Andreev tunneling through a double quantum-dot system coupled to a ferromagnet and a superconductor: effects of mean field electronic correlations

We study the transport properties of a hybrid nanostructure composed of a ferromagnet, two quantum dots, and a superconductor connected in series. By using the non-equilibrium Green's function approach, we have calculated the electric current, the differential conductance and the transmittance for energies within the superconductor gap. In this regime, the mechanism of charge transmission is the Andreev reflection, which allows for a control of the current through the ferromagnet polarization. We have also included interdot and intradot interactions, and have analyzed their influence through a mean field approximation. In the presence of interactions, Coulomb blockade tend to localized the electrons at the double-dot system, leading to an asymmetric pattern for the density of states at the dots, and thus reducing the transmission probability through the device. In particular, for non-zero polarization, the intradot interaction splits the spin degeneracy, reducing the maximum value of the current due to different spin-up and spin-down densities of states. Negative differential conductance (NDC) appears for some regions of the voltage bias, as a result of the interplay of the Andreev scattering with electronic correlations. By applying a gate voltage at the dots, one can tune the effect, changing the voltage region where this novel phenomenon appears. This mechanism to control the current may be of importance in technological applications.Comment: 12 pages, 11 figure

Dimensionality effects in the LDOS of ferromagnetic hosts probed via STM: spin-polarized quantum beats and spin filtering

We theoretically investigate the local density of states (LDOS) probed by a STM tip of ferromagnetic metals hosting a single adatom and a subsurface impurity. We model the system via the two-impurity Anderson Hamiltonian. By using the equation of motion with the relevant Green functions, we derive analytical expressions for the LDOS of two host types: a surface and a quantum wire. The LDOS reveals Friedel-like oscillations and Fano interference as a function of the STM tip position. These oscillations strongly depend on the host dimension. Interestingly, we find that the spin-dependent Fermi wave numbers of the hosts give rise to spin-polarized quantum beats in the LDOS. While the LDOS for the metallic surface shows a damped beating pattern, it exhibits an opposite behavior in the quantum wire. Due to this absence of damping, the wire operates as a spatially resolved spin filter with a high efficiency.Comment: revised tex

Uma análise das barreiras tarifárias no comércio internacional de lácteos.

bitstream/item/57090/1/BOP-32-Uma-Analise-das-Barreiras-Tarifarias-no-Comercio-Internacional-de-Lacteos.pd

Conditioning temperature for inducing uniform ripening of 'Abate Fetel' pears.

The aim of this study was to determine the conditioning temperature period for inducing uniform ripening of ‘Abate Fetel’ pears as well as to determine the maximum storage period with no quality loss. Three harvests were carried out at weekly intervals and each harvest date was considered a factorial experiment (7x3), with seven storage periods at 0 ± 1 °C and 90 ± 5% relative humidity (0; 20; 40; 60; 80; 100 and 120 days) and three periods at room temperature (20 ± 1 °C) (zero, three and six days). The assessed quality attributes were flesh firmness, starch content, weight loss and soluble solids content. Acceptance and purchase intention sensory tests were carried out. Cold storage was efficient in inducing uniform ripening in ‘Abate Fetel’ pears after 20 days at low temperature followed by six days at room temperature for fruit from the three harvest dates. ‘Abate Fetel’ pears harvested at harvest maturity of 57 N can be stored for up to 120 days and commercialized within six days with no quality loss. However, fruit harvested at flesh firmness below 55 N can be stored for 80 days and commercialized within six days or stored for 100 days and commercialized within three days. Key words: Pyrus communis L.. Cold storage. Acceptance. Shelf life. O objetivo deste trabalho foi de definir o tempo necessário de condicionamento por frio para causar a uniformização do amadurecimento de peras ‘Abate Fetel’. Ainda, objetivou-se a determinação do período máximo de armazenamento sem que houvesse prejuízos à qualidade de frutos. Foram realizadas três colheitas em intervalos semanais e cada colheita constituiu um experimento fatorial (7x3), sendo sete períodos de manutenção sob baixa temperatura (0; 20; 40; 60; 80; 100 e 120 dias) e três períodos de manutenção em ambiente simulado a 20 ± 1 °C (zero, três e seis dias). Os atributos de qualidade avaliados foram firmeza de polpa, índice de degradação do amido, perda de massa fresca, teores de sólidos solúveis e aceitabilidade. O condicionamento por frio foi eficiente na indução e uniformização do amadurecimento de peras ‘Abate Fetel’, após 20 dias de manutenção em baixa temperatura seguidos de seis dias em ambiente simulado, para os frutos provenientes das três datas de colheita. Frutos da cultivar Abate Fetel com data de colheita DC1 podem ser armazenados por até 120 dias e comercializados em até seis dias sem que haja comprometimento da qualidade. Já frutos colhidos nas datas de colheita DC2 e DC3 podem ser armazenados por 80 dias e comercializados em até seis dias ou armazenados por 100 dias e comercializados no período de três dias. Palavras-chave: Pyrus communis L.. Armazenamento refrigerado. Aceitabilidade

VELOCITY PROFILE VISUALIZATION OF WATER NATURAL PERCOLATION IN A POROUS MEDIUM

This paper aims to show the profile and the behavior of the velocity of the water flow through a porous medium composed of clay and sand aggregated by burning in an oil furnace. The work models mathematics based on the Navier-Stokes differential equation, which represents the behavior of the water velocity flow in porous medium taking into account parameters of a low velocity laminar flow, increased load loss value and Number of Reynolds > 1. Physical phenomena such as porosity, permeability, particles arrangement, radius and wet perimeter are considered in the equation. The study shows the three-dimensional profile of the water percolation velocity which, originated from the capillary phenomenon, causes a sum of the tensions of increased values able to produce cracks in the medium structure. And, differently from filtration phenomenon, which overcomes the capillarity of the medium by the gravitational force or by efforts applied aiming to increase the flow velocity, the natural percolation opposes to the gravity and to the surrounding pressure moving slowly, reaching the flow at 30 and 40 centimeters depending on the permeability of the porous medium

Postharvest treatments to mitigate the internal browning in "Bartlett" pears.

