Psychological distress and chronic obstructive pulmonary disease in the Renfrew and Paisley (MIDSPAN) study

Background: This study examined whether psychological distress might be a predictor of chronic obstructive pulmonary disease (COPD). Method: The relation between psychological distress at baseline, measured by the general health questionnaire (GHQ), and chronic bronchitis three years later, as measured by the Medical Research Council (MRC) bronchitis questionnaire and forced expiratory flow in one second (FEV1), was examined in 1682 men and 2203 women from the Renfrew and Paisley (MIDSPAN) study. The analyses were run on men and women separately and adjustments were made for age, socioeconomic position, and lung function at baseline (FEV1). People with chronic diseases at baseline were then excluded to give a "healthy" baseline cohort. The effect of psychological distress on individual components of the MRC bronchitis questionnaire and FEV1 was also assessed. Results: In multivariate analyses of the whole cohort baseline psychological distress in women was associated with reduced FEV1 at follow up (OR 1.31 95% CI 1.0 to 1.73) after adjustment. In women, in the healthy cohort, psychological distress was associated with chronic bronchitis (OR 2.00, 95% CI 1.16 to 3.46), symptoms of bronchial infection (OR 2.14, 95% CI 1.44 to 3.19), symptoms of breathlessness (OR 3.02, 95% CI 1.99 to 4.59), and reduced FEV1 (OR 1.62, 95% CI 1.13 to 2.32). In men psychological distress predicted symptoms of bronchial infection (OR 2.09, 95% CI 1.28 to 3.42). Conclusion: This study supports research suggesting that psychological distress is associated with COPD and shows that psychological distress predicts COPD in women. The robustness of the association and the exact mechanism requires further investigation

Feasibility Study of a Bi-directional Centrifugal Pump for DBT class 45 CST Gearbox Used in Underground Coal mining Operation

This paper presents a feasibility study of using a bi-directional centrifugal pump into DBT’s Series 45 CST gearbox. The suitability of other pumps for cooling and the design of a new symmetrical centrifugal pump that would be suited to the series 45 CST gearbox have been reviewed with financial versus functionality and usability. The analysis and results of this study indicate that by introducing the newly designed bi-directional pump, DBT may save over $370k in production costs over 10 years. This equates to a savings of$1850 per gearbox which is about a 26% saving on the current set-up, and thus bi-directional pump is reasonably feasible

Wick's Theorem and a New Perturbation Theory Around the Atomic Limit of Strongly Correlated Electron Systems

A new type of perturbation expansion in the mixing $V$ of localized orbitals with a conduction-electron band in the $U\to\infty$ Anderson model is presented. It is built on Feynman diagrams obeying standard rules. The local correlations of the unperturbed system (the atomic limit) are included exactly, no auxiliary particles are introduced. As a test, an infinite-order ladder-type resummation is analytically treated in the Kondo regime, recovering the correct energy scale. An extension to the Anderson-lattice model is obtained via an effective-site approximation through a cumulant expansion in $V$ on the lattice. Relation to treatments in infinite spatial dimensions are indicated.Comment: selfextracting postscript file containing entire paper (10 pages) including 3 figures, in case of trouble contact author for LaTeX-source or hard copies (prep0994

On the correct continuum limit of the functional-integral representation for the four-slave-boson approach to the Hubbard model: Paramagnetic phase

The Hubbard model with finite on-site repulsion U is studied via the functional-integral formulation of the four-slave-boson approach by Kotliar and Ruckenstein. It is shown that a correct treatment of the continuum imaginary time limit (which is required by the very definition of the functional integral) modifies the free energy when fluctuation (1/N) corrections beyond mean-field are considered. Our analysis requires us to suitably interpret the Kotliar and Ruckenstein choice for the bosonic hopping operator and to abandon the commonly used normal-ordering prescription, in order to obtain meaningful fluctuation corrections. In this way we recover the exact solution at U=0 not only at the mean-field level but also at the next order in 1/N. In addition, we consider alternative choices for the bosonic hopping operator and test them numerically for a simple two-site model for which the exact solution is readily available for any U. We also discuss how the 1/N expansion can be formally generalized to the four-slave-boson approach, and provide a simplified prescription to obtain the additional terms in the free energy which result at the order 1/N from the correct continuum limit.Comment: Changes: Printing problems (due to non-standard macros) have been removed, 44 page

