On the Origin of Green Emission Bands in Fluorene‐Based Conjugated Polymers

Blue‐light‐emitting diodes made of polyfluorenes have low stability and, under operation, rapidly degrade and produce undesirable low‐energy emission bands (green or g‐bands). A spectroelectrochemical study of the degradation process suffered by polyfluorenes is reported here. These polymers lose their electronic properties by electrochemical oxidation and reduction through σ‐bond breaking. In addition, upon electrochemical reduction, the development of a structured green emission band at 485 nm is observed. The position and shape of this band is different from the usual featureless band at 535 nm assigned to fluorenone defects. The green‐light‐emitting product is isolated and analyzed by Fourier‐transform IR spectroscopy; fluorenone formation is excluded. The isolated product is crosslinked; its green emission is probably related to the formation of an intramolecular excimer.     

啁啾光栅滤波器的设计与优化

色散是高速光纤通信系统所面临的挑战之一,针对高速光纤通信系统的特性,设计了一种能够进行色散补偿的啁啾光栅滤波器,利用matlab仿真,分析了所设计的滤波器的反射率和时延特性,最后对所设计的啁啾光栅滤波器进行超高斯切趾优化,达到了理想的优化效果。     

Zwitterionic diaminodicyanoquinodimethanes with enhanced blue-green emission in the solid state

Diaminodicyanoquinodimethane molecules which show strong solid state emission in the blue-green region are developed. The new materials are structurally characterized; extended supramolecular assemblies mediated by H-bond interactions are observed in the crystal lattice. Spectroscopic studies including life-time and fluorescence quantum yield measurements in the solution and solid states are carried out. Emission in the solid state is ∼400 times stronger than that in solution; this can be attributed to the inhibition of the excited state geometry relaxation to a non-radiative state, in the solid. Impact of the molecular structure in the crystals on the solid state light emission is discussed. Semiempirical computational studies provide useful insight into the various structural and spectroscopic features of the new materials. The present observations serve as a pointer to further design strategies for realizing novel blue photoluminescent molecular materials based on the diaminodicyanoquinodimethane framework.     

Kinetic and isotherm studies of the adsorption of Acid Blue 92 using a low-cost non-conventional activated carbon

Adsorbents prepared from waste plants for the treatment of dyeing effluents have high significance in environmental sustainability. In this research, an attempt is made to analyze the applicability of activated carbon prepared from Euphorbia antiquorum L wood by H₃PO₄ activation method for the removal of Acid Blue 92 dye. Various kinetic models were used for the analysis of adsorption kinetics and pseudo second-order model fits well for the selected adsorbent-adsorbate system. The moderate rate of dye uptake indicates that the rate-determining step could be physisorption in nature. Langmuir, Freundlich and Dubinin-Raduskevich isotherm models were applied for the analysis of isotherm data. The positive enthalpy of adsorption substantiates that the adsorption process is endothermic in nature.     

非地层因素井下漏失原因分析及对策

钻井施工中发生井漏的原因是多方面的，主要有两大因素：一是地层原因，如存在溶洞，裂缝等。二是钻井工艺措施方面存在问题，如开泵过猛憋漏地层等，地层本身造成井漏的原因是客观存在的，这里不予分析，而开泵不畅是钻井工作者经常遇到的复杂情况之一，文中从环空间隙，排量，钻井液性能，地层的承压能力等方面入手，对一口因憋漏地层造成起套管的井井漏的原因进行计算，分析，并与其它2口井对比，提出预防和处理“主观井漏”的办法。     

A study of dynamic meta-learning for failure prediction in large-scale systems

Despite years of study on failure prediction, it remains an open problem, especially in large-scale systems composed of vast amount of components. In this paper, we present a dynamic meta-learning framework for failure prediction. It intends to not only provide reasonable prediction accuracy, but also be of practical use in realistic environments. Two key techniques are developed to address technical challenges of failure prediction. One is meta-learning to boost prediction accuracy by combining the benefits of multiple predictive techniques. The other is a dynamic approach to dynamically obtain failure patterns from a changing training set and to dynamically extract effective rules by actively monitoring prediction accuracy at runtime. We demonstrate the effectiveness and practical use of this framework by means of real system logs collected from the production Blue Gene/L systems at Argonne National Laboratory and San Diego Supercomputer Center. Our case studies indicate that the proposed mechanism can provide reasonable prediction accuracy by forecasting up to 82% of the failures, with a runtime overhead less than 1.0 min.     

