331 research outputs found
Molecular modeling of low bandgap diblock co-oligomers with <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"><mml:mrow><mml:mi>π</mml:mi></mml:mrow></mml:math>-bridges for applications in photovoltaics
No full textFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Processo FAPESP: 2012/21983-0Processo FAPESP: 2014/20410-1Processo FAPESP: 2016/18499-0CAPES: 23038.004680/2015-01CNPq: 448310/2014-7CAPES: 88881.068492/2014-01Recently, the diblock co-oligomers concept, a new design method to obtain conjugated organic compounds for varied applications in photovoltaics was proposed. These materials combines the interesting properties of extended systems and the versatility of small molecules, leading to low bandgap materials with improved properties, such as adjustable open circuit voltages and promising optical responses. Aiming to evaluate possible improved routes for the design of such materials, in this report we present a study on the effect of π-bridges incorporation on the properties of diblock co-oligomers. Six different π-bridges were inserted between polythiofene (Th) and polypyrrol (Py) oligomers with five units, following the structure [Th]5-[π-bridge]-[Py]5. The geometry optimization and optical absorption studies were carried out in the density functional theory (DFT) and time dependent-DFT (TD-DFT) frameworks, respectively, using the B3LYP correlation-exchange functional and 6-31G(d,p) basis set. The results point out that compounds with improved opto-electronic properties can be obtained by an appropriated choice of the π-bridges. The possible improvements are associated with the higher delocalization of the π-systems on the molecules, reduction of the effective optical/electronic bandgaps, high optical transition probability between the new highest occupied and lowest unoccupied molecular levels (HOMO–LUMO), optimized charge transport properties and reduced exciton dissociation energies
Interaction between components of polymeric light emitting electrochemical cells: A DFT case study for MDMO-PPV/KCF3SO3/PEO system
No full textPolymer light emitting electrochemical cells (PLECs) are organic electronic devices that define interesting alternatives to organic light-emitting devices. However, despite their potential application, some of the basic operational mechanisms involved in their operation are still not completely understood. In this context, here we report a theoretical attempt to unravel some basic aspects on this subject considering a model system based on poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4- phenylene vinylene] (MDMO-PPV), potassium(I) trifluoromethanesulfonate (KCF3SO3) and polyethylene oxide (PEO). Structural and reactivity properties of the constituents were evaluated via DFT-based electronic structure calculations. Condensed-to-atoms Fukui indexes were estimated via Hirshfeld partition charge to identify preferred sites for PLEC component's interactions. The results suggest that the presence of ionic salt induces significant changes on the semiconducting polymer's electronic properties, which are dependent on the number of salt molecules and their oxidation state, influencing the devices’ charge dynamics (injection and transport), reinforcing previous results obtained for other similar systems.São Paulo State University (UNESP) School of Sciences Posmat, SPSão Paulo State University (UNESP) School of Sciences Physics Department, SPSão Paulo State University (UNESP) Institute of Sciences and Engineering, SPSão Paulo State University (UNESP) School of Sciences Posmat, SPSão Paulo State University (UNESP) School of Sciences Physics Department, SPSão Paulo State University (UNESP) Institute of Sciences and Engineering, S
Reactivity of eumelanin building blocks: A DFT study of monomers and dimers
No full textMelanins are natural pigments with important biological properties and have been considered promising materials for several bio-electronic applications. In spite of it, until now there is no satisfactory understanding of the macromolecular structure of these compounds. In this work, we have employed electronic structure calculations to evaluate the local reactivity on monomeric building blocks of eumelanin and on a varied combination of these units (dimers). The reactivity studies were accomplished by Condensed-to-Atoms Fukui Indexes in a DFT approach. The results have evidenced a dominance order in the reactivity of the building units that guides the polymerization process of melanin. In addition, from the differences of the local reactivities it was possible to better understand the reactions that can take place during eumelanin synthesis and estimate how they could be influenced by experimental conditions.Universidade Estadual PaulistaFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)São Paulo State University (UNESP) School of Sciences Postgraduate Program in Materials Science and Technology (POSMAT)São Paulo State University (UNESP) School of Sciences Department of PhysicsSão Paulo State University (UNESP), Campus of ItapevaSão Paulo State University (UNESP) School of Sciences Postgraduate Program in Materials Science and Technology (POSMAT)São Paulo State University (UNESP) School of Sciences Department of PhysicsSão Paulo State University (UNESP), Campus of ItapevaFAPESP: 2012/03116-7FAPESP: 2013/07296-2CNPq: 420449/2018-3CNPq: 448310/2014-7CAPES: 88882.330142/2019–0
DFT-guided design of melanin-inspired materials for high-performance organic solar cells
