Predictive study of charge transport in disordered semiconducting polymers

We present a theoretical study of charge transport in disordered semiconducting polymers that relates the charge mobility to the chemical structure and the physical morphology in a novel multiscale approach. Our studies, focusing on poly(9,9-dioctylfluorene) (PFO), show that the charge mobility is dominated by pathways with the highest interchain charge-transfer rates. We also find that disorder is not always detrimental to charge transport. We find good agreement with experimental time-of-flight mobility data in highly aligned PFO films.     

Dynamic emulation of mechanical loads using a vector-controlledinduction motor-generator set

This paper addresses the problem of electronic emulation of both linear and nonlinear mechanical loads using a vector-controlled induction machine dynamometer. It is shown that a basic emulation scheme where the dynamometer torque demand is derived from the inverse dynamics of the emulated load is not generally viable, especially if the emulated load is part of a closed-loop speed control system. A new feedforward speed-tracking control scheme for the dynamometer is presented, which preserves the load dynamics and allows for emulation of a large class of nonlinear loads. An experimental rig is described using vector-controlled induction machines as the drive motor and dynamometer, and experimental results showing excellent emulation of both linear and nonlinear load dynamics are presented     

Liquid-crystalline semiconducting polymers with high charge-carrier mobility

Organic semiconductors that can be fabricated by simple processing techniques and possess excellent electrical performance, are key requirements in the progress of organic electronics. Both high semiconductor charge-carrier mobility, optimized through understanding and control of the semiconductor microstructure, and stability of the semiconductor to ambient electrochemical oxidative processes are required. We report on new semiconducting liquid-crystalline thieno[3,2-b ]thiophene polymers, the enhancement in charge-carrier mobility achieved through highly organized morphology from processing in the mesophase, and the effects of exposure to both ambient and low-humidity air on the performance of transistor devices. Relatively large crystalline domain sizes on the length scale of lithographically accessible channel lengths ( approximately 200 nm) were exhibited in thin films, thus offering the potential for fabrication of single-crystal polymer transistors. Good transistor stability under static storage and operation in a low-humidity air environment was demonstrated, with charge-carrier field-effect mobilities of 0.2-0.6 cm(2) V(-1) s(-1) achieved under nitrogen.     

Resting developments: a review of fMRI post-processing methodologies for spontaneous brain activity

Analytic tools for addressing spontaneous brain activity, as acquired with fMRI during the "resting-state," have grown dramatically over the past decade. Along with each new technique, novel hypotheses about the functional organization of the brain are also available to researchers. We review six prominent categories of resting-state fMRI data analysis: seed-based functional connectivity, independent component analysis, clustering, pattern classification, graph theory, and two "local" methods. In surveying these methods, we address their underlying assumptions, methodologies, and novel applications.     

Ratiometric fluorescence detection of mercury ions in water by conjugated polymer nanoparticles

We present dye-doped polymer nanoparticles that are able to detect mercury in aqueous solution at parts per billion levels via fluorescence resonance energy transfer (FRET). The nanoparticles are prepared by reprecipitation of highly fluorescent conjugated polymers in water and are stable in aqueous suspension. They are doped with rhodamine spirolactam dyes that are nonfluorescent until they encounter mercury ions, which promote an irreversible reaction that converts the dyes to fluorescent rhodamines. The rhodamine dyes act as FRET acceptors for the fluorescent nanoparticles, and the ratio of nanoparticle-to-rhodamine fluorescence intensities functions as a ratiometric fluorescence chemodosimeter for mercury. The light harvesting capability of the conjugated polymer nanoparticles enhances the fluorescence intensity of the rhodamine dyes by a factor of 10, enabling sensitive detection of mercury ions in water at levels as low as 0.7 parts per billion.     

