The structure of melt-quenched zeolitic imidazole framework (ZIF) glasses can provide insights into their glass-formation mechanism. We directly detected short-range disorder in ZIF glasses using ultrahigh-field zinc-67 solid-state nuclear magnetic resonance spectroscopy. Two distinct Zn sites characteristic of the parent crystals transformed upon melting into a single tetrahedral site with a broad distribution of structural parameters. Moreover, the ligand chemistry in ZIFs appeared to have no controlling effect on the short-range disorder, although the former affected their phase-transition behavior. These findings reveal structure-property relations and could help design metal-organic framework glasses.

The atomic structure of the Si–O–C tetrahedral network of an amorphous silicon oxycarbide polymer-derived ceramic (PDC) of the composition SiO0.94±0.11C1.13±0.08 was studied at both the short range and the intermediate range using 1D and 2D 29Si nuclear magnetic resonance (NMR) spectroscopic techniques, respectively . The 1D 29Si magic angle-spinning NMR spectrum of the PDC indicates that the Si–O–C network consists of SiO4, SiO3C, SiO2C2, and SiC4 units with relative abundances of approximately 26, 25, 20, and 29%, respectively. The 2D 29Si extended CSA amplification spectrum of this PDC shows that the chemical shift anisotropy (Δ) of the mixed-bond SiO x C4–x units is significantly higher than that of the SiO4 units. On the other hand, the unusually high Δ-value for the SiC4 units was interpreted to be indicative of its role as the connecting element between the Si–O–C network and the free-carbon nanodomains. The 2D 29Si double-quantum correlation NMR spectrum of this PDC indicates that there is extensive direct linking between SiO4 and SiO3C units in the Si–O–C network besides the connectivity between like SiO x C4–x units, while the SiO4 and SiO2C2 units are only linked via a SiO3C unit. In contrast, the SiO3C units show no restriction in linking with the other SiO x C4–x units in the network. Finally, the SiC4 units show significant clustering, which is consistent with their spatial localization at the interface between the Si–O–C network and the sp2 C nanodomains. Such a spatial distribution of the SiO x C4–x units is argued to be consistent with their mass-fractal dimensions measured in previous studies.

Due to the rapid progress in the field of robotics, it is a high time to concentrate on the development of a robot that can manoeuvre in all type of landscapes, ascend and descend stairs and sloping surfaces autonomously. This paper presents details of a prototype robot which can navigate in very rough terrain, ascend and descend staircase as well as sloping surface and cross ditches. The robot is made up of six differentially steered wheels and some passive mechanism, making it suitable to cross long ditches and landscape undulation. Static stability of the developed robot have been carried out analytically and navigation capability of the robot is observed through simulation in different environment, separately. Description of embedded system of the robot has also been presented and experimental validation has been made along with some details on obstacle avoidance. Finally the limitations of the robot have been explored with their possible reasons.

The dynamics of the phosphate chains and the attendant shear relaxation in a short-chain silver phosphate glass-forming liquid with the composition 51.5%Ag2O-48.5% P2O5 are studied using a combination of high-temperature 31P NMR spectroscopy and parallel plate rheometry. The temperature-dependent evolution of the 31P NMR spectral line shapes indicates that the constituent PO4 tetrahedral chains in this liquid undergo rapid rotational reorientation. The time scale of this dynamics is in complete agreement with that of shear relaxation and, thus, must be responsible for the viscous flow of this liquid. These results demonstrate for the first time that, although the shear relaxation of the network oxide glass-forming liquids is typically controlled by the scission and renewal of bonds between the network-forming cations and oxygen atoms, such a scenario may not always be tenable for liquids with low-dimensional structures consisting of chains.

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