Local properties in the two-dimensional t-t'-U model

We have studied the t-t'-U model by means of the composite operator method. The effect of the bare diagonal hopping term t' that appears to be material dependent for high-Tc cuprate superconductors is analyzed in detail. In particular, some local quantities are computed and a comprehensive comparison with the data by numerical simulations on finite size lattices is presented. The result show a good agreement with those obtained by Monte Carlo methods.Comment: 3 pages, 3 figures in one Postscript file, RevTeX, to be published in Physica

The two-dimensional t-t'-U model as a minimal model for cuprate materials

The addition to the Hubbard Hamiltonian of a t' diagonal hopping term, which is considered to be material dependent for high-Tc cuprate superconductors, is generally suggested to obtain a model capable to describe the physics of high-Tc cuprate materials. In this line of thinking, the two-dimensional t-t'-U model has been studied by means of the Composite Operator Method, which allows to determine the dynamics in a fully self-consistent way by use of symmetry requirements, as the ones coming from the Pauli principle. At first, some local quantities have been calculated to be compared with quantum Monte Carlo data. Then, the structure of the energy bands, the shape of the Fermi surface and the position of the van Hove singularity have been computed as functions of the model parameters and studied by the light of the available experimental data. The results of our study show that there exists two sets of parameters that allows the model to describe the relevant features of 1-layer compounds NCCO and LSCO. On the other hand, for the 2-layer compound YBCO is not possible to find a reasonable set of parameters which could reproduce the position of the van Hove singularity as predicted by ARPES experiments. Hence, it results questionable the existence of an unique model that could properly describe the variety of cuprate superconductors, as the t-t'-U model was thought to be.Comment: 8 pages, RevTex, 10 Postscript figures, submitted to Phys. Rev. B. This paper, as many others from the same authors, can be downloaded by anonymous FTP at ftp://pcalea.csied.unisa.i

Incommensurate spin fluctuations in the two-dimensional t-t'-U model

Magnetic properties of the two-dimensional t-t'-U model are investigated by studying the static spin magnetic susceptibility as a function of momentum for various temperatures. The calculations are performed by means of the Composite Operator Method in the static approximation. By increasing the value of the t' parameter the magnetic scattering in the reciprocal space evolves to an isotropic structure. It is shown that the results are in qualitative agreement with the experimental situation observed in LSCO and YBCO compounds.Comment: 3 pages, 6 Postscript figures, RevTeX, submitted to Phys. Lett.

Aislamiento de cepas de Pasteurella multocida toxigénica de un brote natural de rinitis atrófica porcina.

Se realizó un estudio para establecer la presencia de cepas toxigénicas de Pasteurella multocida asociadas con brotes naturales de rinitis atrófica porcina. Se analizaron 185 muestras, 93.5 por ciento correspondieron a hisopos nasales colectados en 2 granjas de cría de la sabana de Bogotá y 6.5 por ciento eran fragmentos de pulmón, con lesiones de neumonía colectados en 1 matadero. Las muestras fueron cultivadas para la identificación de Pasteurella multocida y Bordetella bronchiseptica según los procedimientos bacteriológicos convencionales. Se logró el aislamiento de 50 cepas de Pasteurella multocida. No fue posible aislar Bordetella bronchiseptica de las muestras examinadas. Se encontró que el 76 por ciento de las cepas de Pasteurella multocida pertenecen al grupo D (prueba de floculación de la acriflavina) y el 24 por ciento eran tipo A (decapsulación de la hialuronidasa). Se determinó la sensibilidad a algunos agentes antimicrobianos. Todas las cepas de Pasteurella multocida fueron resistentes a la lincomicina, mientras que la gran mayoría fueron sensibles a sulfamethoxale trimethropin (96 por ciento) y ampicilina (92 por ciento). Se estableció además la habilidad de las cepas de Pasteurella multocida para producir la toxina dermonecrótica, mediante la inoculación intradérmica de cobayos y por la formación de efecto citopático en monoestratos de células VERO. El 24 por ciento de las cepas analizadas fueron toxigénicas, de las cuales el 14 por ciento eran tipo D aisladas de la cavidad nasal y el 2 por ciento de pulmon. En contraste, el 2 por ciento eran serotipo A toxigénico aisladas de la cavidad nasal y el 6 por ciento de muestras de pulmón. Se concluye que estos portadores sanos representan un papel importante en la presentación de la enfermedad. Se discute las implicaciones que estos hallazgos representan no solamente para la epidemiología sino también para el control de la enfermeda

Evidence from Family Studies for Autoimmunity in Arrhythmogenic Right Ventricular Cardiomyopathy: Associations of Circulating Anti-Heart and Anti-Intercalated Disk Autoantibodies with Disease Severity and Family History

