Once again on electromagnetic properties of a domain wall interacting with charged fermions

The response to a magnetic flux is considered of the vacuum state of charged Dirac fermions interacting with a domain wall made of a neutral spinless field in (3+1) dimensions with the fermion mass having a phase variation across the wall. It is pointed out that due to simple C parity arguments the spontaneous magnetization for this system is necessarily zero, thus invalidating some claims to the contrary in the literature. The cancellation of the spontaneous magnetization is explicitly demonstrated in a particular class of models. The same calculation produces a general formula for the electric charge density induced by the magnetic flux -- an effect previously discussed in the literature for axionic domain walls. The distribution of the induced charge is calculated in specific models.Comment: 15 page

Oxygen Reduction Activity of Silk-derived Carbons

Carbonized silk fibroin (CS), which is free of metallic elements, showed high catalytic activity for oxygen-reduction reaction (ORR). The catalytic activity of CS for ORR was greatly enhanced by steam activation forming silk-derived activated carbon (CS-AC). The surface morphology, surface area, pore structure and remaining nitrogen species of the CSs were compared with those of the CS-ACs. The open-circuit potential and the power density of a polymer electrolyte fuel cell using a CS900-AC, which was heat-treated at 900 degrees C prior to the steam activation, and a platinum/C (C: carbon black) anode under pure oxygen and hydrogen gases, respectively, both at 0.2 MPa, were 0.92 V and 142 mW cm(-2) at 80 degrees C. The ORR on the activated carbon, CS900-AC, proceeded with a 3.5-electron reaction at 0.6V (vs. RHE): however, this was improved to a 3.9-electron reaction with the addition of zirconium oxide at 20 wt% to CS900-AC.ArticleJournal of Power Sources. 195(18):5840-5847. (2010)journal articl

Ferromagnetic Domain Wall and Primeval Magnetic Field

We show that coherent magnetic field is generated spontaneously when a large domain wall is created in the early universe. It is caused by two dimensional massless fermions bounded to the domain wall soliton. We point out that the magnetic field is a candidate of primordial magnetic field.Comment: zero point energy missed in previous version is include

Primordial galactic magnetic fields from domain walls at the QCD phase transition

We propose a mechanism to generate large-scale magnetic fields with correlation lengths of 100 kpc. Domain walls with QCD scale internal structure form and coalesce obtaining Hubble scale correlations and align nucleon spins. Due to strong CP violation, nucleons in these walls have anomalous electric and magnetic dipole moments and thus the walls are ferromagnetic. This induces electromagnetic fields with Hubble size correlations. The same CP violation also induces a maximal helicity (Chern-Simons) correlated through the Hubble volume which supports an inverse cascade allowing the initial correlations to grow to 100 kpc today. We estimate the generated electromagnetic fields in terms of the QCD parameters and discuss the effects of the resulting fields.Comment: 5 pages, REVTex. Published versio

Parton energy loss at strong coupling and the universal bound

The apparent universality of jet quenching observed in heavy ion collisions at RHIC for light and heavy quarks, as well as for quarks and gluons, is very puzzling and calls for a theoretical explanation. Recently it has been proposed that the synchrotron--like radiation at strong coupling gives rise to a universal bound on the energy of a parton escaping from the medium. Since this bound appears quite low, almost all of the observed particles at high transverse momentum have to originate from the surface of the hot fireball. Here I make a first attempt of checking this scenario against the RHIC data and formulate a "Universal Bound Model" of jet quenching that can be further tested at RHIC and LHC.Comment: 8 pages, 2 figures, invited plenary talk given at "Hard Probes 2008" Conference, 8-14 June 2008, Illa da Toxa, Galicia, Spai

Expanding frontiers in materials chemistry and physics with multiple anions

During the last century, inorganic oxide compounds laid foundations for materials synthesis, characterization, and technology translation by adding new functions into devices previously dominated by main-group element semiconductor compounds. Today, compounds with multiple anions beyond the single-oxide ion, such as oxyhalides and oxyhydrides, offer a new materials platform from which superior functionality may arise. Here we review the recent progress, status, and future prospects and challenges facing the development and deployment of mixed-anion compounds, focusing mainly on oxide-derived materials. We devote attention to the crucial roles that multiple anions play during synthesis, characterization, and in the physical properties of these materials. We discuss the opportunities enabled by recent advances in synthetic approaches for design of both local and overall structure, state-of-the-art characterization techniques to distinguish unique structural and chemical states, and chemical/physical properties emerging from the synergy of multiple anions for catalysis, energy conversion, and electronic materials