No full textInternational audienceOrganic solar cells (OSCs) have rapidly emerged as a promising alternative to traditional photovoltaic technologies, such as crystalline silicon, due to their potential for low-cost, lightweight, and flexible applications. The development of efficient, non-toxic, and earth-abundant materials has motivated the transition from fullerene-based acceptors to non-fullerene counterparts. While current non-fullerene acceptors offer improved spectral absorption, they still present limitations in terms of absorption bandwidth and exciton dissociation efficiency, which constrain overall device performance. In this work, we designed and computationally evaluated a series of donor and acceptor molecules based on Y6 derivatives and melanin-inspired motifs. Specifically, we investigated the effect of incorporating hydroxyindole-based end groups (EGmel) into the Y6 core structure using density functional theory (DFT). Our findings show that the presence of EGmel broadens optical absorption (red-shift of Δλmax up to ≈ 83.61 nm with gap reduction of up to ΔEgap ≈ −0.28 eV) and enhances electron-donating/acceptance capabilities (up to ΔRD ≈ −0.07 and ΔRA ≈ 0.10), key traits for high-performance OSCs. Furthermore, we assessed a set of melanin-like oligomers as potential donor materials, which showed open-circuit voltage predictions comparable to benchmark donors such as PM6 and D18. These findings underscore the potential of bio-inspired modifications, such as hydroxyindole end groups and indolic donor cores, to improve the performance and sustainability of next-generation organic photovoltaic materials
Exaptation, Degeneracy and Innovation
No full textIn innovation processes, exaptations are innovation-development processes through which an initial attribution of new functionality to existing artifacts leads to new artifacts and eventually new markets. In this article I focus on the theoretical foundations of these processes, proposing a theoretical framework to analyze them. The essay provides a contribution in the following two directions: • a discussion of the different levels of organization through which exaptations emerge in a market system; • an analysis of the complex links between exaptation and degeneracy (a many-tomany rather than one-to-one map between structure and function). Using this theoretical framework, I focus on the need for an analysis of the consequences of exaptations, arguing that exaptations may contribute to emerging degeneracy, which, in turn, may trigger further exaptations. In market systems one form of degeneracy is the coexistence of many structurally different artifacts providing at least in part the same functionality. I present historical examples that suggest that degeneracy increases the complexity of the system: the attribution of functionality previously provided by existing artifacts to new artifacts potentially able to provide them in a new way is a significant process giving raise to new artifacts and new marketsInnovation; Exaptation; Degeneracy; Adaptation;
Effect of cutting management and nitrogen supply on yield and quality of Napier grass (Pennisetum purpureum)
No full textIn a series of cutting experiments, average apparent nitrogen recovery of applied fertilizer N by Napier grass was approximately 50%. Incorporation of cattle manure improved nitrogen utilization. Mixtures with Desmodium intortum substantially improved yield and protein content. There was a fair to good relation between morphology and crude protein content and in vitro organic matter digestibility of Napier grass
Literary representations of maternity in the eighteenth century
No full textThe primary concern of this thesis is the representation, in the eighteenth century, of mothers' bodies. It is also concerned with the treatment of domestic duties which were supposed a consequence of a woman's very nature. Throughout the first seven decades of the century, medical men and virtuosi demonstrated particular interest in the nature of physicality, and especially in women's bodies, pregnancy, and childbirth. 1 will be testing out a widely-held view that dissection and new anatomical findings regarding women's bodies produced a new idealisation of motherhood, and that this was immediately translated into lay-medical and related discourse, and was thus firmly established in middle-class culture by the end of the century. The relationship between primary medical and lay-medical literature raises several questions: my work asks whether lay-medical literature mirrored medical writing, and whether there was a direct translation of material from one to the other. Lay-medical texts for women are especially interesting. They offer an insight into precisely what examples of female nature and correspondingly 'natural' behaviour were intended for women readers. Representations of maternity in specific forms of writing which rely heavily upon women for subject matter are further extended in the second half of this study. 1 have focussed upon two genres, conduct literature and narrative fiction. Neither is conventionally associated with medical or lay-medical discourse, yet both have significant links with these. Conduct literature and narrative fiction have much to offer in this attempt to recover what women were being taught about their bodies and roles; both were concerned with what the body displays externally, and with corresponding ideas of 'naturalness'. Conduct literature for women was enjoying a period of growth and change, and has obvious, direct links with medical texts. Narrative fiction also had important links with medical writing, and 1 will describe these. The dissemination of medical representations of the maternal body was a process which contributed to a contradictory cultural sense of female identity
Xanthomonas campestris pv. campestris (cause of black rot of crucifers) in the genomic era is still a worldwide threat to brassica crops
No full textBackground
Xanthomonas campestris pv. campestris (Xcc) (Pammel) Dowson is a Gram-negative bacterium that causes black rot, the most important disease of vegetable brassica crops worldwide. Intensive molecular investigation of Xcc is gaining momentum and several whole genome sequences are available.
