Viscoelastic properties of amorphous polymers 3: low molecular weight poly(methylphenylsiloxane)

By making creep and recoverable creep measurements of a nearly monodisperse low molecular weight poly(methyl phenyl siloxane) sample, we have found on decreasing temperature towardsT _g that there is continuously a change in the viscoelastic spectrum concomitant with a decrease of the steadystate recoverable compliance. This behavior is exactly the same as previously observed in low molecular weight poly(styrene), proving that this spectacular anomaly in the viscoelasticity of low molecular weight polymers is general and deserves an explanation. Photon correlation spectroscopic measurements performed on the same sample have extended the observation of the viscoelastic response to shorter times and the result corroborates the trend of variation established by the creep data.Dedicated to Prof.Dr. E. W. Fischer on his 65th Birthday. Prof.Dr. Fischer is known for his valuable contribution to fosterine, international collaboration of research in polymer science. This work is an example of his contribution because it would not be possible without him bringing us together. One of us (KLN) would like to take this opportunity to thank Prof. Dr. Fischer for his unwaiving support of the 1st (Crete) and the 2nd (Alicante) International Discussion Meeting on Relaxations in Complex Systems     

Error Bounds and Implicit Multifunction Theorem in Smooth Banach Spaces and Applications to Optimization

In this paper we provide an error bound estimate and an implicit multifunction theorem in terms of smooth subdifferentials and abstract subdifferentials. Then, we derive a subdifferential calculus and Fritz–John type necessary optimality conditions for constrained minimization problems.     

Structure of the asparagine-linked sugar chains of porcine kidney and human urine cerebroside sulfate activator protein

The specific sugar residues and their linkages in the oligosaccharides from pig kidney and human urine cerebroside sulfate activator proteins (saposin B), although previously hypothesized, have been unambiguously characterized. Exhaustive sequential exoglycosidase digestion of the trimethyl-p-aminophenyl derivatives, followed by either matrix-assisted laser desorption/ionization and/or mass spectrometry, was used to define the residues and their linkages. The oligosaccharides were enzymatically released from the proteins by treatment with peptidyl-N-glycosidase F and separated from the proteins by reversed-phase high-performance liquid chromatography (HPLC). Reducing termini were converted to the trimethyl-p-aminophenyl derivative and the samples were further purified by normal-phase HPLC. The derivatized carbohydrates were then treated sequentially with a series of exoglycosidases of defined specificity, and the products of each digestion were examined by mass spectrometry. The pentasaccharides from pig kidney and human urine protein were shown to be of the asparagine-linked complex type composed of mannose-alpha 1-6-mannose-beta 1-4-N-acetylglucosamine-N-acetylglucosamine(alpha 1-6-fucose). This highly degraded structure probably represents the final product of intra-lysosomal exoglycosidase digestion. Oligosaccharide sequencing by specific exoglycosidase degradation coupled with mass spectrometry is more rapid than conventional oligosaccharide sequencing. The procedures developed will be useful for sequencing other oligosaccharides including those from other members of the lipid-binding protein class to which cerebroside sulfate activator belongs. (c) 2000 John Wiley & Sons, Ltd.     

Pyranoxanthones from Calophyllum Inophyllum

Phytochemical investigation of the stem bark of Calophyllum inophyllum resulted in the isolation of a new dipyrenoxanthone, calophinone ( 1 ), together with four related xanthones ( 2–5 ). Identification of the isolated compounds was achieved through intensive studies of their spectral data, especially 2D NMR.     

Mössbauer study of LaNiSn and NdNiSn compounds and their deuterides

Summary LaNiSn and NdNiSn compounds and their deuterides have been studied by variable temperature ¹¹⁹Sn M?ssbauer spectroscopy. The hyperfine parameters obtained experimentally are in good agreement with those derived from first principle calculations. The enlargement of quadrupole splitting observed for LaNiSn after deuteration confirms the lower symmetry of electron density around tin atoms indicated by the calculation of partial Sn-p density of states (DOS). Magnetic ordering is observed at low temperature in deuterided NdNiSn.     

