Crossover between distinct mechanisms of microwave photoresistance in bilayer systems

We report on temperature-dependent magnetoresistance measurements in balanced double quantum wells exposed to microwave irradiation for various frequencies. We have found that the resistance oscillations are described by the microwave-induced modification of electron distribution function limited by inelastic scattering (inelastic mechanism), up to a temperature of T*~4 K. With increasing temperature, a strong deviation of the oscillation amplitudes from the behavior predicted by this mechanism is observed, presumably indicating a crossover to another mechanism of microwave photoresistance, with similar frequency dependence. Our analysis shows that this deviation cannot be fully understood in terms of contribution from the mechanisms discussed in theory.Comment: 7 pages, 4 figure

First report of papaya ringspot virus w infecting momordica charantia in Cuba

During a survey conducted in July 2010, severe mosaic and deformations were observed on the leaves of cerasee (Momordica charantia) in Villa Clara, Cuba. The symptoms resembled those induced by Papaya ringspot virus (PRSV) in papaya (Carica papaya L.) plants (Olarte et al., 2011). Leaf samples were ELISA positive when tested with a specific PRSV antiserum (Agdia, USA). The presence of PRSV was confirmed by the amplification of a 850 bp fragment by RT-PCR using primers specific to the PRSV coat protein gene (unpublished information). BLASTn analysis of the sequences from the RT-PCR amplified product (GenBank accession No. KP019380) showed 94% identity with PRSV-W isolates from Citrullus lanatus in the USA (GenBank accession Nos. JN132439 to JN132457) and PRSV-P isolates (GenBank accession Nos. AF196839 and EF189736). Crude sap extracts from symptomatic M. charantia leaf samples were mechanically inoculated onto Cucurbita moschata and papaya plants. Symptoms developed in the former but not in the latter plants, suggesting the presence of PRSV-W, since only PRSV-P is able to infect papaya plants (Romay et al., 2014). In inoculated plants, the presence of this virus was determined by ELISA. In Cuba, the first molecular detection of PRSV-W was from Cucurbita pepo (Rodríguez- Martínez, personal communication) and PRSV-P has only been reported in papaya plants (Portal et al., 2006). To our knowledge, this is the first report of PRSV-W infecting M. charantia in Cuba. This finding is relevant for the epidemiology, and management of this disease in cucurbits.Instituto de Patología VegetalFil: Cabrera Mederos, Dariel. Instituto Nacional de Tecnología Agropecuaria (INTA). Instituto de Patología Vegetal; ArgentinaFil: Cabrera Mederos, Dariel. Universidad Central “Marta Abreu” de Las Villas. Facultad de Ciencias Agropecuarias; CubaFil: Giolitti, Fabian. Instituto Nacional de Tecnología Agropecuaria (INTA). Instituto de Patología Vegetal; ArgentinaFil: Portal, O. Universidad Central “Marta Abreu” de Las Villas. Facultad de Ciencias Agropecuarias; Cub

Magnetoresistance oscillations in multilayer systems - triple quantum wells

Magnetoresistance of two-dimensional electron systems with several occupied subbands oscillates owing to periodic modulation of the probability of intersubband transitions by the quantizing magnetic field. In addition to previous investigations of these magneto-intersubband (MIS) oscillations in two-subband systems, we report on both experimental and theoretical studies of such a phenomenon in three-subband systems realized in triple quantum wells. We show that the presence of more than two subbands leads to a qualitatively different MIS oscillation picture, described as a superposition of several oscillating contributions. Under a continuous microwave irradiation, the magnetoresistance of triple-well systems exhibits an interference of MIS oscillations and microwaveinduced resistance oscillations. The theory explaining these phenomena is presented in the general form, valid for an arbitrary number of subbands. A comparison of theory and experiment allows us to extract temperature dependence of quantum lifetime of electrons and to confirm the applicability of the inelastic mechanism of microwave photoresistance for the description of magnetotransport in multilayer systems.Comment: 10 pages, 5 figure

Envelhecimento acelerado de aguardentes vínicas na presença de fragmentos de madeira. Influência nos compostos odorantes

