Charge transfer polarisation wave in high Tc oxides and superconductive pairing

A general formalism of quantized charge transfer polarization waves was developed. The nature of possible superconductive pairing between oxygen holes is discussed. Unlike optical phonons, these polarization fields will give rise to dielectric bipolarons or bipolaron bubbles. In the weak coupling limit, a new class of superconductivity is to be expected

Exploring reasons for MD-PhD trainees\u27 experiences of impostor phenomenon

BACKGROUND: Acceptance into U.S. MD-PhD dual-degree programs is highly competitive, and the lengthy training program requires transitioning between multiple phases (pre-clinical-, PhD-research-, and clinical-training phases), which can be stressful. Challenges faced during MD-PhD training could exacerbate self-doubt and anxiety. Impostor phenomenon is the experience of feeling like a fraud, with some high-achieving, competent individuals attributing their successes to luck or other factors rather than their own ability and hard work. To our knowledge, impostor phenomenon among MD-PhD trainees has not been described. This study examined impostor phenomenon experiences during MD-PhD training and reasons trainees attributed to these feelings. METHODS: Individuals in science and medicine fields participated in an online survey that included the 20-item Clance Impostor Phenomenon Scale (CIPS); higher scores (range 20-100) indicate more frequent impostor phenomenon. Some respondents who reported experiencing impostor phenomenon also voluntarily completed a semi-structured interview, sharing experiences during training that contributed to feelings of impostor phenomenon. Interview transcripts were coded and analysed using the constant comparative method and analytic induction to identify themes. RESULTS: Of 959 survey respondents (students and professionals in science and medicine), 13 MD-PhD students and residents completed the survey, nine of whom (five male, four female; four white, five other race-ethnicity) also completed an interview. These participants experienced moderate-to-intense scores on the CIPS (range: 46-96). Four themes emerged from the interview narratives that described participants\u27 experiences of IP: professional identity formation, fear of evaluation, minority status, and, program-transition experiences. All reported struggling to develop a physician-scientist identity and lacking a sense of belonging in medicine or research. CONCLUSIONS: Impostor experiences that MD-PhD participants attributed to bias and micro-aggressions in social interactions with peers, faculty, and patients challenged their professional identity formation as physician-scientists. It is important to further examine how MD-PhD-program structures, cultures, and social interactions can lead to feelings of alienation and experiences of impostor phenomenon, particularly for students from diverse and underrepresented populations in medicine

Post-mining neutralization of acidic surface mine lakes

Twenty core samples and 54 surface sediment samples were taken from surface mine lakes in Missouri, Illinois, and Indiana to determine the rates of neutralization of acid mine lakes. Sediment samples were analyzed for diatom microfossils, selected chemical elements, and the radionuclide, lead-210. The surface samples showed that there were strong differences in diatom microfossils between acidic and neutral lakes but there was no strong difference in sediment chemical composition between acidic and neutral lakes. Of 20 lakes from which cores were examined, 9 showed diatom evidence of neutralization and one of acidification over time. Cores from 5 of these were dated using lead-210 analysis. Diatom microfossils showed that neutralization took from less than 3 years to 30 years to occur. Comparisons between lake sediment and water column chemistry indicated that neither sulfide deposition nor H2S outgasing is likely to play a major role in the neutralization process. Chemical analyses of lake sediment showed that the sediment is a sink for heavy metals. These metals are held as sulfides. There is also a considerable fraction of metal ions strongly bound to clays. This research demonstrates that acid lake neutralization is common, that it occurs over moderate time spans and that the rate is controlled by rates of acid supply from the watershed.U.S. Department of the InteriorU.S. Geological SurveyOpe

Comment on `Experimental and Theoretical Constraints of Bipolaronic Superconductivity in High TcT_{c} Materials: An Impossibility'

We show that objections raised by Chakraverty $et$ $al$ (Phys. Rev. Lett. 81, 433 (1998)) to the bipolaron model of superconducting cuprates are the result of an incorrect approximation for the bipolaron energy spectrum and misuse of the bipolaron theory. The consideration, which takes into account the multiband energy structure of bipolarons and the unscreened electron-phonon interaction clearly indicates that cuprates are in the Bose-Einstein condensation regime with mobile charged bosons.Comment: 1 page, no figure

