Atomistic Simulations of P(NDI2OD-T2) Morphologies: From Single Chain to Condensed Phases

We investigate theoretically the structure, crystallinity, and solubility of a high-mobility n-type semiconducting copolymer, P(NDI2OD-T2), and we propose a set of new force field parameters. The force field is reparametrized against density functional theory (DFT) calculations, with the aim to reproduce the correct torsional angles that govern the polymer chain flexibility and morphology. We simulate P(NDI2OD-T2) oligomers in different environments, namely, in vacuo, in the bulk phase, and in liquid toluene and chloronaphthalene solution. The choice of these solvents is motivated by the fact that they induce different kinds of molecular preaggregates during the casting procedures, resulting in variable device performances. Our results are in good agreement with the available experimental data; the polymer bulk structure, in which the chains are quite planar, is correcly reproduced, yet the isolated chains are flexible enough to fold in vacuo. We also calculate the solubility of P(NDI2OD-T2) in toluene and chloronaphthalene, predicting a much better solubility of the polymer in the latter, also in accordance to experimental observations. Different morphologies and dynamics of the oligomers in the two solvents have been observed. The proposed parameters make it possible to obtain the description of P(NDI2OD-T2) in different environments and can serve as a basis for extensive studies of this polymer semiconductor, such as, for example, the dynamics of aggregation in solvent

Assessment of Structural Traits and Management Related to Dairy Herds in the Peri-urban Area of Bobo Dioulasso (South West of Burkina Faso)

To define mean herd size, structural traits, animal sourcing and use, management and aspects related to the milk production, 118 dairy herds, involved in a FAO dairy development project were studied. The mean herd size after allocation to clusters: Small (≤38 heads), Medium (>38, ≤61 heads) and Large (>61 heads) was 52.8±25.8, ranging from 7 to 134 heads of cattle. The following genotypes: Cross bred (CR) 58.8%, Zebu (ZB) 23.2% and Taurine cattle (TA) 18.0% which were not uniformly distributed neither across nor within herds were identified. Sex ratio was two thirds of females (70.6%), one third of males (28.1%) and a low proportion (1.3%) of castrated males. No mature TA males compared to 53.3% of the male ZB and 31.4% of the male CR, were indicated as potential sires. Investments in purchase of animals were higher in Small than in Medium and Large herds; of all purchased sires 53.8% were found in Small herds vs. 28.2% and 18.0% in Medium and Large. Herd property was equally distributed between single (56.8%) and multi property (43.2%). There was more manpower available per 100 cows in Small, being almost double and triple than in Medium and Large herds. Although milk extracted, was similar in all clusters averaging 2.4±0.5 litres/day/cow, milk off take rate, due to higher proportion of lactating cows, appeared higher in Small herds

Epitaxial growth and thermodynamic stability of SrIrO3/SrTiO3 heterostructures

Obtaining high-quality thin films of 5d transition metal oxides is essential to explore the exotic semimetallic and topological phases predicted to arise from the combination of strong electron correlations and spin-orbit coupling. Here, we show that the transport properties of SrIrO3 thin films, grown by pulsed laser deposition, can be optimized by considering the effect of laser-induced modification of the SrIrO3 target surface. We further demonstrate that bare SrIrO3 thin films are subject to degradation in air and are highly sensitive to lithographic processing. A crystalline SrTiO3 cap layer deposited in-situ is effective in preserving the film quality, allowing us to measure metallic transport behavior in films with thicknesses down to 4 unit cells. In addition, the SrTiO3 encapsulation enables the fabrication of devices such as Hall bars without altering the film properties, allowing precise (magneto)transport measurements on micro- and nanoscale devices.Comment: 5 pages, 3 figure

Electronic and optical properties of families of polycyclic aromatic hydrocarbons: a systematic (time-dependent) density functional theory study

Homologous classes of Polycyclic Aromatic Hydrocarbons (PAHs) in their crystalline state are among the most promising materials for organic opto-electronics. Following previous works on oligoacenes we present a systematic comparative study of the electronic, optical, and transport properties of oligoacenes, phenacenes, circumacenes, and oligorylenes. Using density functional theory (DFT) and time-dependent DFT we computed: (i) electron affinities and first ionization energies; (ii) quasiparticle correction to the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gap; (iii) molecular reorganization energies; (iv) electronic absorption spectra of neutral and $\pm1$ charged systems. The excitonic effects are estimated by comparing the optical gap and the quasiparticle corrected HOMO-LUMO energy gap. For each molecular property computed, general trends as a function of molecular size and charge state are discussed. Overall, we find that circumacenes have the best transport properties, displaying a steeper decrease of the molecular reorganization energy at increasing sizes, while oligorylenes are much more efficient in absorbing low-energy photons in comparison to the other classes.Comment: 26 pages, 9 figures, 4 tables, accepted for pubblication in Chemical Physics (14/04/2011

Social Media, Professional Media, and Mobilization in Contemporary Britain:Explaining the Strengths and Weaknesses of the Citizens’ Movement 38 Degrees

