Metal-organic frameworks (MOFs) represent an emerging class of crystalline materials with well-defined pore structures and hold great potentials in a wide range of important applications. The functionality of MOFs can be further extended by integration with other functional materials, e.g., encapsulating metal nanoparticles, to form hybrid materials with novel properties. In spite of various synthetic approaches that have been developed recently, a facile method to prepare hierarchical hollow MOF nanostructures still remains a challenge. Here we describe a facile emulsion-based interfacial reaction method for the large-scale synthesis of hollow zeolitic imidazolate framework 8 (ZIF-8) nanospheres with controllable shell thickness. We further demonstrate that functional metal nanoparticles such as Pd nanocubes can be encapsulated during the emulsification process and used for heterogeneous catalysis. The inherently porous structure of ZIF-8 shells enables encapsulated catalysts to show size-selective hydrogenation reactions.

These observations suggest that ginsenoside Rb1 could represent promising applications as anti-oxidants for the anti-aging treatment of neurological disorders, such as stroke, in elderly patients. Geriatr Gerontol Int 2017; 17: 338-345.

N-doped carbon materials is of particular attraction for anodes of lithium-ion batteries (LIBs) because of their high surface areas, superior electrical conductivity, and excellent mechanical strength, which can store energy by adsorption/desorption of Li at the interfaces between the electrolyte and electrode. By directly carbonization of zeolitic imidazolate framework-8 nanospheres synthesized by an emulsion-based interfacial reaction, we obtained N-doped hollow carbon nanospheres with tunable shell thickness (20 nm to solid sphere) and different N dopant concentrations (3.9 to 21.7 at %). The optimized anode material possessed a shell thickness of 20 nm and contained 16.6 at % N dopants that were predominately pyridinic and pyrrolic. The anode delivered a specific capacity of 2053 mA h g at 100 mA g and 879 mA h g at 5 A g for 1000 cycles, implying a superior cycling stability. The improved electrochemical performance can be ascribed to (1) the Li adsorption dominated energy storage mechanism prevents the volume change of the electrode materials, (2) the hollow nanostructure assembled by the nanometer-sized primary particles prevents the agglomeration of the nanoparticles and favors for Li diffusion, (3) the optimized N dopant concentration and configuration facilitate the adsorption of Li; and (4) the graphitic carbon nanostructure ensures a good electrical conductivity.

Multisine signal with a low crest factor (CF) can bring a high signal-to-noise ratio for fast frequency response function (FRF) estimation. Synthesis of a low CF multisine with the given amplitude spectrum depends on optimum selection of the initial phases of its cosinusoidal components. The solutions investigated can be generally divided into two branches: (1) the analytical method based on direct formula calculation; and (2) the numerical method based on iterative computations. The analytical method works well only for an equidistant and flat amplitude spectrum, while the numerical method can generally output better results, even for a sparse or non-flat spectrum, but the number of iterations might be huge. This paper presents an improved CF minimization algorithm to synthesize multisine signals based on the combination of the previous Schroeder analytical method and the Van der Ouderaa (VDO) iteration procedure. The improved algorithm adopts the Schroder phases as the iterative initial phases, and employs a logarithmic clip function of the iterative index i in the VDO iteration procedure. Comprehensive experiments of multisine synthesis on three types of cosinusoidal amplitude spectra are performed, and the resulting CFs remain the lowest level in all cases compared with the earlier methods. The proposed algorithm provides a fast and efficient solution to synthesize multisine with the lowest CF for an arbitrary user-prescribed spectrum.

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Portable bioimpedance spectroscopy (BIS) devices are of great value for monitoring the pathological status of biological tissues in clinical and home environments. The two traditional techniques for measuring complex bioimpedance, the bridge method and quadrature demodulation method, are either time-consuming or often associated with high cost, high power consumption, and large board space, and therefore are not ideally suitable for designing a portable device for BIS measurement. This paper describes a novel design of a portable BIS device based on the magnitude-ratio and phase-difference detection method and its implementation using the newest generation of analog electronic products which greatly decrease the complexity of both hardware and software. In order to improve the accuracy of the device, a three-reference calibration algorithm was applied. Experimental sweep-frequency measurements on RC circuits were carried out to preliminarily evaluate the performances of the device. The results obtained by the device were found to be in good agreement with the results measured by a commercial impedance analyzer HP4194, with an overall mean error of 0.014% in magnitude and 0.136 degrees in phase over a frequency range of 20 kHz to 1 MHz.

This paper focuses on the accurate frequency estimation of power signals corrupted by a stationary white noise. The noneven item interpolation FFT based on the triangular self-convolution window is described. A simple analytical expression for the variance of noise contribution on the frequency estimation is derived, which shows the variances of frequency estimation are proportional to the energy of the adopted window. Based on the proposed method, the noise level of the measurement channel can be estimated, and optimal parameters (e.g., sampling frequency and window length) of the interpolation FFT algorithm that minimize the variances of frequency estimation can thus be determined. The application in a power quality analyzer verified the usefulness of the proposed method.

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