Project on comparison of structural parameters and electron density maps of oxalic acid dihydrate

Results obtained from four X-ray and five neutron data sets collected under a project sponsored by the Commission on Charge, Spin and Momentum Densities are analyzed by comparison of thermal parameters, positional parameters and X - N electron density maps. Three sets of theoretical calculations are also included in the comparison. Though several chemically significant features are reproduced in all the experimental density maps, differences in detail occur which caution against overinterpretation of the maps. Large differences between vibrational tensor elements Uij are observed which can often not be corrected by the scaling of all temperature parameters in a set. Positional parameters are reproducible to precisions of 0.001 Å or better. The biggest discrepancies between theoretical and experimental deformation density maps occurs in the lone-pair regions where peaks are higher in the theoretical maps. However, this comparison may be affected by inadequacies in the thermal-motion formalism which must be invoked before experimental and theoretical maps can be compared in a quantitative way

Elastic modulus in the crystalline region of poly(p-phenylene terephthalamide)

Fibres from aromatic polyamides have a much higher Young's modulus than fibres from aliphatic polyamides. In order to contribute to the explanation of this observed difference we looked at one of the ultimate properties, the elastic modulus in the crystalline region in the chain direction (Ecr). We carried out measurements on a bundle of filaments of PRD 49 fibre, which we identified by i.r. and X-ray analyses as poly(p-phenylene terephthalamide). With the X-ray technique we determined the lattice extensions under loading and from these data the Ecr was calculated. The Ecr was found to be 20 × 1011 dyne/cm2 which is in good agreement with the calculated Ecr, but not very different from that of nylon-6,6. The Young's modulus was found to be 11 × 1011 dyne/cm2

Potential of mean force by thermodynamic integration: molecular-dynamics simulation of decomplexation

“Umbrella sampling” has been incorporated in the thermodynamic integration method to obtain a potential of mean force by slow growth molecular-dynamics simulations. The method was tested for liquid argon, for which good agreement was obtained with a standard potential of mean force, as derived from the radial pair-correlation function. For a sodium chloride ion-pair in aqueous solution the calculations showed resonable agreement with a literature result. The method was also applied to the decomplexation of 18-crown-6 and a potassium cation in aqueous solution

A correction procedure for the errors in single-crystal intensities due to the inhomogeneity of the primary X-ray beam

Graphite monochromators are known to give rise to non-homogeneous primary X-ray beams. When intensities of single crystals are measured the effective cross section of a non-spherical crystal in the X-ray beam depends on its orientation in the beam. Therefore, systematic errors in the measured integrated intensities are introduced by the inhomogeneity of the incoming beam. A correction for these errors can be made, knowing the intensity profile of the primary beam and the dimensions and orientation of the crystal in the beam. The correction can conveniently be applied with the absorption correction. Examples of the corrections are given for crystals with rational boundary planes. It is shown that the intensity of an X-ray reflection as a function of the rotation about the scattering vector ( rotation) can be calculated with fair accuracy. In some cases (large elongated crystals in an inhomogeneous beam) correction for absorption only may give results which are worse than those with no correction at all

Admixtures to d-wave gap symmetry in untwinned YBa2Cu3O7 superconducting films measured by angle-resolved electron tunneling

We report on an \textit{ab}-anisotropy of $J_{c \parallel b}/J_{c \parallel a}$ and $I_{c}R_{n \parallel b}/I_{c}R_{n \parallel a}\cong 1.2$ in ramp-edge junctions between untwinned YBa$_{2}$Cu$_{3}$O$_{7}$ and $s$% -wave Nb. For these junctions, the angle $\theta$ with the YBa$_{2}$Cu$_{3}$O$_{7}$ crystal b-axis is varied as a single parameter. The $R_{n}$A($\theta$)-dependence presents 2-fold symmetry. The minima in $I_{c}R_{n}$ at $\theta \cong 50^{\circ}$ suggest a real s-wave subdominant component and negligible $d_{xy}$-wave or imaginary s-wave admixtures. The $I_{c}R_{n}$($\theta$)-dependence is well-fitted by 83% $d_{x^{2}-y^{2}}$-, 15% isotropic $s$- and 2% anisotropic s-wave order parameter symmetry, consistent with $\Delta_{b}/\Delta_{a} \cong 1.5$.Comment: 4 pages, 3 figures, to be published in Physical Review Letter

Neurophysiological markers predicting recovery of standing in humans with chronic motor complete spinal cord injury

The appropriate selection of individual-specific spinal cord epidural stimulation (scES) parameters is crucial to re-enable independent standing with self-assistance for balance in individuals with chronic, motor complete spinal cord injury, which is a key achievement toward the recovery of functional mobility. To date, there are no available algorithms that contribute to the selection of scES parameters for facilitating standing in this population. Here, we introduce a novel framework for EMG data processing that implements spectral analysis by continuous wavelet transform and machine learning methods for characterizing epidural stimulation-promoted EMG activity resulting in independent standing. Analysis of standing data collected from eleven motor complete research participants revealed that independent standing was promoted by EMG activity characterized by lower median frequency, lower variability of median frequency, lower variability of activation pattern, lower variability of instantaneous maximum power, and higher total power. Additionally, the high classification accuracy of assisted and independent standing allowed the development of a prediction algorithm that can provide feedback on the effectiveness of muscle-specific activation for standing promoted by the tested scES parameters. This framework can support researchers and clinicians during the process of selection of epidural stimulation parameters for standing motor rehabilitation

Growing LaAlO3/SrTiO3 interfaces by sputter deposition

Sputter deposition of oxide materials in a high-pressure oxygen atmosphere is a well-known technique to produce thin films of perovskite oxides in particular. Also interfaces can be fabricated, which we demonstrated recently by growing LaAlO3 on SrTiO3 substrates and showing that the interface showed the same high degree of epitaxy and atomic order as is made by pulsed laser deposition. However, the high pressure sputtering of oxides is not trivial and number of parameters are needed to be optimized for epitaxial growth. Here we elaborate on the earlier work to show that only a relatively small parameter window exists with respect to oxygen pressure, growth temperature, radiofrequency power supply and target to substrate distance. In particular the sensitivity to oxygen pressure makes it more difficult to vary the oxygen stoichiometry at the interface, yielding it insulating rather than conducting