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131.
Woon Wong 《时间序列分析杂志》1997,18(2):181-194
A stationary multivariate time series { X t } is defined as linear if it can be written in the form X t = ∑∞ j =−∞ A j e t − j where A j are square matrices and e t are independent and identically distributed random vectors. If the e t } are normally distributed, then { X t is a multivariate Gaussian linear process. This paper is concerned with the testing of departures of a vector stationary process from multivariate Gaussianity and linearity using the bispectral approach. First the definition and properties of cumulants of random matrices are used to obtain the expressions for the higher-order cumulant and spectral vectors of a linear vector process as defined above. Then it is shown that linearity of a vector process implies constancy of the modulus square of its normalized higher-order spectra whereas the component of such a vector process does not necessarily have a linear representation. Finally, statistics for the testing of multivariate Gaussianity and linearity are proposed. 相似文献
132.
Hyun Ju Lim Sung Jun Lee Han Gon Choi Jung Ae Kim Chul Soon Yong Sung Soo Han Seok Kyun Noh Jinho Jang Won Seok Lyoo 《应用聚合物科学杂志》2007,106(5):3268-3272
High‐molecular‐weight atactic poly(vinyl alcohol) (a‐PVA) gels loaded with (R,S)‐2‐(3‐benzoylphenyl)propionic acid (ketoprofen) were prepared from 5, 6, 7, and 8 g/dL solutions of a‐PVA with a number‐average degree of polymerization of 4000 in an ethylene glycol/water mixture with an aging method to identify the effect of the initial polymer concentration on the swelling behavior, morphology, and thermal properties of a‐PVA gels. Then, the release behavior of ketoprofen from a‐PVA gels was investigated. As the polymer concentration decreased, the ability for network formation decreased, and the degree of swelling of the a‐PVA gels increased. In addition, the enthalpy increased with an increase in the a‐PVA concentration, but the melting temperatures of the gels prepared at different initial polymer concentrations were the same; this indicated that tighter gel networks would be formed by a higher polymer chain density. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 相似文献
133.
Eddy characteristics on mass transfer close to free interface 总被引:1,自引:0,他引:1
The velocity fluctuations in the immediate vicinity of a free interface were measured with a hot film anemometer. And mass
transfer rates and eddy exposure times were analyzed by using the method of deterministic approach. These mass transfer rates
were compared with the mass transfer rates by means of concentration measurements in the air-water system.
The eddy exposure time distributions obtained from velocity data were skewed toward the lower time value. The contribution
of eddies wi:h small exposure time was increased as the liquid became more turbulent. The mass transfer rates were mainly
contributed by the Prandtl size eddies and even larger eddies. The mass transfer predictions by the single eddy model employing
a deterministic method were in good agreement with the experimental results by independent measurements of concentration. 相似文献
134.
Jui‐Ming Yeh Chi‐Lun Chen Tai‐Hung Kuo Wen‐Fen Su Hsi‐Ya Huang Der‐Jang Liaw Hsin‐Yi Lu Chi‐Fong Liu Yuan‐Hsiang Yu 《应用聚合物科学杂志》2004,92(2):1072-1079
A series of polymer–clay nanocomposite (PCN) materials consisting of 1,4‐bis(4‐aminophenoxy)‐2‐tert‐butylbenzene–4,4′‐oxydiphthalic anhydride (BATB–ODPA) polyimide (PI) and layered montmorillonite (MMT) clay were successfully prepared by an in situ polymerization reaction through thermal imidization up to 300°C. The synthesized PCN materials were subsequently characterized by Fourier‐Transform infrared (FTIR) spectroscopy, wide‐angle powder X‐ray diffraction (XRD) and transmission electron microscopy (TEM). The effects of material composition on thermal stability, mechanical strength, molecular permeability and optical clarity of bulk PI and PCN materials in the form of membranes were studied by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), molecular permeability analysis (GPA) and ultraviolet‐visible (UV/VIS) transmission spectra, respectively. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1072–1079, 2004 相似文献
135.
8-Hydroxyqunioline end-capped polystyrene was prepared through atom transfer free radical polymerization (ATRP) with 8-(5-chloromethyl) quinolyl acetate as initiator. The results indicated that this polymerization is a first order reaction with respect to monomer conversion. The molecular weight increased linearly with monomer consumption and very narrow distribution of molecular weight was obtained (polydispersity index less than 1.2). The FT-IR and NMR results show that the 8-hydroxyquinloine group was chemically bonded to the polymer end and there is nearly one 8-hydroxyquinoline group in per polymer chain. All those data show that polymerization of styrene at such conditions displayed living characters. The polymer with 8-hydroxyqquinoline end group reacted with triethylaluminum to form polymeric light-emitting complex and single layer LED was prepared by common spin-coating method. The peak wavelength of LED based on synthesized polymeric complex was around 570 nm. 相似文献
136.
The effect of adsorbed polymer on the stability of alumina suspension was investigated. Poly(ethylene oxide) (PEO), poly(acrylic
acid) (PAA) and similar kinds of polymer salts were used as a dispersant. The amount of polymer adsorbed on alumina surface
and the suspension stability was measured. The pH, molecular weight, and concentration were considered as experimental parameters.