A tecnologia de envelhecimento tradicional, que consiste na colocação da aguardente vínica em vasilhas de madeira durante vários anos, é uma técnica morosa e onerosa. Assim, têm vindo a ser introduzidas e desenvolvidas novas técnicas, com o intuito de optimizar o processo e reduzir os custos. Uma dessas novas técnicas consiste em introduzir pedaços de madeira (aparas, toros ou outras formas) na bebida a envelhecer, condicionada em depósitos de inox. Têm sido realizados muitos estudos em vinhos, mas em aguardentes a experimentação é escassa [1, 2]. Assim, este trabalho teve como objectivo avaliar a influência da utilização de alternativas ao envelhecimento de aguardentes em vasilhas de madeira, na composição química das aguardentes obtidas, dando particular atenção aos compostos odorantes provenientes da madeira. Para tal, uma mesma aguardente vínica da Lourinhã foi submetida a um processo de envelhecimento, com três formas de madeira: aguardente colocada em vasilha de madeira (V), aguardente colocada em vasilha de inox com introdução de madeira sob a forma de dominós (D) e aguardente colocada em vasilha de inox com introdução de madeira sob a forma de tábuas (T), tendo sido colhidas amostras de aguardente, ao fim de 180 dias de envelhecimento, para análise e quantificação dos compostos odorantes. Os resultados obtidos mostram que a forma da madeira teve um efeito altamente significativo na maioria dos compostos analisados. No caso dos compostos odorantes derivados da lenhina da madeira (fenois voláteis e vanilina), os teores mais elevados foram encontrados nas aguardentes envelhecidas na presença de fragmentos (dominós ou tábuas), enquanto para os compostos odorantes derivados das hemiceluloses da madeira (ácido acético e aldeídos furânicos) os teores mais elevados foram determinados nas aguardentes envelhecidas em vasilha de madeira. Os resultados deste trabalho sugerem a possibilidade de diferenciação química das aguardentes, em função da tecnologia de envelhecimento

Thermally activated intersubband scattering and oscillating magnetoresistance in quantum wells

Experimental studies of magnetoresistance in high-mobility wide quantum wells reveal oscillations which appear with an increase in temperature to 10 K and whose period is close to that of Shubnikov-de Haas oscillations. The observed phenomenon is identified as magnetointersubband oscillations caused by the scattering of electrons between two occupied subbands and the third subband which becomes occupied as a result of thermal activation. These small-period oscillations are less sensitive to thermal suppression than the largeperiod magnetointersubband oscillations caused by the scattering between the first and the second subbands. Theoretical study, based on consideration of electron scattering near the edge of the third subband, gives a reasonable explanation of our experimental findings.Comment: 9 pages, 5 figure

GC-FID and GC-MS as a tool to screen the influence of wood ageing technologies in the brandies odourless and odourant compounds

The maturation of wine brandies in wooden barrels cause many sensory and physicochemical changes in these alcoholic beverages, namely its flavour modification. Previous work (Caldeira et al. 2008) pointed out the most potent odourant compounds of the wine aged brandies. Some of these compounds proceed from the distillate and others are extracted from the wood. In this study it was quantified, some odourless compounds, such as methanol and higher alcohols and several odorant compounds in brandies aged in presence of two types of wood fragments (staves and tablets), from two different kinds of woods (Limousin oak wood and Portuguese chestnut wood), and compared with those found in the same with brandy aged in wooden barrels. A taster panel have also profiled these brandies and evaluated their overall quality. The methanol and higher alcohols were quantified by GC-FID equipped with a fused silica capillary column of polyethylene glycol according to the official method [NP 3263, 1990]. The odorant compounds were quantified by GC-FID and identified by GC-MS. The results showed that the ageing system is the most discriminant factor, having a significant effect on the level of several odourant compounds. The wood botanical species affected few odourant compounds. The importance of odorant compounds was also demonstrated by the high linear correlations between their contents and the intensity of several sensory attributes. The results show the possibility of using the chromatographic results as a tool to discriminate brandies produced with different ageing technologies

Universal Magnetic Properties of sp3^3-type Defects in Covalently Functionalized Graphene

Using density-functional calculations, we study the effect of sp$^3$-type defects created by different covalent functionalizations on the electronic and magnetic properties of graphene. We find that the induced magnetic properties are {\it universal}, in the sense that they are largely independent on the particular adsorbates considered. When a weakly-polar single covalent bond is established with the layer, a local spin-moment of 1.0 $\mu_B$ always appears in graphene. This effect is similar to that of H adsorption, which saturates one $p_z$ orbital in the carbon layer. The magnetic couplings between the adsorbates show a strong dependence on the graphene sublattice of chemisorption. Molecules adsorbed at the same sublattice couple ferromagnetically, with an exchange interaction that decays very slowly with distance, while no magnetism is found for adsorbates at opposite sublattices. Similar magnetic properties are obtained if several $p_z$ orbitals are saturated simultaneously by the adsorption of a large molecule. These results might open new routes to engineer the magnetic properties of graphene derivatives by chemical means

Sensory and chemical modifications of wine brandy aged with chestnut and oak wood

This work evaluated the sensorial and chemical modifications in brandy aged in presence of two types of wood fragments in comparison with a brandy aged in wooden barrels