Anisotropic softening of collective charge modes in the vicinity of critical doping in a doped Mott insulator

Momentum resolved inelastic resonant x-ray scattering is used to map the evolution of charge excitations over a large range of energies, momenta and doping levels in the electron doped Mott insulator class Nd$_{2-x}$Ce$_x$CuO$_4$. As the doping induced AFM-SC (antiferromagnetic-superconducting) transition is approached, we observe an anisotropic softening of collective charge modes over a large energy scale along the Gamma to (\pi,\pi)-direction, whereas the modes exhibit broadening ($\sim$ 1 eV) with relatively little softening along Gamma to (\pi,0) with respect to the parent Mott insulator (x=0). Our study indicates a systematic collapse of the gap consistent with the scenario that the system dopes uniformly with electrons even though the softening of the modes involves an unusually large energy scale.Comment: 5 pages + 5 Figure

Charge fluctuations and electron-phonon interaction in the finite-UU Hubbard model

In this paper we employ a gaussian expansion within the finite-$U$ slave-bosons formalism to investigate the momentum structure of the electron-phonon vertex function in the Hubbard model as function of $U$ and $n$. The suppression of large momentum scattering and the onset a small-${\bf q}$ peak structure, parametrized by a cut-off $q_c$, are shown to be essentially ruled by the band narrowing factor $Z_{\rm MF}$ due to the electronic correlation. A phase diagram of $Z_{\rm MF}$ and $q_c$ in the whole $U$-$n$ space is presented. Our results are in more than qualitative agreement with a recent numerical analysis and permit to understand some anomalous features of the Quantum Monte Carlo data.Comment: 4 pages, eps figures include

Asymptotically exact mean field theory for the Anderson model including double occupancy

The Anderson impurity model for finite values of the Coulomb repulsion $U$ is studied using a slave boson representation for the empty and doubly occupied $f$-level. In order to avoid well known problems with a naive mean field theory for the boson fields, we use the coherent state path integral representation to first integrate out the double occupancy slave bosons. The resulting effective action is linearized using {\bf two-time} auxiliary fields. After integration over the fermionic degrees of freedom one obtains an effective action suitable for a $1/N_f$-expansion. Concerning the constraint the same problem remains as in the infinite $U$ case. For $T \rightarrow 0$ and $N_f \rightarrow \infty$ exact results for the ground state properties are recovered in the saddle point approximation. Numerical solutions of the saddle point equations show that even in the spindegenerate case $N_f = 2$ the results are quite good.Comment: 19, RevTeX, cond-mat/930502

Application of Hansch’s Model to Capsaicinoids and Capsinoids: A Study Using the Quantitative Structure−Activity Relationship. A Novel Method for the Synthesis of Capsinoids

We describe a synthetic approach for two families of compounds, the capsaicinoids and capsinoids, as part of a study of the quantitative relationship between structure and activity

Effect of strong correlations on the high energy anomaly in hole- and electron-doped high-Tc superconductors

Recently, angle-resolved photoemission spectroscopy (ARPES) has been used to highlight an anomalously large band renormalization at high binding energies in cuprate superconductors: the high energy 'waterfall' or high energy anomaly (HEA). This paper demonstrates, using a combination of new ARPES measurements and quantum Monte Carlo simulations, that the HEA is not simply the by-product of matrix element effects, but rather represents a cross-over from a quasiparticle band at low binding energies near the Fermi level to valence bands at higher binding energy, assumed to be of strong oxygen character, in both hole- and electron-doped cuprates. While photoemission matrix elements clearly play a role in changing the aesthetic appearance of the band dispersion, i.e. the 'waterfall'-like behavior, they provide an inadequate description for the physics that underlies the strong band renormalization giving rise to the HEA. Model calculations of the single-band Hubbard Hamiltonian showcase the role played by correlations in the formation of the HEA and uncover significant differences in the HEA energy scale for hole- and electron-doped cuprates. In addition, this approach properly captures the transfer of spectral weight accompanying both hole and electron doping in a correlated material and provides a unifying description of the HEA across both sides of the cuprate phase diagram.Comment: Original: 4 pages, 4 figures; Replaced: changed and updated content, 12 pages, 6 figure

