Path Integral Description of a Semiclassical Su-Schrieffer-Heeger Model

The electron motion along a chain is described by a continuum version of the Su-Schrieffer-Heeger Hamiltonian in which phonon fields and electronic coordinates are mapped onto the time scale. The path integral formalism allows us to derive the non local source action for the particle interacting with the oscillators bath. The method can be applied for any value of the {\it e-ph} coupling. The path integral dependence on the model parameters has been analysed by computing the partition function and some thermodynamical properties from $T= 1K$ up to room temperature. A peculiar upturn in the low temperature {\it heat capacity over temperature} ratio (pointing to a glassy like behavior) has been ascribed to the time dependent electronic hopping along the chain

Superconductivity from correlated hopping

We consider a chain described by a next-nearest-neighbor hopping combined with a nearest-neighbor spin flip. In two dimensions this three-body term arises from a mapping of the three-band Hubbard model for CuO$_2$ planes to a generalized $t-J$ model and for large O-O hopping favors resonance-valence-bond superconductivity of predominantly $d$-wave symmetry. Solving the ground state and low-energy excitations by analytical and numerical methods we find that the chain is a Luther-Emery liquid with correlation exponent $K_{\rho} = (2-n)^2/2$, where $n$ is the particle density.Comment: 10 pages, RevTeX 3.0 + 2 PostScript figs. Accepted for publication in Phys.Rev.

Psychometric qualities of a brief self-rated fatigue measure:The Fatigue Assessment Scale

Objective: The main aim of this study was to examine the dimensionality and psychometric qualities of a new 10-item fatigue measure, the Fatigue Assessment Scale (FAS). Methods: As part of a longitudinal study, the respondents, all workers with at least 20 working hours per week, completed the FAS, four related fatigue measures, a depression questionnaire, and an emotional stability scale. Results: The FAS had a high internal consistency. The pattern of correlations and factor analysis showed good convergent and divergent validity. The FAS correlated strongly with the other fatigue scales. In a factor analysis of the five fatigue questionnaires, the FAS had the highest factor loading on a clear one-factor solution. Moreover, factor analyses revealed that fatigue, on the one hand, and depression and emotional stability, on the other hand, are separate constructs. Finally, it was shown that 8 out of the 10 FAS items were unbiased concerning gender; two had a uniform bias. Conclusions: The FAS represents a potentially valuable assessment instrument with promising internal consistency reliability and validity. Gender bias in the FAS does not have consequences for use of the FAS.

In search of personality and temperament predictors of chronic fatigue:a prospective study

This prospective study examined the relationships between temperament and personality, on the one hand, and chronic fatigue, on the other hand. The temperament variables were the Five-Factor-Model dimensions Emotional stability and Extraversion as well as Pavlovian temperament traits. The personality variables were the Five-Factor-Model dimensions Agreeableness, Conscientiousness and Autonomy, plus hardiness and Type A behavior pattern. It was expected that these person characteristics were negatively linked to fatigue except for (1) Type A and (2) Conscientiousness and Autonomy, which were scrutinized in an exploratory way. Respondents (N=351), working at least 20 h per week, completed two surveys. The first survey contained the temperament and personality questionnaires and the fatigue scale, while the second one, 2 years later, included the fatigue scale. Results indicated that high scores on the Five-Factor-Model dimensions Emotional Stability and Extraversion, the Pavlovian temperament variable Strength of Inhibition, and the hardiness component Commitment predicted lower fatigue scores. However, when in the analysis fatigue measured 2 years earlier was controlled for, only Extraversion and Strength of Inhibition appeared to be good predictors. Even so, these two predictors did not explain a large proportion of the variance. When men and women were examined separately, personality and temperament predicted almost nihil. In conclusion, when fatigue measured earlier is controlled for, the direct role of temperament and personality decreases enormously.