Micellar effects on the molecular aggregation and fluorescence properties of benzazole-derived push-pull butadienes

The absorption and fluorescence spectral behaviour of 1-(2-benzoxazolyl)-4-(p-dimethylaminophenyl)buta-1,3-diene and its benzothiazolyl analogue (abbreviated as BODB and BTDB, respectively) have been investigated in dioxane-water mixtures and micellar environments using steady-state techniques. In water, water-rich mixtures or premicellar solutions, BODB and BTDB tend to form molecular aggregates labelled as H-aggregates. These aggregates dissociate on adding surfactants forming micellized monomers. In all micellar media the fluorescence quantum yield is greatly enhanced along with a large hypsochromic shift. Also, in TX-100, CTAB and SDS both dienes show dual emission from the locally excited (LE) and intramolecular charge transfer (ICT) states. For BTDB in TX-100 and DODB in all solutions, the LE fluorescence predominates, while for BTDB in CTAB and SDS, the ICT fluorescence is the predominant. The fluorescence shifts suggest that the fluorescing molecules penetrate the core of the micellar unit in TX-100, whereas in CTAB and SDS they occupy the interfacial region. The binding constants and the micelle properties (such as polarity and CMC) have been determined using both dienes as probes.     

DC conduction processes and electrical parameters of the organic semiconducting zinc phthalocyanine, ZnPc, thin films

Electronic conduction in thermally evaporated thin films of organic semiconductor zinc phthalocyanine (ZnPc) has been investigated in a broad temperature range using gold Ohmic contacts. Electronic conduction by charge carrier hopping was dominated at low temperatures and for all applied voltages. At higher temperatures and at voltages just below 2 V conduction was found to obey Ohm's law, while at higher voltages space-charge-limited conduction (SCLC) was the dominated mechanism, which was controlled by hole-trapping states distributed exponentially within the band gap.In freshly prepared samples adsorbed oxygen was responsible for lower hole mobility and higher charge carrier concentrations. Prolonged heating of ZnPc films at 425 K resulted in lower defect state density, and thus reduced trap concentration and higher charge carrier mobility.     

Studies with enaminones: Synthesis and chemical reactivity of 2‐(4‐dimethylamino‐2‐oxobut‐3‐enyl)‐isoindole‐1,3‐dione and of 4‐(4‐dimethylamino‐2‐oxobut‐3‐enyloxy)‐2H‐phthalazin‐1‐one

The title compounds were synthesized via condensing acetonylphthalimide and 4‐acetonyloxyphthalazine‐1‐one with dimethylformamide dimethylacetal (DMFDMA). The reaction of these enaminones with electrophiles and nucleophiles is reported as a route to polyfunctional heteroaromatics.     

A Hilbert space approach to instability in semilinear partial differential equations

A method of R. Bellman in the instability theory of autonomous nonlinear ODE is enlarged to incompass semilinear evolution equations of the form u￠+Lu=f(u)u'+Lu=f(u) in the Hilbert space framework. As a consequence it is shown that linearized instability of solutions to parabolic problems with linear damping in a bounded domain implies the Liapounov instability in those topologies for which the question is meaningful.     

Power saving mechanism for VoIP services over WiMAX systems

The IEEE 802.16 system provides the power saving class (PSC) type II as a power saving algorithm for voice over internet protocol (VoIP) service, but it is not designed to consider silent periods of VoIP traffic. The main objective of this paper is to introduce a power conservation mechanism that combines power saving modes class I, class II and class III which is applicable to VoIP service with silence suppression which basically follows PSC II during talk-spurt periods but in silence periods it combine PSC I and PSC III. According to experimental results, more than 96 % power reduction can be achieved in mutual silence period by using the proposed VoIP power saving mechanism for VoIP services during silent periods with respect to the Quality of Services.     

The management of innovation: strategy, structure, andorganizational climate

Some of the factors that differentiate innovative and less innovative companies are investigated. The companies that have won the Canada Awards for Business Excellence Program for invention and innovation in the past six years are compared to similar groups of companies. The study focuses on the differences in managerial strategy, organizational structure, and organizational climate. The results show that the innovative companies use, or have, more of the following than the less innovative ones: calculated risk taking, management commitment to entrepreneurial activities and innovation, integration and intermingling of talents in teams and task forces, group and collective orientation, and a reward system that reinforces entrepreneurial behavior     

Design of Multilayered K-Band and Ka-Band Slot-Coupled Microstrip 90° Hybrid Couplers Employing Circular Ring Patch Shapes

