Dynamic light scattering as a probe of orientational dynamics in confined liquid crystals

The eigenmodes of director orientational fluctuations in nematic liquid crystals in confined geometries were studied both theoretically and experimentally by dynamic light-scattering tehnique. The fundamental mode of the orientational fluctuations shows a crossover from bulk behavior, dominated by bulk elastic constant K, to surface dominated one, in which the relaxation rate is determined by the ratio of surface anchoring strength W and viscosity eta. The contribution of surface viscosity zeta is also significant when its characteristic length zeta/eta becomes comparable to the size of the confined system. It was measured in nematic liquid crystal in cylindrical pores of polycarbonate (Nuclepore) membranes to be of the order of 10 nm.     

Methyl group dynamics in a confined glass

The European Physical Journal E - We present a neutron scattering investigation on methyl group dynamics in glassy toluene confined in mesoporous silicates of different pore sizes. The experimental...     

Methyl group dynamics in a confined glass

We present a neutron scattering investigation on methyl group dynamics in glassy toluene confined in mesoporous silicates of different pore sizes. The experimental results have been analysed in terms of a barrier distribution model, such a distribution following from the structural disorder in the glassy state. Confinement results in a strong decreasing of the average rotational barrier in comparison to the bulk state. We have roughly separated the distribution for the confined state in a bulk-like and a surface-like contribution, corresponding to rotors at a distance from the pore wall respectively larger and smaller than the spatial range of the interactions which contribute to the rotational potential for the methyl groups. We have estimated a distance of 7 A as a lower limit of the interaction range, beyond the typical nearest-neighbour distance between centers-of-mass (4.7 A).     

Light scattering studies of Brownian motion in confined geometries

Summary Dynamic light scattering can be a useful tool to determine the confinement of Brownian particles whose motion is restricted to dimensions comparable to the wavelength of the light. The theoretical form of the correlation function of the electric field scattered from such trapped particles has been derived and compared with the signal obtained both in a simulated experiment and in a real experiment where the particles are trapped in a glass wedge. This new result can be of relevance for particles trapped in various media such as a porous (transparent) media, a gel, a suspension of lamellar phases or even a concentrated colloidal suspension where a particle is ?trapped? by its neighbours. Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994.     

Hard gamma as probe of nuclear dynamics

Experimental results concerning the ⁵⁸Ni + ⁵⁸Ni at 30 MeV/u and ⁵⁸Ni + ¹⁹⁷Au at 30 and 45 MeV/u reactions are presented. The emission mechanism of hard photons has been exploited to get information on the time evolution of the reactions. From the measured hard gamma multiplicity associated to different classes of heavy residues a quantitative estimate of the reaction centrality has been obtained. Moreover, evidence of a prompt Intermediate Mass Fragment (IMF) emission is shown for the Ni + Au reaction at 45 MeV/u for central collisions exploring the correlation function between thermal photons and IMF’s.     

Structure and dynamics of water confined in a nanoporous sol-gel silica glass: a neutron scattering study

During recent years, the understanding of the modification of the structure and dynamics of water confined in different environments has been the focus of much interest in scientific research. This topic is in fact of great relevance in a lot of technological areas and, in living systems, essential water-related phenomena occur in restricted geometries in cells, and active sites of proteins and membranes, or at their surface. In this paper we report on the most recent up to date account of structural and dynamical properties of confined water in comparison with the bulk state. In particular, as far as structure is concerned, we present new neutron diffraction results on heavy water confined in a fully hydrated sol-gel silica glass (GelSil) as a function of the temperature. At low T, the nucleation of cubic ice superimposed to liquid water, already observed for water within Vycor glasses, is discussed. As far as the dynamics is concerned, we report results of a detailed spectroscopic analysis of diffusive relaxation and vibrational properties of water confined in nanopores of Gelsil glass, at different temperatures and hydration percentages, performed by our research group during recent years by means of incoherent quasi-elastic (IQENS) and inelastic (IINS) neutron scattering. IQENS spectra are analysed in the framework of the relaxing cage model (RCM). IINS spectra show the evolution of the one-phonon-amplitude weighted proton vibrational density of states (VDOS), Z(ω), when water loses its peculiar bulk properties and originates new structural environments due to its surface interactions.     

