• Title/Summary/Keyword: conditional mean

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Analysis of Flame Generated Turbulence for a Turbulent Premixed Flame with Zone Conditional Averaging (영역분할조건평균법에 근거한 난류예혼합화염내 난류운동에너지 생성에 관한 연구)

  • Im, Yong-Hoon;Huh, Kang-Yul
    • 한국연소학회:학술대회논문집
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    • 2003.12a
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    • pp.49-56
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    • 2003
  • Mathematical formulation of the zone conditional two-fluid model is established to consider flame-generated turbulence in premixed turbulent combustion. The conditional statistics of major flow variables are investigated to understand the mechanism of flame generated turbulence. The flow field in burned zone shows substantially increased turbulent kinetic energy, which is highly anisotropic due to reaction kinematics across thin flamelets. The transverse component of rms velocities in burned zone become larger than axial component in the core of turbulent flame brush. The major source or sink terms of turbulent kinetic energy are the interfacial transfer by the mean reaction rate and the work terms by fluctuating pressure and velocity on a flame surface.

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Numerical Study on Methane/Air Turbulent Jet Diffusion Flames Near-Extinction Using Conditional Moment Closure Model (CMC model에 의한 near-extinction methane/air turbulent jet diffusion flame의 수치적 모사)

  • Kang, Seung-Tak;Kim, Seung-Hyun;Huh, Kang-Yul
    • 한국연소학회:학술대회논문집
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    • 2002.11a
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    • pp.11-17
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    • 2002
  • The first-order conditional moment closure (CMC) model is applied to $CH_4$/Air turbulent jet diffusion flames(Sandia Flame D, E and F). The flow and mixing fields are calculated by fast chemistry assumption and a beta function pdf for mixture fraction. Reacting scalar fields are calculated by elliptic CMC formulation. The results for Flame D show reasonable agreement with the measured conditional mean temperature and mass fractions of major species, although with discrepancy on the fuel rich side. The discrepancy tends to increase as the level of local extinction increases. Second-order CMC may be needed for better prediction of these near-extinction flames.

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A study on improvement of the weighted median filter in low noise (저잡음하에서 WM 필터의 개선에 관한 연구)

  • 이용환;서민형;우상근;박장춘
    • Proceedings of the Korean Information Science Society Conference
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    • 1998.10c
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    • pp.467-468
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    • 1998
  • Impulsive noise appears as black and/or white spots in an image. It is usually caused by errors during the image acquisition or transmission through communication channels. This paper presents a study on the impulsive noise reduction filter of digital image. A much more effective method for removing impulse noise is weighted median filtering. But it loses some information by changing center value with no condition. We propose some new technique to change center value with some conditions. In this paper, the performance of conditional weighted median filter is compared to the commonly used median filter, mean filter, max/min filter, and weighted median filter. A quantitative comparison is performed on MSE (Mean Square Error), RMSE (Root Mean Square Error), and SNR (Signal to Noise Ratio). Proposed conditional weighted median filter can yield better performance than regular filters.

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Integer-Valued HAR(p) model with Poisson distribution for forecasting IPO volumes

  • SeongMin Yu;Eunju Hwang
    • Communications for Statistical Applications and Methods
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    • v.30 no.3
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    • pp.273-289
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    • 2023
  • In this paper, we develop a new time series model for predicting IPO (initial public offering) data with non-negative integer value. The proposed model is based on integer-valued autoregressive (INAR) model with a Poisson thinning operator. Just as the heterogeneous autoregressive (HAR) model with daily, weekly and monthly averages in a form of cascade, the integer-valued heterogeneous autoregressive (INHAR) model is considered to reflect efficiently the long memory. The parameters of the INHAR model are estimated using the conditional least squares estimate and Yule-Walker estimate. Through simulations, bias and standard error are calculated to compare the performance of the estimates. Effects of model fitting to the Korea's IPO are evaluated using performance measures such as mean square error (MAE), root mean square error (RMSE), mean absolute percentage error (MAPE) etc. The results show that INHAR model provides better performance than traditional INAR model. The empirical analysis of the Korea's IPO indicates that our proposed model is efficient in forecasting monthly IPO volumes.

Relation between Risk and Return in the Korean Stock Market and Foreign Exchange Market (주가와 환율의 위험-수익 관계에 대한 연구)

  • Park, Jae-Gon;Lee, Phil-Sang
    • The Korean Journal of Financial Management
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    • v.26 no.3
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    • pp.199-226
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    • 2009
  • We examine the intertemporal relation between risk and return in the Korean stock market and foreign exchange market based on the two factor ICAPM framework. The standard GARCH model and the GJR(1993) model are employed to estimate conditional variances of the stock returns and foreign exchange rates. The covariance between the rates of stock returns and changes in the exchange rates are estimated by the constant conditional correlation model of Bollerslev(1990) and the dynamic conditional correlation model of Engle(2002). The multivariate GARCH in mean model and quasi-maximum likelihood estimation method, consequently, are applied to investigate riskreturn relation jointly. We find that the estimated coefficient of relative risk aversion is negative and statistically significant in the post-financial crisis sample period in the Korean stock market. We also show that the expected stock returns are negatively related to the dynamic covariance with foreign exchange rates. Both estimated parameters of conditional variance and covariance in the foreign exchange market, however, are not statistically significant. The GJR model is better than the standard GARCH model to estimate the conditional variances. In addition, the dynamic conditional correlation model has higher explanatory power than the constant correlation model. The empirical results of this study suggest following two points to investors and risk managers in hedging and diversifying strategies for their portfolios in the Korean stock market: first, the variability of foreign exchange rates should be considered, and second, time-varying correlation between stock returns and changes in foreign exchange rates supposed to be considered.

