Disperse dyeing of polyester fibers: Kinetic and equilibrium study

The effect of temperature on the dyeing rate constant k, diffusion coefficient D, time of half‐dyeing t_1/2 was evaluated for the dyeing of polyester fibers with two disperse dyes, an azo and an anthraquinone dye. Activation energies of diffusion E were calculated. The polyester dyeing equilibrium was also studied and the partition coefficient K and standard affinity Δμ° at various temperatures were determined for the anthraquinone dye. Standard enthalpy ΔH° and standard entropy ΔS° of dyeing were also obtained. The same equilibrium parameters were not obtained for the azo dye because of its dyeing behavior. A similar kinetic and equilibrium study was made for the pure azo and anthraquinone compounds free from the dispersing agents present in the commercial dyes and the results are discussed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2785–2790, 2002; DOI 10.1002/app.10254     

Selection Combining Site Diversity Performance in High Altitude Platform Networks

High altitude platform networks operating in Ka-bands and V-bands exhibit severe degradation due to multiple atmospheric phenomena. In such frequencies, site diversity is a very efficient fade mitigation technique. This letter introduces a novel physical analytical model for the evaluation of selection combining site diversity error performance, taking into account the spatial correlation of rain attenuation and the total attenuation statistics. The outage performance of selection combining reception is being calculated through exact close-form formulas. Numerical results highlight the significant improvement against single site reception and determine the optimum relative positioning of main and diverse sites.     

Software Quality Management from a Cross-Cultural Viewpoint

This paper describes our attempts to look at how different cultures influence Software Quality Management (Siakas 1996; Mohamed Walaa-Eldeen and Siakas 1996). Quality of the software product cannot be determined until late in the development cycle. It is widely accepted that reliance has to be placed on process quality as a means of achieving product quality. In recent years software organisations have been making efforts concentrating on improving the process in order to improve software quality. Hofstede (Hofstede 1994) had defined four dimensions of work-related value differences for classifying cultural influences in different countries. These are: power distance, collectivism/individualism, femininity/masculinity and uncertainty avoidance. In this paper software development organisations are being assessed for their awareness and acceptance of Software Quality. These results will be correlated with the work-related values identified by Hofstede. The intention is to identify cultural factors, which may have a bearing on successful adoption and implementation of Software Quality Management. This revised version was published online in August 2006 with corrections to the Cover Date.     

High Responsivity and Response Speed Single‐Layer Mixed‐Cation Lead Mixed‐Halide Perovskite Photodetectors Based on Nanogap Electrodes Manufactured on Large‐Area Rigid and Flexible Substrates

Mixed‐cation lead mixed‐halide perovskites are employed as the photoactive material in single‐layer solution‐processed photodetectors fabricated with coplanar asymmetric nanogap Al–Au and indium tin oxide–Al electrodes. The nanogap electrodes, bearing an interelectrode distance of ≈10 nm, are patterned via adhesion lithography, a simple, low‐cost, and high‐throughput technique. Different electrode shapes and sizes are demonstrated on glass and flexible plastic substrates, effectively engineering the device architecture, and, along with perovskite film and material optimization, paving the way toward devices with tunable operational characteristics. The optimized coplanar nanogap junction perovskite photodetectors show responsivities up to 33 A W^?1, specific detectivity on the order of 10¹¹ Jones, and response times below 260 ns, while retaining a low dark current (0.3 nA) under ?2 V reverse bias. These values outperform the vast majority of perovskite photodetectors reported so far, while avoiding the complicated fabrication steps involved in conventional multilayer device structures. This work highlights the promising potential of the proposed asymmetric nanogap electrode architecture for application in the field of flexible optoelectronics.     

