Concurrent enhancement of percolation and synchronization in adaptive networks

Co-evolutionary adaptive mechanisms are not only ubiquitous in nature, but also beneficial for the functioning of a variety of systems. We here consider an adaptive network of oscillators with a stochastic, fitness-based, rule of connectivity, and show that it self-organizes from fragmented and incoherent states to connected and synchronized ones. The synchronization and percolation are associated to abrupt transitions, and they are concurrently (and significantly) enhanced as compared to the non-adaptive case. Finally we provide evidence that only partial adaptation is sufficient to determine these enhancements. Our study, therefore, indicates that inclusion of simple adaptive mechanisms can efficiently describe some emergent features of networked systems' collective behaviors, and suggests also self-organized ways to control synchronization and percolation in natural and social systems

Are better conducting molecules more rigid?

We investigate the electronic origin of the bending stiffness of conducting molecules. It is found that the bending stiffness associated with electronic motion, which we refer to as electro-stiffness, $\kappa_{e}$, is governed by the molecular orbital overlap $t$ and the gap width $u$ between HOMO and LUMO levels, and behaves as $\kappa_{e}\sim t^{2}/\sqrt{u^2+t^{2}}$. To study the effect of doping, we analyze the electron filling-fraction dependence on $\kappa_{e}$ and show that doped molecules are more flexible. In addition, to estimate the contribution of $\kappa_{e}$ to the total stiffness, we consider molecules under a voltage bias, and study the length contraction ratio as a function of the voltage. The molecules are shown to be contracted or dilated, with $\kappa_{e}$ increasing nonlinearly with the applied bias

The Electronic and Superconducting Properties of Oxygen-Ordered MgB2 compounds of the form Mg2B3Ox

Possible candidates for the Mg2B3Ox nanostructures observed in bulk of polycrystalline MgB2 (Ref.1) have been studied using a combination of Z-contrast imaging, electron energy loss spectroscopy (EELS) and first-principles calculations. The electronic structures, phonon modes, and electron phonon coupling parameters are calculated for two oxygen-ordered MgB2 compounds of composition Mg2B3O and Mg2B3O2, and compared with those of MgB2. We find that the density of states for both Mg2B3Ox structures show very good agreement with EELS, indicating that they are excellent candidates to explain the observed coherent oxygen precipitates. Incorporation of oxygen reduces the transition temperature and gives calculated TC values of 18.3 K and 1.6 K for Mg2B3O and Mg2B3O2, respectively.Comment: Submitted to PR

Credit Risk and the Pricing of Japanese Yen Interest Rate Swaps

In this paper, we investigate the pricing of Japanese yen interest rate swaps during the period 1990-96. We obtain measures of the spreads of the swap rates over comparable Japanese Government Bonds (JGBs) for different maturities and analyze the relationship between the swap spreads and credit risk variables

Credit Risk and the Yen Interest Rate Swap Market

In this paper, we investigate the pricing of Japanese yen interest rate swaps during the period 1990-96. We obtain measures of the spreads of the swap rates over comparable Japanese Government Bonds (JGBs) for different maturities and analyze the relationship between the swap spreads and credit risk variables. Our empirical results in the yen swap market indicate that: 1) the commonly-used assumption of lognormal default-free interest rates and swap spreads is strongly rejected by the data, 2) the term structure of swap spreads displays a humped-shape, and 3) the shocks in the yen swap spread are negatively correlated with the shocks in the comparable default-free spot rates, especially for longer maturities. Our analysis also indicates that yen swap spreads behaved very differently from the credit spreads on Japanese corporate bonds in the early nineties. In contrast to Japanese corporate bonds, we find that the yen swap spread is also significantly related to proxies for the long-term credit risk factor. Furthermore, the swap spread is negatively related to the level and slope of the term structure and positively related to the curvature, indicating that the credit "optionality" is priced in the swap rate. Thus, overall, the yen swap market was sensitive to credit risk during the period of our study

Credit Risk and the Yen Interest Rate Swap Market

In this paper, we investigate the pricing of Japanese yen interest rate swaps during the period 1990-96. We obtain measures of the spreads of the swap rates over comparable Japanese Government Bonds (JGBs) for di erent maturities and analyze the relationship between the swap spreads and credit risk variables. Our empirical results in the yen swap market indicate that: 1) the commonly-used as- sumption of lognormal default-free interest rates and swap spreads is strongly rejected by the data, 2) the term structure of swap spreads displays a humped-shape, and 3) the shocks in the yen swap spread are negatively correlated with the shocks in the comparable default-free spot rates, especially for longer maturities. Our analysis also indicates that yen swap spreads behaved very di erently from the credit spreads on Japanese corporate bonds in the early nineties. In contrast to Japanese corporate bonds, we find that the yen swap spread is also significantly related to proxies for the longterm credit risk factor. Furthermore, the swap spread is negatively related to the level and slope of the term structure and positively related to the curvature, indicating that the credit \optionality" is priced in the swap rate. Thus, overall, the yen swap market was sensitive to credit risk during the period of our study

Electrical switching of magnetic polarity in a multiferroic BiFeO3 device at room temperature

We have directly imaged reversible electrical switching of the cycloidal rotation direction (magnetic polarity) in a (111)-BiFeO3 epitaxial-film device at room temperature by non-resonant x-ray magnetic scattering. Consistent with previous reports, fully relaxed (111)-BiFeO3 epitaxial films consisting of a single ferroelectric domain were found to comprise a sub-micron-scale mosaic of magneto-elastic domains, all sharing a common direction of the magnetic polarity, which was found to switch reversibly upon reversal of the ferroelectric polarization without any measurable change of the magneto-elastic domain population. A real-space polarimetry map of our device clearly distinguished between regions of the sample electrically addressed into the two magnetic states with a resolution of a few tens of micron. Contrary to the general belief that the magneto-electric coupling in BiFeO3 is weak, we find that electrical switching has a dramatic effect on the magnetic structure, with the magnetic moments rotating on average by 90 degrees at every cycle.Comment: 6 pages, 5 figures; corrected figure

Limitations of portfolio diversification through fat tails of the return Distributions: Some empirical evidence

This study investigates the level of risk due to fat tails of the return distribution and the changes of tail fatness (TF) through portfolio diversification. TF is not eliminated through portfolio diversification, and, interestingly, the positive tail has declining fatness until a certain level is reached, while the negative tail has rising fatness. This indicates that fat tails are highly relevant to common factors on systematic risk and that the relevance of common factors is higher for the negative tail compared to the positive tail. In the portfolio diversification effect, the declining fatness of the positive tail further reduces risk, but the rising fatness of the negative tail does not contribute to this effect. The asymmetry between the fatness of the positive and negative tails in the return distribution corresponds to the asymmetry of the trade-off relationship between loss avoidance and profit sacrifice that is expected as a consequence of portfolio diversification. Investors use portfolio diversification to reduce their risk of suffering high losses, but following this strategy means sacrificing high-profit potential. Our study provides empirical confirmation for the practical limitation of portfolio diversification and explains why investors with diversified portfolios suffer high losses from market crashes. An examination of the Northeast Asian stock markets of China, Japan, Korea, and Taiwan show identical results