Time-dependent Gutzwiller approximation for the Hubbard model

We develop a time-dependent Gutzwiller approximation (GA) for the Hubbard model analogous to the time-dependent Hartree-Fock (HF) method. The formalism incorporates ground state correlations of the random phase approximation (RPA) type beyond the GA. Static quantities like ground state energy and double occupancy are in excellent agreement with exact results in one dimension up to moderate coupling and in two dimensions for all couplings. We find a substantial improvement over traditional GA and HF+RPA treatments. Dynamical correlation functions can be easily computed and are also substantially better than HF+RPA ones and obey well behaved sum rules.Comment: 4 pages, 2 figure

Multiplet Effects in the Quasiparticle Band Structure of the f1−f2f^1-f^2 Anderson Model

In this paper, we examine the mean field electronic structure of the $f^1-f^2$ Anderson lattice model in a slave boson approximation, which should be useful in understanding the physics of correlated metals with more than one f electron per site such as uranium-based heavy fermion superconductors. We find that the multiplet structure of the $f^2$ ion acts to quench the crystal field splitting in the quasiparticle electronic structure. This is consistent with experimental observations in such metals as $UPt_3$.Comment: 9 pages, revtex, 3 uuencoded postscript figures attached at en

Time-dependent Gutzwiller theory of magnetic excitations in the Hubbard model

We use a spin-rotational invariant Gutzwiller energy functional to compute random-phase-approximation-like (RPA) fluctuations on top of the Gutzwiller approximation (GA). The method can be viewed as an extension of the previously developed GA+RPA approach for the charge sector [G. Seibold and J. Lorenzana, Phys. Rev. Lett. {\bf 86}, 2605 (2001)] with respect to the inclusion of the magnetic excitations. Unlike the charge case, no assumptions about the time evolution of the double occupancy are needed in this case. Interestingly, in a spin-rotational invariant system, we find the correct degeneracy between triplet excitations, showing the consistency of both computations. Since no restrictions are imposed on the symmetry of the underlying saddle-point solution, our approach is suitable for the evaluation of the magnetic susceptibility and dynamical structure factor in strongly correlated inhomogeneous systems. We present a detailed study of the quality of our approach by comparing with exact diagonalization results and show its much higher accuracy compared to the conventional Hartree-Fock+RPA theory. In infinite dimensions, where the GA becomes exact for the Gutzwiller variational energy, we evaluate ferromagnetic and antiferromagnetic instabilities from the transverse magnetic susceptibility. The resulting phase diagram is in complete agreement with previous variational computations.Comment: 12 pages, 8 figure

Inhomogeneous Gutzwiller approximation with random phase fluctuations for the Hubbard model

We present a detailed study of the time-dependent Gutzwiller approximation for the Hubbard model. The formalism, labelled GA+RPA, allows us to compute random-phase approximation-like (RPA) fluctuations on top of the Gutzwiller approximation (GA). No restrictions are imposed on the charge and spin configurations which makes the method suitable for the calculation of linear excitations around symmetry-broken solutions. Well-behaved sum rules are obeyed as in the Hartree-Fock (HF) plus RPA approach. Analytical results for a two-site model and numerical results for charge-charge and current-current dynamical correlation functions in one and two dimensions are compared with exact and HF+RPA results, supporting the much better performance of GA+RPA with respect to conventional HF+RPA theory.Comment: 14 pages, 6 figure

Slave-Boson Functional-Integral Approach to the Hubbard Model with Orbital Degeneracy

A slave-boson functional-integral method has been developed for the Hubbard model with arbitrary, orbital degeneracy $D$. Its saddle-point mean-field theory is equivalent to the Gutzwiller approximation, as in the case of single-band Hubbard model. Our theory is applied to the doubly degenerate ($D = 2$) model, and numerical calculations have been performed for this model in the paramagnetic states. The effect of the exchange interaction on the metal-insulator (MI) transition is discussed. The critical interaction for the MI transition is analytically calculated as functions of orbital degeneracy and electron occupancy.Comment: Latex 20 pages, 9 figures available on request to [email protected] Note: published in J. Physical Society of Japan with some minor modification