RESUMO -(Atividade alelopática de extratos aquosos de Aristolochia esperanzae O. Kuntze na germinação e no crescimento de Lactuca sativa L. e Raphanus sativus L.). O objetivo deste trabalho foi analisar os efeitos de extratos aquosos de diferentes órgãos de Aristolochia esperanzae na germinação e no crescimento de alface e rabanete. Todos os extratos preparados obedeceram à proporção de 100g de material vegetal fresco para 300mL de água destilada, que produziu o extrato considerado 100% concentrado. A partir deste, foram feitas diluições com água destilada para 75, 50 e 25%. Nos testes de germinação foram avaliados os efeitos dos extratos obtidos de folha, caule, raiz, fruto e flor a 100, 75, 50 e 25%. Para o teste de crescimento foram utilizados extratos de folha, caule e raiz na concentração de 100 e 50%. Nos testes de germinação foram utilizadas quatro repetições de 30 sementes distribuídas em placas de Petri forradas com duas folhas de papel de filtro umedecidas com 5 mL dos referidos extratos, secas durante 12h e reumedecidas com 4,5mL de água destilada. No primeiro teste avaliou-se a percentagem e a velocidade de germinação das sementes. No teste de crescimento, as sementes foram previamente germinadas (2-4mm de radícula) e depois transferidas para caixas plásticas contendo os substratos de papel de filtro e fibra de coco umedecidos com os respectivos extratos. Avaliou-se a altura da parte aérea, o comprimento radicular, a massa seca das plântulas e a presença de anormalidades nas plântulas. Os testes foram mantidos à temperatura constante de 27ºC. Através dos resultados obtidos pode-se concluir que os extratos de folha foram os que mais afetaram a percentagem de germinação e que todos os extratos e as diferentes concentrações retardaram a germinação de sementes de alface e de rabanete. Quanto ao teste de crescimento, podese verificar que os extratos de caule e de raiz causaram anormalidades nas plântulas. As plântulas crescidas no substrato papel de filtro apresentaram maior inibição do crescimento, em relação àquelas crescidas no substrato fibra de coco. A concentração dos extratos foi a principal responsável pelo estímulo ou inibição causada no crescimento das plântulas de alface e rabanete.Palvras-chave: alelopatia, Aristolochia, alface, rabanete ABSTRACT -(Allelopathic activity of aqueous extracts of Aristolochia esperanzae O. Kuntze in the germination and growth of Lactuca sativa L. and Raphanus sativus L.). This work analyzed the effects of aqueous extracts of Aristolochia esperanzae organs in the germination and initial growth of lettuce and radish. All the extracts were prepared using 100g of plant fresh material + 300mL of distilled water to produce the extract 100% concentrated. This extract was diluted with distilled water to produce a final concentrations of 75, 50 and 25%. The germination was evaluated by tests using the extracts of leaf, stem, root, fruit and flower, with concentration of 100, 75, 50, and 25%. In the seedlings growth, the extracts of leaf, stem, and root were used in the con...

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Neste trabalho, objetivou-se avaliar o efeito alelopático de caules e folhas de Andira humilis na germinação de sementes e no crescimento de plântulas de rabanete e alface. Para os experimentos de germinação foram preparados extratos aquosos de caules e folhas de A. humilis nas concentrações de 0, 4, 8, 12 e 16% (p/v). Foram realizadas quatro réplicas de trinta sementes de alface ou de rabanete, distribuídas em placas de Petri forradas com papel-filtro umedecido com 5mL dos extratos, mantidas a 27 ºC e na ausência de luz. As contagens das sementes germinadas foram realizadas a cada 12h, calculando-se a percentagem e a velocidade de germinação. Extratos de caules e folhas reduziram significativamente a velocidade e a percentagem de germinação, em relação ao grupo controle. Os experimentos de crescimento foram realizados com quatro réplicas de oito sementes germinadas de alface ou de rabanete, a 27 ºC, na ausência de luz e em papel-filtro como substrato, sendo avaliadas as concentrações 0, 4 e 12% (p/v). Plântulas de alface e rabanete sofreram inibição significativa em seus comprimentos, pelos extratos de folhas. Extratos de caules a 4 e 12% (p/v) não causaram inibição do crescimento em rabanete. A interferência dos extratos na germinação e no crescimento em alface e rabanete foi desassociada de qualquer efeito do potencial osmótico e do pH, indicando, portanto, atividade alelopática.

