The oxidation of ethylene over a supported platinum catalyst

The complete oxidation of ethylene over a 0.3% Pt/Al₂O₃ catalyst, at ethylene concentration of ≤ 1.0 mol/m³ and oxygen concentrations of 0.16 to 8.6 mol/m³, was studied in a recycle reactor at temperatures of 362 to 472 K. The activity of the catalyst was influenced by pretreatment and reaction conditions causing fluctuations in rate measurements. Nevertheless, a simple rate function, r =Ae^?E/RT[O₂]/[C₂H₄], fitted the data as well as more complicated rate functions.     

Generation of transducers for fluorescence-based microarrays with enhanced sensitivity and their application for gene expression profiling

The present paper describes a novel generation of microchips suitable for fluorescence-based assays, such as cDNA, oligonucleotide, or protein microarrays. The new transducers consist of a fully corrugated surface coated with a thin layer of Ta2O5 as a high refractive index material. Tuning of the incident excitation light beam to abnormal reflection geometry results in a confinement of the energy within the thin metal oxide layer. Consequently, strong evanescent fields are generated at the surface of these microchips and fluorophores located within the fields showed up to a 2 order of magnitude increase in fluorescence intensities relative to the epifluorescence signals. We have attributed this phenomenon as evanescent resonance (ER). Due to the surface architecture, propagation distances of the incident energy and fluorescence photons are in the micrometer range, thus preventing cross talk between adjacent regions. ER microchips offer a significant increase in fluorescence intensities in both "snapshot" fluorescence setups and commercial fluorescence scanners. The underlying principle of the novel chips is explained, and quantitative data on the fluorescence enhancement are provided. To demonstrate their potential, the novel chips are used to investigate the dependence of expression levels from metabolic genes in rat liver on drug treatment. In contrast to competitive hybridization, labeled samples were hybridized to individual ER microchips, and changes were observed by comparing with normalized data from different chips. Results obtained in gene expression profiling experiments with phenobarbital-treated rats are shown.     

Transformation of the multimode terahertz quantum cascade laser beam into a Gaussian, using a hollow dielectric waveguide

We demonstrate that a short hollow dielectric tube can act as a dielectric waveguide and transform the multimode, highly diverging terahertz quantum cascade laser beam into the lowest order dielectric waveguide hybrid mode, EH(11), which then couples efficiently to the free-space Gaussian mode, TEM(00). This simple approach should enable terahertz quantum cascade lasers to be employed in applications where a spatially coherent beam is required.     

Influence of spatial resolution and contrast agent dosage on myocardial T1 relaxation times

Objective

Our aim was to study the influence of small variations in spatial resolution and contrast agent dosage on myocardial T1 relaxation time.

Materials and methods

Twenty-nine healthy volunteers underwent cardiovascular magnetic resonance at 3T twice, including a modified look-locker inversion recovery (MOLLI) technique—3(3)3(3)5—for T1 mapping. Native T1 was assessed in three spatial resolutions (voxel size 1.4 × 1.4 × 6, 1.6 × 1.6 × 6, 1.7 × 1.7 × 6 mm³), and postcontrast T1 after 0.1 and 0.2 mmol/kg gadobutrol. Partition coefficient was calculated based on myocardial and blood T1. T1 analysis was done per segment, per slice, and for the whole heart.

Results

Native T1 values did not differ with varying spatial resolution per segment (p = 0.116–0.980), per slice (basal: p = 0.772; middle: p = 0.639; apex: p = 0.276), and globally (p = 0.191). Postcontrast T1 values were significantly lower with higher contrast agent dosage (p < 0.001). The global partition coefficient was 0.43 ± 0.3 for 0.2 and 0.1 mmol gadobutrol (p = 0.079).

Conclusion

Related to the tested MOLLI technique at 3T, very small variations in spatial resolution (voxel sizes between 1.4 × 1.4 × 6 and 1.7 × 1.7 × 6 mm³) remained without effect on the native T1 relaxation times. Postcontrast T1 values were naturally shorter with higher contrast agent dosage while the partition coefficient remained constant. Further studies are necessary to test whether these conclusions hold true for larger matrix sizes and in larger cohorts.

     

外墙外保温技术在沈阳万科花园新城中的应用

沈阳万科花园新城是国家康居示范工程之一.在墙体节能保温中,通过几种北方地区节能墙体的比较,采用EPS外墙外保温系统,发挥其在外墙外保温技术的优势,取得了社会经济效益.     

