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In this study, CuFeO2 and Mg-doped CuFeO2 powders are synthesized by using a novel chemical solution route under an ambient atmosphere. By regulating the pH of the reaction solution, on the basis of Pourbaix diagrams, and the stoichiometric ratio of copper to iron ions, delafossite CuFeO2 powders are formed at 363 K in an aqueous solution. Mg-doped CuFeO2 powders are also synthesized by using the same chemical route with the trace addition of Mg(II) ions. From the powder X-ray diffraction results, all diffraction peaks are of the delafossite structure with dominated 3R phase and few 2H phase. X-ray photoelectron spectroscopy measurements show that the chemical environments of the Cu and Fe ions are consistent with the binding energies of Cu(I) and Fe(III) in the delafossite structure of CuFeO2. The UV–vis spectra show that the CuFeO2 and Mg-doped CuFeO2 powders are both able to absorb light with wavelengths ranging from 300 to 700 nm. The calculated optical band gaps of the CuFeO2 and Mg-doped CuFeO2 powders are 1.35 and 1.5 eV, respectively. With regard to the application of the powders in the photodegradation of 50 ppm methylene blue, the results suggest that at an incident light irradiation of AM 1.5G, the photodegradation efficiency of the Mg-doped CuFeO2 powder is remarkably better than that of the CuFeO2 powder, which can be attributed to its higher carrier concentration. Furthermore, at an external bias of −1.2 V, these delafossite catalysts are able to convert CO2 to ethylene glycol through an electrocatalytic reaction.

In this study, cubic, octahedral, and rhombic dodecahedral gold nanocrystals synthesized by a seed-mediated growth method were employed as catalysts for the examination of facet-dependent catalytic activity toward NaBH4 reduction of p-nitroaniline to p-phenylenediamine at different temperatures. Different amounts of the nanocrystal solutions were used so that all samples contain particles with the same total surface area. UV–vis absorption spectra monitored the reaction progress. Rhombic dodecahedra showed the best catalytic efficiency at all the temperatures examined. Nanocubes have higher reaction rates than those of octahedra from 25 to 36 °C, so the catalytic activity for the reduction reaction follows the order of {110} > {100} > {111}. However, the reaction rates for octahedra increase rapidly with rising temperature; their reaction rate surpasses that for the nanocubes at 40 °C. Rate constants and activation energies were determined, again showing that the activation energy is lowest for rhombic do...

By using octahedral gold nanocrystals with sizes of approximately 50 nm as the structure-directing cores for the overgrowth of Pd shells, Au-Pd core-shell heterostructures with systematic shape evolution can be directly synthesized. Core-shell octahedra, truncated octahedra, cuboctahedra, truncated cubes, and concave cubes were produced by progressively decreasing the amount of the gold nanocrystal solution introduced into the reaction mixture containing cetyltrimethylammonium bromide (CTAB), H(2)PdCl(4), and ascorbic acid. The core-shell structure and composition of these nanocrystals has been confirmed. Only the concave cubes are bounded by a variety of high-index facets. This may be a manifestation of the release of lattice strain with their thick shells at the corners. Formation of the [CTA](2)[PdBr(4)] complex species has been identified spectroscopically. Time-dependent UV-vis absorption spectra showed faster Pd source consumption rates in the growth of truncated cubes and concave cubes, while a much slower reduction rate was observed in the generation of octahedra. The concave cubes and octahedra were used as catalysts for a Suzuki coupling reaction. They can all serve as effective and recyclable catalysts, but the concave cubes gave higher product yields with a shorter reaction time attributed to their high-index surface facets. The concave cubes can also catalyze a wide range of Suzuki coupling reactions using aryl iodides and arylboronic acids with electron-donating and -withdrawing substituents.

To improve performance of a "dual voice coil" (DVC) actuator speaker in an active noise control (ANC) system, a speaker model that includes coupling dynamics and source of noise pressure is first derived to design an adaptive feed-forward controller based on modified, filtered-X, recursive-least-squares (MFXRLS) algorithm in this investigation. A novel velocity sensor measuring velocity of the speaker face is further developed by use of a frequency-response method. Two transfer functions required for the velocity sensor are identified in two steps: (i) the adaptive feed-forward controller is applied to keep speaker face velocity zero to identify the first transfer function; and (ii) the second transfer function is then obtained experimentally using the first transfer function. Performance of the established velocity sensor is similar to that of a Polytec OFV2100 laser velocity transducer. This velocity sensor is then incorporated with the adaptive feed-forward controller to control the DVC actuator speaker in the ANC system. For a sinusoidal command input of frequency below 390 Hz, the controlled speaker acquires a unit-gain magnitude and zero phase degree, showing that the controller can effectively reduce effects of the speaker dynamics, including coupling dynamics.

Active noise control (ANC)-based systems provide good low-frequency noise attenuation by destructive interference between the secondary signal from an acoustic actuator (speaker) and the primary noise of the acoustic field (duct). A novel secondary-path model that described by two cascaded transfer functions and two disturbances for speaker-duct systems is first developed in this study. One disturbance is imposed on face velocity of actuator speaker that is usually ignored in ANC systems while the other is on sound pressure at a given location in the duct. The transfer functions are identified with measurements from a developed velocity sensor and a microphone, respectively. A combined design of ANC and face velocity control (FVC) based on the identified secondary-path model is further proposed to set up an adaptive feedback ANC/FVC controller with a modified filtered-X recursive least square (FXRLS) algorithm to update controller coefficients to reduce noise levels near microphone location. Results of experiments show that the adaptive feedback ANC/FVC controller has a noise reduction performance of ∼27-46dB for noise at a frequency between 100-200Hz, as compared with ∼10-35dB for that of the conventional feedback ANC design. Furthermore, the adaptive feedback controller reveals a good capability to reduce the noise level for time-varying noise of a frequency sweeping from 100 to 200Hz. Our data demonstrate a substantial improvement in the low-frequency noise attenuation using the developed controller that includes commonly overlooked factors and support the feasibility of our proposed approach in practices.