PEO shows low affinity on the alumina surface while PAA has high affinity. In the case of PAA adsorption, the surface charge
change by polymer adsorption influences suspension stability strongly, but not in the case of PEO adsorption. In simultaneous
adsorption of PEO and PAA, the PAA concentration was fixed and PEO concentration was varied. The stability of suspension increased
with increasing PEO concentration, and this is partly due to the steric stabilization by adsorption of PAA-PEO complex or
adsorption of PEO through pre-adsorbed PAA and the depletion effect of non-adsorbed polymer. Suspension adsorbing sodium salts
of PAA and poly(methacrylic acid) (PMA) each showed similar stability. But, when the PEO and these kinds of salts were added
together to the suspension, the one with PAA sodium salt could keep a higher stability even with lower molecular weights of
PEO compared with suspension with PMA sodium salt. 相似文献
137.
Free radical solution polymerization of styrene has been studied using a binary mixture of symmetrical bifunctional initiators in a filled tubular reactor packed with static mixers. Owing to intensive radial mixing induced by the static mixers, a near plug flow pattern was obtained in the reactor with some axial dispersion effect. The axial mass dispersion coefficient was determined from the residence time distribution experiment and a dynamic axial dispersion model has been developed and solved to investigate steady state and transient behavior of the filled tubular reactor. With a solvent volume fraction of 0.3, the monomer conversion up to 70% was obtained without fouling problems in the temperature range 90 to 120°C. The experimental filled tubular reactor was operated under various reaction conditions and a reasonably good agreement between the model and the experimental data was obtained without using any adjustable parameters. 相似文献
138.
Won Seok Lyoo Han Do Ghim Hee‐Sam Kim Joon Ho Kim Sam Soo Kim Won Sik Yoon Jinwon Lee Sang‐Seob Lee 《应用聚合物科学杂志》2002,86(14):3667-3672
N‐Vinylcarbazole (VCZ) was solution‐polymerized in tetrahydrofuran (THF) at ?20, 0, and 20°C using the photoinitiation method; the effects of the amount of solvent, polymerization temperature, and photoinitiator concentration were investigated. On the whole, the experimental results corresponded to predicted ones. Low polymerization temperature using photoinitiation proved to be successful in obtaining poly(N‐vinylcarbazole) (PVCZ) of a high molecular weight with a smaller temperature rise during polymerization; nevertheless of free radical polymerization by 2,2′‐azobis(2,4‐dimethylvaleronitrile) (ADMVN). The photo‐solution polymerization rate of VCZ in THF was proportional to the 0.47 power of ADMVN concentration. The molecular weight was higher and the molecular weight distribution was narrower with PVCZ polymerized at lower temperatures. For PVCZ prepared in THF at ?20°C using a photoinitiator concentration of 0.00005 mol/mol of VCZ, a weight‐average molecular weight of 510,000 was obtained, with a polydispersity index of 1.73, and a degree of lightness converged to about 99%. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3667–3672, 2002 相似文献
139.
Nanoindentation of organomodified clay filled maleated polypropylene (MAPP) was investigated. The study aims to identify the relative increase in local stiffness in comparison to the increase in mechanical properties of the bulk in polypropylene-based nanocomposites. Such a study allows one to assess confined material property in addition to increased filler volume at the local scale. A mixture of highly intercalated and well exfoliated clay structures, when dispersed in MAPP matrix, was observed under transmission electron microscopy. The degree of exfoliation was found to increase with clay loading, which was attributed to the higher viscosity and mechanical shear forces during melt compounding. Instrumented indentation was performed on (1) clay aggregate supported by MAPP matrix, (2) clay-matrix boundary, and (3) the MAPP matrix. The clay aggregated region generally showed higher stiffness as compared to the matrix. And, the relative increase in indentation stiffness is substantially higher than the relative increase in tensile and compressive stiffnesses for clay reinforced systems. Polymer chain confinement and topological constraint appeared to be operative to enhance local stiffness in the clay aggregated region. Good correlation was, however, obtained between the change in macroscopic stiffness and the change in highly local indentation stiffness as a result of clay reinforcement. 相似文献
140.
Ji‐Sun Im Ju‐Hyung Lee Seung‐Kook An Ki‐Won Song Nam‐Ju Jo Jang‐Oo Lee Kohji Yoshinaga 《应用聚合物科学杂志》2006,100(3):2053-2061
A new type of polyimide/silica (PI/SiO2) hybrid composite films was prepared by blending polymer‐modified colloidal silica with the semiflexible polyimide. Polyimide was solution‐imidized at higher temperature than the glass transition temperature (Tg) using 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA) and 4,4′‐diaminodiphenyl ether (ODA). The morphological observation on the prepared hybrid films by scanning electron microscopy (SEM) pointed to the existence of miscible organic–inorganic phase, which resulted in improved mechanical properties compared with pure PI. The incorporation of the silica structures in the PI matrix also increased both Tg and thermal stability of the resulting films. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2053–2061, 2006 相似文献