On confined fractional charges: a simple model

We address the question whether features known from quantum chromodynamics (QCD) can possibly also show up in solid-state physics. It is shown that spinless fermions of charge $e$ on a checkerboard lattice with nearest-neighbor repulsion provide for a simple model of confined fractional charges. After defining a proper vacuum the system supports excitations with charges $\pm e/2$ attached to the ends of strings. There is a constant confining force acting between the fractional charges. It results from a reduction of vacuum fluctuations and a polarization of the vacuum in the vicinity of the connecting strings.Comment: 5 pages, 3 figure

Eosinophil Response in Guinea Pig Skin to a Low Molecular Weight Eosinophil Chemotactic Factor Extracted from Livers of Mice with Schistosomiasis

A low-molecular weight eosinophil chemotactic factor (ECF-G), isolated and partially purified from livers of mice with schistosomiasis, was injected intradermally into guinea pigs. Biopsies obtained were studied for inflammatory cell accumulation in the injected sites and compared with those in the control sites injected with phosphate buffered saline. Tissue eosinophilia was seen as early as 1hr after injection of ECF-G, but not in the control site. The increase of eosinophilia appeared biphasic with peaks at 6 and 24hr. Mast cells increased in both ECF-G and saline injected sites and the increase was still found at 120hr after injection. Neutrophils also increased in both ECF-G and saline injected sites but disappeared within 48hr.These findings indicate that ECF-G is a tissue and species nonspecific eosinophil chemotactic factor, and injection of ECF-G initiates interaction of eosinophils and mast cells in the skin

Non-resonant inelastic x-ray scattering involving excitonic excitations

In a recent publication Larson \textit{et al.} reported remarkably clear $d$-$d$ excitations for NiO and CoO measured with x-ray energies well below the transition metal $K$ edge. In this letter we demonstrate that we can obtain an accurate quantitative description based on a local many body approach. We find that the magnitude of $\vec{q}$ can be tuned for maximum sensitivity for dipole, quadrupole, etc. excitations. We also find that the direction of $\vec{q}$ with respect to the crystal axes can be used as an equivalent to polarization similar to electron energy loss spectroscopy, allowing for a determination of the local symmetry of the initial and final state based on selection rules. This method is more generally applicable and combined with the high resolution available, could be a powerful tool for the study of local distortions and symmetries in transition metal compounds including also buried interfaces

Spectral signatures of the Luttinger liquid to charge-density-wave transition

Electron- and phonon spectral functions of the one-dimensional, spinless-fermion Holstein model at half filling are calculated in the four distinct regimes of the phase diagram, corresponding to an attractive or repulsive Luttinger liquid at weak electron-phonon coupling, and a band- or polaronic insulator at strong coupling. The results obtained by means of kernel polynomial and systematic cluster approaches reveal substantially different physics in these regimes and further indicate that the size of the phonon frequency significantly affects the nature of the quantum Peierls phase transition.Comment: 5 pages, 4 figures; final version, accepted for publication in Physical Review

A Micro-Raman Spectroscopic Study of Hydrazine-Treated Human Dental Calculus

Hydrazine has been used to remove organic components and to isolate the mineral(s) from human calculus. Micro-Raman measurements were performed on the mineral phase. After the hydrazine-treatment, not only a large reduction in fluorescence but also an increase in Raman signal was observed. The treatment was essential in minimizing thermally-induced chemical changes which could otherwise occur to the original calculus mineral due to the intense laser light. The Raman spectral features of the mineral were nearly all identical among the Raman spectra obtained at many randomly-selected sites by the micro-Raman microbe with a lateral resolution of approximately 1 μm, and were consistent with those of impure hydroxyapatite containing CO32- and HPO42-. The spectra contained typical hydroxyapatite bands including PO43- bands of the v1, v2, v3 and v4 modes and one OH- stretch band. Other minor bands due to the CO32- v1 and v3 modes and bands possibly due to the HPO42- v1, v2 and v4 modes were observable by the technique despite the hydrazine-treatment that could in principle remove the HPO4 and CO3 ions from the mineral. In comparison with pure synthetic hydroxyapatite, the intensity of the OH- stretch band relative to that of the PO43- v1 band was approximately 70% weaker, and the bandwidth of the phosphate v1 band was 200% broader, reflecting various crystal imperfections presumably present in the calculus mineral

Riemannian Metric and Geometric Mean for Positive Semidefinite Matrices of Fixed Rank

This paper introduces a new metric and mean on the set of positive semidefinite matrices of fixed-rank. The proposed metric is derived from a well-chosen Riemannian quotient geometry that generalizes the reductive geometry of the positive cone and the associated natural metric. The resulting Riemannian space has strong geometrical properties: it is geodesically complete, and the metric is invariant with respect to all transformations that preserve angles (orthogonal transformations, scalings, and pseudoinversion). A meaningful approximation of the associated Riemannian distance is proposed, that can be efficiently numerically computed via a simple algorithm based on SVD. The induced mean preserves the rank, possesses the most desirable characteristics of a geometric mean, and is easy to compute.Comment: the present version is very close to the published one. It contains some corrections with respect to the previous arxiv submssio

Bipolarons in the Extended Holstein Hubbard Model

We numerically and analytically calculate the properties of the bipolaron in an extended Hubbard Holstein model, which has a longer range electron-phonon coupling like the Fr\" ohlich model. In the strong coupling regime, the effective mass of the bipolaron in the extended model is much smaller than the Holstein bipolaron mass. In contrast to the Holstein bipolaron, the bipolaron in the extended model has a lower binding energy and remains bound with substantial binding energy even in the large-U limit. In comparison with the Holstein model where only a singlet bipolaron is bound, in the extended Holstein model a triplet bipolaron can also form a bound state. We discuss the possibility of phase separation in the case of finite electron doping.Comment: 5 pages, 3 figure

Inter-Intra Molecular Dynamics as an Iterated Function System

The dynamics of units (molecules) with slowly relaxing internal states is studied as an iterated function system (IFS) for the situation common in e.g. biological systems where these units are subjected to frequent collisional interactions. It is found that an increase in the collision frequency leads to successive discrete states that can be analyzed as partial steps to form a Cantor set. By considering the interactions among the units, a self-consistent IFS is derived, which leads to the formation and stabilization of multiple such discrete states. The relevance of the results to dynamical multiple states in biomolecules in crowded conditions is discussed.Comment: 7 pages, 7 figures. submitted to Europhysics Letter