Bidirectional priming processes in the Simon task.

The Simon effect is mostly explained in terms of dual-route models, which imply unidirectional activation processes from stimulus features to response features. However, there is also evidence that these preactivated response features themselves prime corresponding stimulus features. From this perspective, the Simon effect should only occur whenever the response is unequivocally mapped to just 1 stimulus feature (one-to-one mapping). If, however, more than 1 stimulus feature is mapped to each spatial response (many-to-one mapping), priming activation should spread and thus reduce or eliminate the Simon effect. In a series of 4 Simon task experiments, the authors compared many-to-one with one-to-one mapping, holding stimulus set size constant. As was expected, the Simon effect was only present with one-to-one mapping but was eliminated with many-to-one mapping. The authors therefore suggest that the Simon effect also depends on priming from response features to stimulus features. Theoretical implications of these findings are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Influence of support friability and concentration of α‐olefins on gas‐phase ethylene polymerization over polymer‐supported metallocene/methylaluminoxane catalysts

The effects of support friability (Φ) and ethylene/comonomer ratios were investigated over supported metallocene/methylaluminoxane catalysts prepared with nine different porous polymeric supports and various comonomer concentrations with a 2‐L reactor operated in the semibatch gas‐phase mode at 80°C and 1.4 MPa. Φ of the supports was measured with a newly devised method. The performance of the supported catalysts depended on support Φ as follows. The average homopolymerization activities varied from less than 6 t of polyethylene (PE) (mol of Zr)^?1 h^?1 for low‐Φ catalysts to 10–20 t of PE (mol of Zr)^?1 h^?1 for moderate‐Φ catalysts and up to 100 t of PE (mol of Zr)^?1 h^?1 for the high‐Φ catalysts. The presence of 1‐hexene and propylene comonomers increased the activity of the low‐Φ catalysts by up to 20‐fold and 50‐fold, respectively; that is, there were very marked comonomer effects. Activity enhancement by 1‐hexene was less than 3‐fold for the moderate‐Φ catalysts, whereas the high‐Φ catalysts showed little activity enhancement. Sometimes, 1‐hexene even resulted in activity reductions. Very different particle morphologies were obtained with the catalysts of different Φ's. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 514–527, 2007     

Kinetics of methane combustion over Pt and Pt–Pd catalysts

A kinetic study was performed over thermally aged and steam-aged Pt and Pt–Pd catalysts to investigate the effect of temperature, and methane and water concentrations on the performance of catalysts in the range of interest for environmental applications. It was found that both catalysts permanently lose a large portion of their initial activity as result of exposure to 5 vol.% water in the reactor feed. Empirical power-law and LHHW type of rate equations were proposed for methane combustion over Pt and Pt–Pd catalysts respectively. Optimization was used to determine the parameters of the proposed rate equations using the experimental results. The overall reaction orders of one and zero in methane and water concentration was found for stabilized steam-aged Pt catalyst in the presence and absence of water. The apparent self-inhibition effect caused by methane over Pt–Pd catalyst in the absence of water was associated with the inhibiting effect of water produced during the combustion of methane. A significant reversible inhibition effect was also observed over steam-aged Pt–Pd catalyst when 5 vol.% water vapor was added to the reactor feed stream. A significant reduction in both activity and activation energy was observed above temperatures of approximately 550 °C for steam-aged Pt–Pd catalyst in the presence of water (the activation energy dropped from a value of 72.6 kJ/mol to 35.7 kJ/mol when temperature exceeded 550 °C).     

Quantum cascade lasers with double-quantum-well superlattices

A quantum-cascade laser using a double-quantum-well graded superlattice as the active region is presented. Each SL period consists of two strongly coupled quantum wells resulting in the splitting of the lowest miniband into two minibands. These two minibands can be designed to be flat and to contain delocalized, spatially symmetric wavefunctions under an applied electric field which in turn leads to a high optical dipole for the interminiband transition. In addition, the new design allows independent control of the energy levels of the lowest two minibands, their width and the splitting separating them, enhancing design flexibility. Using a cascade design of 55 pairs of alternated active regions and injectors, pulsed laser action is achieved at λ=11.6 μm. Peak output powers reach 120 mW at 7 K and approximately 12 mW at the maximum operating temperature of 195 K