Polaron and Bipolaron Defects in a Charge Density Wave: a Model for Lightly Doped BaBiO3

BaBiO3 is a prototype ``charge ordering system'' forming interpenetrating sublattices with nominal valence Bi(3+) and Bi(5+). It can also be regarded as a three-dimensional version of a Peierls insulator, the insulating gap being a consequence of an ordered distortion of oxygen atoms. When holes are added to BaBiO3 by doping, it remains insulating until a very large hole concentration is reached, at which point it becomes superconducting. The mechanism for insulating behavior of more lightly-doped samples is formation of small polarons or bipolarons. These are self-organized point defects in the Peierls order parameter, which trap carriers in bound states inside the Peierls gap. We calculate properties of the polarons and bipolarons using the Rice-Sneddon model. Bipolarons are the stable defect; the missing pair of electrons come from an empty midgap state built from the lower Peierls band. Each bipolaron distortion also pulls down six localized states below the bottom of the unoccupied upper Peierls band. The activation energy for bipolaron hopping is estimated.Comment: 9 pages with 8 embedded figures. See also cond-mat/0108089, a paper of 5 pages on the related topic of self-trapped excitons in BaBiO

Risk-based capital and deposit insurance reform

Risk-based capital (RBC) is an important component of deposit insurance reform. This paper provides an empirical analysis of the new 1992 RBC bank standards, applying them to data on virtually all U.S. banks from 1982 to 1989. The data reveal strong associations between several measures of future bank performance (including bankruptcy) and the RBC relative risk weights. These associations suggest that the weights constitute a significant improvement over the old capital standards, although there are several instances in which the weights for specific categories appear to be out of line with the performance results. Tests of the informational value of passing or failing the new and old capital standards show that both have independent information, but that the new RBC standards better predict future bank performance problems. The data also indicate that, in contrast to the old standards, the RBC capital burden falls much more heavily on large banks. As a result, banks representing more than one-fourth of all bank assets would have failed the new RBC standards as of 1989. The new standards are also more stringent overall. More banks would have failed the new standards than the old ones, with larger average capital deficiencies.Deposit insurance ; Bank supervision ; Bank capital

Loan commitments and bank risk exposure

Loan commitments increase a bank's risk by obligating it to issue future loans under terms that it might otherwise refuse. However, moral hazard and adverse selection problems potentially may result in these contracts being rationed or sorted. Depending on the relative risks of the borrowers who do and do not receive commitments, commitment loans could be safer or riskier on average than other loans. the empirical results indicate that commitment loans tend to have slightly better than average performance, suggesting that commitments generate little risk or that this risk is offset by the selection of safer borrowers.Bank loans ; Risk

Efficiency of Financial Institutions: International Survey and Directions for Future Research

This paper surveys 130 studies that apply frontier efficiency analysis to financial institutions in 21 countries. The primary goals are to summarize and critically review empirical estimates of financial institution efficiency and to attempt to arrive at a consensus view. We find that the various efficiency methods do not necessarily yield consistent results and suggest some ways that these methods might be improved to bring about findings that are more consistent, accurate, and useful. Secondary goals are to address the implications of efficiency results for financial institutions in the areas of government policy, research, and managerial performance. Areas needing additional research are also outlined.

Operation LION - Report for period of the flight of Apollo 11

Observations by Lunar International Observers Network and astronauts of lunar phenomena during Apollo 11 fligh

Inefficiency and productivity growth in banking: a comparison of stochastic econometric and thick frontier methods

A comparison of alternative methods for estimating inefficiency and productivity growth in banking, showing that inefficiencies are sufficiently large to dominate scale economies and that measured technological progress has been small, or even negative, as a result of institutional events that occurred during 1977-88.Banks and banking - Costs ; Production (Economic theory)

Small-q electron-phonon scattering and linear dc resistivity in high-T_c oxides

We examine the effect on the DC resistivity of small-q electron-phonon scattering, in a system with the electronic topology of the high-T_c oxides. Despite the fact that the scattering is dominantly forward, its contribution to the transport can be significant due to ``ondulations'' of the bands in the flat region and to the umpklapp process. When the extended van-Hove singularities are sufficiently close to $E_F$ the acoustic branch of the phonons contribute significantly to the transport. In that case one can obtain linear $T$ dependent resistivity down to temperatures as low as 10 K, even if electrons are scattered also by optical phonons of about 500 K as reported by Raman measurements.Comment: LATEX file and 4 Postscript figure

Euclidean Thermal Green Functions of Photons in Generalized Euclidean Rindler Spaces for any Feynman-like Gauge

The thermal Euclidean Green functions for Photons propagating in the Rindler wedge are computed employing an Euclidean approach within any covariant Feynman-like gauge. This is done by generalizing a formula which holds in the Minkowskian case. The coincidence of the found (\be=2\pi)-Green functions and the corresponding Minkowskian vacuum Green functions is discussed in relation to the remaining static gauge ambiguity already found in previous papers. Further generalizations to more complicated manifolds are discussed. Ward identities are verified in the general case.Comment: 12 pages, standard latex, no figures, some signs changed, more comments added, final version to appear on Int. J. Mod. Phys.