Numerical analysis and design of millimeter-wave (mmWave) slot-coupled microstrip 90° hybrid couplers employing circular ring patches, which is operating between 18 and 40 GHz frequency range for K-Band and Ka-Band radar applications, is presented in this paper. The proposed design uses multilayer printed circuit board (PCB) technology that allows having a compact and broad bandwidth coupler. The proposed couplers use broadside coupling between microstrip patches at the top and the bottom layers via an elliptical-shaped slot in the common ground plane (mid-layer). The design uses circular ring shaped broadside coupled patches and an elliptical-shaped slot created in a common ground plane between two identical dielectric substrates. The 3 dB coupler prototype has been fabricated on two 0.127 mm thick Rogers Duroid RT5880 substrates. The circuit occupies the dimensions of less than 5 mm × 5 mm without the extension that is required to insert the connectors. Extensive parametric studies are performed to address the effect of varying the coupler parameters on the coupling values, return losses, isolations, transmission magnitudes and phases through the operational frequency bandwidth. A 3 dB/90° hybrid coupler prototype is fabricated and then tested experimentally using Agilent E8364B PNA Network Analyzer. The simulation and experimental results show a good performance in terms of bandwidth, which covers the entire desired frequency range. In addition, detailed design for different coupling values of the proposed coupler is presented in this paper. The proposed coupler can achieve different coupling values range from 3 up to 9 dB that can be used for switched beam antenna array systems.     

A new compact CMOS C-multiplier

This paper presents a new compact CMOS capacitance multiplier. The multiplier is based on using the translinear principle with MOSFETs operating in subthreshold region. The multiplication factor is controllable to meet the designer requirements. Tanner TSPICE simulator was used to confirm the functionality of the design in 0.18 µm CMOS Technology. The circuit operates from ±0.75 supply voltage. Simulation results indicate that the multiplication factor can be varied from 10 to 300. The functionality of the proposed capacitance multiplier was demonstrated by using it in designing a low pass filter and a relaxation oscillator.     

Polarization‐Sensitive Single‐Wall Carbon Nanotubes All‐in‐One Photodetecting and Emitting Device Working at 1.55 µm

Functional and easy‐to‐integrate nanodevices operating in the telecom wavelength ranges are highly desirable. Indeed, the pursuit for faster, cheaper, and smaller transceivers for datacom applications is fueling the interest in alternative materials to develop the next generation of photonic devices. In this context, single wall carbon nanotubes (SWNTs) have demonstrated outstanding electrical and optical properties that make them an ideal material for the realization of ultracompact optoelectronic devices. Still, the mixture in chirality of as‐synthesized SWNTs and the necessity of precise positioning of SWNT‐based devices hinder the development of practical devices. Here, the realization of operational devices obtained using liquid solution‐based techniques is reported, which allow high‐purity sorting and localized deposition of aligned semiconducting SWNTs (s‐SWNTs). More specifically, devices are demonstrated by combining a polymer assisted extraction method, which enables a very effective selection of s‐SWNTs with a diameter of about 1–1.2 nm, with dielectrophoresis, which localizes the deposition onto silicon wafers in aligned arrays in‐between prepatterned electrodes. Thus, long semiconducting nanotubes directly contact the electrodes and, when asymmetric contacts (i.e., source and drain made of different metals) are used, each device can operate both as photoemitter and as photodetector in the telecom band around 1.55 µm in air at room temperature.     

Preparation of biocompatible system based on electrospun CMC/PVA nanofibers as controlled release carrier of diclofenac sodium

Nanofibers of naturally modified polymer such as carboxymethyl cellulose (CMC) blended with poly(vinyl alcohol) (PVA) at different ratios was obtained by electrospinning technique. The blended solutions of CMC and PVA loaded with and without diclofenac sodium (DS) were electrospun using environmentally benign electrospinning technique in the absence of organic solvents. Scanning electron microscopy (SEM), Fourier transform infrared (FTIR), thermogravimetric analysis (TGA) were used to investigate the surface morphology functional groups, as well as the thermal stability of DS loaded CMC/PVA nanofibers mat. The mechanical properties of the as prepared electrospun nanofibers was also evaluated. The entrapment efficiency and the in vitro release of DS loaded CMC/PVA nanofibers were characterized using UV-Vis spectroscopy. The obtained results displayed that the blended nanofibers have shown a smooth morphology, no beads formation when the concentration of CMC was equal or below 5% and beads formation above 5%. FTIR data demonstrated that there were good interactions between CMC and PVA possibly via the formation of hydrogen bonds. The electrospun blended CMC/PVA nanofibers exhibit good mechanical properties. From the in vitro release data, it was found that with the presence of CMC, the release of DS from the nanofibers mats became sustained controlled. Due to the biocompatibility and low cost of the two blended polymers (CMC and PVA), the blended nanofibers system can be considered as one of the promising materials for the preparation of excellent drug carrier.