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A water-soluble cationic polythiophene derivative, poly[3-(6-{4-tert-butylpyridiniumyl}-hexyl)thiophene-2,5-diyl] [P3(TBP)HT], is combined with anionic poly(3,4-ethylenedioxythiophene):poly(p-styrenesulfonate) (PEDOT:PSS) on indium tin oxide (ITO) substrates via electrostatic layer-by-layer (eLbL) assembly. By varying the number of eLbL layers, the electrode's work function is precisely controlled from 4.6 to 3.8 eV. These polymeric coatings are used as cathodic interfacial modifiers for inverted-mode organic photovoltaics that incorporate a photoactive layer composed of either poly[(3-hexylthiophene)-2,5-diyl] (P3HT) and the fullerene acceptor [6,6-phenyl-C61-butyric acid methyl ester (PC61BM) or the low bandgap polymer [poly({4,8-di(2-ethylhexyloxyl)benzo[1,2-b:4,5-b′]dithiophene}-2,6-diyl)-alt-({5-octylthieno[3,4-c]pyrrole-4,6-dione}-1,3-diyl) (PBDTTPD)] and the electron acceptor [6,6-phenyl-C71-butyric acid methyl ester (PC71BM)]. The power conversion efficiency (PCE) of the resulting photovoltaic device is dependent on the composition of the eLbL-assembled interface and permits the fabrication of devices with efficiencies of 3.8% and 5.6% for P3HT and PBDTTPD donor polymers, respectively. Notably, these devices demonstrate significant stability with a P3HT:PC61BM system maintaining 83% of its original PCE after 1 year of storage and a PBDTTPD:PC71BM system maintaining 97% of its original PCE after over 1000 h of storage in air, according to the ISOS-D-1 shelf protocol.

The optoelectronic and photophysical properties of four regioregular poly[3-(carboxyalkyl)thiophene-2,5-diyl] (P3CAT) with different carboxyalkyl chain lengths (propyl to hexyl) are reported. Each P3CAT is combined with [6,6]-phenyl-C61-butyric acid methyl ester to form the photoactive bulk heterojunction layer for organic photovoltaic devices. The extent of hydrogen bonding and polymer crystallinity in the films has been determined through infrared spectroscopy and X-ray diffraction. The mechanical properties of films are analyzed with nanoindentation, and the measurements suggest that P3CATs are suitable for use in flexible devices. Power conversion efficiencies of up to 2.6% and 1.6% are obtained for devices fabricated in air, and supported on glass and flexible poly(ethylene terephthalate) substrates, respectively. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A cationic and water-soluble polythiophene [poly[3-(6-pyridiniumylhexyl) thiophene bromide] (P3PHT + Br - )] is synthesized and used in combination with anionic poly(3,4-ethylenedioxythiophene):poly(p-styrenesulfonate) (PEDOT:PSS) - to produce hybrid coatings on indium tin oxide (ITO). Two coating strategies are established: i) electrostatic layer-by-layer assembly with colloidal suspensions of (PEDOT:PSS) - , and ii) modification of an electrochemically prepared (PEDOT:PSS) - film on ITO. The coatings are found to modify the work function ofITO such that it could act as a cathode in inverted 2,5-diyl-poly(3-hexylthiophene) (P3HT)/[6,6]-phenyl-C 61 -butyric acid methyl ester (PCBM) polymer photovoltaic cells. The interfacial modifier created from the layer-by-layer assembly route is used to produce efficient inverted organic photovoltaic devices (power conversion efficiency ~2%) with significant long-term stability in excess of 500 h.

Neural representations of even temporally unstructured stimuli can show complex temporal dynamics. In many systems, neuronal population codes show 'progressive differentiation', whereby population responses to different stimuli grow further apart during a stimulus presentation. Here we analysed the response of auditory cortical populations in rats to extended tones. At onset (up to 300 ms), tone responses involved strong excitation of a large number of neurons; during sustained responses (after 500 ms) overall firing rate decreased, but most cells still showed statistically significant rate modulation. Population vector trajectories evoked by different tone frequencies expanded rapidly along an initially similar trajectory in the first tens of milliseconds after tone onset, later diverging to smaller amplitude fixed points corresponding to sustained responses. The angular difference between onset and sustained responses to the same tone was greater than between different tones in the same stimulus epoch. No clear orthogonalization of responses was found with time, and predictability of the stimulus from population activity also decreased during this period compared with onset. The question of whether population activity grew more or less sparse with time depended on the precise mathematical sense given to this term. We conclude that auditory cortical population responses to tones differ from those reported in many other systems, with progressive differentiation not seen for sustained stimuli. Sustained acoustic stimuli are typically not behaviorally salient: we hypothesize that the dynamics we observe may instead allow an animal to maintain a representation of such sounds, at low energetic cost.

We have developed a range of thin film coatings that are transparent in the visible, electrically conducting, adjustably birefringent and capable of aligning calamitic liquid crystals. The coatings were fabricated from indium tin oxide by oblique or glancing angle deposition, and a wide range of microstructures such as helices, chevrons, uniaxial posts and biaxial slabs were produced. Under many deposition conditions, these structures showed optical transmittance and electrical conductivity comparable to standard indium tin oxide, yet a strong form birefringence (Δn > 0.07 at 589 nm) was also measured. In addition, many coatings were found to be capable of aligning liquid crystals along a common director, leading us to conclude that the technology may be useful in liquid crystal displays and other lightwave applications.

We investigate a series of glassy polymer actuators which are found to bend rapidly and reversibly in response to changes in the solvent environment. The actuators are based on hydrogen-bonded liquid crystal networks, and bending motion is created using director profiles engineered to take advantage of the network swelling anisotropy. Strongly polar solvents easily swell the network, forcing bending in one direction, while the less polar solvents extract water to force bending in the opposite direction.

In this report we describe a model that applies Marr's theory of hippocampal function to the problem of map-based navigation. Like many others we attribute a spatial memory function to the hippocampus, but we suggest that the additional functional components required for map-based navigation are located elsewhere in the brain. One of the key functional components in this model is an egocentric map of space, located in the neocortex, that is continuously updated using ideothetic (self-motion) information. The hippocampus stores snapshots of this egocentric map. The modeled activity pattern of head direction cells is used to set the best egocentric map rotation to match the snapshots stored in the hippocampus, resulting in place cells with a nondirectional firing pattern. We describe an evaluation of this model using a mobile robot and demonstrate that with this model the robot can recognize an environment and find a hidden goal. This model is discussed in the context of prior experiments that were designed to discover the map-based spatial processing of animals. We also predict the results of further experiments.