Primary and secondary relaxations in bis-5-hydroxypentylphthalate revisited

The molecular structure of bis-5-hydroxypentylphthalate (BHPP) is like dihexyl phthalate but having appended to it two hydroxyl end groups, which contribute additional dipole moments and capacity for hydrogen-bond formation. In a previously published dielectric study of the primary and secondary relaxations of BHPP, it was found that all the dynamic properties are normal except for the anomalously large width of the primary relaxation loss peak. There are two secondary relaxations, the relaxation time of the slower one increases with increasing pressure, whereas that of the faster one is practically insensitive to pressure. Hence, the slower secondary relaxation is the "universal" Johari-Goldstein (JG) [J. Chem. Phys. 53, 2372 (1970); 55, 4245 (1971)] relaxation in BHPP. All is well except if the observed large width of the primary relaxation were an indication of a corresponding large coupling parameter n=0.45 in the coupling model. Then the predicted relations between the primary relaxation time tau(alpha) and the JG relaxation time tau(JG) found previously to hold in many glass formers would be violated. It was recognized that this singular behavior of BHPP is likely due to broadening of the primary loss peak by the overlapping contributions of two independent dipole moments present in BHPP, and the actual coupling parameter is smaller. However, at the time of publication of the previous work there were not enough data to support this explanation. By making broadband dielectric measurements of dibutyl phthalate (DBP) and dioctyl phthalate (DOP) that have chemical structures closely related to BHPP but with only one dipole moment, we show that all their dynamic properties are almost the same as BHPP but the widths of their primary relaxation loss peaks are significantly narrower corresponding to a smaller coupling parameter n=0.34. The new data presented here indicate that the coupling parameter of BHPP is about the same as DBP and DOP, and the predicted relations between tau(alpha) and tau(JG) of BHPP are brought back in agreement with the experimental data.     

Dynamics of caged ions in glassy ionic conductors

At sufficiently high frequency and low temperature, the dielectric responses of glassy, crystalline, and molten ionic conductors all invariably exhibit nearly constant loss. This ubiquitous characteristic occurs in the short-time regime when the ions are still caged, indicating that it could be a determining factor of the mobility of the ions in conduction at longer times. An improved understanding of its origin should benefit the research of ion conducting materials for portable energy source as well as the resolution of the fundamental problem of the dynamics of ions. We perform molecular dynamics simulations of glassy lithium metasilicate (Li2SiO3) and find that the length scales of the caged Li+ ions motions are distributed according to a Levy distribution that has a long tail. These results suggest that the nearly constant loss originates from "dynamic anharmonicity" experienced by the moving but caged Li+ ions and provided by the surrounding matrix atoms executing correlated movements. The results pave the way for rigorous treatments of caged ion dynamics by nonlinear Hamiltonian dynamics.     

STUDIES OF MULTICOMPONENT COMPLEX OXIDE CATALYSTS FOR OXIDATIVE COUPLING OF METHANE VI.SURFACE BASICITY AND SURFACE ACTIVE OXYGEN SPECIES OF LiTi_xLa_(1-x)O_2 λ MULTICOMPONENT OXIDE CATALYSTS

The surface basicity of Ti-La-Li multicoinponent oxides has been investigated by means of CO2-TPD. The experiment results show that C2 (C2H6 C2H4) selectivity is related to surface basic strength. The surface active oxygen species have also been characterized by means of XPS, O2-TPD and so on. It has been indicated that C2 selectivity and CH4 conversion are correlated with lattice oxygen and the adsorbed oxygen on the surface of the catalyst respectively In the O2-TPD experiments, it has also been found that there are three kinds of oxygen species on the surface of the series catalvsts, which are a (100℃ 750℃) Among them α-oxvgen causes deep oxidation whileβand γ oxygen species are related to oxidalive coupling of methane (OCM).     

EFFECTS OF K_2O AND MnO PROMOTERS ON THE PRODUCTION OF LIGHT ALKENES VIA SYNGAS OVER Fe/SILICALITE-2 CATALYST I.ACTIVITY OF K-Fe-MnO/SILICALIT-2 CATALYST

The activity and the selectivity to light alkenes of silicalite-2 (Si-2) zeolite supported F'e catalyst tor CO hydrogenation can he improved obviously with the addition of K2O and MnO promoters. The results of CO hydrogenation, CO-TPD, CO/H2-TPSR, C2H4/H2-TPSR and C2H4/H2 pulse reaction over K-Fe-MnO/Si-2 catalysts clearly show that the K2O additive into Fe-MnO/Si-2 catalyst leads to a remarkable increase in both the capacity and strength of the strong CO ad-species that will produce much more |Cad| via their disproportionation at higher temperatures. This results in an increase in the CO conversion and the selectivity to light olefins, and a decrease in CH4 formation. Moreover, K2O can suppress the disproportionate of C2H4 that occurs during the reaction as a side-reaction Meanwhile, the MnO promoter mainly prohibits the hydrogenation of C2H4 and C3H6, which is favorable to enhancing the selectivity to C2H4 and C3H6 and decreasing the formation of C2H6, and C3H8. It is also of interest that MnO has har