Loss anisotropy

The success of the model for the loss anisotropy led Owen and Ward to use equivalent assumptions to calculate the modulus anisotropy. The loss anisotropy calculations assume simple shear between the lamellae only, which for parallel lamellae sheet would imply that inter-lamellar shear is not activated when the tensile stress is applied along the initial draw direction i.e. parallel to the lamellar plane normals). A very appreciable fall in tensile modulus was. however, observed in this case, although as e.xpected by comparison with the corresponding loss factor in... 

Figure Bl.6.12 Ionization-energy spectrum of carbonyl sulphide obtained by dipole (e, 2e) spectroscopy [18], The incident-electron energy was 3.5 keV, the scattered incident electron was detected in the forward direction and the ejected (ionized) electron detected in coincidence at 54.7° (angular anisotropies cancel at this magic angle ). The energy of the two outgoing electrons was scaimed keeping the net energy loss fixed at 40 eV so that the spectrum is essentially identical to the 40 eV photoabsorption spectrum. Peaks are identified with ionization of valence electrons from the indicated molecular orbitals.

Dravid et al. examined anisotropy in the electronic structures of CNTs from the viewpoint of momentum-transfer resolved EELS, in addition to the conventional TEM observation of CNTs, cross-seetional TEM and precise analysis by TED [5]. Comparison of the EEL spectra of CNTs with those of graphite shows lower jc peak than that of graphite in the low-loss region (plasmon loss), as shown in Fig. 7(a). It indicates a loss of valence electrons and a change in band gap due to the curved nature of the graphitic sheets. 

Although CNTs showed similar EELS pattern in plasmon-loss and core-loss regions to graphite, SWCNT and fine MWCNT with a diameter less than 5 nm had different features. Furthermore, it has been found out that the angular-dependent EELS along the direction normal to the longitudinal axis of CNT shows stronger contribution from Jt electrons than [Pg.38]

Lorentzian line shapes are expected in magnetic resonance spectra whenever the Bloch phenomenological model is applicable, i.e., when the loss of magnetization phase coherence in the xy-plane is a first-order process. As we have seen, a chemical reaction meets this criterion, but so do several other line broadening mechanisms such as averaging of the g- and hyperfine matrix anisotropies through molecular tumbling (rotational diffusion) in solution. 

The same effect is produced if, instead of physical rotation of the chromophore, energy transfer takes place among them. A randomization of the emitting dipoles in a three-dimensional space results to a limiting value of r equal to zero. If the transport process involves transition dipoles orthogonal to an axis, the limiting value of r is equal to 0.137. The loss of anisotropy... 

From an experimental point of view, if we want to establish whether a loss of anisotropy is due to rotational diffusion or to energy transfer, we must probe very short times when molecular motions are inhibited. This is precisely what we did by observing fluorescence anisotropy on the sub-picosecond time-... 

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