Acridan‐Grafted Poly(biphenyl germanium) with High Triplet Energy,Low Polarizability,and an External Heavy‐Atom Effect for Highly Efficient Sky‐Blue TADF Electroluminescence

We propose the novel σ–π conjugated polymer poly(biphenyl germanium) grafted with two electron‐donating acridan moieties on the Ge atom for use as the host material in a polymer light‐emitting diode (PLED) with the sky‐blue‐emitting thermally activated delayed fluorescence (TADF) material DMAC‐TRZ as the guest. Its high triplet energy (E_T) of 2.86 eV is significantly higher than those of conventional π–π conjugated polymers (E_T=2.65 eV as the limit) and this guest emitter (E_T=2.77 eV). The TADF emitter emits bluer emission than in other host materials owing to the low orientation polarizability of the germanium‐based polymer host. The Ge atom also provides an external heavy‐atom effect, which increases the rate of reverse intersystem crossing in this TADF guest, so that more triplet excitons are harvested for light emission. The sky‐blue TADF electroluminescence with this host/guest pair gave a record‐high external quantum efficiency of 24.1 % at maximum and 22.8 % at 500 cd m^?2.     

Enhanced Thermocatalytic Activity of Porous Yellow ZnO Nanoflakes: Defect‐ and Morphology‐Induced Perspectives

Herein, we report a simple and effective strategy for the synthesis of yellow ZnO (Y‐ZnO) nanostructures with abundant oxygen vacancies on a large scale, through the sulfidation of ZnO followed by calcination. The developed strategy allows retention of the overall morphology of Y‐ZnO compared with pristine ZnO and the extent of oxygen vacancies can be tuned. The influence of oxygen deficiencies, the extent of defect sites, and the morphology of ZnO on its solution‐phase thermocatalytic activity has been evaluated in the synthesis of 5‐substituted‐1H‐tetrazoles with different nitriles and sodium azide. A reasonable enhancement in the reaction rate was achieved by using Y‐ZnO nanoflakes (Y‐ZnO NFs) as a catalyst in place of pristine ZnO NFs. The reaction was complete within 6 h at 110 °C with Y‐ZnO NFs, whereas it took 14 h at 120 °C with pristine ZnO NFs. The catalyst is easy to recycle without a significant loss in catalytic activity.     

Vertical and horizontal synchronization services with outlier detection in underwater acoustic networks

Underwater Acoustic Networks (UANs) have important applications in ocean exploration and lake pollution monitoring. UANs are however different from terrestrial sensor networks due to their highly variable, long propagation delay, and mobility. Clock synchronization is an important protocol to achieve timing‐based sensor communications. In this paper, we propose a three dimensional, scalable UAN time synchronization scheme that can achieve both horizontal (i.e., in the same water depth) and vertical (i.e., from bottom up to the surface) clock synchronization to overcome the effects of long acoustic delay. To secure UAN clock synchronization services, we also propose a two‐step security UAN synchronization model: (1) correlation test and (2) statistical reputation and trust model. The proposed model can detect outlier timestamp data and identify nodes generating insider attacks. Copyright © 2007 John Wiley & Sons, Ltd.     

Influence of coolant injector configuration on film cooling effectiveness for gaseous and liquid film coolants

An experimental investigation is conducted to bring out the effects of coolant injector configuration on film cooling effectiveness, film cooled length and film uniformity associated with gaseous and liquid coolants. A series of measurements are performed using hot air as the core gas and gaseous nitrogen and water as the film coolants in a cylindrical test section simulating a thrust chamber. Straight and compound angle injection at two different configurations of 30°–10° and 45°–10° are investigated for the gaseous coolant. Tangential injection at 30° and compound angle injection at 30°–10° are examined for the liquid coolant. The analysis is based on measurements of the film-cooling effectiveness and film uniformity downstream of the injection location at different blowing ratios. Measured results showed that compound angle configuration leads to lower far-field effectiveness and shorter film length compared to tangential injection in the case of liquid film cooling. For similar injector configurations, effectiveness along the stream wise direction showed flat characteristics initially for the liquid coolant, while it was continuously dropping for the gaseous coolant. For liquid coolant, deviations in temperature around the circumference are very low near the injection point, but increases to higher values for regions away from the coolant injection locations. The study brings out the existance of an optimum gaseous film coolant injector configuration for which the effectiveness is maximum.     

