Mesoporous SSZ-13 zeolite prepared by a dual-template method with improved performance in the methanol-to-olefins reaction

Hierarchical SSZ-13 zeolites were synthesized by combining N,N,N-trimethyl-1-adamantanammonium hydroxide (TMAdOH) as the structure-directing agent for chabazite formation with mono- and diquaternary ammonium-type and organosilane mesoporogens and extensively characterized for their structural, textural, and catalytic properties. Mesoporous SSZ-13 zeolites can be synthesized in one step by combining TMAdOH and the diquaternary ammonium-type surfactant C22-4-4Br2. The mesopore volume increases with the mesoporogen/SDA ratio. The hierarchical zeolites are highly crystalline and exhibit similar Brønsted acidity as SSZ-13. Hierarchical SSZ-13 zeolites display increased lifetime in packed-bed MTO experiments than conventional SSZ-13 at similar light olefins yield. The increased lifetime is due to better utilization of the micropore space. With increasing mesoporosity, the micropore space is used more efficiently, but also the rate of coke formation at the crystal periphery increases. Accordingly, the most stable zeolite is obtained at a relatively low C22-4-4Br2/SDA ratio. These zeolite catalysts can be regenerated without substantial loss of activity.

Novel DGT method with tri-metal oxide adsorbent for in situ spatiotemporal flux measurement of fluoride in waters and sediments

Natural mineral-water interface reactions drive ecosystem/global fluoride (F−) cycling. These small-scale processes prove challenging to monitoring due to mobilization being highly localized and variable; influenced by changing climate, hydrology, dissolution chemistries and pedogenosis. These release events could be captured in situ by the passive sampling technique, diffusive gradients in thin-films (DGT), providing a cost-effective and time-integrated measurement of F− mobilization. However, attempts to develop the method for F− have been unsuccessful due to the very restrictive operational ranges that most F−-absorbents function within. A new hybrid-DGT technique for F− quantification containing a three-phase fine particle composite (Fesingle bondAlsingle bondCe, FAC) adsorbent was developed and evaluated. Sampler response was validated in laboratory and field deployments, passing solution chemistry QC within ionic strength and pH ranges of 0–200 mmol L−1 and 4.3–9.1, respectively, and exhibiting high sorption capacities (98 ± 8 μg cm−2). FAC-DGT measurements adequately predicted up to weeklong averaged in situ F− fluvial fluxes in a freshwater river and F− concentrations in a wastewater treatment flume determined by high frequency active sampling. While, millimetre-scale diffusive fluxes across the sediment-water interface were modeled for three contrasting lake bed sediments from a F−-enriched lake using the new FAC-DGT platform.

1-amenability of A(X) for Banach spaces with 1-unconditional bases

The main result of the note is a characterization of 1-amenability of Banach algebras of approximable operators for a class of Banach spaces with 1-unconditional bases in terms of a new basis property. It is also shown that amenability and symmetric amenability are equivalent concepts for Banach algebras of approximable operators, and that a type of Banach space that was long suspected to lack property A has in fact the property. Some further ideas on the problem of whether or not amenability (in this setting) implies property A are discussed.

Characterisation of Passive Intermodulation in Passive RF Devices with X-parameter

A novel approach to the modelling of passive intermodulation (PIM) generation in passive components with distributed weak nonlinearities is outlined. Based upon the formalism of X-parameters, it provides a unified framework for co-design of antenna beamforming networks, filters, combiners, phase shifters and other passive and active devices containing nonlinearities at RF front-end. The effects of discontinuities and complex circuit layouts can be efficiently evaluated with the aid of the equivalent networks of the canonical nonlinear elements. The main concepts are illustrated by examples of numerical simulations of PIM generation in the transmission lines and comparison with the measurement results.

Micromechanical analysis of cohesive granular materials using the discrete element method with an adhesive elasto-plastic contact model

An adhesive elasto-plastic contact model for the discrete element method with three dimensional non-spherical particles is proposed and investigated to achieve quantitative prediction of cohesive powder flowability. Simulations have been performed for uniaxial consolidation followed by unconfined compression to failure using this model. The model has been shown to be capable of predicting the experimental flow function (unconfined compressive strength vs. the prior consolidation stress) for a limestone powder which has been selected as a reference solid in the Europe wide PARDEM research network. Contact plasticity in the model is shown to affect the flowability significantly and is thus essential for producing satisfactory computations of the behaviour of a cohesive granular material. The model predicts a linear relationship between a normalized unconfined compressive strength and the product of coordination number and solid fraction. This linear relationship is in line with the Rumpf model for the tensile strength of particulate agglomerate. Even when the contact adhesion is forced to remain constant, the increasing unconfined strength arising from stress consolidation is still predicted, which has its origin in the contact plasticity leading to microstructural evolution of the coordination number. The filled porosity is predicted to increase as the contact adhesion increases. Under confined compression, the porosity reduces more gradually for the load-dependent adhesion compared to constant adhesion. It was found that the contribution of adhesive force to the limiting friction has a significant effect on the bulk unconfined strength. The results provide new insights and propose a micromechanical based measure for characterising the strength and flowability of cohesive granular materials. 

