Tuneable Singlet Exciton Fission and Triplet–Triplet Annihilation in an Orthogonal Pentacene Dimer

Fast and highly efficient intramolecular singlet exciton fission in a pentacene dimer, consisting of two covalently attached, nearly orthogonal pentacene units is reported. Fission to triplet excitons from this ground state geometry occurs within 1 ps in isolated molecules in solution and dispersed solid matrices. The process exhibits a sensitivity to environmental polarity and competes with geometric relaxation in the singlet state, while subsequent triplet decay is strongly dependent on conformational freedom. The near orthogonal arrangement of the pentacene units is unlike any structure currently proposed for efficient singlet exciton fission and may lead to new molecular design rules.     

Synthesis and Characterization of 2D Molybdenum Carbide (MXene)

Large scale synthesis and delamination of 2D Mo₂CT _x (where T is a surface termination group) has been achieved by selectively etching gallium from the recently discovered nanolaminated, ternary transition metal carbide Mo₂Ga₂C. Different synthesis and delamination routes result in different flake morphologies. The resistivity of free‐standing Mo₂CT _x films increases by an order of magnitude as the temperature is reduced from 300 to 10 K, suggesting semiconductor‐like behavior of this MXene, in contrast to Ti₃C₂T _x which exhibits metallic behavior. At 10 K, the magnetoresistance is positive. Additionally, changes in electronic transport are observed upon annealing of the films. When 2 μm thick films are tested as electrodes in supercapacitors, capacitances as high as 700 F cm^?3 in a 1 m sulfuric acid electrolyte and high capacity retention for at least 10,000 cycles at 10 A g^?1 are obtained. Free‐standing Mo₂CT _x films, with ≈8 wt% carbon nanotubes, perform well when tested as an electrode material for Li‐ions, especially at high rates. At 20 and 131 C cycling rates, stable reversible capacities of 250 and 76 mAh g^?1, respectively, are achieved for over 1000 cycles.     

采用印刷电极和插头的Paper Jamz吉他

Paper Jamz是一款玩具电吉他,它与真正的电吉他非常相似,电源为三颗AAA电池,靠一个内置的11/2英寸扬声器来发出声音。它的名称及25美元的低价都暗示着该吉他是采用印刷电极和信号线。这可以当作一个研究的案例,即如何用强大的微控制器和一些电容触控感应输入,做出复杂的产品。     

Effect of Sintering on the Thermoelectric Transport Properties of Bulk Nanostructured Bi0.5Sb1.5Te3 Pellets Prepared by Chemical Synthesis

Considerable research effort has gone into improving the performance of traditional thermoelectric materials such as Bi_2?x Sb _x Te₃ through a variety of nanostructuring approaches. Bottom-up, chemical approaches have the potential to produce very small nanoparticles (?100?nm) with narrow size distribution and controlled shape. For this study, nanocrystalline powder of Bi_0.5Sb_1.5Te₃ was synthesized using a ligand-assisted chemical method, and consolidated into pellets with cold pressing followed by sintering in Ar atmosphere. The thermoelectric transport properties were measured from 7?K to 300?K as a function of sintering temperature. Sintering is found to increase ZT and to move the maximum in ZT to lower temperatures due to a reduction in the free charge concentration. Hall mobility studies indicate that sintering increases the electron mean free path more than it increases the phonon mean free path up to sintering temperature of 598?K. A maximum ZT of 0.42 was measured at temperature of 275?K.     

Geometrical Characteristics and Surface Polarity of Inclined Crystallographic Planes of the Wurtzite and Zincblende Structures

Inclined crystallographic planes of the wurtzite structure were investigated in comparison with the zincblende structure in terms of surface geometry characteristics. The ball–stick model indicates that the semipolar surface possesses a surface polarity resembling the anion polarity, which agrees with the common experimental observations of epitaxial growth preference for the cation-polarity surface over the surface. The wurtzite surface was found to share geometrical similarities with the zincblende {100} surface uniquely among the possible semipolar planes. This finding encourages epitaxial growth on the plane of wurtzite semiconductors, e.g., GaN, with the potential of avoiding atomic step formations typically associated with off-axis crystallographic planes.     

