Relations between DFT and CI approximation

Relations between the two quantum chemical methods density functional theory (DFT) and configuration interaction (CI) are studied. As a result a new expression of the density functional based on CI approximation is presented. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 74: 55–58, 1999     

Pulse wave velocity with 4D flow MRI: Systematic differences and age-related regional vascular stiffness

Purpose

The objective of this study was to compare multiple methods for estimation of PWV from 4D flow MRI velocity data and to investigate if 4D flow MRI-based PWV estimation with piecewise linear regression modeling of travel-distance vs. travel time is sufficient to discern age-related regional differences in PWV.

Methods

4D flow MRI velocity data were acquired in 8 young and 8 older (age: 23 ± 2 vs. 58 ± 2 years old) normal volunteers. Travel-time and travel-distance were measured throughout the aorta and piecewise linear regression was used to measure global PWV in the descending aorta and regional PWV in three equally sized segments between the top of the aortic arch and the renal arteries. Six different methods for extracting travel-time were compared.

Results

Methods for estimation of travel-time that use information about the whole flow waveform systematically overestimate PWV when compared to methods restricted to the upslope-portion of the waveforms (p < 0.05). In terms of regional PWV, a significant interaction was found between age and location (p < 0.05). The age-related differences in regional PWV were greater in the proximal compared to distal descending aorta.

Conclusion

Care must be taken as different classes of methods for the estimation of travel-time produce different results. 4D flow MRI-based PWV estimation with piecewise linear regression modeling of travel-distance vs. travel time can discern age-related differences in regional PWV well in line with previously reported data.     

Trace Determination and Pressure Estimation of Fluorine F2 Caused by Irradiation Damage in Minerals and Synthetic Fluorides

Irradiated alkali and earth alkali halides can form metal colloids and halogen molecules, which stay trapped inside the crystal. In this paper we provide ¹⁹F NMR spectroscopic evidence of trapped F₂ fluids in heavy ion‐bombarded synthesized LiF crystals as well as in a variety of the mineral Villiaumite (NaF). This is the 2nd mineral in which F₂ is unambiguously detected in nature. The trace quantification of the latter is in the order of magnitude of 10^?6 mol g^?1. Pressures and densities of the F₂ fluids are estimated based on the theory of nuclear spin relaxation in dilute gases.     

Monodromy Groups of Irregular Elliptic Surfaces

Monodromy groups, i.e. the groups of isometries of the intersection lattice L _X H ₂/torsion generated by the monodromy action of all deformation families of a given surface, have been computed by the author for any minimal elliptic surface with p _g > q = 0. New and refined methods are now employed to address the cases of minimal elliptic surfaces with p _g q > 0. Thereby we get explicit families such that any isometry is in the group generated by their monodromies or does not respect the invariance of the canonical class or the spinor norm. The monodromy is also shown to act by the full symplectic group on the first homology modulo torsion.     

Cyanoisocyanoacetylene,N≡C−C≡C−N≡C

Vacuum pyrolysis of the precursor complex [(CO)₅Cr(CN−CCl=CF−CN)] resulted in the isolation and structure elucidation by molecular spectroscopy of isomer 1 . According to ab initio calculations 1 is 109 kJ mol⁻¹ less stable than NC−C≡C−CN, which has been known for some time. An accurate equilibrium structure for 1 has been determined with mixed experimental and theoretical methods.     

On the diffeomorphism groups of elliptic surfaces

In this paper we determine for relatively minimal elliptic surfaces with positive Euler number the image of the natural representation of the group of orientation preserving self-diffeomorphisms on , the second homology group reduced modulo torsion. To this end we construct as many embedded spheres of square such that an isometry not induced from any combination of reflections at such spheres or from ‘complex conjugation’ can be shown not to be induced from some diffeomorphism at all. This is done with the help of Seiberg-Witten-invariants. Received: 18 December 1995 / Revised version: 27 January 1997     

Distance measurements in spin-1/2 systems by 13C and 31P solid-state NMR in dense dipolar networks

In this article solid-state NMR methods for the determination of internuclear dipole-dipole couplings between homonuclear spin-1/2 nuclei are presented. They are suitable for relatively dense dipolar networks which are still dominated by 2-spin interactions. C-/R-symmetry theory is applied to create a double-quantum average Hamiltonian using phase-modulated radio-frequency irradiation and magic-angle sample-rotation. Symmetry derived pulse sequences with improved compensation against chemical shift anisotropies were found assuming a small isotropic chemical shift difference and using numerical calculations of the spin dynamics. Moreover it is shown that a constant time procedure can be used to acquire reliable double-quantum build-up curves even in systems in which damping obscures oscillations in their symmetric build-up curve. This technique is demonstrated on four crystalline model compounds with 31P and 13C spin systems typical for inorganic and biological applications. Comparison to crystal structure data indicates that the distances derived this way from 31P and 13C double-quantum NMR carry only small systematic errors caused for example by anisotropic J-coupling, dipolar contributions from adjacent spins and relaxation.