Low complexity greedy detection method with generalized multicarrier index keying OFDM

Multicarrier Index Keying (MCIK) is a recently developed technique that modulates subcarriers but also indices of the subcarriers. In this paper a novel low-complexity detection scheme of subcarrier indices is proposed for an MCIK system and addresses a substantial reduction in complexity over the optimalmaximum likelihood (ML) detection. For the performance evaluation, a closed-form expression for the pairwise error probability (PEP) of an active subcarrier index, and a tight approximation of the average PEP of multiple subcarrier indices are derived in closed-form. The theoretical outcomes are validated usingsimulations, at a difference of less than 0.1dB. Compared to the optimal ML, the proposed detection achieves a substantial reduction in complexity with small loss in error performance (<= 0.6dB).

Distribution-based adaptive bounding genetic algorithm for continuous optimisation problems

A new search-space-updating technique for genetic algorithms is proposed for continuous optimisation problems. Other than gradually reducing the search space during the evolution process with a fixed reduction rate set ‘a priori’, the upper and the lower boundaries for each variable in the objective function are dynamically adjusted based on its distribution statistics. To test the effectiveness, the technique is applied to a number of benchmark optimisation problems in comparison with three other techniques, namely the genetic algorithms with parameter space size adjustment (GAPSSA) technique [A.B. Djurišic, Elite genetic algorithms with adaptive mutations for solving continuous optimization problems – application to modeling of the optical constants of solids, Optics Communications 151 (1998) 147–159], successive zooming genetic algorithm (SZGA) [Y. Kwon, S. Kwon, S. Jin, J. Kim, Convergence enhanced genetic algorithm with successive zooming method for solving continuous optimization problems, Computers and Structures 81 (2003) 1715–1725] and a simple GA. The tests show that for well-posed problems, existing search space updating techniques perform well in terms of convergence speed and solution precision however, for some ill-posed problems these techniques are statistically inferior to a simple GA. All the tests show that the proposed new search space update technique is statistically superior to its counterparts.

Orbits of operators commuting with the Volterra operator

Asymptotic estimates of the norms of orbits of certain operators that commute with the classical Volterra operator V acting on L-P[0,1], with 1 0, but also to operators of the form phi (V), where phi is a holomorphic function at zero. The method to obtain the estimates is based on the fact that the Riemann-Liouville operator as well as the Volterra operator can be related to the Levin-Pfluger theory of holomorphic functions of completely regular growth. Different methods, such as the Denjoy-Carleman theorem, are needed to analyze the behavior of the orbits of I - cV, where c > 0. The results are applied to the study of cyclic properties of phi (V), where phi is a holomorphic function at 0.

Use of breakpoint combination sensitivity testing as a simple and convenient method to evaluate the combined effects of ceftazidime and tobramycin on Pseudomonas aeruginosa and Burkholderia cepacia complex isolates in vitro

An in vitro method of determining the activity of antibiotics in combination which is simple and convenient to perform and which could be used routinely in clinical microbiology laboratories is desirable. We investigated the activity, against Pseudomonas aeruginosa and Burkholderia cepacia complex clinical isolates, of ceftazidime and tobramycin in combination using a broth macrodilution sensitivity method based on breakpoint minimum inhibitory concentrations and compared the results obtained using this method with those obtained using the microtitre checkerboard method. There was good agreement in interpretation of results between the two methods for both P. aeruginosa (90%) and B. cepacia complex isolates (70%) with tobramycin and for P. aeruginosa isolates (70%) with ceftazidime. As the breakpoint combination sensitivity testing method employs only four tubes and does not require initial determination of individual antibiotic minimum inhibitory concentrations, it is simpler and more convenient for determining the activity of antibiotics in combination than the microtitre checkerboard method. The use of this method in routine microbiology laboratories to determine the activity of antibiotic combinations against clinical isolates should optimise treatment of infection by ensuring that appropriate antibiotic combinations are prescribed. (C) 2004 Elsevier B.V. All rights reserved.

Innovative qualitative research methods with children aged 4-7 years

There is a growing body of knowledge that uses innovative qualitative methods to support and facilitate the involvement of young children, aged 7 years and under, in the research process. Across several fields of study the recent growth in research that engages with young children stands in sharp contrast with the situation just a few years ago where there was a dearth of activity and knowledge in this area. Designed to seek their views, experiences and perspectives the range of methods is now burgeoning. This chapter explores reasons for the growth in the use of innovative qualitative methods, the underlying principles through which the engagement of young children has been achieved and the different types of method with detailed case examples. For each method the main critical issues regarding their effectiveness are identified and discussed in further detail. The latter sections of the chapter focus on contemporary issues regarding the use of innovative methods. Highlighted, in particular, are some of the common concerns and criticisms with regards to the trustworthiness, reliability, validity and generalizability of the data that is collated using innovative qualitative methods.

