NMR-spektroskopische Untersuchungen an 15N-markierten N-Phosphorylphosphazenen und Imidodiphosphorsäure-Derivaten

N.M.R. Spectroscopic Studies of ¹⁵N Labelled N-Phosphorylphosphazenes and Imidodiphosphoric Acid Derivatives ¹⁵N labelled compounds were prepared and investigated by means of ³¹P- and ¹⁵N-NMR spectroscopy. The chemical shift values δ_P and δ_N, and the coupling constants ¹J_PN and ²J_PP are discussed and interpreted qualitatively by semiempirical quantumchemical calculations (CNDO/2) using POPLE 'S ΔE-model.     

NMR-spektroskopische Untersuchungen an Mercaptophosphazenen. II. NMR-spektroskopische Untersuchungen an 15N-markierten Mercaptophosphazenen

N.M.R. Spectroscopic Investigations of Thiophosphazenes. II. N.M.R. Spectroscopic Investigations of ¹⁵N Labelled Thiophosphazenes Completely ¹⁵N labelled compounds of the type ¹⁵N₃P₃Cl_6?n(SR)_n, R = Et or Ph; n = 0, 2, 4, or 6, and of the type ¹⁵N₄P₄Cl_8?n(SR)_n, R = Et; n = 0, 4, or 8, were prepared and investigated by means of both ³¹P n.m.r. spectroscopy and ¹⁵N n.m.r. spectroscopy respectively. The coupling constants ²J_PP, in some cases only found by simulating the spectra, and the coupling constants ¹J_PN are given. The values of these coupling constants and their relation are discussed. The general tendency is visible, that with increasing coupling constant ¹J_PN the coupling constant ²J_PP decreases. With increasing grade of substitution n the ¹⁵N chemical shifts are changed to higher fields.     

Correlation decay of Lagrangian velocity differences in locally isotropic turbulence

The dynamical correlation decay of eddies in fully developed turbulent flows is considered. Eddies of different sizesr are represented by Galilei invariant velocity differences of two fluid elements moving along with the flow, which start a distancer apart. The equal-time statistical properties of the flow are used as partly theoretical, partly experimental input. The method used is the continued fraction representation of the time evolution operator's resolvent. Neglecting memory effects we find the decay rate in the inertial subrange being determined by the ratio of the energy dissipation and the eddy fluctuation strength (represented by the static second order structure function). The decay rate for small eddies,r0, tends to a Reynolds number dependent constant. The influence of intermittency on the dynamics via statics is evaluated. Inadequate experimental and theoretical information about higher order static structure functions renders an evaluation of the memory contribution impossible. Scaling arguments indicate decreasing relative importance of memory effects in the inertial subrange with increasingr.     

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Measurement of the orientational elastic constants and the twist viscosity of nematic side chain polymers

Abstract

The temperature dependence of the three elastic constants k _ii (i = 1, 2, 3) and the twist viscosity γ₁ of two nematic side chain polyacrylates and one comparable low molecular weight compound have been measured by means of the Freedericksz effect. The change from the low to the high molecular liquid crystal causes a change of the ratio k ₃₃/k ₁₁ from greater to less than unity, but the order of magnitude of the elastic constants remains the same. In contrast, the twist viscosity of the polymeric liquid crystal is about 1000 times greater in magnitude than that of a comparable low molecular weight liquid crystal. The activation energy for the viscosity of the polymer differs by a factor 3–4 from that of the low molecular weight liquid crystal. The elastic constants as well as the twist viscosity show a quadratic dependence on the order parameter S over a wide temperature range.     

Quantification of regional intrapulmonary oxygen partial pressure evolution during apnea by (3)He MRI

We present a new method to determine in vivo the temporal evolution of intrapulmonary oxygen concentrations by functional lung imaging with hyperpolarized (3)Helium ((3)He-->). Single-breath, single-bolus visualization of (3)He--> administered to the airspaces is used to analyze nuclear spin relaxation caused by the local oxygen partial pressure p(O(2))(t). We model the dynamics of hyperpolarization in the lung by rate equations. Based hereupon, a double acquisition technique is presented to separate depolarization by RF pulses and oxygen induced relaxation. It permits the determination of p(O(2)) with a high accuracy of up to 3% with simultaneous flip angle calibration using no additional input parameters. The time course of p(O(2)) during short periods of breathholding is found to be linear in a pig as well as in a human volunteer. We also measured the wall relaxation time in the lung and deduced a lower limit of 4.3 min.     

Backward production of the B meson in K−p interactions at 4.2 GeVc

The backward production of the B(1235) meson is studied in the reaction K^?p→Σ^?π⁺ω. This reaction is observed in the final state Σ^?π⁺π⁺π^?π⁰. A π⁺ω mass enhancement is visible in the region of the B meson for events with small |u|K^? →Σ^?) squared four-momentum transfer. The properties of the enhancement agree with those of the B meson. The cross section for K^?p→Σ^?B⁺ at $\text{4.15}\text{GeV}\text{c}$ incident K^? momentum is (3.2 ± 0.5) μb. The backward production of the B meson is compared with similar baryon exchange productions of the A₁ and C(Q₁) axial vector mesons observed in the same experiment.