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991.
Muñoz MG Encinar M Bonales LJ Ortega F Monroy F Rubio RG 《The journal of physical chemistry. B》2005,109(10):4694-4699
The dynamics of the liquid-air interface of aqueous solutions of a tensioactive triblock copolymer (Pluronic F-68) has been studied using surface quasielastic light scattering over a broad range of concentrations and temperatures. Ancillary surface tension and bulk rheometry data have been obtained for the same system. The results show that the classical theoretical spectrum for monolayers on a Newtonian fluid can be applied only for concentrations below 4.10(-2) mM. For concentrations above c = 14 mM a clear peak centered at zero frequency appears in the spectrum. This feature is incompatible with the classical theoretical spectrum. The SQELS spectra have been described in terms of the theory of Wang and Huang [Wang, C. H.; Huang, Q. R. J. Chem. Phys. 1997, 107, 5898] considering that the loss modulus of the concentrated solutions shows the existence of two relaxation modes even at low frequencies. The theory is able to explain the existence of a peak centered at zero frequency in the spectra, and the theoretical spectra point out the existence of an elastic peak together with the capillary one. There is a reasonable agreement between the relaxation times and the product Gtau obtained from the fits of the SQELS spectra to the theory of Wang and Huang and those obtained from bulk rheology. 相似文献
992.
The polycrystalline Bi8Fe6Ti3O27 compound was prepared by a high-temperature solid-state reaction technique. Preliminary structural analysis by X-ray diffraction
(XRD) confirms the formation of a single-phase compound in an orthorhombic crystal system at room temperature. The elemental
content of the compound was analyzed by EDAX microanalysis. Microstructural analysis by scanning electron microscopy (SEM)
shows that the compound has well defined grains, which are distributed uniformly throughout the surface of the pellet sample.
Detailed studies of temperature-dependent dielectric response at various frequencies show dielectric anomalies at 380, 389
and 403°C for 10 kHz, 100 kHz, and 1 MHz respectively. The hysteresis loop observed by applying an electric field of 12 kV/cm
on the poled sample with smaller remanent polarization supports the existence of ferroelectricity in this material. The value
of d33 of the compound was found to be 19 pC/N.
相似文献
993.
From the hexane extract of the West Indian gorgonian Pseudopterogorgia elisabethae, two diterpenes, cumbiasins A (1) and B (2), having a novel tetracyclic carbon skeleton named cumbiane, have been isolated. In addition, we have isolated cumbiasin C (3), a ring cleavage product of cumbiasin B that possesses an unusual carbocyclic framework named seco-cumbiane. The structures and relative configurations of metabolites 1-3 were elucidated by interpretation of overall spectral data, which included 2D NMR correlation methods, IR, UV, and accurate mass measurements (HREI-MS and HRFAB-MS). The carbocyclic skeletons of the cumbiasins are unprecedented and represent new classes of C20 rearranged diterpenes. Cumbiasins A and B display mild in vitro anti-tuberculosis activity. 相似文献
994.
M. Ram Murty 《Proceedings Mathematical Sciences》1987,97(1-3):247-250
Let a∈Q and denote byE
a the curvey
2 = (x
2
+ l)(x + a). We prove thatE
a(Fp) is cyclic for infinitely many primesp. This fact was known previously only under the assumption of the generalized Riemann hypothesis.
Research partially supported by NSERC grant A9418. 相似文献
995.
Ram K. Agarwal Prakash C. Jain Miss Veena Kapur Miss Sunita Sharma Anant K. Srivastava 《Transition Metal Chemistry》1980,5(1):237-239
Summary Crystalline thorium(IV) chelates with monoN-oxides of 2,2-bipyridine (bipyNO) and 1,10-phenanthroline (phenNO), ThX4 · 2L (X = Cl, Br, NO3 or NCS) and ThX4 · 3L (X = I or ClO4, and I = bipyNO or phenNO) have been synthesised and characterized on the basis of i.r. spectra, molar conductance, molecular weights, t.g.a. and d.t.a. data. All the complexes are weakly diamagnetic and contain bipyNO and phenNO bonded to thorium(IV) through nitrogen and oxygen. The coordination number of thorium(IV) varies from six to twelve depending on the nature of the anions.Author on leave from L. R. Postgraduate College, Sahibabad (Ghaziabad) and to whom all correspondence should be directed. 相似文献
996.
A.G. González J.D. Martín C. Pérez M.A. Ramírez F. Ravelo 《Tetrahedron letters》1981,22(50):5071-5072
The total synthesis of obtusenol (), a dibrominated sesquiterpene isolated from the red alga , has been achieved by a three-step synthesis starting from commercial farnesol. 相似文献
997.
998.
999.
M.Ram Murty 《Journal of Number Theory》1983,16(2):147-168
Let be a family of number fields which are normal and of finite degree over a given number field K. Consider the lattice L(scF) spanned by all the elements of . The generalized Artin problem is to determine the set of prime ideals of K which do not split completely in any element H of L(scF), H≠K. Assuming the generalized Riemann hypothesis and some mild restrictions on , we solve this problem by giving an asymptotic formula for the number of such prime ideals below a given norm. The classical Artin conjecture on primitive roots appears as a special case. In another case, if is the family of fields obtained by adjoining to the q-division points of an elliptic curve E over , the Artin problem determines how often E(p) is cyclic. If E has complex multiplication, the generalized Riemann hypothesis can be removed by using the analogue of the Bombieri-Vinogradov prime number theorem for number fields. 相似文献
1000.
Ram Munjal S.S. Nandwani S.P. Puri 《Journal of Physics and Chemistry of Solids》1974,35(12):1715-1718
The temperature variation of second order Doppler shift of 57Fe embedded as a dilute impurity in Ni host has been calculated by incorporating both the force constant change and the mass change at the site of the impurity. Comparison of the calculations with available measurements of second order Doppler shift gives definite evidence for the change of force constant λ′/λ. It appears that λ′/λ lies in the range 2·1–2·7 around the defect site. The analysis of the data in the high temperature limit further confirms this inference. 相似文献