689 research outputs found
Review of morphology dependent charge carrier mobility in MEH-PPV
Charge carrier mobility in poly(2-methoxy,5(2'-ethyl-hexyloxy)-p-phenylene vinylene) (MEH-PPV) films were measured as a function of temperature and electric field parallel and perpendicular to the substrate for devices prepared from different solvents and under different processing conditions Bulk structural morphology was characterized by various X-ray diffraction measurements such as wide angle, small angle and X-ray reflection. Surface morphology was characterized using various scanning probe microscopic techniques Mobilities were found to follow Gaussian disorder model (GDM) and to be highly anisotropic not only depending on the solvents used but also on the film preparation method such as spin-coating or drop-casting While no direct correlation was found between charge carrier mobility and photoluminescence, charge transport parameters were correlated with structural morpholog
Calibration and Uncertainty Quantification of Convective Parameters in an Idealized GCM
Parameters in climate models are usually calibrated manually, exploiting only
small subsets of the available data. This precludes both optimal calibration
and quantification of uncertainties. Traditional Bayesian calibration methods
that allow uncertainty quantification are too expensive for climate models;
they are also not robust in the presence of internal climate variability. For
example, Markov chain Monte Carlo (MCMC) methods typically require
model runs and are sensitive to internal variability noise, rendering them
infeasible for climate models. Here we demonstrate an approach to model
calibration and uncertainty quantification that requires only model
runs and can accommodate internal climate variability. The approach consists of
three stages: (i) a calibration stage uses variants of ensemble Kalman
inversion to calibrate a model by minimizing mismatches between model and data
statistics; (ii) an emulation stage emulates the parameter-to-data map with
Gaussian processes (GP), using the model runs in the calibration stage for
training; (iii) a sampling stage approximates the Bayesian posterior
distributions by sampling the GP emulator with MCMC. We demonstrate the
feasibility and computational efficiency of this calibrate-emulate-sample (CES)
approach in a perfect-model setting. Using an idealized general circulation
model, we estimate parameters in a simple convection scheme from synthetic data
generated with the model. The CES approach generates probability distributions
of the parameters that are good approximations of the Bayesian posteriors, at a
fraction of the computational cost usually required to obtain them. Sampling
from this approximate posterior allows the generation of climate predictions
with quantified parametric uncertainties
High brightness solution-processed OLEDs employing linear, small molecule emitters
Two novel linear oligomers that can be solution-processed to form green organic light-emitting diodes (OLEDs) are reported. Each oligomer has a donor-acceptor structure, incorporating a benzothiadiazole core with bifluorene arms attached at the 4- and 7-positions. Further electron donor behaviour is inferred from a terminal triphenylamine unit in Green 2. The resulting solution-processed OLEDs exhibited excellent performance, with a maximum luminance of 20 388 cd m-2 recorded for Green 2
A discursive psychology analysis of emotional support for men with colorectal cancer
Recent research into both masculinity and health, and the provision of social support for people with cancer has focussed upon the variations that may underlie broad assumptions about masculine health behaviour. The research reported here pursues this interest in variation by addressing the discursive properties of talk about emotional support, by men with colorectal cancer - an understudied group in the social support and cancer literature. Semi-structured interviews were conducted with eight men with colorectal cancer, and the transcripts analysed using an intensive discursive psychology approach. From this analysis two contrasting approaches to this group of menâs framing of emotional support in the context of cancer are described. First, talk about cancer was positioned as incompatible with preferred masculine identities. Second, social contact that affirms personal relationships was given value, subject to constraints arising from discourses concerning appropriate emotional expression. These results are discussed with reference to both the extant research literature on masculinity and health, and their clinical implications, particularly the advice on social support given to older male cancer patients, their families and friends
BODIPY-based conjugated polymers for broadband light sensing and harvesting applications
The synthesis of novel low band-gap polymers has significantly improved light sensing and harvesting in polymer-fullerene devices. Here the synthesis of two low band-gap polymers based on the 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene core (BODIPY), and either bis(3,4-ethylenedioxythiophene) (bis-EDOT) or its all-sulfur analogue bis(3,4-ethylenedithiathiophene) (bis-EDTT) are described. The polymers demonstrate ambipolar charge transport and are shown to be suitable for broadband light sensing and solar energy harvesting in solution-processable polymer-fullerene devices
Thiazole-induced rigidification in substituted dithieno-tetrathiafulvalene : the effect of planarisation on charge transport properties
Two novel tetrathiafulvalene (TTF) containing compounds 1 and 2 have been synthesised via a four-fold Stille coupling between a tetrabromo-dithienoTTF 5 and stannylated thiophene 6 or thiazole 4. The optical and electrochemical properties of compounds 1 and 2 have been measured by UV-vis spectroscopy and cyclic voltammetry and the results compared with density functional theory (DFT) calculations to confirm the observed properties. Organic field effect transistor (OFET) devices fabricated from 1 and 2 demonstrated that the substitution of thiophene units for thiazoles was found to increase the observed charge transport, which is attributed to induced planarity through S-N interactions of adjacent thiazole nitrogen atoms and TTF sulfur atoms and better packing in the bulk
An air-stable DPP-thieno-TTF copolymer for single-material solar cell devices and field effect transistors
