Scanning tunneling microscopy and tunneling spectroscopy studies of niobium-containing H6+xP2W18?xNbxO62 (x=0, 1, 2, 3)Wells-Dawson heteropolyacid catalysts to probe their redox property and oxidation catalysis

Niobium-containing H_6+x P₂W_18−x Nb _x O₆₂ (x=0, 1, 2, 3) Wells-Dawson heteropolyacids (HPAs) were investigated by scanning tunneling microscopy (STM) and tunneling spectroscopy (TS) in order to elucidate their redox properties. The HPAs formed two-dimensional well-ordered monolayer arrays on graphite surface and exhibited a distinctive current-voltage behavior called negative differential resistance (NDR) in their tunneling spectra. NDR peak voltage measured on HPA molecule was correlated with reduction potential and absorption edge energy determined by electrochemical method and UV-visible spectroscopy, respectively. NDR peak voltage of H_6+x P₂W_18−x Nb _x O₆₂ Wells-Dawson HPAs appeared at less negative voltage with increasing reduction potential and with decreasing absorption edge energy. Oxidative dehydrogenation of isobutyraldehyde was also carried out as a model reaction to probe oxidation catalysis of the HPAs. The trend of NDR peak voltage of H_6+x P₂W_18−x Nb _x O₆₂ Wells-Dawson HPAs was well consistent with the trend of yield for methacrolein.     

X-ray photoelectron spectroscopic characterization of molybdenum nitride thin films

The elemental composition and chemical states of a series of Mo nitride thin films have been investigated using x-ray photoelectron spectroscopy (XPS). The chemical composition and stoichiometry of the films were also tracked as a function of the preparative parameters: the nitrogen ion dose, ion accelerating energy and substrate temperature. At the lowest ion dose, the Mo concentration increased to a depth of ∼300 ?. The nitrogen concentration in the film decreased with increasing the ion energy. An increase in the ion energy to 100 and 200 kV led to a lower N/Mo ratio as compared to that at 50 kV. The magnitude of the binding energy separation at room temperature was smaller than that at higher temperatures. This difference might be due to the presence of B1-MoN at higher temperatures and the existence of δ-MoN at lower temperatures.     

Isolation of a Pyrazine Alarm Pheromone Component from the Fire Ant, <Emphasis Type=Italic>Solenopsis invicta</Emphasis>

Alarm pheromones in social insects are an essential part of a complex of pheromone interactions that contribute to the maintenance of colony integrity and sociality. The alarm pheromones of ants were among the first examples of animal pheromones identified, primarily because of the large amount of chemical produced and the distinctive responses of ants to the pheromone. However, the alarm pheromone of the fire ant, Solenopsis invicta, eluded identification for over four decades. We identified 2-ethyl-3,6-dimethylpyrazine as an alarm pheromone component of S. invicta. Worker fire ants detect the pyrazine alarm pheromone at 30 pg/ml, which is comparable to alarm pheromone sensitivities reported for other ant species. The source of this alarm pheromone are the mandibular glands, which, in fire ants, are not well developed and contain only about 300 pg of the compound, much less than the microgram quantities of alarm pheromones reported for several other ant species. Female and male sexuals and workers produce the pyrazine, which suggests that it may be involved in fire ant mating flight initiation, as well as the typical worker alarm response. This is the first report of 2-ethyl-3,6-dimethylpyrazine from a Solenopsis species and the first example of this alkaloid functioning as an alarm pheromone.     

The optimal composition of the filter-media for coping with daily flow-rate fluctuation

The fluctuation of inlet flow in a water treatment plant can change the filtration rate abruptly and ultimately reduce the filtration performance by leaking the detained particles in filter media. The surface wave, occurring in the intake well by the fluctuation of inlet flow, reaches the filtration process in a very short time (about 10 minutes), which makes it impossible to control the filtration rate stably. In this study the authors evaluated the effect of daily flow-rate fluctuation on the performance of sand filtration process, and the dual media composition was proposed to improve the filtration performance. Comparative column tests were carried out for the various dual media, such as sand and anthracite compositions. From the results of column tests, dual media with the composition of sand 45 cm and anthracite 30 cm is more effective than the single media with sand in filtration process. In addition, irrespective of dual media composition, the managing ability to cope with that fluctuation tends to be weak at the end of allowable filtration duration time.     

