Design of Dual-band Branch-Line Coupler Based on Shunt Open-Circuit DCRLH Cells

In this article, the shunt open-circuit dual composite right/left-handed (DCRLH) cell is initially proposed and one dual-band branch-line coupler based on the proposed cells is designed. It is found that, compared with DCRLH cell, the frequency selectivity, matching condition and adjustment range of the shunt open-circuit DCRLH cell improve greatly. Moreover, the shunt open-circuit DCRLH cell exhibits two adjustable frequency points with -90degrees phase shift within its first two passbands. In order to explore this exotic property effectively, the influence of the primary geometrical parameter is investigated through parametric analysis. Thus, one dual-band branch-line coupler based on the shunt open-circuit DCRLH cells is designed. Both simulated and measured results indicate that comparative performance is achieved. Different from part of previous dual-band branch line couplers, for the proposed coupler, the signs of phase difference of two output ports within the two operating frequency bands are identical with each other. This branch-line coupler is quite suitable for the application which is sensitive to the variation of phase difference and its effective area is compact

The Influence of Side Chain Modifications on the Properties of Imine Based Organic Cage Compounds

This thesis mainly aims to investigate the influence of side chain modifications on the properties of imine based organic cage compounds. A series of [2+3] isostructural POCs with n-butyl, perfluorinated n-butyl, and partially fluorinated n-butyl groups, is synthesized by precursor modification strategy and the structure-property relationship between the degree of fluorination of the alkyl chains and gas sorption properties for perfluorocarbons (PFCs) is studied in detail. The cage with fluorinated side chains shows excellent selectivities for PFCs over N2 (e.g., SH = 41475 for c-C4F8 vs N2), due to fluorine-fluorine interactions. This strategy extends to introducing n-fluorinated alkyl chains of different lengths from perfluoromethyl to perfluorohexyl into [2+3] POCs. The impact of chain lengths on gas uptakes and selectivities for PFCs, sulphur hexafluoride (SF6), and nitrogen trifluoride (NF3) over not only N2 but also O2 or CO2 is explored. The cage with perfluoropentyl chains displays outstanding selective adsorption properties for these fluorinated gases (F-gases) over N2 or O2, while the cage with perfluorobutyl chains still remained the most selective for F-gases over CO2 (e.g., SH = 19631 for c-C4F8 vs CO2). Moreover, the solid packing of POCs significantly influences gas sorption. [2+3] POC with perfluoromethyl groups exhibits different porous and non-porous polymorphic forms, influenced by crystallographic packing and the orientation of middle flexible phenyl groups in terphenyl units. The specific surface of [2+3] POC can be significantly enhanced by elongated π systems of terphenyl units and the optimization of activation conditions. Lastly, a series of [4+4] truncated tetrahedral nitrogen-rich POCs, synthesized from prochiral tripyrroltrialdehyde and side chain-modified amines, reveals face-oriented polyhedra in the crystalline state through X-ray crystallography

Tweeting for Learning: A Critical Analysis of Research on Microblogging in Education Published in 2008-2011

This study critically analyzed the current body of published research on microblogging in education (MIE) to build a deep and comprehensive understanding of this increasingly popular phenomenon. Twenty-one studies on MIE in 2008-2011 were selected based on the selection criteria and analyzed to answer the following questions: (a) What types of research have been published on MIE? (b) How was microblogging used for teaching and learning in these studies? (c) What educational benefits did microblogging have on teaching and learning? and (d) What suggestions and implications did the current research have for future MIE research and practices? The analysis suggested that microblogging has a potential to encourage participation, engagement, reflective thinking as well as collaborative learning under different learning settings. The quality of research, however, varies greatly, suggesting a need for rigorous research on MIE. The analysis has implications for MIE practices as well as research and development efforts

Nonadiabatic effects in the H+H_2 exchange reaction: accurate quantum dynamics calculations at a state-to-state level

Real wave packet propagations were carried out on both a single ground electronic state and two-coupled-electronic states of the title reaction to investigate the extent of nonadiabatic effects on the distinguishable-atom reaction cross sections. The latest diabatic potential matrix of Abrol and Kuppermann [J. Chem. Phys. 116, 1035 (2002)] was employed in the present nonadiabatic quantum state-to-state scattering calculations over a total energy range-from threshold (the zero point of the reagent H_2) to 3.0 eV. Based on the assumption that the hydrogen atoms are distinguishable in the collisions where the inelastic and elastic ones are excluded, no significant nonadiabatic effects have been found in the calculations of the full state-to-state integral and differential cross sections up to a total energy of 3.0 eV for product vibrational levels v' = 0, 1, 2, 3. Our results therefore confirm the recent and the previous studies of the geometric phase effects in H+H_2 employing a different diabatic double many-body expansion potential matrix or a different BKMP2 potential energy surface

A convenient tandem one-pot synthesis of donor-acceptor-type triphenylene 2,3-dicarboxylic esters from diarylacetylene

A tandem one-pot method for the direct synthesis of polysubstituted triphenylene 2,3-dicarboxylic esters with different substitution patterns was developed by enyne metathesis of diarylacetylene, followed by Diels–Alder, aromatization and a cyclization cascade