard Deviation) response spectra above 10 Hz revealed higher values than the design response spectra and those below 10 Hz revealed much lower values fur both horizontal and vertical response spectra. These results suggest that the response spectra (Reg. Guide 1.60), used as seismic design code for nuclear facilities in Korea, especially above about 10 Hz, should be reexamined fur apllication to the nuclear power plants structures operated in the Korean Peninsula.

• Journal of Life Science
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• v.20 no.5
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• pp.676-682
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• 2010

This study focused on typing of the extended-spectrum $\beta$-lactamase (ESBL) produced in organisms isolated from a natural environment, rather than a clinical setting. Samples were collected from drain water issuing from a sewage plant in Kwanganri (Busan, Korea). Following double disk synergy testing, 29 strains were selected as potential ESBL positive strains. Of these, 15 strains were transconjugants of the sodium azide resistant recipient strain Escherichia coli J53 and analyzed biochemically including indole, methyl-red, Voges-Proskauer, Simmon's citrate, decarboxylase-dihydrolase and sugar-fermentation tests. The tests classified the 15 strains as Klebsiella pneumoniae (n=13) and Escherichia coli (n=2). The type of ESBL from each strain was deduced by isoelectric focusing point analysis and DNA sequencing. The results indicated that the types of ESBL were SHV-12 (n=4) and SHV-12/TEM-1 (n=9) from K. pneumoniae and TEM-1 (n=2) from E. coli strains.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.5C
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• pp.439-444
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• 2010

In this paper, we derive and analyze the channel capacity of the spread spectrum watermarking (SSW) system as an information-theoretic point of view in closed-form approximation formula in order to analyze the effect of the wireless multipath/shadowing channel. It is important to analyze the channel capacity to transmit an additive data through existing wireless channel by the SSW system. From the results, we confirm that the channel capacity of the SSW system can be determined by the HWR, WNR, PN length and host sampling frequency. Also, we verified that the variation of the channel capacity when the SSW system applied to Nakagami-m fading and Log-normal shadowing channel. The results of this paper can be applied to general spread spectrum watermarking system.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.34 no.6
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• pp.705-712
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• 2001

It is of great importance to represent the directional ocean waves in a laboratory basin for hydraulic model tests. The directional ocean waves can be expressed as a linear superposition of a large number of component waves with different frequencies and propagating directions. The aim of the study is to check the wave generating characteristics by serpent-type wave generating system in PKNU (Pukyong National University) which is composed of 10 piston-type wave generators. In the experiment, spatial variation of irregular wave heights and propagating angles are measured in the multi-directional wave maker basin. Target wave directional spectrum is reproduced in the area of multi-directional wave maker basin. The directional spreading of the generated waves varied spacially in the basin. They differed from target spectrum as the measurement point becomes far from the center line normal to the generator face, The effective generation area where that target can be reproduced is limited to the triangular area attached the generator face. According to the results, it is emphasized that the effective experiment area in the basin considered wave generator characteristics should be determined in consideration of experimental conditions including structural shapes, water depth, wave directionality etc.

• Journal of Satellite, Information and Communications
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• v.10 no.3
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• pp.6-10
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• 2015

RF energy harvesting technology is a promising technology for generating the electrical power from ambient RF signal to operate low-power consumption devices(eg. sensor) in wireless communication networks. This paper, motivated by this and building upon existing CR(Cognitive Radio) network model, proposes a optimal control policy for RF energy harvesting CR networks model where secondary users that have low power consumption harvest ambient RF energy from transmission by nearby active primary users, while periodically sensing and opportunistically accessing the licensed spectrum to the primary user's network. We consider that primary users and secondary users are distributed as Poisson point processes and contact with their intended receivers at fixed distances. Finally we can derive the optimal frame duration, transmission power and density of secondary user from the proposed model that can maximize the secondary users's throughput under the given several conditions and suggest future directions of research.

• Journal of Satellite, Information and Communications
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• v.12 no.3
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• pp.98-102
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• 2017

In this paper, we study RF-powered backscatter cognitive radio networks to improve the performance for the secondary user which is backscatter radio based wireless sensors. In our proposed model, we consider an avoiding the doubly round-trip attenuation to add a carrier emitter and utilization of spectrum sensing information. When the primary channel is busy, the secondary user is able to harvest RF energy from the channel through a hybrid-access point (H-AP) and a carrier emitter. When the channel becomes idle, the secondary user will be use the harvested energy to operate wireless sensors, to use the sensing and to backscatter through the carrier emitter. We model mathematically the deterministic and multisource elements of a number of tagged channels. In the proposed communication environment, we show the BER performance of the backscatter communication using WiFi signal.