The X-ray scattering intensities (I(k)) of linear alkanols OH­(CH2) n−1CH3 obtained from experiments (methanol to 1-undecanol) and computer simulations (methanol to 1-nonanol) of different force field models are comparatively studied particularly in order to explain the origin and the properties of the scattering pre-peak in the k-vector range 0.3–1 Å–1. The experimental I(k) values show two apparent features: the pre-peak position k P decreases with increasing n, and more intriguingly, the amplitude A P goes through a maximum at 1-butanol (n = 4). The first feature is well reproduced by all force-field models, while the second shows strong model dependence. The simulations reveal various shapes of clusters of the hydroxyl head-group from n>2. k P is directly related to the size of the meta-objects corresponding to such clusters surrounded by their alkyl tails. The explanation of the A P turnover at n = 4 is more involved in terms of cancellations of atom–atom structure factor S(k) contributions related to domain ordering. The flexibility of the alkyl tails tends to reduce the cross contributions, thus revealing the crucial importance of this parameter in the models. Force fields with all-atom representation are less successful in reproducing the pre-peak features for smaller alkanols, n<6, possibly because they blur the charge ordering process since all atoms bear partial charges. The analysis clearly shows that it is not possible to obtain a model-free explanation of the features of I(k).

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Resonance fluorescence of a single trapped ion is spectrally analyzed using a heterodyne technique. Motional sidebands due to the oscillation of the ion in the harmonic trap potential are observed in the fluorescence spectrum. From the width of the sidebands the cooling rate is obtained and found to be in agreement with the theoretical prediction.PACS: 32.80. Pj, 42.50.Lc, 42.50.Vk Since the first preparation of a single atom in a Paul trap and observation of its resonance fluorescence [1], investigation of this light has revealed a range of unique properties. Examples are its nonclassical nature [2] and the highly nonlinear response, in the form of sudden intensity jumps, of a multi-level atom to continuous laser excitation [3]. The fluorescence is, at the same time, a unique tool for determining the state of the atom. This is particularly obvious for a single particle where each photon emission marks the respective projection of the atomic wave function into the final state of the corresponding transition. It is also of great interest to study, through its resonance fluorescence, the motion of a single laser-excited particle, e.g. for investigating laser cooling schemes or in connection with proposals for quantum state manipulation or quantum information processing with trapped particles [4].

Employing X-ray photon correlation spectroscopy, we measure the kinetics and dynamics of a pressure-induced liquid−liquid phase separation (LLPS) in a water−lysozyme solution. Scattering invariants and kinetic information provide evidence that the system reaches the phase boundary upon pressure-induced LLPS with no sign of arrest. The coarsening slows down with increasing quench depths. The g 2 functions display a two-step decay with a gradually increasing nonergodicity parameter typical for gelation. We observe fast superdiffusive (γ ≥ 3/2) and slow subdiffusive (γ < 0.6) motion associated with fast viscoelastic fluctuations of the network and a slow viscous coarsening process, respectively. The dynamics age linearly with time τ ∝ t w , and we observe the onset of viscoelastic relaxation for deeper quenches. Our results suggest that the protein solution gels upon reaching the phase boundary.

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