Dynamics of sorbitol and maltitol over a wide time-temperature range

The relaxation behaviour of two molecular glass-forming systems, namely sorbitol and maltitol, are investigated in the large temperature range relevant to the glass-transition. These data are obtained by combining three techniques, i.e. low-frequency mechanical spectroscopy, medium and high frequency dielectric spectroscopy, and viscosity measurements. This procedure allows to determine the relaxation map of these polyols on a wide time range [10^-9-10⁷ s]. Two different relaxation processes can be observed. The principal α-relaxation process exhibits a complex behaviour, comprising a non-Arrhenius temperature dependence above T _g (supercooled liquid state), and an Arrhenius behaviour below T _g (glassy state). A secondary β-relaxation is observed at higher frequencies with an Arrhenius temperature dependence. The secondary process appears in the same time-temperature range in both polyols. Consequently the molecular root of this relaxation is most likely the same in these complementary chemical systems. On the other hand, the time scale on which the α and β processes cross is very different for these two polyols. We relate this feature to the differences in the relative contributions of intra and inter-molecular interactions due to the different chemical architecture of these polyols.     

Molecular mobility of sorbitol and maltitol: A ^13C NMR and molecular dynamics approach

Molecular mobility in two similar organic glass formers, namely sorbitol and maltitol, is studied in order to understand their difference in the cross-over between and relaxations, far above their respective glass transition temperatures. In this goal, the individual mobility of each carbon atom of the 6 carbon chain present both in sorbitol and maltitol is studied by means of ^13C nuclear magnetic resonance and molecular dynamics simulations. Both techniques imply that the mobility of carbons located at the end of the 6 carbon chain is greater than that of any other carbon of this chain and that the difference in carbon mobility is greater within the sorbitol moiety of maltitol than in sorbitol. The relaxation time obtained by magnetic resonance for carbons at the end of the 6 carbon chain is related to the relaxation time and the one of carbons in the middle of the chain is in relation with the value of the relaxation time. This result may suggest that the merging between the and relaxation processes in both sugars would be related to the decrease of the differences in mobility between the atoms of 6 carbon chain. Received 4 October 1999 and Received in final form 27 December 1999     

Spin-wave contributions to nuclear magnetic relaxation in magnetic metals

The longitudinal and transverse nuclear magnetic relaxation rates 1/T ₁(T) and 1/T ₂(T) are calculated for three- and two-dimensional (3D and 2D) metallic ferro- and antiferromagnets (FM and AFM) with localized magnetic moments in the spin-wave temperature region. The contribution of the one-magnon decay processes is strongly enhanced in comparison with the standard T-linear Korringa term, especially for the FM case. For the 3D AFM case this contribution diverges logarithmically, the divergence being cut at the magnon gap ω due to magnetic anisotropy, and for the 2D AFM case as ω^-1. The electron-magnon scattering processes yield T ²ln(T/ω) and T ²/ω^1/2-terms in 1/T ₁ for the 3D AFM and 2D FM cases, respectively. The two-magnon (“Raman”) contributions are investigated and demonstrated to be large in the 2D FM case. Peculiarities of the isotropic 2D limit (where the correlation length is very large) are analyzed. Received 29 November 1999 and Received in final form 6 June 2000     

Conductivity relaxation in glass: Compositional contributions to non-exponentiality

That ionic conductivity in glass is a non-exponential process and has been known for many years. The amorphous structure of glass and hence a distribution of cation sites has often been thought to be the cause for the non-exponentiality. Almost completely unresearched, however, has been the effect of glass composition on the nature of the relaxation process. In this paper, we review the observations that have been made of the relationships between glass composition and the non-exponential character of the conductivity relaxation as well combine our recent wide composition range studies of sodium aluminoborate and lithium phosphate glasses to delineate the major features of the correlation. By examining glass compositions ranging from 0.02 to 60 mole% alkalioxide, it is observed that the rapid development of non-exponentiality within 1% Na₂O is accompanied by a similar rapid decrease in the average cation-cation separation distance, this being calculated using the composition and density. Other quantities such as the dc conductivity or activation energy are observed to vary too slowly with composition to produce a linear correlation with the extent of non-exponentiality as monitored in the parameter of the stretched exponentialkww function.     

Intramolecular and intermolecular contributions to the spin-lattice relaxation of protons in benzene and cyclohexane

Temperature dependences are found for the intramolecular and intermolecular contributions to the spin-lattice relaxation of protons in benzene and cyclohexane by dilution in deuterated analogs. The intermolecular contribution in benzene is discussed on the basis of the model for the molecular distribution found from x-ray diffraction studies. The Hubbard correction to the intermolecular contribution is calculated on the basis of the experimental parameters corresponding to rotation and translation. The results imply discontinuous translational motion of molecules in both liquids.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 3, pp. 116–121, March, 1971.In conclusion the author thanks T. N. Khazanovich for useful advice.     

Mesonic and binding contributions to the nuclear Drell-Yan process

We have evaluated the Drell-Yan cross section in nuclei paying special attention to the meson cloud contribution from pions and ϱ-mesons, for which an accurate calculation using the meson nuclear spectral functions is used. Similarly, the nucleonic contribution is evaluated in terms of a relativistic nucleon spectral function. Fair agreement with experiment is found for different nuclei and the results show a sizeable contribution from the renormalized meson cloud. In order to reproduce the experiment a novel element is introduced, consisting of a gradual energy loss of the incoming proton in its pass through the nucleus which produces a strong A dependence at x₁ large.     