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Estimation of the joint conditional distribution for repeatedly measured bivariate cholesterol data using Gaussian copula (가우시안 코플라를 이용한 반복측정 이변량 자료의 조건부 결합 분포 추정)

  • Kwak, Minjung
    • The Korean Journal of Applied Statistics
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    • v.30 no.2
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    • pp.203-213
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    • 2017
  • We study estimation and inference of joint conditional distributions of bivariate longitudinal outcomes using regression models and copulas. We consider a class of time-varying transformation models and combine the two marginal models using Gaussian copulas to estimate the joint models. Our models and estimation method can be applied in many situations where the conditional mean-based models are inadequate. Gaussian copulas combined with time-varying transformation models may allow convenient and easy-to-interpret modeling for the joint conditional distributions for bivariate longitudinal data. We apply our method to an epidemiological study of repeatedly measured bivariate cholesterol data.

Linear estimation of conditional eddies in turbulence (난류구조의 조건와류에 대한 선형적 평가)

  • 성형진
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.12 no.5
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    • pp.1175-1188
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    • 1988
  • Linear estimation in isotropic turbulence is examined to approximate conditional averages in the form of fluctuating velocity fields conditioned on local velocity. The conditional flow fields and their associated vorticity field are computer using experimental data [Van Atta and Chen] and energy spectrum model [Driscoll and Kennedy]. It appears that ring vorticies could be the dominant structure. Due to the extremely large vorticity in the viscous region of a conditional ring vortex, the energy spectrum model can be used appropriately by changing the Reynolds number. The hairpin vortex could be detected by combining vorticies in isotropic field with an anisotropic orientation imbedded in uniform mean shear flow and this is consistent with other studies [Kim and Moin].

Multivariate Mean Inactivity Time Functions with Reliability Applications

  • Kayid, M.
    • International Journal of Reliability and Applications
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    • v.7 no.2
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    • pp.127-140
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    • 2006
  • AIn this paper we introduce and study a multivariate notions of mean inactivity time (MIT) functions. Basic properties of these functions are derived and their relationship to the multivariate conditional reversed hazard rate functions is studied. A partial ordering, called MIT ordering, of non-negative random vectors is introduced and its basic properties are presented. Its relationship to reversed hazard rate ordering is pointed out. Finally, using the MIT ordering, a bivariate and multivariate notions of IMIT (increasing mean inactivity time) class is introduced and studied.

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Regression Analysis of Doubly censored data using Gibbs Sampler for the Incubation period

  • Yoo Hanna;Lee Jae Won
    • Proceedings of the Korean Statistical Society Conference
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    • 2004.11a
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    • pp.237-241
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    • 2004
  • In standard time-to-event or survival analysis, the occurrence times of the event of interest are observed exactly or are right-censored. However in certain situations such as the AIDS data, the incubation period which is the time between HIV infection time and the diagnosis of AIDS is usually doubly censored. That is the HIV infection time Is interval censored and also the time of the diagnosis of AIDS is right censored. In this paper, we Impute the Interval censored infection time using the conditional mean imputation and estimate the coefficient factor of the regression analysis for the incubation period using Gibbs sampler. We applied parametric and semi-parametric methods for the analysis of the Incubation period and compared the results.

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Speech Enhancement Using Multiple Kalman Filter (다중칼만필터를 이용한 음성향상)

  • 이기용
    • Proceedings of the Acoustical Society of Korea Conference
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    • 1998.08a
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    • pp.225-230
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    • 1998
  • In this paper, a Kalman filter approach for enhancing speech signals degraded by statistically independent additive nonstationary noise is developed. The autoregressive hidden markov model is used for modeling the statistical characteristics of both the clean speech signal and the nonstationary noise process. In this case, the speech enhancement comprises a weighted sum of conditional mean estimators for the composite states of the models for the speech and noise, where the weights equal to the posterior probabilities of the composite states, given the noisy speech. The conditional mean estimators use a smoothing spproach based on two Kalmean filters with Markovian switching coefficients, where one of the filters propagates in the forward-time direction with one frame. The proposed method is tested against the noisy speech signals degraded by Gaussian colored noise or nonstationary noise at various input signal-to-noise ratios. An app개ximate improvement of 4.7-5.2 dB is SNR is achieved at input SNR 10 and 15 dB. Also, in a comparison of conventional and the proposed methods, an improvement of the about 0.3 dB in SNR is obtained with our proposed method.

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