• 호남수학학술지
• /
• 제44권4호
• /
• pp.485-503
• /
• 2022

In this work, a discontinuous singular Dirac system is studied. For this system, a spectral function is constructed. Finally, by using the spectral function, a spectral expansion formula is given.

• 대한음성학회:학술대회논문집
• /
• 대한음성학회 2006년도 추계학술대회 발표논문집
• /
• pp.131-134
• /
• 2006

Quality of narrowband speech $(0{\sim}4kHz)$ can be enhanced by the bandwidth expansion technique, by which the high- band components are estimated. This paper proposes the bandwidth expansion method using the spline codebook based spectral folding. For the performance evaluation, the PESQ(Perceptual Evaluation of Speech Quality) scores are measured as the objective measurement In addition, the MOS (Mean Opinion Score) and the preference tests are performed as the subjective measurement. The results show our proposed method outperforms the existing spline based one.

• 방송공학회논문지
• /
• 제16권5호
• /
• pp.714-721
• /
• 2011

MPEG 오디오에서는 오디오 신호의 효율적인 압축을 위해서 마스킹 효과, spectral band replication을 이용한 고주파 성분 합성, parametric stereo를 이용한 채널 확장 등의 기술을 이용하고 있다. 본 논문에서는 이 중 최신 기술에 해당하는 채널 확장 기술에 대해서 소개한다. 또한, MPEG 오디오 코덱 중 이 기술을 이용하는 HE-AAC v.2, MPEG Surround, Spatial Audio Object Coding(SAOC), Unified Speech and Audio Coding (USAC)에 대해 기술 소개 및 방송의 적용 예를 기술한다.

• Structural Engineering and Mechanics
• /
• 제28권2호
• /
• pp.129-152
• /
• 2008

This paper considers the solution of the stochastic differential equations (SDEs) with random operator and/or random excitation using the spectral SFEM. The random system parameters (involved in the operator) and the random excitations are modeled as second order stochastic processes defined only by their means and covariance functions. All random fields dealt with in this paper are continuous and do not have known explicit forms dependent on the spatial dimension. This fact makes the usage of the finite element (FE) analysis be difficult. Relying on the spectral properties of the covariance function, the Karhunen-Loeve expansion is used to represent these processes to overcome this difficulty. Then, a spectral approximation for the stochastic response (solution) of the SDE is obtained based on the implementation of the concept of generalized inverse defined by the Neumann expansion. This leads to an explicit expression for the solution process as a multivariate polynomial functional of a set of uncorrelated random variables that enables us to compute the statistical moments of the solution vector. To check the validity of this method, two applications are introduced which are, randomly loaded simply supported reinforced concrete beam and reinforced concrete cantilever beam with random bending rigidity. Finally, a more general application, randomly loaded simply supported reinforced concrete beam with random bending rigidity, is presented to illustrate the method.

• 한국세라믹학회지
• /
• 제32권7호
• /
• pp.769-776
• /
• 1995

Infrared radiators of a cordierite system [cordierite (2MgO.2Al2O3.5SiO2)＋30wt% clay＋X wt% MnO2 (X=0, 0.1, 0.25, 0.5, 1.0, 1.5, 2.0, 2.5)] were manufactured by a slurry casting method. Thermal and physical properties of these infrared radiators were studied by the measurement of spectra emissivity, thermal expansion coefficient and apparent density, SEM and EPMA analyses were also carried out. The thermal expansion coefficient and apparent density were decreased with increasing amouonts of MnO2 additives. On the other hand, the spectral emissivity was increased in the wavelength below 4.5${\mu}{\textrm}{m}$. Also, infrared radiators of the cordierite system, of which the spectral emisivity was 0.8, could be attainable in the wavelength above 4.5${\mu}{\textrm}{m}$. The infrared radiator of the cordierite system with 2.0wt% MnO2, of which the spectral emissivity was approximately 1.0, could be attainable in the wavelength between 4.5${\mu}{\textrm}{m}$ and 8${\mu}{\textrm}{m}$. The spectral emissivity of the specimen containing 2.0wt% MnO2 was higher than others in the wavelength between 8${\mu}{\textrm}{m}$ and 14${\mu}{\textrm}{m}$.