Taxonomy
Bacteria; Phylum Proteobacteria; Class Gammaproteobacteria; Order Xanthomonadales; Family Xanthomonadacea; Genus Xanthomonas; Species X. campestris.
Host range and symptoms
Xcc can cause disease in a large number of species of Brassicaceae (ex-Cruciferae), including economically important vegetable Brassica crops and a number of other cruciferous crops, ornamentals and weeds, including the model plant Arabidopsis thaliana. Black rot is a systemic vascular disease. Typical disease symptoms include V-shaped yellow lesions starting from the leaf margins and blackening of the veins.
Race structure, pathogenesis and epidemiology
Collections of Xcc isolates have been differentiated into physiological races based on the response of several brassica species lines. Black rot is a seed-borne disease. The disease is favoured by warm, humid conditions and can spread rapidly from rain dispersal and irrigation water.
Disease control
The control of black rot is difficult and relies on the use of pathogen-free planting material and the elimination of other potential inoculum sources (infected crop debris and cruciferous weeds). Major gene resistance is very rare in B. oleracea (brassica C genome). Resistance is more readily available in other species, including potentially useful sources of broad-spectrum resistance in B. rapa and B. carinata (A and BC genomes, respectively) and in the wild relative A. thaliana.
Genome
The reference genomes of three isolates have been released. The genome consists of a single chromosome of approximately 5 100 000 bp, with a GC content of approximately 65% and an average predicted number of coding DNA sequences (CDS) of 4308.
Important genes identified
Three different secretion systems have been identified and studied in Xcc. The gene clusters xps and xcs encode a type II secretion system and xps genes have been linked to pathogenicity. The role of the type IV secretion system in pathogenicity is still uncertain. The hrp gene cluster encodes a type III secretion system that is associated with pathogenicity. An inventory of candidate effector genes has been assembled based on homology with known effectors. A range of other genes have been associated with virulence and pathogenicity, including the rpf, gum and wxc genes involved in the regulation of the synthesis of extracellular degrading enzymes, xanthan gum and lipopolysaccharides
Global root zone storage capacity from satellite-based evaporation
No full textThis study presents an "Earth observation-based" method for estimating root
zone storage capacity – a critical, yet uncertain parameter in hydrological
and land surface modelling. By assuming that vegetation optimises its root
zone storage capacity to bridge critical dry periods, we were able to use
state-of-the-art satellite-based evaporation data computed with independent
energy balance equations to derive gridded root zone storage capacity at
global scale. This approach does not require soil or vegetation information,
is model independent, and is in principle scale independent. In contrast to
a traditional look-up table approach, our method captures the variability in
root zone storage capacity within land cover types, including in rainforests
where direct measurements of root depths otherwise are scarce. Implementing
the estimated root zone storage capacity in the global hydrological model
STEAM (Simple Terrestrial Evaporation to Atmosphere Model) improved evaporation simulation overall, and in particular during the
least evaporating months in sub-humid to humid regions with moderate to high
seasonality. Our results suggest that several forest types are able to create
a large storage to buffer for severe droughts (with a very long return period),
in contrast to, for example, savannahs and woody savannahs (medium length
return period), as well as grasslands, shrublands, and croplands (very short
return period). The presented method to estimate root zone storage capacity
eliminates the need for poor resolution soil and rooting depth data that form
a limitation for achieving progress in the global land surface modelling community
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