Hole- and electron-vibrational couplings in oligoacene crystals: intramolecular contributions

The hole-vibrational coupling is reported for anthracene, tetracene, and pentacene on the basis of a joint experimental and theoretical study of ionization spectra using high-resolution gas-phase photoelectron spectroscopy and first-principles correlated quantum-mechanical calculations. The hole-vibrational coupling is found to be significantly smaller than the electron-vibrational coupling in the case of these oligomers; however, both quantities are predicted to converge to the same value when increasing the chain length.     

A new approach to the relaxation process in gravitational systems

A reformulation of the kinetic theory of N-body gravitational systems, retaining periodic trajectories in the mean field, leads to an intrinsically non-markovian evolution equation, and a √N dependence of the relaxation time. Explicit calculations are carried out for one-dimensional systems.     

Separation of quadrupolar and magnetic contributions to spin-lattice relaxation in the case of a single isotope

We present a NMR pulse double-irradiation method which allows one to separate magnetic from quadrupolar contributions in the spin–lattice relaxation. The pulse sequence fully saturates one transition while another is observed. In the presence of a Δm = 2 quadrupolar contribution, the intensity of the observed line is altered compared to a standard spin-echo experiment. We calculated analytically this intensity change for spins I = 1, , , thus providing a quantitative analysis of the experimental results. Since the pulse sequence we used takes care of the absorbed radiofrequency power, no problems due to heating arise. The method is especially suited when only one NMR sensitive isotope is available. Different cross-checks were performed to prove the reliability of the results obtained. The applicability of this method is demonstrated by a study of the plane oxygen ¹⁷O (I = ) in the high-temperature superconductor YBa₂Cu₄O₈: the ¹⁷O spin–lattice relaxation rate consists of magnetic as well as quadrupolar contributions.     

Magnetic contributions to high energy inverse bremsstrahlung process

Magnetic contribution to inverse bremsstrahlung is estimated at high energies. It begins to dominate over the Coulomb contribution in the ratioCE ₂ ² tan² (θ ₂/2) (1+sin² (θ ₂/2)) whereE ₂ andθ ₂ denote the energy and angle of the accelerated electron andC is essentially a nuclear constant.     

Intermolecular dipole-dipole relaxation of (129)Xe dissolved in water

Intermolecular (129)Xe-(1)H nuclear Overhauser effects and (129)Xe longitudinal relaxation time measurements were used to demonstrate that the dipole-dipole coupling is the dominant relaxation mechanism for (129)Xe in water, at room temperature. (129)Xe-(1)H cross-relaxation rates were derived to be sigma(XeH) approximately 3.2 +/- 0.3 x 10(-3) s(-1), independent of xenon pressure (in the range of 1-10 bar) and of the presence of oxygen. Corresponding xenon-proton internuclear distances were calculated to be 2.69 +/- 0.12 A. Using the magnitude of the dipole-dipole coupling and the spin density ratio between dissolved xenon and bulk water, it is estimated that (129)Xe-(1)H spin polarization-induced nuclear Overhauser effects would yield little net proton signal enhancement in water.     

Spin-lattice relaxation and intramolecular motions in transferrin on the Mössbauer spectroscopy data

A new approach for the investigation of intramolecular motions in proteins, based on the study of spin-lattice relaxation of the iron atom of the protein active centres, has been developed. The gamma-resonance spectra have been obtained for the globules of transferrin enriched with⁵⁷Fe. They possessed a paramagnetic hyperfine structure up to room temperature. This afforded the opportunity to experimentally investigate high temperature conformational motions in proteins and to study their influence on the spin-lattice relaxation. A theoretical model of relaxational spectra calculations has been developed, which enabled us to extract the frequency distribution of the spin-lattice relaxation from the shape of the spectra. The approach developed for the study of intramolecular dynamics of proteins based on the examination of spin-lattice relaxation in gamma-resonance spectra increases the frequency scale by at least one order in comparison with conventional methods.     

An alternative model to the two-magnon magnetic relaxation process in permalloy films

The thickness dependence of the linewidth difference for parallel and perpendicular ferromagnetic resonance in permalloy films at x-band and room temperature is calculated for the exchange conductivity-constant damping theory and is compared with experiment. The results are in good agreement for thin (d< 800 Å) and thick (d > 1500 Å) films. The data show a somewhat greater difference than the theory for intermediate thickness. The result indicate that a previously proposed two-magnon interpretation for the observed difference may be inappropriate.     

Hard- and soft-fermion-pole contributions to single transverse-spin asymmetry for Drell-Yan process

We study the single transverse-spin asymmetry for the Drell-Yan lepton pair production based on the twist-3 mechanism in the collinear factorization. We calculate all the hard-pole (HP) and the soft-fermion-pole (SFP) contributions to the single-spin-dependent cross section originating from the quark-gluon correlation functions in the transversely polarized nucleon in the leading order with respect to the QCD coupling constant. Combined with the soft-gluon-pole (SGP) contribution, this completes the corresponding twist-3 cross section. In the real photon limit, where all the HP contributions are transformed into the SFP contribution, we find that the SFP partonic hard cross section for the two independent quark-gluon correlation functions coincides in each scattering channel, as in the case of the inclusive light-hadron production. Our result enables one to extract the quark-gluon correlation functions from the forthcoming experiments at several facilities such as RHIC and J-PARC.