Generation of tooth profile for roots rotor based on virtual linkage associated with Assur group

This article, for the first time, presents the generation of Roots rotor tooth profiles based on an Assur-group-associated virtual linkage method. Taking the original Roots rotor as an example, structure and geometry of the Roots rotor are introduced, and based on the principle of inversion, an equivalent virtual linkage is identified for generating dedendum tooth profile of the rotor. Using linkage decomposition associated with elemental Assur groups, algorithm for computing the tooth curve is constructed leading to the explicit expression of rotor profile and the corresponding numerical simulation, verifying the validity of the proposed approach. For demonstration purpose, the virtual linkage method is then extended to the generation of tooth profiles for the variants of Roots rotors with arc-cycloidal curves and arc-involute curves. Integrated with computer-aided design, computer-aided engineering and computer-aided manufacturing software platforms, as well as the three-dimensional printing technology, this article provides an efficient and intuitive approach for Roots rotor system design, analysis and development

The periodic Anderson model from the atomic limit and FeSi

The exact Green's functions of the periodic Anderson model for $U\to \infty$ are formally expressed within the cumulant expansion in terms of an effective cumulant. Here we resort to a calculation in which this quantity is approximated by the value it takes for the exactly soluble atomic limit of the same model. In the Kondo region a spectral density is obtained that shows near the Fermi surface a structure with the properties of the Kondo peak. Approximate expressions are obtained for the static conductivity $$ and magnetic susceptibility $\chi (T)$ of the PAM, and they are employed to fit the experimental values of FeSi, a compound that behaves like a Kondo insulator with both quantities vanishing rapidly for $T\to 0$. Assuming that the system is in the intermediate valence region, it was possible to find good agreement between theory and experiment for these two properties by employing the same set of parameters. It is shown that in the present model the hybridization is responsible for the relaxation mechanism of the conduction electrons.Comment: 26 pages and 8 figure

Apparatus for a Search for T-violating Muon Polarization in Stopped-Kaon Decays

The detector built at KEK to search for T-violating transverse muon polarization in K+ --> pi0 mu+ nu (Kmu3) decay of stopped kaons is described. Sensitivity to the transverse polarization component is obtained from reconstruction of the decay plane by tracking the mu+ through a toroidal spectrometer and detecting the pi0 in a segmented CsI(Tl) photon calorimeter. The muon polarization was obtained from the decay positron asymmetry of muons stopped in a polarimeter. The detector included features which minimized systematic errors while maintaining high acceptance.Comment: 56 pages, 30 figures, submitted to NI

Condition Indices as Surrogates of Energy Density and Lipid Content in Juveniles of Three Fish Species

To guide the selection of condition indices for juvenile fishes, we compared the ability of several indirect condition indices (those based on length-mass relationships, the hepatosomatic index, and relative lipid estimates from the Distell fish fatmeter) to assess energy density and lipid content of Summer Flounder Paralichthys dentatus, Striped BassMorone saxatilis, and Atlantic Croakers Micropogonias undulatus. These species use estuarine areas as nurseries, but they have different life history strategies and ecological niches that affect their energy storage strategies. We tested hypotheses that differences in the distribution and role of lipids as energy stores among species would influence the suitability of condition indices for estimating energy and lipid content. Length-based indices were most suitable for estimating energy and lipid content of juvenile Summer Flounder and Striped Bass, suggesting that length-based indices may be appropriate for juveniles that store energy as proteins (i.e., juveniles with low lipid content). The fatmeter suitably predicted energy and lipid content of Atlantic Croakers, indicating its potential for assessing condition of juveniles that store lipids for migration and that display a high range of observed lipid content. Even though a small size range was examined, fish length improved predictions of energy and lipid content for some of the indirect condition indices for Atlantic Croakers and Summer Flounder, suggesting that fish length should be considered when developing relationships among measures of condition. The selection of condition indices should be tailored to the life stage and species of interest based on the energy and lipid storage strategies used by the fish