Synthesis of boron nitride nanotubes using thermal chemical vapor deposition of ball milled boron powder

Thermal chemical vapor deposition (TCVD) produces relatively pure boron nitride nanotubes (BNNTs), while it may not be enough for production. A ball milling–annealing process is beneficial in quantity; however, the generation of the impurity is most concerned. In this regard, we explored the dual syntheses of BNNTs based on the chemical reactions of solid and gaseous boron with nitrogen, respectively. Synthesis mechanisms for both were also analyzed by presenting the stepwise reaction routes. With these understandings, the production of BNNTs could be increased, while the impurities are reduced when compared with the individual one, once the experimental conditions are optimized.     

Atmospheric Aging of Asian Dust Particles During Long Range Transport

Variations of mixing state and chemical constituents of Asian dust (AD) particles having different transport pathways were investigated by measuring hygroscopicity and volatility of size-selected (1 μm) dust particles, and their morphology and elemental composition in Gwangju, Korea. Also, hygroscopicity and volatility of possible candidate chemical species that can be included in the dust particles was measured in a laboratory for comparison with field data. A significant amount of dust particles were found to be aged by internally mixing with hygroscopic and volatile species in different ways, depending on their transport pathway. Formation of hygroscopic CaCl₂ and/or cloud processing of dust particles with sea-salt species were proposed as being central to the formation of hygroscopic species in the “less polluted AD” (in which the air mass arrived at sampling site without passing over significant industrial areas), and the existence of hygroscopic species in the “highly polluted AD” (in which the air mass passed over major industrial areas) was explained by the interaction of dust particles with anthropogenic pollutants (i.e., Ca(NO₃)₂ formation by heterogeneous reaction of HNO₃ with dust particles and condensation of hygroscopic H₂SO₄ or (NH₄)₂SO₄ onto the dust particles). Volatile carbonaceous species, which would exist on the surface of the dust particles, were also observed and their fraction significantly increased in the highly polluted AD due to a higher possibility to encounter air masses containing a significant amount of carbonaceous species. Morphological and elemental data identified three types of aged dust particles (reacted dust, cloud-processed dust, and aggregated dust). The production of various aged dust particles depending on their transport pathways has important implications on their different effects on cloud formation, radiation balance, and human health from original dust particles.

Copyright 2012 American Association for Aerosol Research     

Examining the effects of velocity ratio of the pressurized flow to the main inlet flow on coagulants dispersion in pump diffusion mixer

This study was conducted to evaluate the ratio of the pressurized flow to the main inlet flow, which has been considered one of the most important parameters for operating the pump diffusion mixer (PDM). Computational fluid dynamics (CFD) simulation was employed to evaluate the conventional operation rule of PDM and to propose a supplementary operating parameter and criterion. Test simulation of CFD was carried out for the 21 cases of flow ratio in a full scale PDM. The values of local velocity gradient were calculated in each case to analyze the simulation results in more detail. A wet test was conducted to verify CFD simulation results, which measures the factual coagulant dispersion distribution at a distance of 5.4 m from deflector. From results of both CFD simulation and wet test, the flow ratio was adequate as an operating parameter or criterion; also, the velocity ratio (dimensionless) of the pressurized flow to the main inlet was useful in predicting the performance of PDM. In addition, the injected coagulant could be dispersed evenly in overall cross section on the condition that the velocity ratio is at least over 20.     

One-step large-scale synthesis of micrometer-sized silver nanosheets by a template-free electrochemical method

We have synthesized micrometer-sized Ag nanosheets via a facile, one-step, template-free electrochemical deposition in an ultra-dilute silver nitrate aqueous electrolyte. The nanosheet growth was revealed to occur in three stages: (1) formation of polygonal Ag nuclei on a substrate, (2) growth of {112}-faceted nanowire from the nuclei, and (3) anisotropic growth of (111)-planar nanosheets, approximately 20 to 50 nm in thickness and 10 μm in width, in the <112>−direction. The vertical growth of the facet nanowire was induced by the strong interface anisotropy between the deposit and electrolyte due to the ultra-dilute concentration of electrolyte and high reduction potential. The thickness of Ag nanosheets was controllable by the adjustment of the reduction/oxidation potential and frequency of the reverse-pulse potentiodynamic mode.     

