In Search of the Perfect Triple BB Bond: Mechanical Tuning of the Host Molecular Trap for the Triple Bond B≡B Fragment

The coordination of the B2 fragment by two σ-donor ligands L: could lead to a diboryne compound with a formal triple bond L:→B≡B←:L. σ-Type coordination L:→B leads to an excess of electrons around the B2 central fragment, whereas π-back-donation from the B≡B moiety to ligand L has a compensation effect. Coordination of the σ-donor and π-acceptor ligand is accompanied by the lowering of the BB bond order. Here, we propose a new approach to obtain the perfect triple BB bond through the incorporation of the BB unit into a rigid molecular capsule. The idea is the replacement of π-back-donation, as the principal stabilization factor in the linear NBBN structure, with the mechanical stabilization of the BB fragment in the inert molecular capsule, thus preserving the perfect B≡B triple bond. Quantum-chemical calculations show that the rigid molecular capsule provided a linear NBBN structure and an unusually short BB bond of 1.36 Å. Quantum-chemical calculations of the proposed diboryne adducts show a perfect triple bond B≡B without π-back-donation from the B2 unit to the host molecule. Two mechanisms were tested for the molecular design of a diboryne adduct with a perfect B≡B triple bond: the elimination of π-back-donation and the construction of a suitable molecular trap for the encapsulation of the B2 unit. The second factor that could lead to the strengthening or stretching of a selected chemical bond is molecular strain produced by the rigid molecular host capsule, as was shown for B≡B and for C≡C triple bonds. Different derivatives of icosane host molecules exhibited variation in BB bond length and the corresponding frequency of the BB stretch. On the other hand, this group of molecules shows a perfect triple BB bond character and they all possess a similar level of HOMO.

Relationship Between Behavioral and Stimulus Frequency Otoacoustic Emissions Delay-Based Tuning Estimates

Purpose The phase delay of stimulus frequency otoacoustic emissions (SFOAEs) has been proposed as a noninvasive, objective, and fast source for estimating cochlear mechanical tuning. However, the implementation of SFOAEs clinically has been thwarted by the gaps in understanding of the stability of SFOAE delay-based tuning estimates and their relationship to behavioral measures of tuning. Therefore, the goals of this study were (a) to investigate the relationship between delay-based tuning estimates from SFOAEs and simultaneously masked psychophysical tuning curves (PTCs) and (b) to assess the across- and within-session repeatability of tuning estimates from behavioral and OAE measures. Method Three sets of behavioral and OAE measurements were collected in 24 normal-hearing, young adults for two probe frequencies, 1 and 4 kHz. For each participant, delay-based tuning estimates were derived from the phase gradient of SFOAEs. SFOAE-based and behavioral estimates of tuning obtained using the fast-swept PTC paradigm were compared within and across sessions. Results In general, tuning estimates were sharper at 4 kHz compared to 1 kHz for both PTCs and SFOAEs. Statistical analyses revealed a significant correlation between SFOAE delay-based tuning and PTCs at 4 kHz, but not 1 kHz. Lastly, SFOAE delay-based tuning estimates showed better intra- and intersession repeatability compared to PTCs. Conclusions SFOAE phase-gradient delays reflect aspects of cochlear mechanical tuning, in that a frequency dependence similar to that of basilar membrane tuning was observed. Furthermore, the significant correlation with PTCs at 4 kHz and the high repeatability of SFOAE-based tuning measures offer promise of an objective, nonbehavioral assay of tuning in human ears.

Design and Analysis of Reconfigurable DMTL phase Shifter for High Speed Applications by Mechanical Tuning

Tremendous advancement in the field of Radio-frequency were developed through Micro-fabrication techniques, these technologies miniaturize device in a micro-scale behavior for improved device performances. These technologies are developing rapidly due to its distinct features and wide usage in various applications ranging from switches to sensing devices. The principal behind this work is to build a MEMS based Reconfigurable DMTL phase shifter based on RF MEMS switch with improved device phenomenon like switching speed, low actuating voltage, losses and stress factors. The RF switch is build in a series behavior through co-planar waveguides. Generally switching speed is a major concern in RF MEMS devices because of the presence of the actuating elements within the structure which in turn hinders the device ability to function. The phase shifter designed helps in improving the overall switching speed of the device without electrical or dimension alternation of the device. In this paper, we are implementing a PUSH PULL based RF MEMS reconfigurable switch which was structurally altered based on triangular cantilevers in order to enhance the device switching speed. This would develop and enable better application in terms of reconfigurable phase shifter which can be operated at the wider bandgap applications. Even the resonant frequency enhancement was made which provokes an increase of 13% in terms of the switching speed.