Phononic canonical quasicrystalline waveguides

The dynamic behavior of the class of periodic waveguides whose unit cells are generated through a quasicrystalline sequence can be interpreted geometrically in terms of a trace map that embodies the recursive rule obeyed by traces of the transmission matrices. We introduce the concept of canonical quasicrystalline waveguides, for which the orbits predicted by the trace map at specific frequencies, called canonical frequencies, are periodic. In particular, there exist three families of canonical waveguides. The theory reveals that for those (i) the frequency spectra are periodic and the periodicity depends on the canonical frequencies, (ii) a set of multiple periodic orbits exists at frequencies that differ from the canonical ones, and (iii) perturbation of the periodic orbit and linearization of the trace map define a scaling parameter, linked to the golden ratio, which governs the self-similar structure of the spectra. The periodicity of the waveguide responses is experimentally verified on finite specimens composed of selected canonical unit cells

Ga2O3 polymorphs: Tailoring the epitaxial growth conditions

Gallium oxide is a wide bandgap n-type semiconductor highly interesting for optoelectronic applications (e.g., power electronics and solar blind UV photodetectors). Besides its most thermodynamically stable monoclinic β phase, Ga2O3 can crystallize in different polymorphs; among them the corundum α and the orthorhombic ϵ phases are the most promising ones. In this review we focus on the main aspects that promote the nucleation and stable growth of these Ga2O3 polymorphs. Particular emphasis is given to the ϵ phase since it is recently gaining increasing attention in the scientific community because of: (i) its higher lattice symmetry with respect to β-Ga2O3, which could favour the realization of heterostructures, (ii) the possibility to be grown on cheap sapphire substrates and (iii) its peculiar piezoelectric properties. While the growth of β-Ga2O3 is widely studied and understood, a thorough and comprehensive analysis of the chemical and physical aspects that allow for the stabilization of the metastable Ga2O3 phases with different synthesis methods is still missing. Therefore, the present review aims at filling this gap, by analysing the relevant growth parameters for several growth techniques (MOVPE, HVPE, mist-CVD, MBE, and PLD), highlighting similarities and differences, looking for a unified framework to understand the growth and nucleation of different Ga2O3 polymorphs. As a conclusion, we highlight practical guidelines for the deposition of the different Ga2O3 polymorphs with all the discussed thin film growth techniques

Carbon based substrates for interfacing neurons: Comparing pristine with functionalized carbon nanotubes effects on cultured neuronal networks

Pristine (as prepared) carbon nanotube (CNT) based substrates have been widely used to grow and interface neurons in culture. Nerve cells normally differentiate on CNTs and the synaptic networks, newly formed at the interface with this material, usually show an improved robustness in signal transfer. However manipulation of pristine CNTs is often prevented by their low dispersibility and tendency to aggregate in most solvents. This issue can be at least partially solved by adding solubilizing groups to the surface of CNT, which also helps improving their biocompatibility. It becomes therefore of crucial importance to determine whether chemically manipulated CNTs may maintain their performance in improving nerve signaling. Here we study and compare the impact in vitro on neuronal signaling of two classes of chemically modified multiwalled CNTs in reference to pristine CNTs, which are known to be a substrate able to boost neuronal growth and communication. We found that the extent of functionalization and the nature of the functional groups on MWNT sidewalls affect the conductivity and the biological effects of the final derivatives. This information is important for the future design of biointegrated devices

Efeito da irrigação na produção do capim-mombaça: relação com variáveis do balanço hídrico.

O objetivo do trabalho foi verificar o efeito da irrigação sobre a produção do capim-mombaça (Panicum maximum cv. Mombaça) e relacionar a resposta produtiva à irrigação com variáveis do balanço hídrico. A produção de forragem foi avaliada em áreas irrigadas sob pivô central e em condição de sequeiro, de dezembro de 2004 a janeiro de 2007. A taxa média de acúmulo de forragem (kg MS/ha.dia) do capim-mombaça irrigado foi superior ao não irrigado nos ciclos de inverno e primavera, onde as diferenças foram mais evidentes. O armazenamento relativo de água no solo foi a variável de balanço hídrico que melhor correlacionou-se com a produção relativa entre os sistemas

Interceptação da radiação fotossinteticamente ativa em capim-mombaça: horário de medida.

A partir de medições contínuas da interceptação da radiação fotossinteticamente ativa (RFA) realizada com sensores quânticos lineares em um dossel de capim-mombaça (Panicum maximum cv. Mombaça), este trabalho teve por objetivo determinar qual o horário de medição a campo que melhor representa a média diária de interceptação da RFA. A interceptação foi avaliada com sensores lineares instalados na altura do resíduo pósdesfolha, em 7 períodos de rebrotação, entre junho de 2010 e agosto de 2011 em São Carlos, SP (20°57'S, 47°50'W, altitude 860 m). A interceptação horária da RFA apresentou maiores diferenças em relação a média diária e maiores variações entre as leituras para os horários mais próximos do nascer e por do sol. Períodos de rebrotação do capimmombaça com maiores valores de índice de área foliar apresentaram menores variações durante os horários de leitura. Na média dos períodos de rebrotação avaliados, leituras de interceptação da RFA pelo capim-mombaça realizadas as 11 e 16 horas foram mais próximas da média diária, indicando para as condições experimentais serem estes horários onde leituras instantâneas mais se aproximam do valor diário da interceptação da RFA