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Oxorhenium(V) complexes [ReOX3(PPh3)2] (X = Cl, Br) react with phenylacetylene under formation of complexes with ylide-type ligands. Compounds of the compositions [ReOCl3(PPh3){C(Ph)C(H)(PPh3)}] (1), [ReOBr3(OPPh3){C(Ph)C(H)(PPh3)}] (2), and [ReOBr3(OPPh3){C(H)C(Ph)(PPh3)}] (3) were isolated and characterized by X-ray diffraction. They contain a ligand, which was formed by a nucleophilic attack of released PPh3 at coordinated phenylacetylene. The structures of the products show that there is no preferable position for this attack. Cleavage of the Re–C bond in 3 and dimerization of the organic ligand resulted in the formation of the [{(PPh3)(H)CC(Ph)}2]2+ cation, which crystallized as its [(ReOBr4)(OReO3)]2– salt.
AgTcO4 reacts with R3ECl compounds (E = C, Si, Ge, Sn, Pb; R = Me, iPr, tBu, Ph), tBu2SnCl2, or PhMgCl under formation of novel trioxotechnetium(VII) derivatives. The carbon and silicon derivatives readily undergo decomposition, which was proven by 99Tc NMR spectroscopy and the isolation of decomposition products such as [TcOCl3(THF)(OH2)]. Compounds [Ph3GeOTcO3], [(THF)Ph3SnOTcO3], [(O3TcO)SntBu2(OH)]2, and [(THF)4Mg(OTcO3)2] are more stable and were isolated in crystalline form and characterized by X-ray diffraction.
As the field strength and, therefore, the operational frequency in MRI is increased, the wavelength approaches the size of the human head/body, resulting in wave effects, which cause signal decreases and dropouts. Several multichannel approaches have been proposed to try to tackle these problems, including RF shimming, where each element in an array is driven by its own amplifier and modulated with a certain (constant) amplitude and phase relative to the other elements, and Transmit SENSE, where spatially tailored RF pulses are used. In this article, a relatively inexpensive and easy to use imaging scheme for 7 Tesla imaging is proposed to mitigate signal voids due to B1 field inhomogeneity. Two time-interleaved images are acquired using a different excitation mode for each. By forming virtual receive elements, both images are reconstructed together using GRAPPA to achieve a more homogeneous image, with only small SNR and SAR penalty in head and body imaging at 7 Tesla.
The objectives of the present work are to characterize the Gas Metal Arc Welding process of DP 600 sheet steel and to summarize the modelling techniques. The time-temperature evolution during the welding cycle was measured experimentally and modelled with the softwaretool SimWeld. To model the phase transformations during the welding cycle dilatometer tests were done to quantify the parameters for phase field modelling by MICRESS®. The important input parameters are interface mobility, nucleation density, etc. A contribution was made to include austenite to bainite transformation in MICRESS®. This is useful to predict the microstructure in the fast cooling segments. The phase transformation model is capable to predict the microstructure along the heating and cooling cycles of welding. Tensile tests have shown the evidence of failure at the heat affected zone, which has the ferrite-tempered martensite microstructure.
The CellDrum technology (The term 'CellDrum technology' includes a couple of slightly different technological setups for measuring lateral mechanical tension in various types of cell monolayers or 3D-tissue constructs) was designed to quantify the contraction rate and mechanical tension of self-exciting cardiac myocytes. Cells were grown either within flexible, circular collagen gels or as monolayer on top of respective 1-mum thin silicone membranes. Membrane and cells were bulged outwards by air pressure. This biaxial strain distribution is rather similar the beating, blood-filled heart. The setup allowed presetting the mechanical residual stress level externally by adjusting the centre deflection, thus, mimicking hypertension in vitro. Tension was measured as oscillating differential pressure change between chamber and environment. A 0.5-mm thick collagen-cardiac myocyte tissue construct induced after 2 days of culturing (initial cell density 2 x 10(4) cells/ml), a mechanical tension of 1.62 +/- 0.17 microN/mm(2). Mechanical load is an important growth regulator in the developing heart, and the orientation and alignment of cardiomyocytes is stress sensitive. Therefore, it was necessary to develop the CellDrum technology with its biaxial stress-strain distribution and defined mechanical boundary conditions. Cells were exposed to strain in two directions, radially and circumferentially, which is similar to biaxial loading in real heart tissues. Thus, from a biomechanical point of view, the system is preferable to previous setups based on uniaxial stretching.
