排序方式: 共有7条查询结果,搜索用时 406 毫秒
1
1.
For about thirty years, time series models with time-dependent coefficients have sometimes been considered as an alternative
to models with constant coefficients or non-linear models. Analysis based on models with time-dependent models has long suffered
from the absence of an asymptotic theory except in very special cases. The purpose of this paper is to provide such a theory
without using a locally stationary spectral representation and time rescaling. We consider autoregressive-moving average (ARMA)
models with time-dependent coefficients and a heteroscedastic innovation process. The coefficients and the innovation variance
are deterministic functions of time which depend on a finite number of parameters. These parameters are estimated by maximising
the Gaussian likelihood function. Deriving conditions for consistency and asymptotic normality and obtaining the asymptotic
covariance matrix are done using some assumptions on the functions of time in order to attenuate non-stationarity, mild assumptions
for the distribution of the innovations, and also a kind of mixing condition. Theorems from the theory of martingales and
mixtingales are used. Some simulation results are given and both theoretical and practical examples are treated.
Received 2004; Final version 23 December 2004 相似文献
2.
3.
S. K. Shakshooki L. Szirtes A. Azrak M. Ahmed S. Khalil 《Journal of Radioanalytical and Nuclear Chemistry》1989,132(1):49-58
Solid amorphous Zr-, Ti- and ZrxTi(1–x) phosphates (where x=0.10, 0.33, 0.66, and 0.90) in various sodium forms were contacted with an excess of solid oxalic acid dihydrate to its molten state for a given time. The oxalic acid was removed by extraction and the residue was washed with redistilled water. As a result of this, crystalline forms of Zr-, Ti-, and ZrxTi(1–x) phosphates were obtained. Using various sodium forms of the initial samples, higher rate of crystallisation resulted than that found in case of hydrogen forms of initial samples. 相似文献
4.
Azrak Sami M. El Awad Gohl Jared A. Moon Robert J. Schueneman Gregory T. Davis Chelsea S. Youngblood Jeffrey P. 《Cellulose (London, England)》2021,28(14):9149-9168
Cellulose - This work investigated the redispersion and setting behavior of highly loaded (~?18 wt.% solids in water) pastes of cellulose nanofibrils (CNFs) with carboxymethyl cellulose... 相似文献
5.
Forti Endrina S. El Awad Azrak Sami M. Ng Xin Y. Cho Whirang Schueneman Gregory T. Moon Robert J. Fox Douglas M. Youngblood Jeffrey P. 《Cellulose (London, England)》2021,28(10):6449-6465
Cellulose - In this work, water-soluble polymers were screened through solution casting and polyvinyl alcohol (PVA) and poly(2-ethyl-2-oxazoline) (PEOX) were found as reinforcement agents for... 相似文献
6.
S. K. Shakshooki L. Szirtes A. Azrak M. Ahmed S. Khalil 《Journal of Radioanalytical and Nuclear Chemistry》1989,136(2):133-139
Solid amorphous mixed zirconium-titanium phosphates, with general formula ZrxTi/1–x//HPO4/2.n H2O/ where x=0.1–1, and n=3–5/, are mixed with an excess of solid oxalic acid dihydrate and digested in molten oxalic acid. Then oxalic acid is removed by extraction and the residue washed with dilute /O.OlM/ HCl solution and bidistilled water. As a result of this method, crystalline mixed zirconium-titanium phosphate is formed. 相似文献
7.
Ben Jadi S. El Guerraf A. Kiss A. El Azrak A. Bazzaoui E.A. Wang R. Martins J. I. Bazzaoui M. 《Journal of Solid State Electrochemistry》2020,24(7):1551-1565
Journal of Solid State Electrochemistry - Nafion 112/polyaniline (Na/PANi) composite membranes were synthesized by chemical polymerization of aniline on the perfluorinated structure for use in... 相似文献
1