Nuclear Structure and Response based on Correlated Realistic NN Interactions

Starting from the Argonne V18 nucleon-nucleon (NN) interaction and using the Unitary Correlation Operator Method, a correlated interaction v_UCOM has been constructed, which is suitable for calculations within restricted Hilbert spaces. In this work we employ the v_UCOM in Hartree-Fock, perturbation-theory and RPA calculations and we study the ground-state properties of various closed-shell nuclei, as well as some excited states. The present calculations provide also important feedback for the optimization of the v_UCOM and valuable information on its properties. The above scheme offers the prospect of ab initio calculations in nuclei, regardless of their mass number. It can be used in conjunction with other realistic NN interactions as well, and with various many-body methods (Second RPA, QRPA, Shell Model, etc.).Comment: 3 pages, incl. 2 figures; Proc. Int. Conf. on Frontiers in Nuclear Structure, Astrophysics and Reactions (FINUSTAR), Kos, Greece, Sept.200

Universality aspects of the d=3 random-bond Blume-Capel model

The effects of bond randomness on the universality aspects of the simple cubic lattice ferromagnetic Blume-Capel model are discussed. The system is studied numerically in both its first- and second-order phase transition regimes by a comprehensive finite-size scaling analysis. We find that our data for the second-order phase transition, emerging under random bonds from the second-order regime of the pure model, are compatible with the universality class of the 3d random Ising model. Furthermore, we find evidence that, the second-order transition emerging under bond randomness from the first-order regime of the pure model, belongs to a new and distinctive universality class. The first finding reinforces the scenario of a single universality class for the 3d Ising model with the three well-known types of quenched uncorrelated disorder (bond randomness, site- and bond-dilution). The second, amounts to a strong violation of universality principle of critical phenomena. For this case of the ex-first-order 3d Blume-Capel model, we find sharp differences from the critical behaviors, emerging under randomness, in the cases of the ex-first-order transitions of the corresponding weak and strong first-order transitions in the 3d three-state and four-state Potts models.Comment: 12 pages, 12 figure

Nuclear collective excitations using correlated realistic interactions: the role of explicit RPA correlations

We examine to which extent correlated realistic nucleon-nucleon interactions, derived within the Unitary Correlation Operator Method (UCOM), can describe nuclear collective motion in the framework of first-order random-phase approximation (RPA). To this end we employ the correlated Argonne V18 interaction in calculations within the so-called "Extended" RPA (ERPA) and investigate the response of closed-shell nuclei. The ERPA is a renormalized RPA version which considers explicitly the depletion of the Fermi sea due to long-range correlations and thus allows us to examine how these affect the excitation spectra. It is found that the effect on the properties of giant resonances is rather small. Compared to the standard RPA, where excitations are built on top of the uncorrelated Hartree-Fock (HF) ground state, their centroid energies decrease by up to 1 MeV, approximately, in the isovector channel. The isoscalar response is less affected in general. Thus, the disagreement between our previous UCOM-based RPA calculations and the experimental data are to be attributed to other effects, mainly to a residual three-body force and higher-order configurations. Ground-state properties obtained within the ERPA are compared with corresponding HF and perturbation-theory results and are discussed as well. The ERPA formalism is presented in detail

Uncovering the secrets of the 2d random-bond Blume-Capel model

The effects of bond randomness on the ground-state structure, phase diagram and critical behavior of the square lattice ferromagnetic Blume-Capel (BC) model are discussed. The calculation of ground states at strong disorder and large values of the crystal field is carried out by mapping the system onto a network and we search for a minimum cut by a maximum flow method. In finite temperatures the system is studied by an efficient two-stage Wang-Landau (WL) method for several values of the crystal field, including both the first- and second-order phase transition regimes of the pure model. We attempt to explain the enhancement of ferromagnetic order and we discuss the critical behavior of the random-bond model. Our results provide evidence for a strong violation of universality along the second-order phase transition line of the random-bond version.Comment: 6 LATEX pages, 3 EPS figures, Presented by AM at the symposium "Trajectories and Friends" in honor of Nihat Berker, MIT, October 200

