Low-field microwave absorption and magnetoresistance in iron nanostructures grown by electrodeposition on n-type lightly-doped silicon substrates

In this study we investigate magnetic properties, surface morphology and crystal structure in iron nanoclusters electrodeposited on lightly-doped (100) n-type silicon substrates. Our goal is to investigate the spin injection and detection in the Fe/Si lateral structures. The samples obtained under electric percolation were characterized by magnetoresistive and magnetic resonance measurements with cycling the sweeping applied field in order to understand the spin dynamics in the as-produced samples. The observed hysteresis in the magnetic resonance spectra, plus the presence of a broad peak in the non-saturated regime confirming the low field microwave absorption (LFMA), were correlated to the peaks and slopes found in the magnetoresistance curves. The results suggest long range spin injection and detection in low resistive silicon and the magnetic resonance technique is herein introduced as a promising tool for analysis of electric contactless magnetoresistive samples.Comment: 12 pages, 5 figure

Complexity of colouring problems restricted to unichord-free and \{square,unichord\}-free graphs

A \emph{unichord} in a graph is an edge that is the unique chord of a cycle. A \emph{square} is an induced cycle on four vertices. A graph is \emph{unichord-free} if none of its edges is a unichord. We give a slight restatement of a known structure theorem for unichord-free graphs and use it to show that, with the only exception of the complete graph $K_4$, every square-free, unichord-free graph of maximum degree~3 can be total-coloured with four colours. Our proof can be turned into a polynomial time algorithm that actually outputs the colouring. This settles the class of square-free, unichord-free graphs as a class for which edge-colouring is NP-complete but total-colouring is polynomial

Fixed-income arbitrage strategies: swap spread arbitrage and yield curve arbitrage

Abstract. There is a mythical question, well described by Duarte, Longstaff and Yu (2006), whether fixed-income arbitrage strategies are truly arbitrage or merely strategies that earn small positive returns most of the time, but occasionally experience dramatic losses. The question can be summarized in the anecdote “picking up nickels in front of a steamroller”. This master’s thesis studies two of these specific fixed-income arbitrage strategies: Swap Spread Arbitrage and Yield Curve Arbitrage. The methodology used in this master’s thesis is to apply these two arbitrage strategies through time from November 1988 to December 2011, using R language coding developed by the author of the master’s thesis, and to analyze their risk and return characteristics. The data used in this master’s thesis was gathered from different sources such as: Bloomberg™, Federal Reserve System (FED), Thompson Reuters Datastream™, Federal Reserve Bank of St. Louis, Kenneth French and Yahoo® Finance. The main hypothesis of this thesis is that the global financial crisis of 2008 had a big impact on these strategies return indexes. This proved to be wrong. These two fixed-income arbitrage strategies seem profitable on the long run even under financial crisis cycles, as they generate positive excess returns, and Yield Curve Arbitrage strategy even with significant α

Caracterização e análise da rentabilidade financeira do cultivo da teca (Tectona grandis L.f.) para produção de madeira em Rio Branco, Acre.

A teca (Tectona grandis L.f.), planta originária da Ásia, encontra-se em expansão nas regiões Centro-Oeste e Norte do Brasil. O principal produto dessa espécie é a madeira de alta qualidade, muito utilizada em móveis finos e na construção naval. O valor de mercado para a madeira de teca madura, livre de nós e com diâmetro para serraria, chega a superar o da espécie mogno (Swietenia macrophylla King). Apesar da potencialidade de mercado para a teca, no Brasil ainda são escassos os trabalhos que avaliam o potencial econômico dessa espécie considerando as várias formas de manejo. Assim, estudos dessa natureza contribuirão para o planejamento e administração dos atuais e futuros plantios de teca. Tendo como referência estudos sobre os povoamentos de teca nos estados do Acre e Rondônia, este trabalho tem como objetivo determinar, em diferentes estratégias de manejo, o valor presente líquido (VPL), a relação benefício-custo (RBC), a taxa interna de retorno (TIR) e analisar a sensibilidade dos indicadores econômicos quanto à oscilação na taxa mínima de atratividade (TMA) e nos preços da madeira.bitstream/item/28922/1/Circular-tec.-53.pd

Acyclic orientations with path constraints

Many well-known combinatorial optimization problems can be stated over the set of acyclic orientations of an undirected graph. For example, acyclic orientations with certain diameter constraints are closely related to the optimal solutions of the vertex coloring and frequency assignment problems. In this paper we introduce a linear programming formulation of acyclic orientations with path constraints, and discuss its use in the solution of the vertex coloring problem and some versions of the frequency assignment problem. A study of the polytope associated with the formulation is presented, including proofs of which constraints of the formulation are facet-defining and the introduction of new classes of valid inequalities