A Nonlinear Stability Analysis for Thermoconvective Magnetized Ferrofluid Saturating a Porous Medium

The generalized energy method is developed to study the nonlinear stability analysis for a magnetized ferrofluid layer heated from below saturating a porous medium, in the stress-free boundary case. The mathematical emphasis is on how to control the nonlinear terms caused by magnetic body force. By introducing a suitable generalized energy functional, we perform a nonlinear energy stability (conditional) analysis. It is found that the nonlinear critical stability magnetic thermal Rayleigh number does not coincide with that of linear instability analysis, and thus indicates that the subcritical instabilities are possible. However, it is noted that, in case of non-ferrofluid, global nonlinear stability Rayleigh number is exactly the same as that for linear instability. For lower values of magnetic parameters, this coincidence is immediately lost. The effect of magnetic parameter, M ₃, and medium permeability, Da, on subcritical instability region has also been analyzed. It is shown that with the increase of magnetic parameter (M ₃) and Darcy number (Da), the subcritical instability region between the two theories decreases quickly. We also demonstrate coupling between the buoyancy and magnetic forces in nonlinear energy stability analysis as well as in linear instability analysis.     

Growth morphology of zinc tris(thiourea) sulphate crystals

The growth morphology of crystals of zinc tris(thiourea) sulphate (ZTS) is investigated experimentally, and computed using the Hartman-Perdok approach. Attachment energies of the observed habit faces are calculated for determining their relative morphological importance. A computer code is developed for carrying out these calculations. A special procedure is adopted for computing the cohesive energy of a slice of the structure parallel to any rational crystallographic plane. For estimating the cohesive energies, formal charges on the experimentally determined atomic positions in the molecules of ZTS are calculated by ab initio molecular-orbital computations, with wave functions obtained by the Hartree-Fock procedure. Fairly good agreement with the observed crystal morphology is obtained for a model of growth mechanism in which ZTS is assumed to exist in solution sa szinc tris(thiourea) ions and sulphate ions.     

Dioxygen activation at non-heme diiron centers: characterization of intermediates in a mutant form of toluene/o-xylene monooxygenase hydroxylase

We report the generation and characterization of an intermediate in a mutant form of the toluene/o-xylene monooxygenase hydroxylase component from Pseudomonas stutzeri OX1. The reaction of chemically reduced I100W variant in the presence of the coupling protein, ToMOD, with dioxygen was monitored by stopped-flow UV/visible spectroscopy. Rapid-freeze quench (RFQ) samples were also generated for EPR and M?ssbauer spectroscopy. A transient species is observed in the UV/visible spectrum with an absorption maximum at 500 nm. EPR and M?ssbauer spectra of RFQ samples identified this species as a diiron(III,IV) cluster spin-coupled to a neutral W radical. A diamagnetic precursor to the mixed-valent diiron(III,IV) was also observed at an earlier time point, with M?ssbauer parameters typical of high-spin FeIII. We have tentatively assigned this antiferromagnetically coupled diiron(III) intermediate as a peroxo-bridged cluster, and this complex has also been observed in preliminary studies of the wild-type hydroxylase.     

Dose response and kinetic analysis of thermoluminescence of Li–Zn fluoroborate glass

The intention of this study is to explore the thermoluminescence properties of beta-irradiated Li–Zn fluoroborate glass. The glow-curve corresponding to 10?Gy shows two peaks when measured at 1°C/s. The dose response of the glass to beta irradiation was investigated. The trapping level parameters such as activation energy, frequency factor and order of kinetics associated with the observed glow-peak were determined using different methods. The thermoluminescence is affected by thermal quenching. A possible mechanism for the thermoluminescence is described.     

Synthesis,characterization and phase transition studies in 4-hexyloxy benzylidene 4’-alkoxyanilines

Synthesis and the characterization through polarizing optical microscope (POM) textures in number of 4-hexyloxy benzylidene 4’-alkoxyanilines, 6O.Om with m = 4, 6 to 10 liquid crystalline materials are carried out. Furthermore, the density and thermal expansion coefficient results reveal that the phase transitions present, viz., isotropic–nematic, nematic–SmC and SmC–SmI show first-order nature as expected. The transition temperatures obtained thorough the differential scanning calorimetry is found to be in agreement with the literature data. The first two compounds exhibit only the nematic phase while the next four compounds show enantiotropic SmC phase as per the literature data. The compound with m = 10 exhibits monotropic SmI phase. However, we, the authors, are able to observe this phase in addition to SmC and nematic through POM only as per the literature. The parameters calculated across the phase transitions and in the phases are in agreement with the body of the data available.