Abstract:Species interactions have been recently depicted as networks, in which each species is connected to one or more other species in binary interaction matrices. Forty networks of epiphytic orchid and host tree species were assessed in Brazilian gallery forests. The nestedness of the networks was estimated with the NODF index and the significance was tested with null models. The phylogenetic structure of the network was also assessed, by searching for phylogenetic signals in the number of interactions and in the similarity of interacting species. In total, 105 orchid species and 132 host tree species were sampled. A nested pattern in all orchid–host tree networks was found. However, phylogenetic signals were not observed. The results support that the host specificity of orchids is small and most of the interactions occur among generalist orchids and generalist host trees. While the concept of species-specificity can thus be rejected, the extreme alternative – that interacting orchids and host trees are not a random subset of the regional species pool – can be dismissed as well. However, factors other than phylogenetic history may structure interaction networks of epiphytic orchids and host trees.

Transition metal dichalcogenides (TMDs) offer a platform for obtaining two-dimensional materials with excellent properties for diverse applications. However, the exploration of the properties of two-dimensional TMDs based on transition metals from Fe, Co, Ni, and Cu groups is scarce. Therefore, to contribute to the understanding of these materials, we performed a density functional theory investigation of 36 MQ 2 compounds (M = Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Os, Ir, Pt, Ag, Au; Q = S, Se, Te), employing for each of them layered and nonlayered crystal structural phases previously reported for TMDs. We found that layered crystal structures are energetically favored for Ni group compounds and that the intralayer octahedral coordination has lower energy than the trigonal prismatic phase for all compositions. The layered phases Fe and Ni group compounds have weak interlayer binding dominated by van der Waals interactions, whereas the remaining materials have high exfoliation energies. We identified 17 semiconductor monolayers among the lowest energy layered phases, with band gaps that vary from 0.45 to 2.62 eV, and their valence and conduction band offsets are mainly determined by the positions of M d-states and Q p-states, which contribute both to the valence and conduction edge states. Semiconductor heterojunctions that can be formed with the stacking of monolayers were mostly classified into type-II band alignments, whereas type-I heterojunctions are more likely formed with Ni group TMDs. Estimates for the power conversion efficiency of solar cells based on the type-II heterojunctions resulted in 10 systems with efficiency > 15%, suggesting potential application in photovoltaic devices. This study unveils the understanding of the properties of TMDs of the groups 8–11, paving the way for the design of their van der Waals heterostructures.

Lead-free all-inorganic perovskites have been widely investigated as alternative materials to replace organic lead-based perovskites in solar cells. Although thousands of studies have been reported, several questions remain in debate, e.g., the role of structural phases and octahedra distortions in the optoelectronic and excitonic properties. Here, we report a theoretical investigation of those effects in the CsGeX3 (X = Cl, Br, I) perovskites by the combination of hybrid density functional theory calculations, spin–orbit coupling for the valence states, maximally localized Wannier functions tight-binding framework, and solution of the Bethe–Salpeter equation (BSE). In contrast to CsGeCl3 and CsGeBr3, which has an energetic preference for distorted cubic structures, hexagonal phases yield the lowest energy for CsGeI3, i.e., the X atomic radius plays an important role in the relative stability. Our results show that octahedra distortion lowers the total energy and increases the energy band gap substantially (above 1.0 eV), which can be explained by volume increasing and Jahn–Teller symmetry breaking that affects the character of the valence band maximum and conduction band minimum. From our BSE calculations, the quasi-particle effects are weak in the absorption coefficient; however, its magnitude depends on the structure phase and octahedra distortions. The spectroscopy limited maximum efficiency approach yields almost constant power conversion efficiency, despite substantial variations in the band gaps. The obtained values are consistent with experimental results in contrast to the Shockley–Queisser limit. We also predict the existence of optimal thickness for maximum efficiency, which (for example) is about 11.6 μm for the super cubic CsGeCl3.

We have performed an ab initio investigation of the electronic properties of the graphene sheet adsorbed by Ru adatoms (Ru/graphene). For a particular set of triangular arrays of Ru adatoms, we find the formation of four (spin-polarized) Dirac cones attributed to a suitable overlap between two hexagonal lattices: one composed by the C sites of the graphene sheet, and the other formed by the surface potential induced by the Ru adatoms. Upon the presence of spin-orbit coupling (SOC) nontrivial band gaps take place at the Dirac cones promoting several topological phases. Depending on the Ru concentration, the system can be topologically characterized among the phases i) Quantum Spin Hall (QSH), ii) Quantum Anomalous Hall(QAH), iii) metal iv) or trivial insulator. For each concentration, the topological phase is characterized by the ab-initio calculation of the Chern number.