Single particle spectra in deep inelastic scattering as a probe of small x dynamics

We study the transverse momentum () spectrum of charged particles produced in deep inelastic scattering (DIS) at small Bjorken x in the central region between the current jet and the proton remnants. We calculate the spectrum at large with the BFKL ln (1/x) resummation included and then repeat the calculation with it omitted. We find that data favour the former. We normalize our BFKL predictions by comparing with HERA data for DIS containing a forward jet. The shape of the x distribution of DIS + jet data is also well described by BFKL dynamics. Received: 4 May 1998 / Published online: 21 August 1998     

Enhancement of the radiative channel in nuclear forward scattering

Two observations of nuclear forward scattering of Mössbauer radiation are presented. In one, a magnetic-resonance device was used to chop the γ-ray beam. After the beam was turned off, the nuclear target became a strong emitter of γ-rays in the forward direction. In the other observation, the energy of the intermediate excited nuclear state was changed suddenly by a hyperfine magnetic field reversal and the de-excitation of the nuclei occurred with the forward emission of γ-rays at the shifted frequency. In both cases, the enhancement of the radiative channel of nuclear scattering was observed.     

Characteristics of slow and fast ion dynamics in a lithium metasilicate glass

Molecular dynamics simulations of lithium metasilicate (Li(2)SiO(3)) glass have been performed. The motion of lithium ions is divided into slow (A) and fast (B) categories in the glassy state. The waiting time distribution of the jump motion of each component shows power law behavior with different exponents. Slow dynamics are caused by localized jump motions and the long waiting time. On the other hand, the fast dynamics of the lithium ions in Li(2)SiO(3) are characterized as Lévy flight caused by cooperative jumps. Short intervals of jump events also occur in the fast dynamics in the short time region. Both the temporal and spatial terms contribute to the dynamics acceleration and the heterogeneity caused by these two kinds of dynamics is illustrated. The slow dynamics characteristics of the "glass transition" and in the "mixed alkali effect" are discussed.     

The muon as a deep nuclear probe

The status of the Fermilab Experiment E 802 entitled Deep inelastic muon interaction with nuclear targets using emulsion telescope technique is reported. GeV muons in matter probe deep within the nucleus to yield rich information on the quark structure and other features. The EMC effect, the modification of the quark response due to various nuclear environments along with topological and scaling characteristics are being studied. The status of the collaborative project INT-9118888 sanctioned by the National Science Foundation (USA) to enable participation of the Jadvapur University Group in collaboration with Fermilab in E 782 along with E 802 is also reported. E 782 is a unique bubble chamber muon experiment investigating the deep inelastic structure functions using the Tohoku Bubble Chamber and is a Tohoku University, Japan-Fermilab (USA) collaboration involving also other institutes in the USA and the Institute of High Energy Physics, China.     

Origin of the slow dynamics and the aging of a soft glass

We study by light microscopy a soft glass consisting of a compact arrangement of polydisperse multilamellar vesicles. We show that its slow and nonstationary dynamics results from the unavoidable small fluctuations of temperature, which induce intermittent local shear deformations in the sample, because of thermal expansion and contraction. Temperature-induced shear provokes both reversible and irreversible rearrangements whose amplitude decreases with time, leading to an exponential slowing down of the dynamics with sample age.     

Quasielastic neutron scattering in the high-field phase of a Haldane antiferromagnet

Inelastic neutron scattering experiments on the Haldane-gap quantum antiferromagnet Ni(C5D14N2)2-N3(PF6) are performed in magnetic fields below and above the critical field H(c) at which the gap closes. Quasielastic neutron scattering is found for H>H(c), indicating topological excitations in the high-field phase.     

On the identification of the nuclear forward glory in heavy-ion scattering

We present a simple method which enables us to identify the occurence of a forward glory in heavy ion scattering data. The method is successfully applied to the elastic scattering data of ¹²C (65 MeV), ¹³C (60 MeV), ¹⁵N (85 MeV) and ¹⁶O (75 MeV) on ²⁸Si. Received: 2 July 1999 / Revised version: 3 December 1999     

MOTIF: Evaluation of time spectra for nuclear forward scattering

The computer program MOTIF calculates time dependences for nuclear forward scattering (NFS) of synchrotron radiation and allows fully automatic fits of experimental data. A multiple scattering technique of calculations directly in space and time is used. The source code of MOTIF is written in Fortran 77. It has been worked out since 1993 and tested on several Unix platforms by fitting the NFS time spectra of ⁵⁷Fe, ¹¹⁹Sn, ¹⁵¹Eu, ¹⁶¹Dy, and ¹⁸¹Ta nuclei in various compounds with different timeindependent and timedependent hyperfine interactions.     

Hadron-nucleus scattering as a function of nuclear size

High-energy hadron-nucleus collisions, when viewed in terms of nuclear size, exhibit a remarkable simplicity. The data suggest that nuclear matter is extremely opaque to hadrons, and that fast-forward hadrons (x≳0.3) arise solely from peripheral collisions. This picture naturally explains why the production ratios of different hadron species are target independent at large x.