Electrodynamics and radiofrequency antenna concepts for human magnetic resonance at 23.5 T (1 GHz) and beyond

Magnetic Resonance Materials in Physics, Biology and Medicine - This work investigates electrodynamic constraints, explores RF antenna concepts and examines the transmission fields (B 1 + ) and RF...     

Cortical areas and the control of self-determined finger movements: an fMRI study

We investigated cortical areas involved in the control of self-determined finger movements. In a tapping task, subjects tapped with different movement frequencies in two different movement conditions (predetermined vs self-determined). fMRI provided evidence for the involvement of the horizontal and ascending parts of the intraparietal sulcus (IPS), the left superior frontal gyrus and the posterior cingulate gyrus in the control of self-determined finger movements. Higher movement frequency increased the extent of activated area only in the horizontal part of IPS. The results suggest a major role of the IPS in controlling sequences of finger movements. This area probably serves as a region for integration of motor, sensory and sensorimotor feedback information used for movement control.     

Additive Manufacturing of Co-Ni-Ga High-Temperature Shape Memory Alloy: Processability and Phase Transformation Behavior

Metallurgical and Materials Transactions A - Co-Ni-Ga high-temperature shape memory alloy is additively processed by selective laser melting for the first time. Reversible martensitic...     

Cladded steel for clutch disc carriers

Forschung im Ingenieurwesen - Current clutch disc carriers are often heat treated in complex ways to provide for the required wear resistance. Using steels cladded by hot rolling could be a cost...     

The traveling heads: multicenter brain imaging at 7 Tesla

Objective

This study evaluates the inter-site and intra-site reproducibility of 7 Tesla brain imaging and compares it to literature values for other field strengths.

Materials and methods

The same two subjects were imaged at eight different 7 T sites. MP2RAGE, TSE, TOF, SWI, EPI as well as B1 and B0 field maps were analyzed quantitatively to assess inter-site reproducibility. Intra-site reproducibility was measured with rescans at three sites.

Results

Quantitative measures of MP2RAGE scans showed high agreement. Inter-site and intra-site reproducibility errors were comparable to 1.5 and 3 T. Other sequences also showed high reproducibility between the sites, but differences were also revealed. The different RF coils used were the main source for systematic differences between the sites.

Conclusion

Our results show for the first time that multi-center brain imaging studies of the supratentorial brain can be performed at 7 T with high reproducibility and similar reliability as at 3T. This study develops the basis for future large-scale 7 T multi-site studies.

     

On the fatigue crack growth–microstructure relationship in ultrafine-grained interstitial-free steel

The crack growth behavior in an ultrafine-grained (UFG) interstitial-free (IF) steel processed by equal channel angular pressing (ECAP) was investigated utilizing miniaturized compact-tension specimens with different microstructural characteristics. The current results demonstrate that both the ECAP processing route and the direction of crack growth with respect to the extrusion direction dictate the crack growth behavior in UFG IF steel. Specifically, the highest crack growth rates and the lowest threshold values were observed for the lowest grain size. Moreover, an unusual deviation from the expected direction of crack expansion was observed, where the deviation depended on the processing route and direction of crack growth. This deviation is attributed to the presence of elongated structures in the microstructure, which were mainly detectable in the UFG IF steel following a small number of pressings, and to a smaller extent in the optimized microstructures. Specifically, these elongated structures formed parallel to the material’s plastic flow during ECAP processing and moved the crack away from the expected direction of growth due to the high stress concentration zones they created along with the process-induced damages.     

Additively manufactured cellular structures: Impact of microstructure and local strains on the monotonic and cyclic behavior under uniaxial and bending load

In order to meet the demand for optimized light-weight parts, the development of load adapted structures has begun to play a key role in today's research. Promising candidates are complex cellular structures, which can be adapted to the loading conditions by use of Additive Manufacturing techniques. The current study addresses the mechanical behavior of open cellular structures produced by Selective Laser Melting. Samples of Ti–6Al–4V were processed, heat-treated and tested under monotonic and cyclic loading applying both uniaxial and bending loads. To reveal microstructure – mechanical property – relationships an in situ approach using electron back scatter diffraction and digital image correlation was applied.The results clarify the impact of a post-SLM heat treatment on the mechanical performance of cellular structures made from Ti–6Al–4V. Local strains determined by DIC reveal structure weaknesses already at low degrees of deformation and at an early stage of lifetime. The in situ approach helps in understanding the mechanical behavior and allows for local adaptation of the cell design in order to obtain improved load adapted structures.