Practices of Legibility Making in Indian Cities: Property Mapping Through Geographic Information Systems and Slum Listing in Government Schemes

Property mapping through use of geographic information systems (GIS) and slum listing are practices of official knowledge production in government improvement schemes in Indian cities. Our comparative analysis of these two practices is in concert with recent amplifications of Scott's analytical scheme around the notion of legibility making. In both cases knowledge production in practice encounters an “amorphous state.” Government representatives and interests frequently intermingle with non-governmental representatives and interests. This influences knowledge production in practice with different implications for government scheme implementation and participation in urban governance. We find that slum listing supports scheme implementation better than GIS property mapping. The latter seeks to translate the notion of a clear delineation between state and non-state into organizational and technical design for legibility making. It stops short of reaching larger aims of the scheme and comes to focus on the problem of incomplete knowledge and mechanisms of self-referential monitoring. The more organic practice of slum listing involves dispersed paper and desktop technologies and relies on traditional sites of knowledge production in the city. It is adjusted to and enacted by an amorphous state. The official knowledge produced is temporary in nature, and as such allows for incremental and partially reversible scheme implementation. Slum listing retains channels of negotiation with city administration and politicians, which are vital for poorer sections of the urban populace. Our study is relevant to policy and future research, because as of 2012 the new national slum improvement scheme requires implementation of GIS also for slum data collection and management. The question is, whether the new scheme will run into similar problems as GIS property mapping or whether it puts at risk existing channels of negotiation.     

Electrospun poly lactic acid (PLA) fibres: Effect of different solvent systems on fibre morphology and diameter

The selection of an appropriate non-hazardous solvent or solvent system is essential to determine the rheological properties and electrospinnability of the solution, the productivity, and the morphology of nanofibres. In this study, poly lactic acid (PLA) solutions were prepared in various pure solvents and binary-solvent systems to investigate the effect of different solution properties on nanofibre morphology and diameter. Viscosity, conductivity and surface tension of each solution were measured. Nanofibre morphology was observed by scanning electron microscopy (SEM). Of all the solvent systems used acetone/dimethylformamide gave the highest fibre productivity and finest defect-free nanofibres. Therefore this solvent system was studied in more detail, varying the solvent ratio. Also the polymer concentration in this solvent system was varied to investigate the effect on nanofibre morphology and solution properties. Morphological investigations were done in correlation with rheological measurements: beaded nanofibrous structures were collected from solutions with concentration around the critical chain entanglement concentration (C_e), while defect-free nanofibres were produced when the concentration was increased to about twice the entanglement concentration. Further investigation of the effect of the PLA concentration on the elastic (G′) and the plastic (G″) moduli showed a sudden increase of the elastic moduli (G′) at the critical chain entanglement concentration. The results showed that the solvent properties, boiling point, viscosity, conductivity and surface tension, have a significant effect on process productivity, morphology and diameter distribution of the PLA nanofibres.     

Large work function shift of organic semiconductors inducing enhanced interfacial electron transfer in organic optoelectronics enabled by porphyrin aggregated nanostructures

We report on large work function shifts induced by the coverage of several organic semiconducting （OSC） films commonly used in organic light emitting diodes （OLEDs） and organic photovoltaics （OPVs） with a porphyrin aggregated layer. The insertion between the organic film and the aluminum cathode of an aggregated layer based on the meso-tetrakis（1-methylpyridinium-4-yl） porphyrin chloride （porphyrin 1）, with its molecules adopting a face-to-face orientation parallel to the organic substrate, results in a significant shift of the OSC work function towards lower values due to the formation of a large interfacial dipole and induces large enhancement of either the OLED or OPV device efficiency. OLEDs based on poly[（9,9-dioctylfluorenyl-2,7-diyl）-co-（1,4-benzo-2,1＇,3-thiadiazole）J （F8BT） and incorporating the porphyrin 1 at the cathode interface exhibited current efficiency values up to 13.8 cd/A, an almost three-fold improvement over the efficiency of 4.5 cd/A of the reference device. Accordingly, OPVs based on poly（3- hexylthiophene） （P3HT）, [6,6]-phenyl-C61 butyric acid methyl ester （PC61BM） and porphyrin 1 increased their external quantum efficiencies to 4.4% relative to 2.7% for the reference device without the porphyrin layer. The incorporation of a layer based on the zinc meso-tetrakis （1-methylpyridinium-4-yl）porphyrin chloride （porphyrin 2）, with its molecules adopting an edge-to-edge orientation, also introduced improvements, albeit more modest in all cases, highlighting the impact of molecular orientation.     

