Understanding Local and Macroscopic Electron Mobilities in the Fullerene Network of Conjugated Polymer‐based Solar Cells: Time‐Resolved Microwave Conductivity and Theory

The efficiency of bulk heterojunction (BHJ) organic photovoltaics is sensitive to the morphology of the fullerene network that transports electrons through the device. This sensitivity makes it difficult to distinguish the contrasting roles of local electron mobility (how easily electrons can transfer between neighboring fullerene molecules) and macroscopic electron mobility (how well‐connected is the fullerene network on device length scales) in solar cell performance. In this work, a combination of density functional theory (DFT) calculations, flash‐photolysis time‐resolved microwave conductivity (TRMC) experiments, and space‐charge‐limit current (SCLC) mobility estimates are used to examine the roles of local and macroscopic electron mobility in conjugated polymer/fullerene BHJ photovoltaics. The local mobility of different pentaaryl fullerene derivatives (so‐called ‘shuttlecock’ molecules) is similar, so that differences in solar cell efficiency and SCLC mobilities result directly from the different propensities of these molecules to self‐assemble on macroscopic length scales. These experiments and calculations also demonstrate that the local mobility of phenyl‐C₆₀ butyl methyl ester (PCBM) is an order of magnitude higher than that of other fullerene derivatives, explaining why PCBM has been the acceptor of choice for conjugated polymer BHJ devices even though it does not form an optimal macroscopic network. The DFT calculations indicate that PCBM's superior local mobility comes from the near‐spherical nature of its molecular orbitals, which allow strong electronic coupling between adjacent molecules. In combination, DFT and TRMC techniques provide a tool for screening new fullerene derivatives for good local mobility when designing new molecules that can improve on the macroscopic electron mobility offered by PCBM.     

Multi-parameter performance analysis for decentralized cognitive radio networks

In this paper, we investigate the impact of primary user activity, secondary user activity, interface switching, channel fading and finite-length queuing on the performance of decentralized cognitive radio networks. The individual processes of these service-disruptive effects are modeled as Markov chains based on cross-layer information locally available at the network nodes. A queuing analysis is conducted and various performance measures are derived regarding the packet loss, throughput, spectral efficiency, and packet delay distribution. Numerical results demonstrate the impact of various system parameters on the system performance, providing insights for cross-layer design and autonomous decision making in decentralized cognitive radio networks.     

Studies on parametric sensitivity and safe operation criteria of batch processes

Heat accumulation in batch reactors may eventually lead to a temperature runaway. Critical values of process parameters were used to investigate process safety. Parameter sensitivity is discussed for a wide range of operating conditions. Two criteria for safe operation are presented, based on critical values of process parameters.     

A Convergence-Free Predistortion Technique for Adaptive Linearisation of RF Power Amplifiers

Adaptive digital baseband predistortion is a well-known linearisation technique for removing intermodulation products that radio frequency power amplifiers (PAs) introduce. This paper proposes a new baseband predistortion method that is based on a non-iterative, fast adaptation algorithm without convergence restrictions. The response of the PA in a batch of training magnitude stimuli is used for the computation of the predistortion gain. The latter is directly extracted in rectangular form without prior transformations and AM/AM and AM/PM non-linearities sequential estimation. The influence of the gain table size and the imperfections of the modulator and demodulator in the method's performance are examined. Experimental measurements of an in-house prototype show a linearity improvement of about 25 dB.     

Morphological study on the effect of elastomeric impact modifiers in polypropylene systems

The morphological effect of elastomeric impact modifiers has been studied in polypropylene systems by wide-angle and small-angle X-ray diffractometry, small-angle light scattering, light and electron microscopy and differential scanning calorimetry. It was established that the incorporation of an impact modifier altered the superstructure of the polypropylene matrix by decreasing the average size of spherulites through which the impact strength of the composite may be influenced. The changes in the mechanical and thermal properties are probably caused by the interphase between the amorphous elastomeric modifier and the polypropylene spherulites. The particle size of the dispersed elastomer is of vital importance in toughening of the amorphous polymer while in the crystalline resin, the changes in the superstructure also seem to be very important. Above T_g, the amorphous impact modifier acts as an energy absorber which markedly influences the crazing susceptibility of the polypropylene matrix.     

The delayed depolarization in rat cutaneous afferent axons is reduced following nerve transection and ligation, but not crush: implications for injury-induced axonal Na+ channel reorganization

Two distinct populations of Na+ channels (kinetically fast and slow) are present on the cell bodies and axons of cutaneous afferent neurons; the fast current is increased and the slow current reduced in amplitude following nerve injury. The present study was undertaken to determine if similar changes occur on the axons of these neurons following peripheral nerve injury. The compound action potentials from rat sural nerves were recorded in a sucrose gap chamber. Following application of 4-aminopyridine, a prominent and well-characterized depolarization (the delayed depolarization) followed the action potential. This potential, only present on cutaneous afferent axons, has been correlated with activation of a slow Na+ current. The delayed depolarization was reduced after nerve transection. The refractory period of transmission of the action potential was shortened in the transected nerves, but that of the delayed depolarization was prolonged. The changes were largest when the sural nerve was cut and ligated [control: 38.1 +/- 1.7% (n = 5); injury: 24.5 +/- 2.8% (n = 5), P < 0.05], which prevented reconnection to its peripheral target. When the nerve was crushed and allowed to reestablish peripheral target connections, the delayed depolarization was minimally effected. These results indicate that the changes in Na+ channel organization following peripheral target disconnection observed on cutaneous afferent cell bodies also occur on their axons.     

Miscibility of some chlorinated poly(hydrocarbons) with ethylene-acrylic rubber

The compatibility of an ethylene-acrylic rubber (R) with poly (chloroprene) (CR) and two chlorinated poly-ethylenes, containing 48 (CPE 48) and 25 (CPE 25) wt.-% chlorine, was investigated. Blends with the latter polymer were studied in the complete composition range. The techniques used were phase-contrast microscopy, differential scanning calorimetry, dynamic mechanical and stress-strain testing. The single T_g relaxation of blends and its almost linear variation with composition, together with results obtained using the techniques mentioned, support the view that the systems are miscible at the segmental level. At low rubber contents an antiplasticisation effect was observed for the R/CPE 25 system. At high rubber compositions a small reduction of crystallinity and a melting point depression of the PE phase in CPE were observed. Various equations proposed to predict the T_g of blends and their modulus using pure component data were also tested at varying compositions and temperatures.