The Predictability of Excess Returns on UK Bonds: a Non-Linear Approach

This paper provides an empirical description of the behaviour of excess returns on UK government discount bonds in terms of risk factors such as the forward premium, the slope of the term structure, dividend yields and excess stock returns. We identify the existence of a time-varying term structure of expected excess returns. Further, the dynamics of the expected returns are characterised by regime-switching behaviour where the transition from one regime to the other is controlled by the slope of the term structure of interest rates. The first regime, which is characterised by flat or downward sloping term structures, occurs during periods of economic recession. The second regime, which is characterised by upward sloping term structures, occurs during periods of economic expansion. The main risk factors explaining expected returns are the slope of the term structure in the recessionary regime and the excess stock returns in the expansionary regime

Quantum Phase Transition in a Graphene Model

We present results for the equation of state of a graphene-like model in an effort to understand the properties of its quantum phase transition. The N_f fermion species interact through a three dimensional instantaneous Coulomb potential. Since there are no reliable analytical tools that work for all values of N_f and the coupling constant g, we rely on Monte Carlo simulations to calculate the critical properties of the model near the phase transition. We consider the four-component formulation for the fermion fields, which arises naturally as the continuum limit of the staggered fermion construction in (2+1) dimensions. In the limit of infinitely strong Coulomb interaction, the system undergoes a quantum phase transition at a critical number of fermion species N_fc ~ 4.7. We also calculate the values of the critical exponents at the quantum phase transition.Comment: 4 pages, 3 figures, presented at the 25th international conference on Low Temperature Physics, 6-13 August 2008, Amsterda

The oscillatory distribution of distances in random tries

We investigate \Delta_n, the distance between randomly selected pairs of nodes among n keys in a random trie, which is a kind of digital tree. Analytical techniques, such as the Mellin transform and an excursion between poissonization and depoissonization, capture small fluctuations in the mean and variance of these random distances. The mean increases logarithmically in the number of keys, but curiously enough the variance remains O(1), as n\to\infty. It is demonstrated that the centered random variable \Delta_n^*=\Delta_n-\lfloor2\log_2n\rfloor does not have a limit distribution, but rather oscillates between two distributions.Comment: Published at http://dx.doi.org/10.1214/105051605000000106 in the Annals of Applied Probability (http://www.imstat.org/aap/) by the Institute of Mathematical Statistics (http://www.imstat.org

Magnetic and Electric Excitations in Split Ring Resonators

We studied the electric and magnetic resonance of U-shaped SRRs. We showed that higher order excitation modes exist in both of the electric and magnetic resonances. The nodes in the current distribution were found for all the resonance modes. It turns out that the magnetic resonances are the modes with odd-number of half-wavelength of the current wave, i.e. 1/2, 3/2 and 5/2 wavelengths modes, and the electric resonances are modes with integer number of whole-wavelength of current wave, i.e. 1, 2 and 3 wavelengths modes. We discussed the electric moment and magnetic moment of the electric and magnetic resonances, and their dependence to the length of two parallel side arms. We show that the magnetic moment of magnetic resonance vanishes as the length side arms of the SRR reduces to zero, i.e. a rod does not give any magnetic moment or magnetic resonance.Comment: Journal-ref and DOI link adde

Effective material parameter retrieval for thin sheets: theory and application to graphene, thin silver films, and single-layer metamaterials

An important tool in the field of metamaterials is the extraction of effective material parameters from simulated or measured scattering parameters of a sample. Here we discuss a retrieval method for thin-film structures that can be approximated by a two-dimensional scattering sheet. We determine the effective sheet conductivity from the scattering parameters and we point out the importance of the magnetic sheet current to avoid an overdetermined inversion problem. Subsequently, we present two applications of the sheet retrieval method. First, we determine the effective sheet conductivity of thin silver films and we compare the resulting conductivities with the sheet conductivity of graphene. Second, we apply the method to a cut-wire metamaterial with an electric dipole resonance. The method is valid for thin-film structures such as two-dimensional metamaterials and frequency-selective surfaces and can be easily generalized for anisotropic or chiral media.Comment: 5 pages, 5 figure

Do pingers cause stress in fish? An experimental tank study with European sardine, Sardina pilchardus (Walbaum, 1792) (Actinopterygii, Clupeidae), exposed to a 70 kHz dolphin pinger

Date of acceptance: 06/12/2014 Acknowledgments The study was funded by the Portuguese Ministry of Science (Fundac¸a˜o para a Cieˆncia e Tecnologia– FCT) through a PhD Grant of SG (SFRH/BD/47931/2008). We would like to thank the captain of the purse-seiner (Jose´ Manuel Saveedra) and his crew for facilitating the capture and transport of live fish. Moreover, we want to thank Ana Marcalo for suggestions on the experimental design, Manuel Garci for technical advice on underwater video recordings and James Turner from the company Future Oceans for providing technical details on the 70 kHz dolphin pingers. We would also like to acknowledge the scientific advice of Dr. Jose Iglesias and the technical and logistic support for the preparation of the laboratory and the materials for tank experiments by Enrique Martınez Gonzalez, Ricardo Pazo and other staff at the aquaculture facilities of the Spanish Institute for Oceanography (IEO) and the Marine Sciences Station of Toralla (ECIMAT) in Vigo. Furthermore, we are grateful to Francisco de la Granda Grandoso for his practical assistance during the fish tank experiments and to Juan Santos Blanco for helping with statistical analysis. Finally, we would like to thank Pilar Riobo Agula, Amelia Fernandez Villamarin, Jose Franco Soler, Jose Luis Munoz, Angela Benedetti, Marcos Antonio Lopez Patio and Marta Conde Sieira for scientific advice and practical support with cortisol analysis and Rosana Rodrıguez for preparing histological samples for us.Peer reviewe