• 대한수학회지
• /
• 제54권4호
• /
• pp.1175-1187
• /
• 2017

The spectral problem $$-y^{{\prime}{\prime}}+q(x)y={\lambda}y,\;0 < x < 1, \atop y(0)cos{\beta}=y^{\prime}(0)sin{\beta},\;0{\leq}{\beta}<{\pi};\;{\frac{y^{\prime}(1)}{y(1)}}=h({\lambda})$$ is considered, where ${\lambda}$ is a spectral parameter, q(x) is real-valued continuous function on [0, 1] and $$h({\lambda})=a{\lambda}+b-\sum\limits_{k=1}^{N}{\frac{b_k}{{\lambda}-c_k}},$$ with the real coefficients and $a{\geq}0$, $b_k$ > 0, $c_1$ < $c_2$ < ${\cdots}$ < $c_N$, $N{\geq}0$. The sharpened asymptotic formulae for eigenvalues and eigenfunctions of above-mentioned spectral problem are obtained and the uniform convergence of the spectral expansions of the continuous functions in terms of eigenfunctions are presented.

• Structural Engineering and Mechanics
• /
• 제75권3호
• /
• pp.311-325
• /
• 2020

In applying the spectral stochastic finite element methods to the frequency response analysis, the conventional methods are known to give unstable and inaccurate results near the natural frequencies. To address this issue, a new sensitivity based stabilized formulation for stochastic frequency response analysis is proposed in this paper. The main difference over the conventional spectral methods is that the polynomials of random variables are applied to both numerator and denominator in approximating the harmonic response solution. In order to reflect the resonance behavior of the structure, the denominator polynomials is constructed by utilizing the natural frequency sensitivity and the random mode superposition. The numerator is approximated by applying a polynomial chaos expansion, and its coefficients are obtained through the Galerkin or the spectral projection method. Through various numerical studies, it is seen that the proposed method improves accuracy, especially in the vicinities of structural natural frequencies compared to conventional spectral methods.

• 산업기술연구
• /
• 제20권A호
• /
• pp.239-245
• /
• 2000

Sintered $Al_2TiO_5$ has a very low thermal expansion and an infrared radiative selectively emitting large amounts of far infrared rays. However, it is week in mechanical strength. Spectral infrared emittance, thermal expansion coefficient, and mechanical strength of $Al_2TiO_5$-clay composites were studied to develop a material for far infrared radiators. The composites containing 10~50 mass% Jungsan clay had high emittance in the range of 2,000~500cm-1. The bending strength of the $Al_2TiO_5$-clay composites increased with increasing clay content. The $Al_2TiO_5$-clay composites with a clay content of 50mass% and heat-treated at $1,200^{\circ}C$ had a large strength for infrared radiators ; 86MPa. The average linear thermal expansion coefficient from $200{\sim}1,000^{\circ}C$ of the 50mass% jungsan clay containing compo sited heat-treated at $1,200^{\circ}C$ was lower than $3.87{\times}10-6/^{\circ}C$.

• Structural Engineering and Mechanics
• /
• 제28권3호
• /
• pp.281-294
• /
• 2008

In this paper, linear elastic isotropic structures under the effects of both stochastic operators and stochastic excitations are studied. The analysis utilizes the spectral stochastic finite elements (SSFEM) with its two main expansions namely; Neumann and Homogeneous Chaos expansions. The random excitation and the random operator fields are assumed to be second order stochastic processes. The formulations are obtained for the system solution of the two dimensional problems of plane strain and plate bending structures under stochastic loading and relevant rigidity using the previously mentioned expansions. Two finite element programs were developed to incorporate such formulations. Two illustrative examples are introduced: the first is a reinforced concrete culvert with stochastic rigidity subjected to a stochastic load where the culvert is modeled as plane strain problem. The second example is a simply supported square reinforced concrete slab subjected to out of plane loading in which the slab flexural rigidity and the applied load are considered stochastic. In each of the two examples, the first two statistical moments of displacement are evaluated using both expansions. The probability density function of the structure response of each problem is obtained using Homogeneous Chaos expansion.

• 한국원자력학회:학술대회논문집
• /
• 한국원자력학회 1998년도 추계학술발표회요약집
• /
• pp.48-48
• /
• 1998