Tungsten oxides as interfacial layers for improved performance in hybrid optoelectronic devices

Tungsten oxide (WO₃) films with thicknesses ranging from 30 to 100 nm were grown by Hot Filament Vapor Deposition (HFVD). Films were studied by X-Ray Photoemission Spectroscopy (XPS) and were found to be stoichiometric. The surface morphology of the films was characterized by Atomic Force Microscopy (AFM). Samples had a granular form with grains in the order of 100 nm. The surface roughness was found to increase with film thickness. HFVD WO₃ films were used as conducting interfacial layers in advanced hybrid organic-inorganic optoelectronic devices. Hybrid-Organic Light Emitting Diodes (Hy-OLEDs) and Organic Photovoltaics (Hy-OPVs) were fabricated with these films as anode and/or as cathode interfacial conducting layers. The Hy-OLEDs showed significantly higher current density and a lower turn-on voltage when a thin WO₃ layer was inserted at the anode/polymer interface, while when inserted at the cathode/polymer interface the device performance was found to deteriorate. The improvement was attributed to a more efficient hole injection and transport from the Fermi level of the anode to the Highest Occupied Molecular Orbital (HOMO) of a yellow emitting copolymer (YEP). On the other hand, the insertion of a thin WO₃ layer at the cathode/polymer interface of Hy-OPV devices based on a polythiophene-fullerene bulk-heterojunction blend photoactive layer resulted in an increase of the produced photogenerated current, more likely due to improved electron extraction at the Al cathode.     

Reduction of Tungsten Oxide: A Path Towards Dual Functionality Utilization for Efficient Anode and Cathode Interfacial Layers in Organic Light‐Emitting Diodes

Here, we report on the dual functionality of tungsten oxide for application as an efficient electron and hole injection/transport layer in organic light‐emitting diodes (OLEDs). We demonstrate hybrid polymer light‐emitting diodes (Hy‐PLEDs), based on a polyfluorene copolymer, by inserting a very thin layer of a partially reduced tungsten oxide, WO_2.5, at the polymer/Al cathode interface to serve as an electron injection and transport layer. Significantly improved current densities, luminances, and luminous efficiencies were achieved, primarily as a result of improved electron injection at the interface with Al and transport to the lowest unoccupied molecular orbital (LUMO) of the polymer, with a corresponding lowering of the device driving voltage. Using a combination of optical absorption, ultraviolet spectoscopy, X‐ray photoelectron spectroscopy, and photovoltaic open circuit voltage measurements, we demonstrate that partial reduction of the WO₃ to WO_2.5 results in the appearance of new gap states just below the conduction band edge in the previously forbidden gap. The new gap states are proposed to act as a reservoir of donor electrons for enhanced injection and transport to the polymer LUMO and decrease the effective cathode workfunction. Moreover, when a thin tungsten oxide film in its fully oxidized state (WO₃) is inserted at the ITO anode/polymer interface, further improvement in device characteristics was achieved. Since both fully oxidized and partially reduced tungsten oxide layers can be deposited in the same chamber with well controlled morphology, this work paves the way for the facile fabrication of efficient and stable Hy‐OLEDs with excellent reproducibility.     

In search for a widely applicable and accepted software quality model for software quality engineering

Software Quality Engineering is an emerging discipline that is concerned with improving the approach to software quality. It is important that this discipline be firmly rooted in a quality model satisfying its needs. In order to define the needs of this discipline, the meaning of quality is broadly defined by reviewing the literature on the subject. Software Quality Engineering needs a quality model that is usable throughout the software lifecycle and that it embraces all the perspectives of quality. The goal of this paper is to propose the characteristics of a quality model suitable for such a purpose, through the comparative evaluation of existing quality models and their respective support for Software Quality Engineering.