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PurposeAn MRI scanner is equipped with global shim systems for shimming one region of interest (ROI) only. However, it often fails to reach state‐of‐the‐art when shimming two isolated regions of interest simultaneously, even though the two‐area shimming can be essential in scan scenarios, such as bilateral breasts or dyadic brains. To address these challenges, a hybrid active and passive local shimming technique is proposed to simultaneously shim two isolated region‐of‐interest areas within the whole FOV. MethodsA local passive shimming system is constructed by optimized bilateral ferromagnetic chip arrays to compensate for the magnet's significant high‐order B₀inhomogeneities at the boundary of the manufacturer's specified homogeneous volume, thus locally improving the available FOV. The local active shimming consists of 40‐channel DC loops powered by 64‐channel current amplifiers. With the optimized current distribution, active shimming can correct the residual low‐order B₀inhomogeneities and subject‐specific field inhomogeneities. In addition, active shimming is used to homogenize the center frequencies of the two regions. ResultsWith the implementation of the hybrid active and passive local shimming, the 95% peak‐to‐peak was reduced from 1.92 to 1.12 ppm by 41.7%, and RMS decreased from 0.473 to 0.255 ppm by 46.1% in a two‐phantom experiment. The volume ratio containing MR voxels within a 0.5‐ppm frequency span increased from 64.3% to 81.3% by 26.3%. ConclusionThe proposed hybrid active and passive local shimming technique uses both passive and active local shimming, and it can efficiently shim two areas simultaneously, which is an unmet need for a commercial MRI scanner. 

Graph-based semi-supervised learning is the problem of propagating labels from a small number of labelled data points to a larger set of unlabelled data. This paper is concerned with the consistency of optimization-based techniques for such problems, in the limit where the labels have small noise and the underlying unlabelled data is well clustered. We study graph-based probit for binary classification, and a natural generalization of this method to multi-class classification using one-hot encoding. The resulting objective function to be optimized comprises the sum of a quadratic form defined through a rational function of the graph Laplacian, involving only the unlabelled data, and a fidelity term involving only the labelled data. The consistency analysis sheds light on the choice of the rational function defining the optimization. 

Bistable electroactive polymers (BSEP) combine shape memory with large-strain actuation at the rubbery state to achieve rigid-to-rigid actuation. The stiffness of the BSEP is tunable via glass transition or phase changing. The reversible melting-crystallization of the polymer chains in the phase changing BSEP contributes to the stiffness change within a narrow temperature range. A modulus change of more than 1000 folds can be achieved within 3 °C. Additionally, large actuation strains rivaling those of VHB acrylic elastomers can be obtained at the rubbery state. Explorations regarding potential applications of this material have been focused on tactile displays. In one design, Joule heating of a serpentine-shaped compliant electrode coated on a BSEP film, coupled with a pneumatic pressure source has been employed to raise diaphragm dots with 1.5 mm base diameter to heights up to 0.7 mm. The resulting Braille electronic readers could thus be actuated with low voltages. 

Abstract Computational studies revealed that dirhodium tetrakis(1,2,2‐triarylcyclopropanecarboxylate) (Rh₂(TPCP)₄) catalysts adopt distinctive high symmetry orientations, which are dependent on the nature of the aryl substitution pattern. The parent catalyst, Rh₂(TPCP)₄, and those with ap‐substituent at the C1 aryl, such as Rh₂(p‐BrTPCP)₄and Rh₂(p‐PhTPCP)₄, adopt aC₂‐symmetric structure. Rh₂(3,5‐di(p‐^tBuC₆H₄)TPCP)₄, 3,5‐disubstituted at the C1 aryl, adopts aD₂‐symmetric structure, whereas catalysts with ano‐substituent at the C1 aryl, such as Rh₂(o‐Cl‐5‐BrTPCP)_4,adopt aC₄‐symmetric structure.