Purpose:
MRI plays a leading diagnostic role in assessing the musculoskeletal (MSK) system and is well established for most questions at clinically used field strengths (up to 3 T). However, there are still limitations in imaging early stages of cartilage degeneration, very fine tendons and ligaments, or in locating nerve lesions, for example. 7 T MRI of the knee has already received increasing attention in the current published literature, but there is a strong need to develop new radiofrequency (RF) coils to assess more regions of the MSK system. In this work, an eight-channel transmit/receive RF array was built as a multipurpose coil for imaging some of the thus far neglected regions. An extensive coil characterization protocol and first in vivo results of the human wrist, shoulder, elbow, knee, and ankle imaged at 7 T will be presented.
Methods:
Eight surface loop coils with a dimension ofurn:x-wiley:00942405:media:mp7176:mp7176-math-0001 were machined from FR4 circuit board material. To facilitate easy positioning, two coil clusters, each with four loop elements, were combined to one RF transmit/receive array. An overlapped and shifted arrangement of the coil elements was chosen to reduce the mutual inductance between neighboring coils. A phantom made of body-simulating liquid was used for tuning and matching on the bench. Afterward, the S-parameters were verified on a human wrist, elbow, and shoulder. For safety validation, a detailed compliance test was performed including full wave simulations of the RF field distribution and the corresponding specific absorption rate (SAR) for all joints. In vivo images of four volunteers were assessed with gradient echo and spin echo sequences modified to obtain optimal image contrast, full anatomic coverage, and the highest spatial resolution within a reasonable acquisition time. The performance of the RF coil was additionally evaluated by in vivo B1 mapping.
Results:
A comparison of B1 per unit power, flip angle distribution, and anatomic images showed a fairly homogeneous excitation for the smaller joints (elbow, wrist, and ankle), while for the larger joints, the shoulder and especially the knee, B1 inhomogeneities and limited penetration depth were more pronounced. However, the greater part of the shoulder joint could be imaged.In vivo images rendered very fine anatomic details such as fascicles of the median nerve and the branching of the nerve bundles. High-resolution images of cartilage, labrum, and tendons could be acquired. Additionally, turbo spin echo (TSE) and inversion recovery sequences performed very well.
Conclusions:
This study demonstrates that the concept of two four-channel transmit/receive RF arrays can be used as a multipurpose coil for high-resolutionin vivo MR imaging of the musculoskeletal system at 7 T. Not only gradient echo but also typical clinical and SAR-intensive sequences such as STIR and TSE performed well. Imaging of small structures and peripheral nerves could in particular benefit from this technique.
Purpose: Image analysis by the retinal vessel analyzer (RVA) observes retinal vessels in their dynamic state online noninvasively along a chosen vessel segment. It has been found that high-frequency diameter changes in the retinal artery blood column along the vessel increase significantly in anamnestically healthy volunteers with increasing age and in patients with glaucoma during vascular dilation. This study was undertaken to investigate whether longitudinal sections of the retinal artery blood column are altered in systemic hypertension.
Methods: Retinal arteries of 15 untreated patients with essential arterial hypertension (age, 50.9 ± 11.9 years) and of 15 age-matched anamnestically healthy volunteers were examined by RVA. After baseline assessment, a monochromatic luminance flicker (530–600 nm; 12.5 Hz; 20 s) was applied to evoke retinal vasodilation. Differences in amplitude and frequency of spatial artery blood column diameter change along segments (longitudinal arterial profiles) of 1 mm in length were measured and analyzed using Fourier transformation.
Results: In the control group, average reduced power spectra (ARPS) of longitudinal arterial profiles did not differ when arteries changed from constriction to dilation. In the systemic hypertension group, ARPS during constriction, baseline, and restoration were identical and differed from ARPS during dilation (P < 0.05). Longitudinal arterial profiles in both groups showed significant dissimilitude at baseline and restoration (P < 0.05).
Conclusions: The retinal artery blood column demonstrates microstructural alterations in systemic hypertension and is less irregular along the vessel axis during vessel dilation. These microstructural changes may be an indication of alterations in vessel wall rigidity, vascular endothelial function, and smooth muscle cells in this disease, leading to impaired perfusion and regulation.
Various models have been proposed for the prediction of the necessary support pressure at the face of a shallow tunnel. To assess their quality, the collapse of a tunnel face was modelled with small-scale model tests at single gravity. The development of the failure mechanism and the support force at the face in dry sand were investigated. The observed displacement patterns show a negligible influence of overburden on the extent and evolution of the failure zone. The latter is significantly influenced, though, by the initial density of the sand: in dense sand a chimney-wedge-type collapse mechanism developed, which propagated towards the soil surface. Initially, loose sand did not show any discrete collapse mechanism. The necessary support force was neither influenced by the overburden nor the initial density. A comparison with quantitative predictions by several theoretical models showed that the measured necessary support pressure is overestimated by most of the models. Those by Vermeer/Ruse and Léca/Dormieux showed the best agreement to the measurements.