Tailoring ionic liquid catalysts: structure, acidity and catalytic activity of protonic ionic liquids based on anionic clusters, [(HSO4)(H2SO4)x]− (x = 0, 1, or 2)

Aiming at inexpensive Brønsted-acidic ionic liquids, suitable for industrial-scale catalysis, a family of protonic ionic liquids based on nitrogen bases and sulfuric acid has been developed. Variation of the molar ratio of sulfuric acid, χH2SO4, was used to tune acidity. The liquid structure was studied using 1H NMR and IR spectroscopies, revealing the existence of hydrogen-bonded clusters, [(HSO4)(H2SO4)]−, for χH2SO4 > 0.50. Acidity, quantified by Gutmann Acceptor Number (AN), was found to be closely related to the liquid structure. The ionic liquids were employed as acid catalysts in a model reaction; Fischer esterification of acetic acid with 1-butanol. The reaction rate depended on two factors; for χH2SO4 > 0.50, the key parameter was acidity (expressed as AN value), while for χH2SO4 > 0.50 it was the mass transport (solubility of starting materials in the ionic liquid phase). Building on this insight, the ionic liquid catalyst and reaction conditions have been chosen. Conversion values of over 95% were achieved under exceptionally mild conditions, and using an inexpensive ionic liquid, which could be recycled up to eight times without diminution in conversion or selectivity. It has been demonstrated how structural studies can underpin rational design and development of an ionic liquid catalyst, and in turn lead to a both greener and economically viable process.

HOS-Based Semi-Blind Spatial Equalization for MIMO Rayleigh Fading Channels

In this paper we concentrate on the direct semi-blind spatial equalizer design for MIMO systems with Rayleigh fading channels. Our aim is to develop an algorithm which can outperform the classical training based method with the same training information used, and avoid the problems of low convergence speed and local minima due to pure blind methods. A general semi-blind cost function is first constructed which incorporates both the training information from the known data and some kind of higher order statistics (HOS) from the unknown sequence. Then, based on the developed cost function, we propose two semi-blind iterative and adaptive algorithms to find the desired spatial equalizer. To further improve the performance and convergence speed of the proposed adaptive method, we propose a technique to find the optimal choice of step size. Simulation results demonstrate the performance of the proposed algorithms and comparable schemes.

Paralytic shellfish poisoning detection by surface plasmon resonance-based biosensors in shellfish matrixes.

The detection of paralytic shellfish poisoning (PSP) toxins in contaminated shellfish is essential for human health preservation. Ethical and technical reasons have prompted the search for new detection procedures as an alternative to the mouse bioassay. On the basis of the detection of molecular interactions by surface plasmon resonance (SPR) biosensors, an inhibition assay was developed using an anti-GTX2/3 antibody (GT13-A) and a saxitoxin-CM5 chip. This assay allowed for quantification of saxitoxin (STX), decarbamoyl saxitoxin (dcSTX), gonyautoxin 2,3 (GTX2/3), decarbamoyl gonyautoxin 2,3 (dcGTX2/3), gonyautoxin 5 (GTX5), and C 1,2 (C1/2) at concentrations from 2 to 50 ng/mL. The interference of five shellfish matrixes with the inhibition assay was analyzed. Mussels, clams, cockles, scallops, and oysters were extracted with five published methods. Ethanol extracts and acetic acid/heat extracts (AOAC Lawrence method) performed adequately in terms of surface regeneration and baseline interference, did not inhibit antibody binding to the chip surface significantly, and presented STX calibration curves similar to buffer controls in all matrixes tested. Hydrochloric acid/heat extracts (AOAC mouse bioassay method) presented surface regeneration problems, and although ethanol-acetic acid/dichloromethane extracts performed well, they were considered too laborious for routine sample testing. Overall the best results were obtained with the ethanol extraction method with calibration curves prepared in blank matrix extracts. STX recovery rate with the ethanol extraction method was 60.52 ± 3.72%, with variations among species. The performance of this biosensor assay in natural samples, compared to two AOAC methods for PSP toxin quantification (mouse bioassay and HPLC), suggests that this technology can be useful as a PSP screening assay. In summary, the GT13-A-STX chip inhibition assay is capable of PSP toxin detection in ethanol shellfish extracts, with sufficient sensitivity to quantify the toxin in the range of the European regulatory limit of 80 g/100 g of shellfish meat.