Comparison of probability density functions for analyzing irradiance statistics due to atmospheric turbulence

A large number of model probability density functions (PDFs) are used to analyze atmospheric scintillation statistics. We have analyzed scintillation data from two different experimental setups covering a range of scintillation strengths to determine which candidate model PDFs best describe the experimental data. The PDFs were fitted to the experimental data using the method of least squares. The root-mean-squared fitting error was used to monitor the goodness of fit. The results of the fitting were found to depend strongly on the scintillation strength. We find that the log normally modulated Rician and the log normal PDFs are the best fit to the experimental data over the range of scintillation strengths encountered.     

A contemporary view of coronal heating

Determining the heating mechanism (or mechanisms) that causes the outer atmosphere of the Sun, and many other stars, to reach temperatures orders of magnitude higher than their surface temperatures has long been a key problem. For decades, the problem has been known as the coronal heating problem, but it is now clear that 'coronal heating' cannot be treated or explained in isolation and that the heating of the whole solar atmosphere must be studied as a highly coupled system. The magnetic field of the star is known to play a key role, but, despite significant advancements in solar telescopes, computing power and much greater understanding of theoretical mechanisms, the question of which mechanism or mechanisms are the dominant supplier of energy to the chromosphere and corona is still open. Following substantial recent progress, we consider the most likely contenders and discuss the key factors that have made, and still make, determining the actual (coronal) heating mechanism (or mechanisms) so difficult.     

Atomic force microscopy of the morphology and mechanical behaviour of barnacle cyprid footprint proteins at the nanoscale

Barnacles are a major biofouler of man-made underwater structures. Prior to settlement, cypris larvae explore surfaces by reversible attachment effected by a ‘temporary adhesive’. During this exploratory behaviour, cyprids deposit proteinaceous ‘footprints’ of a putatively adhesive material. In this study, footprints deposited by Balanus amphitrite cyprids were probed by atomic force microscopy (AFM) in artificial sea water (ASW) on silane-modified glass surfaces. AFM images obtained in air yielded better resolution than in ASW and revealed the fibrillar nature of the secretion, suggesting that the deposits were composed of single proteinaceous nanofibrils, or bundles of fibrils. The force curves generated in pull-off force experiments in sea water consisted of regions of gradually increasing force, separated by sharp drops in extension force manifesting a characteristic saw-tooth appearance. Following the relaxation of fibrils stretched to high strains, force–distance curves in reverse stretching experiments could be described by the entropic elasticity model of a polymer chain. When subjected to relaxation exceeding 500 ms, extended footprint proteins refolded, and again showed saw-tooth unfolding peaks in subsequent force cycles. Observed rupture and hysteresis behaviour were explained by the ‘sacrificial bond’ model. Longer durations of relaxation (>5 s) allowed more sacrificial bond reformation and contributed to enhanced energy dissipation (higher toughness). The persistence length for the protein chains (L_P) was obtained. At high elongation, following repeated stretching up to increasing upper strain limits, footprint proteins detached at total stretched length of 10 µm.     

Making light work: illuminating the future of biomedical optics

In 1996, the Royal Society held a Discussion Meeting entitled 'Near-infrared spectroscopy and imaging of living systems'. In 2010, this topic was revisited in a Theo Murphy Royal Society Scientific Discussion Meeting entitled 'Making light work: illuminating the future of biomedical optics'. The second meeting provided the opportunity for leading researchers to reflect on how the technology, methods and applications have evolved over the past 14 years and assess where they have made a major impact. Particular emphasis was placed on discussions of future prospects and associated challenges. This Introduction provides an overview of the state of the art of near-infrared spectroscopy (NIRS) and biomedical optics, with specific reference to the contributed papers from the invited speakers included in this issue. Importantly, we also reflect on the contributions from all of the attendees by highlighting the issues raised during oral presentations, facilitated panel sessions and discussions, and use these to summarize the current opinion on the development and application of optical systems for use in the clinical and life sciences. A notable outcome from the meeting was a plan to establish a biennial international conference for developers and users of NIRS technologies.