诱惑系统架构师与电源供应商的数字电源技术

数字电源指望通过改善维护成本和可靠性、降低电源元件成本、简化BOM来降低系统电源总成本。设计者必须为传统的笨拙电源子系统增加智能。数字电源控制与管理IC有助于这些目标的实现。     

Characteristics of the heterologously expressed human lanosterol 14α‐demethylase (other names: P45014DM,CYP51, P45051) and inhibition of the purified human and Candida albicans CYP51 with azole antifungal agents

Human and Candida albicans CYP51 were purified to homogeneity after GAL10‐based heterologous expression in yeast in order to resolve the basis for the selective inhibition of the fungal enzyme over the human orthologue by the azole drugs ketoconazole and itraconazole, used in the treatment of systemic fungal infection. The purified proteins have similar spectral characteristics, both giving a maximum at 448 nm in reduced carbon monoxide difference spectra. Substrate affinity constants of 20·8 and 29·4 μM and V_max of 0·15 and 0·47 nmol/min/nmol were observed for C. albicans and human enzymes, respectively, in reconstituted enzymatic assays, using an intermediate of the demethylation reaction [32‐³H]‐3β‐hydroxylanost‐7‐en‐32‐ol as the substrate. Both enzymes gave similar type II spectra on titration with drugs, but a reduced affinity was observed for human CYP51 using the ability of carbon monoxide to displace the drug as a ligand and by calculation of IC₅₀. However, although the results indicate higher affinity of the drugs for their target CYP51 in the major fungal pathogen C. albicans, when compared directly to CYP51 from humans, the difference was less than 10‐fold. This difference is an order of magnitude lower than previously reported data based on measurements using unpurified human CYP51 enzyme preparations. Consequently, increased azole doses to combat resistant candidaemia may well inhibit endogenous human CYP51 and the potential consequences are discussed. Copyright © 1999 John Wiley & Sons, Ltd.     

Identification and control for heart rate regulation during treadmill exercise

This paper proposes a novel integrated approach for the identification and control of Hammerstein systems to achieve desired heart rate profile tracking performance for an automated treadmill system. For the identification of Hammerstein systems, the pseudorandom binary sequence input is employed to decouple the identification of dynamic linear part from input nonlinearity. The powerful epsilon-insensitivity support vector regression method is adopted to obtain sparse representations of the inverse of static nonlinearity in order to obtain an approximate linear model of the Hammerstein system. An Hinfinity controller is designed for the approximated linear model to achieve robust tracking performance. This new approach is successfully applied to the design of a computer-controlled treadmill system for the regulation of heart rate during treadmill exercise. Minimizing deviations of heart rate from a preset profile is achieved by controlling the speed of the treadmill. Both conventional proportional-integral-derivative (PID) control and the proposed approaches have been employed for the controller design. The proposed algorithm achieves much better heart rate tracking performance.     

Indium tin oxide-free semi-transparent inverted polymer solar cells using conducting polymer as both bottom and top electrodes

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is investigated as a transparent cathode to replace indium tin oxide (ITO) in inverted polymer solar cells. Increasing the thickness of the PEDOT:PSS electrode leads to a reduction in transparency and sheet resistance which lowers the photocurrent but increases the fill factor of the solar cells. The offset of photocurrent and fill factor as the thickness is increased leads to a saturation of the power conversion efficiency to 3%. These electrodes were applied to flexible substrates showing similar device performance to glass based devices. Cyclic bending test of these flexible polymer electrodes show improved conversion efficiency retention (92%) when compared to flexible ITO based electrodes (50%) after 300 bend cycles. In addition to using PEDOT:PSS as a cathode replacement for ITO in inverted solar cells, its use as a semi-transparent anode replacement to Ag is also examined. Semi-transparent inverted solar cells fabricated with ITO as the cathode and PEDOT:PSS as the top anode electrode were demonstrated showing efficiencies of 2.51% while replacement of both ITO and Ag with PEDOT:PSS as both the cathode and anode show efficiencies of 0.47%.     

OLEDs 面临的挑战

尽管基于有机发光二极管(OLED)的显示器的优点已被广泛认同,但是这项技术,尤其是其有源器件的产品在开拓市场份额上,依然非常艰难.是什么阻碍了OLEDs显示器获得更广泛的认可呢?