Dye reduction catalyzed by palladium nanoparticles has been investigated in water and surfactant media. The initial rate of dye reduction strongly depends on the nature of the reducing agent and dye. In most cases the rate becomes surface controlled and depends on the E1/2 values of the dye and the reducing agent. However, stronger reducing agents make the reduction process a diffusion controlled one. A detailed study has been carried out to understand the effect of surfactant on the reaction rate. A variation of the reaction rates has been observed in surfactants above and below the critical micelle concentration (cmc). Below the cmc, surfactants are adsorbed onto the Pd surface and act as a binding site for both the dye and the reducing agent. Above the cmc, surfactants form micelles which provide additional binding sites. Catalytic selectivity was also achieved by proper selection of reducing agent and surfactant.
In situ structural evolution from Cu(OH)2 nanobelts to copper nanowires has been studied by transmission electron microscopy in a vacuum of 3 × 10-8 Torr. The decomposition follows the sequence of Cu(OH)2 → CuO → Cu2O → Cu. The decomposition from Cu(OH)2 to CuO is attributed to electron beam radiation damage. The reduction from CuO to Cu2O is attributed to heat-induced decomposition between 50 and 200 °C. For the Cu(OH)2 nanobelts synthesized using the copper grid with and without a carbon coating, the decomposition from Cu2O to Cu takes place between 200 and 300 °C and 300 and 600 °C, and the final Cu takes the forms of polycrystalline nanowires sheathed with graphitic carbon and nanoparticles, respectively. Therefore, because of the nanostructured nature of the nanowires and large surface area, introducing carbon into the sample synthesis can reduce the decomposition temperature by almost half. This study demonstrates a possible approach for creating metallic copper nanowires by heat-induced decomposition under vacuum at 300 °C or even lower.
Dependency parsing is one of the basic research of natural language processing. In recent years, transition-based and graph-based methods have been used widely, but there are still some problems such as feature limitation and high time complexity. In this paper, we proposed a new method named Leaf Detection based Dependency Parsing (LD-Parser), which is a bottom-up framework to detect leaf nodes of the dependency parsing tree. We use LSTM to construct a classifier to generate labels for each word and then remove the leaf nodes that are adjacent to their corresponding parents. Besides, an attention mechanism is introduced to sum the children of nodes as an extra feature according to the attention weight. We make experiments on Universal Dependencies in several languages. Experiments show that the LD-Parser with Attention performs better than transition-based and graph-based methods in dependency parsing tasks for short sentences.
Piezoelectricity, a phenomenon known for centuries, is an effect that is about the production of electrical potential in a substance as the pressure on it changes. The most well known material that has piezoelectric effect is the provskite structured Pb(Zr, Ti)O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (PZT), which has found huge applications in electromechanical sensors, actuators and energy generators. But PZT is an electric insulator and it is less useful for building electronic devices. Wurtzite structures, such as ZnO, GaN, InN and ZnS, also have piezoelectric properties but they are not extensively used as much as PZT in piezoelectric sensors and actuators due to their small piezoelectric coefficients. In fact, due to the polarization of ions in a crystal that has non-central symmetry, a piezoelectric potential (piezopotential) is created in the crystal by applying a stress. For materials such as ZnO, GaN, InN in the wurtzite structure family, the effect of piezopotential to the transport behavior of charge carriers is significant due to their multiple functionalities of piezoelectricity, semiconductor and photon excitation. By utilizing the advantages offered by these properties, a few new fields have been created. Electronics fabricated by using inner-crystal piezopotential as a "gate" voltage to tune/control the charge transport behavior is named piezotronics, with applications in strain/force/pressure triggered/controlled electronic devices, sensors and logic units. Piezo-phototronic effect is a result of three-way coupling among piezoelectricity, photonic excitation and semiconductor transport, which allows tuning and controlling of electro-optical processes by strain induced piezopotential. The objective of this talk is to introduce the fundamentals of piezotronics and piezo-phototronics and to give an updated progress about their applications in energy science (LED, solar cell), electronics and sensors.
