ROTATIONAL-DYNAMICS OF SOLID C-70 - A NEUTRON-SCATTERING STUDY

PMID: 10011126PMID: 10011126 This work at the University of Sussex at supported by the Science and Engineering Research Council, U.K.PMID: 10011126 This work at the University of Sussex at supported by the Science and Engineering Research Council, U.K.PMID: 10011126 This work at the University of Sussex at supported by the Science and Engineering Research Council, U.K.We report the results of neutron-diffraction and low-energy neutron-inelastic-scattering experiments on high-purity solid C-70 between 10 and 640 K. Thermal hysteresis effects are found to accompany structural changes both on cooling and on heating. The observed diffuse scattering intensity does not change with temperature. At 10 K broad librational peaks are observed at 1.82(16) meV [full width at half maximum=1.8(5) meV]. The peaks soften and broaden further with increasing temperature. At and above room temperature, they collapse into a single quasielastic line. At 300 K, the diffusive reorientational motion appears to be somewhat anisotropic, becoming less so with increasing temperature. An isotropic rotational diffusion model, in which the motions of adjacent molecules are uncorrelated, describes well the results at 525 K. The temperature dependence of the rotational diffusion constants is consistent with a thermally activated process having an activation energy of 32(7) meV.This work at the University of Sussex at supported by the Science and Engineering Research Council, U.K

The diet and feeding ecology of Conger conger (L. 1758) in the deep waters of the Eastern Ionian Sea

The diet of the European conger eel Conger conger was investigated for the first time in the Eastern Mediterranean. Fish dominated the European conger eel diet in the deep waters of E. Ionian Sea. All other prey taxa were identified as accidental preys. However, intestine analysis showed that Natantia, Brachyura and Cephalopoda might have a more important contribution in the diet of the species. C. conger exhibited a benthopelagic feeding behavior as it preyed upon both demersal and mesopelagic taxa. The high vacuity index and the low stomach and intestine fullness indicated that the feeding intensity of the species in the deep waters of Eastern Ionian Sea was quite low. C. conger feeding strategy was characterised by specialisation in various resource items. A between-phenotype contribution to niche width was observed for some prey categories. European Conger eel feeding specialisation seemed to be an adaptation to a food-scarce environment, as typified in deep-water habitat

Low-temperature structural model of hcp solid C70_{70}

We report intermolecular potential-energy calculations for solid C_${70}$ and determine the optimum static orientations of the molecules at low temperature; we find them to be consistent with the monoclinic structural model proposed by us in an earlier report [Solid State Commun. {\bf 105), 247 (1998)]. This model indicates that the C_5 axis of the molecule is tilted by an angle $\approx$18^o from the monoclinic b axis in contrast with the molecular orientation proposed by Verheijen {\it et al.} [J. Chem. Phys. {\bf 166}, 287 (1992)] where the C_5 axis is parallel to the monoclinic b axis. In this calculation we have incorporated the effective bond charge Coulomb potential together with the Lennard-Jones potential between the molecule at the origin of the monoclinic unit cell and its six nearest neighbours, three above and three below. The minimum energy configuration for the molecular orientations turns out to be at $\theta$=18^o, $\phi$=8^o, and $\psi$=5^o, where $\theta$, $\phi$, and $\psi$ define the molecular orientations.Comment: ReVTeX (4 pages) + 2 PostScript figure

Optical absorption in the strong coupling limit of Eliashberg theory

We calculate the optical conductivity of superconductors in the strong-coupling limit. In this anomalous limit the typical energy scale is set by the coupling energy, and other energy scales such as the energy of the bosons mediating the attraction are negligibly small. We find a universal frequency dependence of the optical absorption which is dominated by bound states and differs significantly from the weak coupling results. A comparison with absorption spectra of superconductors with enhanced electron-phonon coupling shows that typical features of the strong-coupling limit are already present at intermediate coupling.Comment: 10 pages, revtex, 4 uuencoded figure

A magnetization and 11^{11}B NMR study of Mg1−x_{1-x}Alx_xB2_2 superconductors

We demonstrate for the first time the magnetic field distribution of the pure vortex state in lightly doped Mg$_{1-x}$Al$_x$B$_2$ ($x\leq 0.025$) powder samples, by using $^{11}$B NMR in magnetic fields of 23.5 and 47 kOe. The magnetic field distribution at T=5 K is Al-doping dependent, revealing a considerable decrease of anisotropy in respect to pure MgB$_2$. This result correlates nicely with magnetization measurements and is consistent with $\sigma$-band hole driven superconductivity for MgB$_2$

Reversible Pressure-Induced Amorphization in Solid C70 : Raman and Photoluminescence Study

