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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
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