Electrostatics of electron-hole interactions in van der Waals heterostructures

The role of dielectric screening of electron-hole interaction in van der Waals heterostructures is theoretically investigated. A comparison between models available in the literature for describing these interactions is made and the limitations of these approaches are discussed. A simple numerical solution of Poissons equation for a stack of dielectric slabs based on a transfer matrix method is developed, enabling the calculation of the electron-hole interaction potential at very low computational cost and with reasonable accuracy. Using different potential models, direct and indirect exciton binding energies in these systems are calculated within Wannier-Mott theory, and a comparison of theoretical results with recent experiments on excitons in two-dimensional materials is discussed.Comment: 10 pages, 8 figure

All-strain based valley filter in graphene nanoribbons using snake states

A pseudo-magnetic field kink can be realized along a graphene nanoribbon using strain engineering. Electron transport along this kink is governed by snake states that are characterized by a single propagation direction. Those pseudo-magnetic fields point towards opposite directions in the K and K' valleys, leading to valley polarized snake states. In a graphene nanoribbon with armchair edges this effect results in a valley filter that is based only on strain engineering. We discuss how to maximize this valley filtering by adjusting the parameters that define the stress distribution along the graphene ribbon.Comment: 8 pages, 6 figure

Logarithmic periodicities in the bifurcations of type-I intermittent chaos

The critical relations for statistical properties on saddle-node bifurcations are shown to display undulating fine structure, in addition to their known smooth dependence on the control parameter. A piecewise linear map with the type-I intermittency is studied and a log-periodic dependence is numerically obtained for the average time between laminar events, the Lyapunov exponent and attractor moments. The origin of the oscillations is built in the natural probabilistic measure of the map and can be traced back to the existence of logarithmically distributed discrete values of the control parameter giving Markov partition. Reinjection and noise effect dependences are discussed and indications are given on how the oscillations are potentially applicable to complement predictions made with the usual critical exponents, taken from data in critical phenomena.Comment: 4 pages, 6 figures, accepted for publication in PRL (2004

Boolean Chaos

We observe deterministic chaos in a simple network of electronic logic gates that are not regulated by a clocking signal. The resulting power spectrum is ultra-wide-band, extending from dc to beyond 2 GHz. The observed behavior is reproduced qualitatively using an autonomously updating Boolean model with signal propagation times that depend on the recent history of the gates and filtering of pulses of short duration, whose presence is confirmed experimentally. Electronic Boolean chaos may find application as an ultra-wide-band source of radio wavesComment: 10 pages and 4 figur

Prevalência de anticorpos anti-Toxoplasma gondii em caprinos.

Resumo: A Toxoplasmose pode ser congênita ou adquirida e representa uma das infecções parasitárias mais comuns em caprinos, de qualquer faixa etária, raça e/ou sexo. Estudos epidemiológicos realizados no Brasil e no mundo apontam que a prevalência de anticorpos anti-Toxoplasma gondii varia entre 10% a 86%, independente do sistema de produção adotado. Objetivou-se com este estudo avaliar a prevalência de anticorpos anti-Toxoplasma gondii em caprinos de oito propriedades rurais de Quixadá, Ceará. Foram realizadas coletas de sangue por venipunção da jugular de 93 cabritos, machos e fêmeas, com mais de quatro meses de idade; 54 matrizes e três reprodutores. Os sangues foram centrifugados a 3000xg por 10 minutos para obtenção do soro. Estes foram armazenados em tubos tipo eppendorf® e congelados a -20°C até o momento da realização do teste ELISA indireto, usando como antígeno taquizoítos de T. gondii. A pesquisa foi aprovada pela Comissão de Ética no Uso de Animais da FCAV-UNESP, sob o protocolo 014465/12. As análises estatísticas foram realizadas no programa EPI Info 7.0.9.7 utilizando-se o teste Qui-quadrado. A prevalência de anticorpos anti-T. gondii encontrada: nas oito propriedades foi de 23,33% (35/150) e para as diferentes categorias animais de 15,05% (14/93) para crias; 37,04% (20/54) para matrizes e 33,33% (1/3) para os reprodutores, quando essas foram comparadas houve diferença estatística entre crias x matrizes (P = 0,0006) e crias x reprodutores (P = 0,004). Com relação ao sexo a prevalência encontrada para fêmeas foi de 25,21% (30/119) e para machos de 16,13% (5/31), não foi observada diferença estatística (P = 0,16). O sistema de produção adotado na maioria das propriedades era misto, ou seja, produzia-se carne e leite. Em todas as propriedades estudadas foi encontrado pelo menos um animal soropositivo para T. gondii, demonstrando que formas infectantes do protozoário estão presentes na região estudada. [Prevalence of Toxoplasma gondii antibodies in goats]. Congenital or acquired toxoplasmosis is one of the most common parasitic infections in goats of any age, race and sex. Epidemiological studies carried out in Brazil and around the world show that the prevalence of Toxoplasma gondii antibodies ranges from 10% to 86%, regardless of the adopted production system. The objective of this study was to evaluate the prevalence of antibodies to Toxoplasma gondii in goats from eight farms in Quixadá, Ceará. Blood samples were collected by jugular venipuncture of 93 male and female little goats, older than four months; 54 does and three bucks (breeders). The blood samples were centrifuged at 3000xg for 10 minutes to separate the serum. Serum samples were stored in Eppendorf ® tubes and frozen at -20°C for further testing by the indirect ELISA using as antigen tachyzoites of T. gondii. The study was approved by the Ethics Committee on Animal Use of FCAV - UNESP, under protocol 014465/12. Statistical analyses were performed by the Epi Info 7.0.9.7 software using the Chi-square test. The prevalence of T. gondii antibody for the eight properties studied was as follows: 23.33% (35/150) while within the animal categories, they were 15.05% (14/93) for offspring; 37.04% (20/54) for does; 33% (1/3) for bucks. The statistical analysis showed significant differences between offspring x does (P=0.0006) and offspring x bucks (P=0.004). With respect to gender, the prevalence for does was 25.21% (30/119) while for bucks, it was 16.13% (5/31), but they were not statistically different (P=0.16). The production system adopted in the majority of properties was mixed, that is, they produced meat and milk. All the properties had at least one animal positive for T. gondii, demonstrating that infectious forms of the parasite are present in the studied region.Edição dos Resumos do I Simpósio Internacional de Medicina Veterinária Preventiva (SIMPREV), Jaboticabal, 2013

Unidade de produção e suplementação estratégica de ovinos na fase de recria.

O presente trabalho foi conduzido para estabelecer um módulo de produção e suplementação alimentar para ovinos na estação seca, baseado no uso de áreas de pastagem diferidas, associado à suplementação concentrada composta por proteína proveniente de espécies leguminosas, e energia oriunda de sorgo em grãos.bitstream/CNPC-2010/23023/1/cot98.pd