This article was published in the journal Political Studies [SAGE © The Author(s)] and the definitive version is available at: https://doi.org/10.1177/0032321716631350Digital media continue to reshape political activism in unexpected ways. Within a period of a few years, the internet-enabled UK citizens’ movement 38 Degrees has amassed a membership of 3 million and now sits alongside similar entities such as America’s MoveOn, Australia’s GetUp! and the transnational movement Avaaz. In this article, we contribute to current thinking about digital media and mobilisation by addressing some of the limitations of existing research on these movements and on digital activism more generally. We show how 38 Degrees’ digital network repertoires coexist interdependently with its strategy of gaining professional news media coverage. We explain how the oscillations between choreographic leadership and member influence and between digital media horizontalism and elite media-centric work constitute the space of interdependencies in which 38 Degrees acts. These delicately balanced relations can quickly dissolve and be replaced by simpler relations of dependence on professional media. Yet despite its fragility, we theorise about how 38 Degrees may boost individuals’ political efficacy, irrespective of the outcome of individual campaigns. Our conceptual framework can be used to guide research on similar movements

Fermi Surface Topology and Rashba-Edelstein Charge-Spin Conversion in Lead-Halide Perovskites

The conversion of charge current into spin current by the Rashba-Edelstein effect enables the reciprocal control of electron charge and magnetization in magnetoelectric and magneto-optical devices. The fundamentals of this effect are described in 3D lead-halide perovskites: due to spin-momentum locking, a strong charge-spin conversion, widely tunable by the injected charge density, is envisaged. The analysis highlights the close relationship between charge-spin conversion and the topological transition occurring from the low-density, torus-shaped Fermi surface (genus 1) to the high-density, simply connected Fermi surfaces (genus 0). At room temperature, spin-polarizations as large as approximate to 10% are obtained for input charge currents in the approximate to 102 to 106 Acm(-2) range; at low temperature, almost full spin-polarization can be achieved, owed to the large, impurity scattering-limited mobilities. The results qualify lead-halide perovskites as suitable materials for spin-orbitronic applications

Mean Field Theory of Josephson Junction Arrays with Charge Frustration

Using the path integral approach, we provide an explicit derivation of the equation for the phase boundary for quantum Josephson junction arrays with offset charges and non-diagonal capacitance matrix. For the model with nearest neighbor capacitance matrix and uniform offset charge $q/2e=1/2$, we determine, in the low critical temperature expansion, the most relevant contributions to the equation for the phase boundary. We explicitly construct the charge distributions on the lattice corresponding to the lowest energies. We find a reentrant behavior even with a short ranged interaction. A merit of the path integral approach is that it allows to provide an elegant derivation of the Ginzburg-Landau free energy for a general model with charge frustration and non-diagonal capacitance matrix. The partition function factorizes as a product of a topological term, depending only on a set of integers, and a non-topological one, which is explicitly evaluated.Comment: LaTex, 24 pages, 8 figure

Photoprotection in metal halide perovskites by ionic defect formation

Photostability is critical for long-term solar cell operation. While light-triggered defects are usually reported as evidence of material degradation, we reveal that the formation of certain defects in metal halide perovskites is crucial for protection against intense or prolonged light exposure. We identify an inherent self-regulating cycle of formation and recovery of ionic defects under light exposure that mitigates the overheating of the lattice due to hot carrier cooling, which allows exposure to several thousand suns without degrading. The excess energy instead dissipates by forming defects, which in turn alters the optoelectronic properties of the absorber, resulting in a temporary reduction of photon absorption. Defects gradually recover to restore the original optoelectronic properties of the absorber. Photoprotection is a key feature for the photostability in plants. Thus, finding a protection mechanism in metal halide perovskites similar to those in nature is encouraging for the development of long-term sustainable solar cells

The democratic interface: technology, political organization, and diverging patterns of electoral representation

Democracies are experiencing historic disruptions affecting how people engage with core institutions such as the press, civil society organizations, parties, and elections. These processes of citizen interaction with institutions operate as a democratic interface shaping self-government and the quality of public life. The electoral dimension of the interface is important, as its operation can affect all others. This analysis explores a growing left-right imbalance in the electoral connection between citizens, parties, elections, and government. This imbalance is due, in part, to divergent left-right preferences for political engagement, organization, and communication. Support on the right for clearer social rules and simpler moral, racial and nationalist agendas are compatible with hierarchical, leader-centered party organizations that compete more effectively in elections. Parties on the left currently face greater challenges engaging citizens due to the popular meta-ideology of diversity and inclusiveness and demands for direct or deliberative democracy. What we term connective parties are developing technologies to perform core organizational functions, and some have achieved electoral success. However, when connective parties on the left try to develop shared authority processes, online and offline, they face significant challenges competing with more conventionally organized parties on the right

Colloidal synthesis and characterization of Bi2S3 nanoparticles for photovoltaic applications

Bismuth sulfide is a promising n-type semiconductor for solar energy conversion. We have explored the colloidal synthesis of Bi2S3 nanocrystals, with the aim of employing them in the fabrication of solution-processable solar cells and to replace toxic heavy metals chalcogenides like PbS or CdS, that are currently employed in such devices. We compare different methods to obtain Bi2S3 colloidal quantum dots, including the use of environmentally benign reactants, through organometallic synthesis. Different sizes and shapes were obtained according to the synthesis parameters and the growth process has been rationalized by comparing the predicted morphology with systematic physical-chemistry characterization of nanocrystals by X-ray diffraction, FT-IR spectroscopy, Transmission Electron Microscopy (TEM)