Following an approach developed in our group to incorporate tetrathiafulvalene (TTF) units into conjugated polymeric systems, we have studied a low band gap polymer incorporating TTF as a donor component. This polymer is based on a fused thieno-TTF unit that enables the direct incorporation of the TTF unit into the polymer, and a second comonomer based on the diketopyrrolopyrrole (DPP) molecule. These units represent a donorâacceptor copolymer system, p(DPP-TTF), showing strong absorption in the UVâvisible region of the spectrum. An optimized p(DPP-TTF) polymer organic field effect transistor and a single material organic solar cell device showed excellent performance with a hole mobility of up to 5.3 Ă 10â2 cm2/(V s) and a power conversion efficiency (PCE) of 0.3%, respectively. Bulk heterojunction organic photovoltaic devices of p(DPP-TTF) blended with phenyl-C71-butyric acid methyl ester (PC71BM) exhibited a PCE of 1.8%
Streaming instabilities in converging geometry
We present an investigation into counter-streaming electron beams converging towards, and diverging from, a single point in two dimensions, leading to two-stream and current filamentation instabilities, which have radial and azimuthal density modulations, respectively. Using a semi-analytical approach and numerical simulations, we find no evidence for the two-stream instability in this geometry, but show that the system is unstable to the development of current filamentation
Observational and theoretical evidence for frictional-viscous flow at shallow crustal levels
Along the Hikurangi Subduction Margin, accretionary prism uplift has exposed the Hungaroa fault zone, an inactive thrust developed within the Middle to Late Eocene Wanstead Formation. Within the ~33 m-wide fault core, deformation of the smectitic, calcareous mudstone matrix produced a penetrative foliation that locally wraps around clasts. Deformation occurred at temperatures constrained by syntectonic calcite vein clumped isotope thermometry, which yielded a narrow range of Î47 values between 0.445 ± 0.024â° and 0.482 ± 0.013â°, corresponding to a mean calcite precipitation temperature of 82â12+13 °C. Optical and scanning electron microscopy analyses reveal that calcite underwent: dissolution along stylolites and clast, vein, and microlithon margins; precipitation in foliation-parallel and foliation-perpendicular extension veins; and precipitation in hybrid veins and strain fringes. Maximum differential stress estimates obtained from calcite twin densities (44.1 ± 13.9 to 96.6 ± 20.8 MPa) are consistent with those sustainable by a cohesionless fault at ~3 km depth with a friction coefficient in the range measured for two calcareous mudstones (ÎŒ = 0.38 to 0.50) and a micrite clast (ÎŒ = 0.61 and 0.64). Marlstone clasts within the foliated calcareous mudstone matrix contain mutually cross-cutting shear fractures and extension veins with crack-seal textures, providing evidence for temporal fluctuations in shear strength resulting from pore fluid overpressure transients. At strain rates imposed during laboratory experiments, frictional sliding involves granular flow processes. Yet, calcite microstructures indicate that diffusive mass transfer played an important role in accommodating deformation. We model the fault zone rheology assuming diffusion-controlled frictional-viscous flow, with deformation at strain rates γˆ10â9 sâ1 able to have taken place at very low shear stresses (Ï < 10 MPa) given sufficiently short diffusion distances (d < 0.1 mm), even in the absence of pore fluid overpressures. However, if grain-scale and fracture-scale processes change the diffusion distance, fault zones deforming via frictional-viscous flow can exhibit temporally variable strain rates. Thus, our results suggest that the shallow (up-dip) limit of the seismogenic zone is not a simple function of temperature in fault zones governed by a frictional-viscous flow rheology
Somatic mutations and clonal dynamics in healthy and cirrhotic human liver.
The most common causes of chronic liver disease are excess alcohol intake, viral hepatitis and non-alcoholic fatty liver disease, with the clinical spectrum ranging in severity from hepatic inflammation to cirrhosis, liver failure or hepatocellular carcinoma (HCC). The genome of HCC exhibits diverse mutational signatures, resulting in recurrent mutations across more than 30 cancer genes1-7. Stem cells from normal livers have a low mutational burden and limited diversity of signatures8, which suggests that the complexity of HCC arises during the progression to chronic liver disease and subsequent malignant transformation. Here, by sequencing whole genomes of 482 microdissections of 100-500 hepatocytes from 5 normal and 9 cirrhotic livers, we show that cirrhotic liver has a higher mutational burden than normal liver. Although rare in normal hepatocytes, structural variants, including chromothripsis, were prominent in cirrhosis. Driver mutations, such as point mutations and structural variants, affected 1-5% of clones. Clonal expansions of millimetres in diameter occurred in cirrhosis, with clones sequestered by the bands of fibrosis that surround regenerative nodules. Some mutational signatures were universal and equally active in both non-malignant hepatocytes and HCCs; some were substantially more active in HCCs than chronic liver disease; and others-arising from exogenous exposures-were present in a subset of patients. The activity of exogenous signatures between adjacent cirrhotic nodules varied by up to tenfold within each patient, as a result of clone-specific and microenvironmental forces. Synchronous HCCs exhibited the same mutational signatures as background cirrhotic liver, but with higher burden. Somatic mutations chronicle the exposures, toxicity, regeneration and clonal structure of liver tissue as it progresses from health to disease.This work was supported by a Wellcome Trust and Cancer Research UK (CRUK) Grand Challenge Award (C98/A24032). P.J.C. is a Wellcome Trust Senior Clinical Fellow (WT088340MA); S.F.B. was supported by the Swiss National Science Foundation (P2SKP3-171753 and P400PB-180790); M.A.S. is supported by a Rubicon fellowship from NWO (019.153LW.038); the Cambridge Human Research Tissue Bank is supported by the NIHR Cambridge Biomedical Research Centre; and M.H. is supported by a CRUK Clinician Scientist Fellowship (C52489/A19924)
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