Internal browning is an important disorder in pear fruit which can lead to economic losses. Pears (Pyrus communis L. cv. Bartlett) were harvested at early harvest maturity of 90 N from a commercial orchard in southern Brazil. Methyl jasmonate, ethanol, and 1-methylcyclopropene vapor treatments were carried out for 24 hours in order to mitigate the internal browning disorder. Fruit were stored for up to 150 days at 0 ± 1 °C and 90 ± 5 % RH. Pears exhibited internal browning in 37 % of the control samples after 90 days of cold storage. However, no internal browning symptoms were observed in the 1-MCP treatment. The first symptoms in 1-MCP samples were noticed after 120 days of cold storage (12 %)and reached 100 % in five days at room temperature. 1-MCP-treated pears showed flesh firmness values of 82 N after 90 days of cold storage and 18.7 N when they were removed from the cold storage and kept at 20 °C. The greatest acceptance index was attributed to 1- MCP pears after 90 days at 0 ± 1 °C followed by 5 days at 20 ± 1 °C (89.35). High acceptance indexes were attributed to MeJa (77.95) and control pears (76.40) after 30 days in cold storage followed by 5 days at room temperature. 1-MCP (0.3 µL L-1 , 24 hours at 0 ± 1 °C) treatment delays ripening and mitigates the internal browning in early harvested ?Bartlett? pears, that can be stored for up to 90 days at 0 ± 1 °C

Extension of storage and quality maintenance of 'Rocha' and 'Packham's Triumph' pears using modified atmosphere packaging (Bag-It-Fresh).

'Rocha' anel 'Packham's Ttiumph ' pears were harvested in January 2011 when the fruit in, the orchard reached flesh Iirmncss values of 67.6 anel 74.7 N, respectivelyResumo S11-3

Uso da tomografia de raios-x na determinação de densidade básica da madeira e proporção de lenho inicial e tardio.

Organizado por Patricia Póvoa de Mattos, Celso Garcia Auer, Rejane Stumpf Sberze, Katia Regina Pichelli e Paulo César Botosso

Extended cold storage of winter pears by modified atmosphere packaging.

The aim of this work was to evaluate the effect of passive modified atmosphere packaging (MAP) on the maintenance of fruit quality during the extended storage of ‘Rocha’ and ‘Packham’s Triumph’ pears. Fruit were packed in linear low density polyethylene (100 mm), with 6% BIF 1500 additive placed into perforated plastic boxes and kept at 0 ± 1 °C and 90 ± 5% RH for up to 180 days. MAP reduced weight loss by 14.8% for ‘Rocha’ and 11.5% for ‘Packham’s’ pears after 180 days in cold storage and retained the green color of the skin, which means that the yellowing visual perception was delayed in 60 and 90 days for ‘Rocha’ and ‘Packham’s’ pears, respectively. A strong softening was observed for ‘Packham’s’ pears after being kept for 150 days at 0° C followed by 5 days at room temperature, which did not limit the storage of both pear cultivars under modified atmosphere packaging. MAP created by linear low density polyethylene (100 mm), with 6% BIF 1500 additive extended in 30 days the cold storage for ‘Rocha’ and 60 days for ‘Packham’s’ pears. Index terms: Pyrus communis L., ‘Rocha’, ‘Packham’s Triumph’, polyethylene film, water loss, acceptance. O objetivo deste trabalho foi avaliar a eficiência da atmosfera modificada na manutenção dos atributos de qualidade e na extensão do armazenamento refrigerado de peras "Rocha" e "Packham's Triumph". Os frutos foram acondicionados em filme de polietileno de baixa densidade linear (100 ?m) com aditivo BIF 1.500 6% no interior de caixas plásticas vazadas e mantidos a 0 ± 1 °C e 90 ± 5% UR por até 180 dias. A atmosfera modificada reduziu em 14,8% a perda de massa de peras "Rocha" e em 11,5% a de peras "Packham's", após 180 dias de refrigeração, e mostrou-se útil na preservação da coloração verde dos frutos, retardando em 60 e 90 dias a percepção visual do amarelecimento da casca de peras "Rocha e Packham's", respectivamente. Houve amolecimento excessivo da polpa de peras "Packham"s" controle após 150 dias a 0 °C, seguidos por 5 dias a 20 °C, o que não limitou o armazenamento das peras de ambas as cultivares sob atmosfera modificada. A atmosfera modificada proporcionada pela embalagem de polietileno de baixa densidade linear (100 ?m) com aditivo BIF 1.500 6%, proporcionou a extensão de 30 dias no período de armazenamento refrigerado de peras ?Rocha? e de 60 dias para "Packham's Triumph". Termos para indexação: Pyrus communis L., "Rocha", "Packham"s Triumph", filme de polietileno, perda de massa, aceitabilidad