Dielectric spectroscopy studies of hydrated protein demonstrate smooth temperature variations of conductivity. This observation suggests no cusplike fragile-to-strong crossover (FSC) in the protein's hydration water. The FSC at T approximately 220 K was postulated recently on the basis of neutron scattering studies [Chen, Proc. Natl. Acad. Sci. U.S.A. 103, 9012 (2006)] and was proposed to be the main cause for the dynamic transition in hydrated proteins. Following Swenson et al. , we ascribe the neutron results to a secondary relaxation. We emphasize that no cusplike solvent behavior is required for the protein's dynamic transition.

We report a comparison of high resolution inelastic x-ray Brillouin scattering to coherent inelastic neutron scattering for amorphous deuterated polybutadiene, done for one temperature in the glass phase and another one in the melt. The x-ray scattering proves to be by far the better technique for such a polymer within its present resolution bounds. The neutron scattering allows one to extend these measurements to a much better resolution, showing an additional quasielastic signal in the melt. The results suggest x-ray measurements at higher momentum transfer, to see whether they are complementary to neutrons. ͓S1063-651X͑99͒50109-8͔ PACS number͑s͒: 63.50.ϩx, 64.70.Pf The most pronounced difference between the vibrational properties of crystals and glasses appears at low energies E Ϸ2 -5 meV. In ordered crystals, this region is usually dominated by acoustic vibrations which show a Debye-like density of states g(E)ϳE 2 . However, the vibrational spectra in all disordered systems have a g(E) which significantly exceeds the one expected in the Debye model ͓1͔. The excess g(E) appears as a peak, the so-called boson peak, in the dynamic structure factor S(Q,E) in neutron and Raman scattering spectra of glasses ͓2͔. The nature of these excess vibrations is at present a subject of intense discussion.Significant information about the nature of the atomic motion at the boson peak can be obtained from an analysis of S(Q,E), accessible by neutron and x-ray scattering. However, each technique has its characteristic limitations. Inelastic neutron scattering ͑INS͒ spectroscopy has a kinematic limitation at small Q which is related to the velocity of neutrons: if the latter is lower than the longitudinal sound velocity, then one cannot reach Brillouin conditions. Due to that reason INS is mainly used for an analysis of S(Q,E) at higher Q ranges, the so-called Umklapp scattering around the first and the second diffraction peak, i.e., at 0.5-5 Å Ϫ1 . The recent developement of high-resolution inelastic x-ray scattering ͑IXS͒ allows to measure the Brillouin spectra of glasses without any kinematic limitation. However, up to now these measurements were restricted to the Brillouin Q range, i.e., to QϽ1 Å Ϫ1 , and still have only a resolution of about 1.5 meV, which does not allow one to analyze S(Q,E) below this frequency. Nevertheless, these data clearly demonstrate the presence of a strong soundlike contribution to S(Q,E) at energies around and above the boson peak ͓3͔.In the present Rapid Communication we report combined IXS and INS measurements on deuterated 1,4-polybutadiene ͑PB͒ in the liquid and in the glassy state. This combination enabled the measurement of the dynamic structure factor for both Brillouin and Umklapp scattering. In our experiment, the former is significantly weaker than the latter. We present a quantitative analysis, which gives an estimate of the soundlike contribution and demonstrates the way one can check different model approaches using both IXS and INS.PB, a well-known glass forming polymer, was cho...