Helical edge states in multiple topological mass domains

The two-dimensional topological insulating phase has been experimentally discovered in HgTe quantum wells (QWs). The low-energy physics of two-dimensional topological insulators (TIs) is described by the Bernevig-Hughes-Zhang (BHZ) model, where the realization of a topological or a normal insulating phase depends on the Dirac mass being negative or positive, respectively. We solve the BHZ model for a mass domain configuration, analyzing the effects on the edge modes of a finite Dirac mass in the normal insulating region (soft-wall boundary condition). We show that at a boundary between a TI and a normal insulator (NI), the Dirac point of the edge states appearing at the interface strongly depends on the ratio between the Dirac masses in the two regions. We also consider the case of multiple boundaries such as NI/TI/NI, TI/NI/TI and NI/TI/NI/TI.Comment: 11 pages, 15 figure

Helical edge states in multiple topological mass domains

The two-dimensional topological insulating phase has been experimentally discovered in HgTe quantum wells (QWs). The low-energy physics of two-dimensional topological insulators (TIs) is described by the Bernevig-Hughes-Zhang (BHZ) model, where the realization of a topological or a normal insulating phase depends on the Dirac mass being negative or positive, respectively. We solve the BHZ model for a mass domain configuration, analyzing the effects on the edge modes of a finite Dirac mass in the normal insulating region (soft-wall boundary condition). We show that at a boundary between a TI and a normal insulator (NI), the Dirac point of the edge states appearing at the interface strongly depends on the ratio between the Dirac masses in the two regions. We also consider the case of multiple boundaries such as NI/TI/NI, TI/NI/TI and NI/TI/NI/TI.Comment: 11 pages, 15 figure

Análise microbiológica e estabilidade de farinha de cascas e albedo de maracujá e arroz pelo processo de extrusão termoplástica.

Edição dos Resumos do VI Congresso Latinoamericano e XII Congresso Brasileiro de Higienistas de Alimentos, II Encontro Nacional de Vigilância das Zoonoses, IV Encontro do Sistema Brasileiro de Inspeção de Produtos de Origem Animal, Gramado, abr. 2013

Scanning Tunneling Microscope Operating as a Spin-diode

We theoretically investigate spin-polarized transport in a system composed of a ferromagnetic Scanning Tunneling Microscope (STM) tip coupled to an adsorbed atom (adatom) on a host surface. Electrons can tunnel directly from the tip to the surface or via the adatom. Since the tip is ferromagnetic and the host surface (metal or semiconductor) is non-magnetic we obtain a spin-diode effect when the adatom is in the regime of single occupancy. This effect leads to an unpolarized current for direct bias (V > 0) and polarized current for reverse (V < 0) bias voltages, if the tip is nearby the adatom. Within the nonequilibrium Keldysh technique we analyze the interplay between the lateral displacement of the tip and the intra adatom Coulomb interaction on the spindiode effect. As the tip moves away from the adatom the spin-diode effect vanishes and the currents become polarized for both V > 0 and V < 0. We also find an imbalance between the up and down spin populations in the adatom, which can be tuned by the tip position and the bias. Finally, due to the presence of the adsorbate on the surface, we observe spin-resolved Friedel oscillations in the current, which reflects the oscillations in the calculated LDOS of the subsystem surface+adatom.Comment: 11 pages, 4 figures. Submitte

Prevalence of Salmonella on tomatoes from organic and conventional production in Rio de Janeiro (Brazil).

Outbreaks of salmonellosis associated with tomatoes have been related over the past fifteen years. Tomatoes may become surface contaminated with Salmonella spp. from production of consumption. Purpose: The purpose of this study was to evaluate the prevalence of Salmonella spp. on tomatoes surface from organic and conventional production. Samples were collected in the street cendors and supermarkets, and analzed by two methods; the mini-VIDAS SLM assay a specific enzyme-linked fluorescent immonoassay (ELFA) rapid method and the conventional FDA-BAM. Methods: A total of 263 tomatoes were collected during a two-year (2010-2012) survey. A hundred twenty-seven were from organic production, 61 from supermarkets and 66 from street vendors. From conventional production 136 samples were collected, being 84 from supermarkets and 52 from street vendors. All samples were simultaneously surface analyzed by mini-VIDAS SLM and FDA BAM. Results: Salmonella spp. was not detected by the conventional method and two false positives were found by mini-VIDAS SLM. Significance: Surface tomatoes from organic and conventional production analyzed in the city of Rio de Janeiro showed no potential Salmonella risk to their consumption

Controle químico de Phoma sorghina em sementes de arroz (Oryza sativa L.).

O desenvolvimento de epidemias de P. sorghina em arroz é mais frequente com período de chuva prolongados quando a associação do patógeno com a semente assume grande importância. O presente experimento teve como objetivo a avaliação do efeito do tratamento químico de sementes de arroz no controle do agente causal da queima das glumelas, assim como a possibilidade do desenvolvimento de uma escala de avaliação na diferenciação das sementes desta cultura portadora do patógeno. Entre os fungicidas utilizados o Benomyl mostrou-se mais eficiente que o Iprodione e o Captan no controle de P. sorghina. Não foram observadas diferenças estatísticas entre os métodos de avaliação (severidade e incidência) dos fungicidas quanto a eficiência no controle do patógeno. Como o controle obtido não foi absoluto, este resultado indica a necessidade tanto do estudo de novos produtos e/ou dosagens no controle deste patógeno como do efeito do inóculo remanescente nas sementes sob a germinação, o vigor das plântulas e o desenvolvimento de epidemias em condições de campo. A escala de avaliação empregada não colaborou para a diferenciação das sementes de arroz associadas com o patógeno