A RAKE Receiver With an ICI/ISI Equalizer for a CCK Modem

In this paper, we first derive the theoretical performance of a complementary code keying (CCK) code on an additive white Gaussian noise (AWGN) channel and over a multipath channel. To derive the error performance, we use the weight and cross-correlation distributions of the CCK code for optimal and suboptimal decoding, respectively, based on union bound. In addition, we propose a RAKE receiver for a CCK modem, which is suitable for a multipath environment with a large delay spread. The RAKE receiver principle is acceptable for modest multipath because it can coherently combine multipath components to provide signal-to-noise ratio (SNR) enhancement. However, as the delay spread is larger and the data rate of systems goes higher, intersymbol interference (ISI) generated due to multipath environments are increased. To handle the increasing ISI, the CCK modem needs an equalization technique to remove the ISI, together with RAKE processing. Thus, our proposed system is based on a channel matched filter (CMF) with a decision feedback equalizer (DFE). The CMF is applied for RAKE processing, whereas the DFE structure is used for ISI cancellation. In our system, ISI is calculated and removed by using a decoded CCK codeword.     

Protein nanopatterns and biosensors using gold binding polypeptide as a fusion partner

An efficient strategy for immobilizing proteins on a gold surface was developed by employing the gold binding polypeptide (GBP) as a fusion partner. Using the enhanced green fluorescent protein (EGFP), severe acute respiratory syndrome coronavirus (SARS-CoV) envelope protein (SCVme), and core streptavidin (cSA) of Streptomyces avidinii as model proteins, specific immobilization of the GBP-fusion proteins onto the gold nanoparticles and generation of protein nanopatterns on the bare gold surface were demonstrated. The GBP-fused SCVme bound to gold nanoparticles successfully interacted with its antibody and showed changes in absorbance and color, allowing efficient diagnosis of SARS-CoV. The fusion proteins could be successfully immobilized on the gold surface by nanopatterning and microcontact printing as examined by atomic force microscopy and surface plasmon resonance analysis. The poly(dimethylsiloxane) microfluidic channels were created on the gold surface and were used for antigen-antibody and DNA-DNA interaction studies. Specific immobilization of GBP-EGFP fusion protein and its interaction with the antibody in the microchannels could be demonstrated. By immobilizing the DNA probe through the use of GBP-fused cSA, specific hybridization of the target DNA prepared from Salmonella could also be achieved. The GBP-fusion method allows immobilization of proteins onto the gold surface without surface modification and in bioactive forms suitable for studying protein-protein, DNA-DNA, and other biomolecular interaction studies. Furthermore, these studies can be carried out in a microfluidic system, which allows high-throughput analysis of biomolecular interactions.     

Microstructural studies of PMMA impregnated mortars

Studies on cement concrete microstructures are carried out to explain experimentally observed phenomenon and for modeling of concrete at the macroscopic level. In this article, the preparation of polymer impregnated mortar (PIC) is carried out by partially or fully replacing the pores in the cement mortars (OPC) by PMMA. The effect of this polymer impregnation on density and morphology of the cement matrix is studied. The microstructural changes in the mortar, on exposure of these specimens to hydrochloric acid and sea water for 7 and 28 days, are also investigated in this article. The above studies indicated that the polymer addition decreased the voids in the mortar thereby preventing leaching of water soluble salts present in the OPC. It was observed that the polymer also prevented the external chemical media from permeating into the cement matrix and undergoing interactions with it. It is concluded that the durability and chemical resistance properties of the PIC are better compared with OPC. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of Pretreatment Conditions on the Catalytic Activity of Benzene Combustion Over SBA-15-Supported Copper Oxides

The effect of the pretreatment conditions on the catalytic combustion of benzene over copper oxides supported on SBA-15 was investigated. The catalytic activities of the reduced catalysts were higher than those of the unreduced catalysts, indicating that the metallic Cu is much more active than the copper oxides.