On the reversibility of environmental contamination with persistent organic pollutants

An understanding of the factors that control the time trends of persistent organic pollutants (POPs) in the environment is required to evaluate the effectiveness of emission reductions and to predict future exposure. Using a regional contaminant fate model, CoZMo-POP 2, and a generic bell-shaped emission profile, we simulated time trends of hypothetical chemicals with a range of POP-like partitioning and degradation properties in different compartments of a generic warm temperate environment, with the objective of identifying the processes that may prevent the reversibility of environmental contamination with POPs after the end of primary emissions. Evaporation from soil and water can prevent complete reversibility of POP contamination of the atmosphere after the end of emissions. However, under the selected conditions, only for organic chemicals within a narrow range of volatility, that is, a logarithm of the octanol air equilibrium partition coefficient between 7 and 8, and with atmospheric degradation half-lives in excess of a few month can evaporation from environmental reservoirs sustain atmospheric levels that are within an order of magnitude of those resulting from primary emissions. HCB and α-HCH fulfill these criteria, which may explain, why their atmospheric concentrations have remained relatively high decades after their main primary emissions have been largely eliminated. Soil-to-water transfer is found responsible for the lack of reversibility of POP contamination of the aqueous environment after the end of emissions, whereas reversal of water-sediment exchange, although possible, is unlikely to contribute significantly. Differences in the reversibility of contamination in air and water suggests the possibility of changes in the relative importance of various exposure pathways after the end of primary emissions, namely an increase in the importance of the aquatic food chain relative to the agricultural one, especially if the former has a benthic component. Since simulated time trends were strongly dependent on degradation half-lives, partitioning properties and selected environmental input parameters, it should not be surprising, that different field studies often generate highly divergent time trends.     

Relationship between ADC performance and requirements of digital-IF receiver for WCDMA base-station

The recent rapid development of digital wireless systems has led to the need for multistandard, multichannel radiofrequency (RF) transceivers. The paper presents the relationship between the performance of a bandpass-sampling analog-to-digital converter (ADC) and the requirements of a digital intermediate-frequency receiver for a wideband code-division multiple-access (WCDMA) base-station. As such, the ADC signal-to-noise ratio (SNR), the derivation of the receiver sensitivity using the SNR/spurious free dynamic range (SFDR) of the ADC, the effect of the ADC clock jitter and receiver linearity, plus the relationship between the receiver IF and the ADC sampling frequency are all analyzed. As a result, when a WCDMA base-station receiver has a data rate of 12.2 kbps, bit error rate (BER) of 0.001, and channel index, k, of 5 (sampling frequency of 122.88 MHz and IF of 92.16 MHz), the performance of a bandpass-sampling ADC was analytically determined to require a resolution of 14 bits or more, SNR of 66.6 dB or more, SFDR of 86.5 dBc or more, and total jitter of 0.2 ps or less, including internal ADC jitters and clock jitters.     

Effect of sintering atmosphere on phase stability,and electrical conductivity of proton-conducting Ba(Zr0.84Y0.15Cu0.01)O3−δ

The phase stability and electrical conductivity of a proton-conducting oxide, Ba(Zr_0.84Y_0.15Cu_0.01)O_3−δ (BZYCu), sintered under various atmospheres was systematically investigated. The partial pressures of oxygen (PO₂)$\left(P_{{\text{O}}_2}\right)$ and barium (P_Ba) were used as the tunable experimental parameters to control the surrounding atmosphere during sintering. According to the analysis, the potentially volatile species BaCO₃, formed by the decomposition of BZYCu under a CO₂-containing atmosphere at around 600 °C, was found to induce barium losses by evaporation. These barium losses, and the associated Y₂O₃ segregation, were the decisive factor in determining the phase stability and electrical conductivity of the resulting BZYCu; both of these properties deteriorated with barium evaporation. Maintaining the optimum balance of PO₂$P_{{\text{O}}_2}$ and P_Ba during sintering is crucial for minimizing Y₂O₃ segregation by kinetically suppressing the volatilization of barium.     

Microwave Assisted Synthesis of Cyclic Carbonate Using Homogeneous and Heterogeneous Ionic Liquid Catalysts

A comparative study was effectuated between the catalytic performance of homogeneous and silica supported ionic liquids (SSILs) for the cycloaddition of epoxides and CO₂ under microwave irradiation by varying the reaction parameters. Compared to the classical heating mode, both catalysts showed higher activity at moderate reaction condition through microwave irradiation.     

Preparation of poly-lactic acid nano/microparticles using supercritical anti-solvent with enhanced mass transfer

Supercritical anti-solvent precipitation with enhanced mass transfer (SAS-EM) was applied for the production of micro and sub-microparticles of poly-lactic acid (PLA). SAS-EM technique uses an ultrasonic vibrating surface to enhance mass transfer rate between supercritical CO₂ and solvent. Without applying ultrasonic power, which is same as SAS process, PLA particles with average diameters ranging between 1 μm and 3 μm were obtained. Using SAS-EM with the power supply of 200 W, spherical PLA particles smaller than 1 μm were obtained. The particle size was able to be controlled in the range of 0.4 μm–1.0 μm, by adjusting the power supply of ultrasonic field, the system pressure and temperature.