Disorder Effects in the Bipolaron System Ti4_{4}O7_{7} Studied by Photoemission Spectroscopy

We have performed a photoemission study of Ti$_{4}$O$_{7}$ around its two transition temperatures so as to cover the metallic, high-temperature insulating (bipolaron-liquid), and low-temperature insulating (bipolaron-crystal) phases. While the spectra of the low-temperature insulating phase show a finite gap at the Fermi level, the spectra of the high-temperature insulating phase are gapless, which is interpreted as a soft Coulomb gap due to dynamical disorder. We suggest that the spectra of the high-temperature disordered phase of Fe$_{3}$O$_{4}$, which exhibits a charge order-disorder transition (Verwey transition), can be interpreted in terms of a Coulomb gap.Comment: 4 pages, 3 epsf figures embedde

The Gibbs-Thomson formula at small island sizes - corrections for high vapour densities

In this paper we report simulation studies of equilibrium features, namely circular islands on model surfaces, using Monte-Carlo methods. In particular, we are interested in studying the relationship between the density of vapour around a curved island and its curvature-the Gibbs-Thomson formula. Numerical simulations of a lattice gas model, performed for various sizes of islands, don't fit very well to the Gibbs-Thomson formula. We show how corrections to this form arise at high vapour densities, wherein a knowledge of the exact equation of state (as opposed to the ideal gas approximation) is necessary to predict this relationship. Exploiting a mapping of the lattice gas to the Ising model one can compute the corrections to the Gibbs-Thomson formula using high field series expansions. We also investigate finite size effects on the stability of the islands both theoretically and through simulations. Finally the simulations are used to study the microscopic origins of the Gibbs-Thomson formula. A heuristic argument is suggested in which it is partially attributed to geometric constraints on the island edge.Comment: 27 pages including 7 figures, tarred, gzipped and uuencoded. Prepared using revtex and espf.sty. To appear in Phys. Rev.

Low 25(OH) vitamin D concentrations in international UK track and field athletes

Objective. While it is recognised that vitamin D deficiency iscommon in the general population, there have been no studies inelite athletes in the UK. This observational study aimed to assessthe 25 hydroxy-vitamin D (25(OH)D) status of elite athletes onthe Great Britain track and field team.Methods. A cross-sectional observational study was performedby analysing blood results from elite athletes on the British athleticsteam (N=63; mean ± standard deviation (SD) age 24.9±4.2 years).Athletes on the elite programme were offered blood tests throughthe winter and summer of 2009 and were eligible for inclusion inthe study.Results. Nineteen per cent (n=12) of athletes in the currentstudy can be classified as 25(OH)D deficient (<20 mcg/l), while afurther 29% (n=18) can be classified as having insufficient serum25(OH)D levels (20 - 30 mcg/l). Female sex (insufficent anddeficient OH(D) prevalence 58%, n=18) and dark skin (prevalence65%, n=20) were found to be independent predictors of serum25(OH)D levels of <30 mcg/l.Conclusion. This study reveals a notable prevalence of low serum25(OH)D levels in elite athletes and subsequent management ofdeficient athletes is likely to be of importance for athlete health.The impact of these results on athletic performance remains to bedetermined, and clinical trials to assess performance, particularlymuscular performance, following correction of 25(OH)D status indeficient athletes are required

Unconventional spin density wave in (TMTSF)2PF6 below T* ~ 4K

The presence of subphases in spin-density wave (SDW) phase of (TMTSF)2PF6 below T* ~ 4K has been suggested by several experiments but the nature of the new phase is still controversial. We have investigated the temperature dependence of the angular dependence of the magnetoresistance in the SDW phase which shows different features for temperatures above and below T*. For T > 4K the magnetoresistance can be understood in terms of the Landau quantization of the quasiparticle spectrum in a magnetic field, where the imperfect nesting plays the crucial role. We propose that below T* ~ 4K the new unconventional SDW (USDW) appears modifying dramatically the quasiparticle spectrum. Unlike conventional SDW the order parameter of USDW depends on the quasiparticle momentum. The present model describes many features of the angular dependence of magnetoresistance reasonably well. Therefore, we may conclude that the subphase in (TMTSF)2PF6 below T* ~ 4K is described as SDW plus USDW.Comment: 7 pages, 9 figures, RevTeX4; misprint corrected, references updated, a few sentences adde