Biomedical subjects

U Scheler

Publications and source records attributed to U Scheler.

12 recordsLinked to original sources

PubMed2003

Separation of velocity distribution and diffusion using PFG NMR.

Pulsed field gradient (PFG) NMR is applied to investigate flow processes. In this case the NMR signal experiences phase modulation due to flow and signal attenuation due to the distribution of velocities. The velocity distribution consists of one part originating from diffusion and of a second part, the distribution of the directed motion. The usual PFG-experiment in which the gradient strength is incremented cannot distinguish between both. Incrementing velocity at constant gradient strength keeps the contribution from diffusion constant but changes the absolute width of the velocity distribution. So the signal is attenuated again, but only due to the distribution of the directed motion. The phase modulation as a signature of flow is not affected by this strategy, because velocity and gradient strength are Fourier conjugated. The key advantage of this approach is the possibility of measuring very low velocities, which only cause a very slight phase modulation that is easily covered by diffusion. The method is discussed here for very slow flow in a rheometer cell.

Journal Article↗

PubMed1998

High-speed MAS-NMR investigations on radiation-modified fluoropolymers.

Fluoropolymers possess an interesting combination of physical and chemical properties. In order to utilize these properties in combination with other materials, the compatibility of the fluoropolymers with those materials has to be improved by a suitable modification process. As one modification process the irradiation with high-energy electrons has been applied. High-speed MAS solid-state NMR has been used to characterize the structural changes in fluoropolymers resulting from the irradiation. The high MAS rotation frequencies, applied here, average the anisotropy of the chemical shift and the homonuclear dipolar coupling. Despite the fact that the electron irradiation results in a low concentration of modifications, the dynamic range of the solid-state NMR experiment is sufficient to detect and characterize the modifications.

Anisotropy↗

PubMed1996

Proton fluorine wideline separation experiments on poly (vinylidene difluoride).

Two-dimensional heteronuclear proton-fluorine correlation solid-state spectroscopy is demonstrated on a sample of poly (vinylidene difluoride) (PVDF). This allows the correlation of structural information contained in the fluorine chemical shift in one dimension with information on mobility from proton wideline spectra in the second dimension. The effect of the heteronuclear fluorine-proton dipolar coupling on the proton linewidth is investigated separately. The incorporation of magnetization filters into the preparation period enables one to measure the wideline separation (WISE) spectra for the amorphous or the crystalline parts of the sample separately.

Fluorine↗

PubMed1996

Spatially resolved solid-state MAS-NMR-spectroscopy.

A comprehensive account of spatially resolved solid-state MAS NMR of 13C is given. A device generating field gradients rotating synchronously with the magic angle spinner is described. Spatial resolution and sensitivity are compared for phase and frequency encoding of spatial information. The suppression of spinning sidebands is demonstrated for both cases. Prior knowledge about the involved materials can be used for the reduction of data from spatially resolved spectra to map chemical structure. Indirect detection via 13C NMR gives access to the information about mobility from proton-wideline spectra. Two-dimensional solid-state spectroscopy with spatial resolution is demonstrated for a rotor synchronized MAS experiment which resolves molecular order as a function of space. By comparison of different experiments the factors affecting the spatial resolution are investigated.

Carbon Isotopes↗

PubMed1993

Spinning sidebands from chemical shift anisotropy in 13C MAS imaging.

Solid state imaging by 13C MAS imaging is described. The spinning sidebands occurring at moderate spinning speeds, which disturb the images, can be suppressed by TOSS. For rigid solids the spatial resolution that can be achieved in this way is better than that of 1H images at the same spinning speed. Spatially resolved spectra with or without spinning sidebands can likewise be recorded providing information about the isotropic and the anisotropic chemical shifts which can be exploited for the study of structure, order and dynamics. The techniques are demonstrated on a phantom made with 13C-labelled glycine.

Anisotropy↗

PubMed1979

[Subtotal parathyroidectomy in the advanced stages of renal osteodystrophy].

In 7 haemodialysis patients with progressing renal osteopathy a partly subtotal, partly total parathyroidectomy was carried out. Postoperatively in all cases a clinical improvement developed, which, however, in part was only transient. The laboratory parameters showed a rapid tendency to normalisation, the X-ray diagnostic finding and the bone mineral content remained essentially unchanged, also the histological skeletal findings. The results are compiled in form of tables. The value of the diagnostic measures which should precede a subtotal parathyroidectomy is discussed. At present the different postoperative courses apparently cannot be prospectively estimated with the help of the hitherto usual diagnostic measures. On the basis of the partly good results and of the operation risk which is to be thoroughly demanded of a haemodialysis patient it seems that after having used all conservative possibilities the surgical interventions nevertheless indicated in progressing renal osteopathy.

Adult↗

PubMed1976