Reliability of the step phase detection using inertial measurement units: pilot study

The use of inertial sensors for the gait event detection during a long-distance walking, for example, on different surfaces and with different walking patterns, is important to evaluate the human locomotion. Previous studies demonstrated that gyroscopes on the shank or foot are more reliable than accelerometers and magnetometers for the event detection in case of normal walking. However, these studies did not link the events with the temporal parameters used in the clinical practice; furthermore, they did not clearly verify the optimal position for the sensors depending on walking patterns and surface conditions. The event detection quality of the sensors is compared with video, used as ground truth, according to the parameters proposed by the Gait and Clinical Movement Analysis Society. Additionally, the performance of the sensor on the foot is compared with the one on the shank. The comparison is performed considering both normal walking and deviations to the walking pattern, on different ground surfaces and with or without constraints on movements. The preliminary results show that the proposed methodology allows reliable detection of gait events, even in case of abnormal footfall and in slipping surface conditions, and that the optimal location to place the sensors is the shank

Quantum Chemical Study of B(C₆F₅)₃‑Catalyzed Hydrosilylation of Carbonyl Group

The hydrosilylation reaction of a carbonyl group catalyzed by tris­(penta­fluoro­phenyl)­borane, B­(C₆F₅)₃, is investigated by using the DFT method. M06-2X level calculations suggest the presence of a stable complex between trimethylsilane and B­(C₆F₅)₃. The attack of the carbonyl group in acetone from the back side of the Si–H bond prompts the abstraction of the hydride ion by B­(C₆F₅)₃. This reaction path is lower in free energy than the conventional carbonyl-activation path via a four-membered cyclic transition state. The silane-activation mechanism is supported in this case, in agreement with experimental results reported by Piers and by Oestreich. The calculations show, on the other hand, that the silane-activation mechanism does not apply to the reaction catalyzed by BF₃. This difference in mechanisms arises from a stronger electrophilicity of the boron center in B­(C₆F₅)₃ than in BF₃ toward a hydride ion, as demonstrated by an analysis of reactive orbitals. Attractions between the silane part and the fluorine atoms at the <i>ortho</i> positions of C₆F₅ groups in the Lewis acid assist the path by making up for the destabilization of the reacting system that is caused by the distortion of the B­(C₆F₅)₃ framework in forming a bond with the hydrogen of silane

Quantum Chemical Study of the Reaction of 3‑(Trimethylsilyl)cyclohexa-1,4-dienes with B(C₆F₅)₃

The reaction of 3-(trimethylsilyl)­cyclohexa-1,4-diene with tris­(pentafluorophenyl)­borane, B­(C₆F₅)₃, has been investigated by using the M06-2X DFT method with the PCM model. The Lewis acid B­(C₆F₅)₃ is most likely to abstract a hydrogen at the C6 position in 3-(trimethylsilyl)­cyclohexa-1,4-diene from the face opposite to the SiMe₃ group. The product complex of the abstraction easily dissociates into [SiMe₃(C₆H₆)]⁺ and [HB­(C₆F₅)₃]⁻ or a loosely bound ion pair in dichloromethane. The dissociated ions give the complex in another structure from which the reagent, Me₃Si–H–B­(C₆F₅)₃, for the following hydrosilylation reaction is generated. The calculations suggest that the transformation to the complex structure that leads to the key reagent is more difficult in toluene and in benzene and is very difficult in <i>n</i>-pentane. The mechanism of hydrosilylation of alkenes is discussed, estimating the Lewis acidity of the silicon center in Me₃Si–H–B­(C₆F₅)₃, Me₃SiH, and SiMe₃⁺

Quantum Chemical Study of Diels–Alder Reactions Catalyzed by Lewis Acid Activated Oxazaborolidines

The catalytic activity of Lewis acid activated oxazaborolidines in the Diels–Alder reaction between cyclopentadiene and methacrolein is investigated by using the DFT method. Oxazaborolidine is not able to coordinate to methacrolein in the absence of AlBr₃ because the bonding stabilization is too small to cover the destabilization arising from the deformation of the two species. Accordingly, oxazaborolidine hardly catalyzes the cycloaddition by itself. The calculations show that the attachment of AlBr₃ to the nitrogen atom of oxazaborolidine enhances the Lewis acidity of its boron center and enables it to coordinate to methacrolein. When the AlBr₃-assisted oxazaborolidine is once coordinated, the catalytic activity originates mainly from the oxazaborolidine framework, and to a smaller extent from the attached AlBr₃ part. The Lewis acid AlBr₃ plays an additional role to facilitate the reaction by reducing the overlap repulsion between the diene and the dienophile. The attachment of AlBr₃ to the oxygen atom, another Lewis basic site in oxazaborolidine, also gives a stable AlBr₃–oxazaborolidine complex, but the reaction catalyzed by this complex is not preferred to that catalyzed by the complex in which AlBr₃ is attached to the nitrogen atom. The electrophilicity of boron center in oxazaborolidine and those in the AlBr₃–oxazaborolidine complexes are compared in terms of localized reactive orbitals