Aharonov-Bohm effect for an exciton in a finite width nano-ring

We study the Aharonov-Bohm effect for an exciton on a nano-ring using a 2D attractive fermionic Hubbard model. We extend previous results obtained for a 1D ring in which only azimuthal motion is considered, to a more general case of 2D annular lattices. In general, we show that the existence of the localization effect, increased by the nonlinearity, makes the phenomenon in the 2D system similar to the 1D case. However, the introduction of radial motion introduces extra frequencies, different from the original isolated frequency corresponding to the excitonic Aharonov- Bohm oscillations. If the circumference of the system becomes large enough, the Aharonov-Bohm effect is suppressed

Localisation and finite-size effects in graphene flakes

We show that electron states in disordered graphene, with an onsite potential that induces inter-valley scattering, are localised for all energies at disorder as small as of the band width of clean graphene. We clarify that, in order for this Anderson-type localisation to be manifested, graphene flakes of size or larger are needed. For smaller samples, due to the surprisingly large extent of the electronic wave functions, a regime of apparently extended (or even critical) states is identified. Our results complement earlier studies of macroscopically large samples and can explain the divergence of results for finite-size graphene flakes

Res Ipsa Loquitur in Medical Malpractice

The Cloak of Protection encompassing the physician in the practice of his profession is no longer to be taken for granted. Recent decisions in Alaska, California, Louisiana, Oregon, and Wisconsin have swept aside the traditional limitations in the use of the res ipsa loquitur doctrine. They impose all but strict liability upon the medical profession for mistakes occurring during treatment or surgery

Analysis of Systematic Risk: Decomposition and Portfolio Efficiency

This dissertation comprises three essays that tackle various aspects of linear asset pricing models. The first essay, recognizing the dependence problem between factors, in the context of linear multi-factor models, proposes an optimal procedure to find orthogonalized risk premia, which also facilitates the decomposition of the coefficient of determination. Importantly, the new risk premia may diverge significantly from the original ones. The decomposition of risk allows one to explicitly examine the impact of individual factors on the return variation of risky assets, which provides discriminative power for factor selection. The procedure is experimentally robust even for small samples. Empirically we find that even though on average, approximately eighty (sixty-five) percent of style (industry) portfolios\u27 volatility is explained by the market and size factors, other factors such as value, momentum and contrarian still play an important role for certain portfolios. The components of systematic risk, while dynamic over time, generally exhibit negative correlation between market, on one side, and size, value, momentum and contrarian , on the other side.;In the second essay we apply Marginal Conditional Stochastic Dominance (MCSD) tests to returns on sentiment-beta sorted portfolios and sentiment-arbitrage portfolios, constructed using the Baker and Wurgler (2007) index of sentiment levels. The theory of MCSD demonstrates that, if one (mutually exclusive) subset of a core portfolio dominates another, conditional on the return distribution of the core portfolio, then the core portfolio is inefficient for all utility-maximizing risk-averse investors. Based on returns on the U.S. equity market, we show that both positively and negatively sentiment sensitive stocks are conditionally and stochastically dominated by sentiment insensitive stocks. Moreover, we find dominance among sentiment-arbitrage portfolios, constructed with positively sensitive vs. insensitive, insensitive vs. negatively sensitive, and positively vs. negatively sensitive stocks. Therefore, we conclude that the market portfolio is stochastically inefficient.;The third essay builds on the theory of the FX market, which shows that investing in a high yielding currency would generate zero average returns, due to its depreciation with respect to the home currency. Empirically, it has been shown that high yielding currencies actually appreciate. The Consumption CAPM applied in the FX market argues that a high yielding currency also exposes investors to more consumption risk, hence the positive excess returns. The literature on the FX market proposes different strategies that generate abnormal returns based on the forward puzzle . This paper investigates whether the returns obtained through a specific strategy that combines mean reversion and momentum in the FX market, are a compensation for risk. We find that the risk factors corresponding to an extended version of the Consumption CAPM can explain 99% of the variation in currency excess returns. We compare this model with other asset pricing models and conclude that none of them can provide a similarly good explanation

Res Ipsa Loquitur in Medical Malpractice

The Cloak of Protection encompassing the physician in the practice of his profession is no longer to be taken for granted. Recent decisions in Alaska, California, Louisiana, Oregon, and Wisconsin have swept aside the traditional limitations in the use of the res ipsa loquitur doctrine. They impose all but strict liability upon the medical profession for mistakes occurring during treatment or surgery

Spin-phonon coupling in antiferromagnetic chromium spinels

The temperature dependence of eigenfrequencies and intensities of the IR active modes has been investigated for the antiferromagnetic chromium spinel compounds CdCr2O4, ZnCr2O4, ZnCr2S4, ZnCr2Se4, and HgCr2S4 by IR spectroscopy for temperatures from 5 K to 300 K. At the transition into the magnetically ordered phases, and driven by spin-phonon coupling, most compounds reveal significant splittings of the phonon modes. This is true for geometrically frustrated CdCr2O4, and ZnCr2O4, for bond frustrated ZnCr2S4 and for ZnCr2Se4, which also is bond frustrated, but dominated by ferromagnetic exchange. The pattern of splitting is different for the different compounds and crucially depends on the nature of frustration and of the resulting spin order. HgCr2S4, which is almost ferromagnetic, exhibits no splitting of the eigenfrequencies, but shows significant shifts due to ferromagnetic spin fluctuations.Comment: 15 pages, 6 figure

Coupling of phonons and electromagnons in GdMnO_3

The infrared and Terahertz properties of GdMnO_3 have been investigated as function of temperature and magnetic field, with special emphasis on the phase boundary between the incommensurate and the canted antiferromagnetic structures. The heterogeneous incommensurate phase reveals strong magnetodielectric effects, characterized by significant magnetoelectric contributions to the static dielectric permittivity and by the existence of electrically excited magnons (electromagnons). In the commensurate canted antiferromagnetic phase the magnetoelectric contributions to the dielectric constant and electromagnons are suppressed. The corresponding spectral weight is transferred to the lowest lattice vibration demonstrating the strong coupling of phonons with electromagnons.Comment: 5 pages, 4 figure