Cubic, rhombic dodecahedral, octahedral, and corner-truncated octahedral gold nanocrystals with sizes of tens of nanometers have been used as building blocks to form micrometer-sized supercrystals by slowly evaporating a water droplet on a substrate placed in a moist environment. Drying the droplet at 90 °C was found to yield the best supercrystals. Supercrystals were evenly distributed throughout the entire substrate surface originally covered by the droplet. Diverse supercrystal morphologies have been observed. Nanocubes formed roughly cubic supercrystals. Rhombic dodecahedra were assembled into truncated triangular pyramidal supercrystals. Rhombic dodecahedral, octahedral, and hexapod-shaped supercrystals were generated through the assembly of octahedra. Corner-truncated octahedra formed tetrapod-shaped supercrystals at room temperature, but octahedral, truncated triangular pyramidal, and square pyramidal supercrystals at 90 °C. Nanocrystal assembly was found to be strongly shape-guided. Expulsion of excess surfactant to the surfaces of supercrystals suggests that responsive adjustment of surfactant concentration during particle assembly mediates supercrystal formation. Transmission X-ray microscopy and optical microscopy have been employed to follow the supercrystal formation process. Surprising rotational water current near the droplet perimeter carrying the initially formed supercrystals has been observed. Supercrystals appear to grow from the edge of the droplet toward the central region. Supercrystals assembled from octahedra inherently contain void spaces and possibly connected channels. The mesoporosity of these supercrystals was confirmed by infiltrating H(2)PdCl(4) into the supercrystal interior and reducing the precursor to form Pd nanoparticles. The embedded Pd particles can still catalyze a Suzuki coupling reaction, demonstrating the application of these supercrystals for molecular transport, sensing, and catalysis.

In this study, we have developed for the first time a fast and energy-efficient method for the synthesis of PbS nanocrystals with systematic shape evolution from cubic to truncated cubic, cuboctahedral, truncated octahedral, and octahedral structures. The method involves the addition of a small volume of preheated lead acetate and thioacetamide (TAA) mixture to an aqueous growth solution of lead acetate, thioacetamide, cetyltrimethylammonium bromide, and nitric acid. By varying the amount of thioacetamide added to the growth solution, PbS nanocrystals with different morphologies were generated in 2 h at 90 °C. Slight experimental modifications were adopted to generate truncated octahedra. The nanocrystals have very uniform dimensions with average sizes of 32-47 nm. Their structures have been extensively examined by electron microscopy. Nanocube sizes can also be tuned within a range. UV/Vis absorption spectra of PbS cubes, cuboctahedra, and octahedra all show decreasing but continuous absorption from 300 nm to beyond 1000 nm. By monitoring the speed of darkening of solution color, particle growth rate was found to be fastest for nanocubes, followed by truncated cubes, cuboctahedra, and octahedra. These monodisperse nanocrystals can readily form self-assembled structures. Truncated cubes and octahedra that form monolayer and multilayer packing arrangements have also been studied. This green approach to the synthesis of PbS nanocrystals with fine size and shape control should allow for investigations of their facet-dependent properties and the fabrication of novel heterostructures.

Gold nanocubes, octahedra, and rhombic dodecahedra with roughly two sets of particle sizes have been successfully synthesized via a seed-mediated growth approach. All six samples were analyzed for comparative surface-enhanced Raman scattering (SERS) activity. All of these Au nanostructures were found to yield strong enhancement at a thiophenol concentration of 10(-7) M and are excellent SERS substrates. Rhombic dodecahedra with a rhombus edge length of 32 nm showed significantly better enhancement than the other samples and can reach a detection limit of 10(-8) M. Simulations of the binding energies of thiophenol on the different faces of gold and electric near-field intensities of these nanocrystals have been performed to evaluate the experimental results. Superior SERS activity of these nanocrystals can be expected toward the detection of many other molecules.

This paper presents a multi-loop control approach for dynamic modeling, self-balancing and position control of a ball robot (Ballbot) with inverse mouse-ball driving mechanism actuated by two independent brushless motors simultaneously. A completely non-decoupling dynamic model of the robot incorporating with viscous and static frictions is derived using Newtonian mechanics. Two multi-loop controllers are then proposed to accomplish robust self-balancing and position control (regulation) of the robot with exogenous disturbances. Computer simulations and experimental results are conducted for illustration of the effectiveness of the proposed control method.

This paper presents techniques for dynamic modeling and control of a Ball robot (Ballbot) with inverse mouse-ball drive that is accomplished by simultaneously activating two independent brushless motors. Under this driving scheme, a completely dynamic model of the robot moving in a flat terrain is established constructed based on Lagrangian mechanics. With the model, a sliding-mode control is proposed based on backstepping to accomplish robust balancing and agile path tracking of the robot with exogenous disturbances. Computer simulations are conducted for illustration of the effectiveness of the proposed modeling and control method.

We incorporated gold nanoparticles (Au NPs) in inverted organic photovoltaic devices to enhance the device performance. The photocurrent and fill factors were improved after the addition of Au NPs into the Cs2CO3 buffer layer. The photoluminescent measurements revealed a significant increase of light absorption of the photoactive layer. We attribute the improvement to local field enhancement induced by the localized surface plasmon resonance. Further, through the study of the morphologies of the cathode interfaces, we found that the rough surfaces might increase the device resistances. This drawback, however, was overwhelmed by the advantageous plasmonic effects.