Color filter array design using random patterns with blue noise chromatic spectra

We propose two new types of random patterns with R, G, B colors, which allow to design color filter arrays (CFAs) with good spectral properties. Indeed, the chrominance channels have blue noise characteristics, a property which maximizes the robustness of the acquisition system to aliasing. With these new CFAs, the demosaicking artifacts appear as incoherent noise, which is less visually disturbing than the moiré structures characteristic of CFAs with periodic patterns.     

Tetraphenylimidazole‐Based Excited‐State Intramolecular Proton‐Transfer Molecules for Highly Efficient Blue Electroluminescence

Aiming for highly efficient blue electroluminescence, we have designed and synthesized a novel class of tetraphenylimidazole‐ based excited‐state intramolecular proton‐transfer (ESIPT) molecules with covalently linked charge‐transporting functional groups (carbazole‐ and oxadiazole‐functionalized hydroxyl‐substituted tetraphenylimidazole (HPI), i.e., HPI‐Cbz and HPI‐Oxd, respectively). High T_g (ca. 130 °C) amorphous films of HPI‐Cbz and HPI‐Oxd showed intense and ideal blue‐light emission (λ_max = 462 and 468 nm, Φ_PL = 0.44 and 0.38) with a large Stokes shift of over 160 nm and a narrow full width at half‐maximum of less than 65 nm. Organic light‐emitting devices using HPI‐Cbz and HPI‐Oxd as the emitting layer generated an efficient blue electroluminescence (EL) emission peaking at around 460 nm with excellent CIE coordinates of (x, y) = (0.15, 0.11). A maximum external quantum efficiency of 2.94%, and a maximum brightness of 1 229 cd m⁻² at 100 mA cm⁻², as well as a low turn‐on voltage of 4.8 V were achieved in this work.     

1‐Methyl‐2‐(anthryl)‐imidazo[4,5‐f][1,10]‐phenanthroline: A Highly Efficient Electron‐Transport Compound and a Bright Blue‐Light Emitter for Electroluminescent Devices

A new organic blue‐light emitter 1‐methyl‐2‐(anthryl)‐imidazo[4,5‐f][1,10]‐phenanthroline ( 1 ) has been synthesized and fully characterized. The utility of compound 1 as a blue‐light emitter in electroluminescent (EL) devices has been evaluated by fabricating a series of EL devices A where compound 1 functions as an emitter. The EL spectrum of device series A has the emission maximum at 481 nm with the CIE (Commission Internationale de l'Eclairage) color coordinates 0.198 and 0.284. The maximum luminance of devices in series A is 4000 cd m^–2 and the best external quantum efficiency of device series A is 1.82 %. The utility of compound 1 as an electron injection–electron transport material has been evaluated by constructing a set of EL devices B where 1 is used as either the electron‐injection layer or the electron injection–electron transport layer. The performance of device series B is compared to the standard device in which Alq₃ (tris(8‐hydroxyquinoline) aluminum) is used as the electron injection–electron transport layer. The experimental results show that the performance of 1 as an electron injection–electron transport material is considerably better than Alq₃. The stability of device series B is comparable to that of the standard Alq₃ device. The excellent performance of 1 as an electron injection/transport material may be attributed to the strong intermolecular interactions of 1 in the solid state as revealed by single‐crystal X‐ray diffraction analysis. In addition, compound 1 is a colorless material with a much larger highest occupied molecular orbital–lowest unoccupied molecular (HOMO–LUMO) gap than Alq₃, which renders it potentially useful for a wide range of applications in EL devices.