We have studied single crystals of $C_{70}$ by Raman scattering and photoluminescence in the pressure range from 0 to 31.1 GPa. The Raman spectrum at 31.1 GPa shows only a broad band similar to that of the amorphous carbon without any trace of the Raman lines of $C_{70}$. After releasing the pressure from 31.1 GPa, the Raman and the photoluminescence spectra of the recovered sample are that of the starting $C_{70}$ crystal. These results indicate that the $C_{70}$ molecules are stable upto 31.1 GPa and the amorphous carbon high pressure phase is reversible, in sharp contrast to the results on solid $C_{60}$. A qualitative explaination is suggested in terms of inter- versus intra-molecular interactions.Comment: To appear in Phys. Rev. Lett., 12 pages, RevTeX (preprint format), 3 figures available upon reques

Superconductivity in Fullerides

Experimental studies of superconductivity properties of fullerides are briefly reviewed. Theoretical calculations of the electron-phonon coupling, in particular for the intramolecular phonons, are discussed extensively. The calculations are compared with coupling constants deduced from a number of different experimental techniques. It is discussed why the A_3 C_60 are not Mott-Hubbard insulators, in spite of the large Coulomb interaction. Estimates of the Coulomb pseudopotential $\mu^*$, describing the effect of the Coulomb repulsion on the superconductivity, as well as possible electronic mechanisms for the superconductivity are reviewed. The calculation of various properties within the Migdal-Eliashberg theory and attempts to go beyond this theory are described.Comment: 33 pages, latex2e, revtex using rmp style, 15 figures, submitted to Review of Modern Physics, more information at http://radix2.mpi-stuttgart.mpg.de/fullerene/fullerene.htm

Towards population-based structural health monitoring, part IV : heterogeneous populations, transfer and mapping

Population-based structural health monitoring (PBSHM) involves utilising knowledge from one set of structures in a population and applying it to a different set, such that predictions about the health states of each member in the population can be performed and improved. Central ideas behind PBSHM are those of knowledge transfer and mapping. In the context of PBSHM, knowledge transfer involves using information from a structure, defined as a source domain, where labels are known for a given feature, and mapping these onto the unlabelled feature space of a different, target domain structure. If the mapping is successful, a machine learning classifier trained on the transformed source domain data will generalise to the unlabelled target domain data; i.e. a classifier built on one structure will generalise to another, making Structural Heath Monitoring (SHM) cost-effective and applicable to a wide range of challenging industrial scenarios. This process of mapping features and labels across source and target domains is defined as domain adaptation, a subcategory of transfer learning. However, a key assumption in conventional domain adaptation methods is that there is consistency between the feature and label spaces. This means that the features measured from one structure must be the same dimension as the other (i.e. the same number of spectral lines of a transmissibility), and that labels associated with damage locations, classification and assessment, exist on both structures. These consistency constraints can be restrictive, limiting to which types of population domain adaptation can be applied. This paper, therefore, provides a mathematical underpinning for when domain adaptation is possible in a structural dynamics context, with reference to topology of a graphical representation of structures. By defining when conventional domain adaptation is applicable in a structural dynamics setting, approaches are discussed that could overcome these consistency restrictions. This approach provides a general means for performing transfer learning within a PBSHM context for structural dynamics-based features

Estimation of the iron bioavailability in green vegetables using an in vitro digestion/Caco-2 cell model

It is estimated that over 30% of the global population is anaemic, half of which is due to iron deficiency. The bioavailability of iron from vegetables is low and variable, and influenced by food composition and matrix. We have therefore determined the relative bioavailability of iron in five types of green vegetable, spinach, broccoli, savoy cabbage, curly kale and green pepper, by measuring the ferritin response in a simulated digestion/Caco-2 cell model. Savoy cabbage gave the highest ferritin response and analysis of the digest showed that the iron was present in low molecular weight fractions which contained glucose, fructose, organic acids and amino acids. The addition of fructose 1,6-biphosphate to the Caco-2 cells increased iron uptake 2-fold. These results demonstrate that cabbage was the best source of bioavailable iron out of the vegetables studied and suggest that the formation of complexes with fructose derivatives contribute to increase the iron bioavailability

A Novel Methodology Using Simplified Approaches for Identification of Cracks in Beams

Abstract In this paper, natural frequency based forward and inverse methods are proposed for identifying multiple cracks in beams. Forward methods include simplified definition of the natural frequency drops caused by the cracks. The ratios between natural frequencies obtained from multi-cracked and un-cracked beams are determined by an approach that uses the local flexibility model of cracks. This approach does not consider nonlinear crack effects that can be easily neglected when the number of cracks is not excessive. In addition, an expression, which removes the necessity of repeating natural frequency analyses, is given for identifying the connection between the crack depths and natural frequency drops. These simplified approaches play crucial role in solving inverse problem using constituted crack detection methodology. Solution needs a number of measured modal frequency knowledge two times more than the number of cracks to be detected. Efficiencies of the methods are verified using the natural frequency ratios obtained by the finite element package. The crack detection methodology is also validated using some experimental natural frequency ratios given in current literature. Results show that the locations and depths ratios of cracks are successfully predicted by using the methods presented