Background: Serum anti-heart autoantibodies (AHA) and anti-intercalated disk autoantibodies (AIDA) are autoimmune markers in myocarditis. In arrhythmogenic right ventricular cardiomyopathy (ARVC) myocarditis has been reported. To provide evidence for autoimmunity, we searched for AHA and AIDA in ARVC. Methods: We studied: 42 ARVC probands, 23 male, aged 42, interquartile range (IQR) 33;49, 20 from familial and 22 non-familial pedigrees; 37 clinically affected relatives (AR), 24 male aged 35, IQR 18;46; 96 healthy relatives (HR), 49 male, aged 27, IQR 17;45. Serum AHA and AIDA were tested by indirect immunofluorescence on human myocardium and skeletal muscle in 171 of the 175 ARVC individuals and in controls with: non-inflammatory cardiac disease (NICD) (n=160), ischemic heart failure (IHF) (n=141), normal blood donors (NBD) (n=270). Screening of five desmosomal genes was performed in probands; when a sequence variant was identified, cascade family screening followed, blind to immunological results. Results: AHA frequency was higher (36.8%) in probands, AR (37.8%) and HR (25%) than in NICD (1%), IHF (1%) or NBD (2.5%) (p=0.0001). AIDA frequency was higher in probands (8%, p=0.006), in AR (21.6%, p=0.00001) and in HR (14.6% p=0.00001) than in NICD (3.75%), IHF (2%) or NBD (0.3%). AHA positive status was associated with higher frequency of palpitation (p=0.004), ICD implantation (p=0.021), lower left ventricular ejection fraction (LVEF) (p=0.004), AIDA positive status with both lower RV and LVEF (p=0.027 and p=0.027 respectively). AHA and/or AIDA positive status in the proband and/or at least one of the respective relatives was more common in familial (17/20, 85%) than in sporadic (10/22, 45%) pedigrees (p=0.007). Conclusions: Presence of AHA and AIDA provides evidence of autoimmunity in the majority of familial and in almost half of sporadic ARVC. In probands and in AR these antibodies were associated with disease severity features; longitudinal studies are needed to clarify whether they may predict ARVC development in HR or if they be a result of manifest ARVC

Reducing the environmental impact of surgery on a global scale: systematic review and co-prioritization with healthcare workers in 132 countries

Abstract Background Healthcare cannot achieve net-zero carbon without addressing operating theatres. The aim of this study was to prioritize feasible interventions to reduce the environmental impact of operating theatres. Methods This study adopted a four-phase Delphi consensus co-prioritization methodology. In phase 1, a systematic review of published interventions and global consultation of perioperative healthcare professionals were used to longlist interventions. In phase 2, iterative thematic analysis consolidated comparable interventions into a shortlist. In phase 3, the shortlist was co-prioritized based on patient and clinician views on acceptability, feasibility, and safety. In phase 4, ranked lists of interventions were presented by their relevance to high-income countries and low–middle-income countries. Results In phase 1, 43 interventions were identified, which had low uptake in practice according to 3042 professionals globally. In phase 2, a shortlist of 15 intervention domains was generated. In phase 3, interventions were deemed acceptable for more than 90 per cent of patients except for reducing general anaesthesia (84 per cent) and re-sterilization of ‘single-use’ consumables (86 per cent). In phase 4, the top three shortlisted interventions for high-income countries were: introducing recycling; reducing use of anaesthetic gases; and appropriate clinical waste processing. In phase 4, the top three shortlisted interventions for low–middle-income countries were: introducing reusable surgical devices; reducing use of consumables; and reducing the use of general anaesthesia. Conclusion This is a step toward environmentally sustainable operating environments with actionable interventions applicable to both high– and low–middle–income countries

Dynamical incommensurability in the 2D Hubbard model

The recent discovery of incommensurate fluctuations in yttrium compounds has reopened the problem of finding new appropriate frameworks to describe the variety of experimental features presented by cuprate superconductors. According to this, the imaginary part of the dynamical spin magnetic susceptibility of the Hubbard model has been studied by means of the composite operator method. By varying the frequency, the crossover between the two antiferromagnetic regimes has been found. The incommensurability issue has been studied and discussed. © 1999 Elsevier Science B. V. All rights reserved

The overdoped regime in La2-xSrxCuO4

Recent experimental data for the overdoped La2-xSrxCuO4 have firmly established the properties which characterize the transition between the superconducting and the Fermi liquid metallic phases (x̃ ≃ 0.25). The thermodynamic response functions show a pronounced feature at this point, while the Fermi surface undergoes a dramatic change. By use of the Composite Operator Method for the two-dimensional Hubbard model, it is found that the presence of a van Hove singularity in the lower Hubbard band can explain these behaviors. © 1998 Elsevier Science Ltd. All rights reserved

The superconducting gap in the two-dimensional Hubbard model

Superconductivity with singlet d-wave pairing has been studied for the two-dimensional single-band Hubbard model by means of the composite operator method. Results are given for the one-particle energy gap as a function of wave vector

Two-scale analysis of the SU(N) Kondo Model

We show how to resolve coherent low-energy features embedded in a broad high-energy background by use of a fully self-consistent calculation for composite particle operators. The method generalizes the formulation of Roth, which linearizes the dynamics of composite operators at any energy scale. Self-consistent equations are derived and analyzed in the case of the single-impurity SU(N) Kondo model