Lee; Fridkin, V.M.; Petukhova, N.N.; and Yudin, S.G., "Phase transition in the surface structure in copolymer films of vinylidene fluoride (70%) with trifluoroethylene (30%)" (2000). Surface structures and a surface structure phase transition are identified that are distinct from the known bulk ferroelectric-paraelectric phase transition of crystalline copolymer films of vinylidene fluoride ͑70%͒ with trifluoroethylene ͑30%͒. The temperature-dependent changes in the surface structure are accompanied by the physical rotation of the polar group ͑CH 2 -CF 2 ͒. These changes in the surface structure are compared to the bulk phase transition. We show that the bulk structural transition, while distinct from the surface, is qualitatively similar in both thick and thin Langmuir-Blodgett-grown films.

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Abstract.Results of a ground-based optical monitoring campaign on NGC 5548 in June 1998 are presented. The broad-band fluxes (U , B, V ), and the spectrophotometric optical continuum flux F λ (5100Å) monotonically decreased in flux while the broad-band R and I fluxes and the integrated emission-line fluxes of Hα and Hβ remained constant to within 5%. On June 22, a short continuum flare was detected in the broad band fluxes. It had an amplitude of about ∼18% and it lasted only ≈90 min. The broad band fluxes and the optical continuum F λ (5100Å) appear to vary simultaneously with the EUV variations. No reliable delay was detected for the broad optical emission lines in response to the EUVE variations. Narrow Hβ emission features predicted as a signature of an accretion disk were not detected during this campaign. However, there is marginal evidence for a faint feature at λ 4962Å with F W HM 6Å redshifted by ∆v 1100 km s −1 with respect to Hβnarrow.

Resultsof a ground-based optical monitoring campaign on 3C 390.3 in 1994-95 are presented. The broad-band fluxes (B, V , R, and I), the spectrophotometric optical continuum flux F λ (5177Å), and the integrated emission-line fluxes of Hα, Hβ, Hγ, He i λ5876, and He ii λ4686 all show a nearly monotonic increase with episodes of milder short-term variations superposed. The amplitude of the continuum variations increases with decreasing wavelength (4400 -9000Å). The optical continuum variations follow the variations in the ultraviolet and X-ray with time delays, measured from the centroids of the cross-correlation functions, typically around 5 days, but with uncertainties also typically around 5 days; zero time delay between the high-energy and low-energy continuum variations cannot be ruled out. The strong optical emission lines Hα , Hβ , Hγ , and He i λ5876 respond to the high-energy continuum variations with time delays typically about 20 days, with uncertainties of about 8 days. Thereis some evidence that He ii λ4686 responds somewhat more rapidly, with a time delay of around 10 days, but again, the uncertainties are quite large (∼ 8 days).The mean and rms spectra of the Hα and Hβ line profiles provide indications for the existence of at least three distinct components located at ±4000 and 0 km s −1 relative to the line peak. The emission-line profile variations are largest near line center.