Current trends in surgical treatment of parapneumonic effusions and empyema thoracis

Surgical treatment of complicated parapneumonic effusions and empyema thoracis consists of drainage and obliteration of the pleural space. Two scientific Societies have published guidelines concerning management of empyema thoracis in the near past. American College of Chest Physicians (2000) has defined criteria of high-risk for poor outcome. Parapneumonic effusions which met the criteria of high-risk for poor outcome should undergo at least chest tube drainage, that is however unsuccessful in 25-50% of cases. Intrapleural instillation of fibrinolytics, thoracoscopic drainage and thoracotomy were, according to ACCP experts, accepted modalities of management. According to British Thoracic Society guidelines (2003), surgical treatment should be offered after failure of conservative treatment with antibiotics and chest tube drainage. We have nowadays enough evidence that early thoracoscopic drainage reduces hospitalization, chest tube drainage duration and that is successful initial treatment in 90% of cases. Minimally invasive thoracoscopic drainage can effectively drain loculations, inflammatory intrapleural fluid and gel, obliterate the pleural cavity and achieve strategic position of chest drains. Thoracoscopic drainage is unsuccessful management for organizing empyemas, where decortication is the treatment of choice. Early involvement of thoracic surgeons and early thoracoscopic drainage may effectively change the prognosis and outcome of complicated parapneumonic effusions and empyema thoracis

Low-energy dipole excitations towards the proton drip-line: doubly magic 48Ni

The properties of the low-energy dipole response are investigated for the proton-rich doubly magic nucleus $^{48}$Ni, in a comparative study of two microscopic models: fully self-consistent Relativistic Random-Phase Approximation(RRPA) based on the novel density-dependent meson-exchange interactions, and Continuum Random-Phase Approximation(CRPA) using Skyrme-type interactions with the continuum properly included. Both models predict the existence of the low-energy soft mode, i.e. the proton pygmy dipole resonance (PDR), for which the transition densities and RPA amplitudes indicate the dynamics of loosely bound protons vibrating against the rest of the nucleons. The CRPA analysis indicates that the escape width for the proton PDR is rather large, as a result of the coupling to the continuum.Comment: 12 pages, 3 figures, accepted for publication in Phys. Lett.

Multicritical Points and Crossover Mediating the Strong Violation of Universality: Wang-Landau Determinations in the Random-Bond d=2d=2 Blume-Capel model

The effects of bond randomness on the phase diagram and critical behavior of the square lattice ferromagnetic Blume-Capel model are discussed. The system is studied in both the pure and disordered versions by the same efficient two-stage Wang-Landau method for many values of the crystal field, restricted here in the second-order phase transition regime of the pure model. For the random-bond version several disorder strengths are considered. We present phase diagram points of both pure and random versions and for a particular disorder strength we locate the emergence of the enhancement of ferromagnetic order observed in an earlier study in the ex-first-order regime. The critical properties of the pure model are contrasted and compared to those of the random model. Accepting, for the weak random version, the assumption of the double logarithmic scenario for the specific heat we attempt to estimate the range of universality between the pure and random-bond models. The behavior of the strong disorder regime is also discussed and a rather complex and yet not fully understood behavior is observed. It is pointed out that this complexity is related to the ground-state structure of the random-bond version.Comment: 12 pages, 11 figures, submitted for publicatio

Surgical treatment of pulmonary metastases. Review of the literature a propos of a case-series of 25 recent cases

Surgery is the optimal treatment for pulmonary metastases from certain extrathoracic tumors (soft tissue sar­comas, colorectal and renal cancer, breast cancer and others) which fulfill some strict criteria, such as control of the primary site, long disease free interval and absence of other extrathoracic metastases (with the exception of hepatic metastases from colorectal cancer that can be also eradicated with surgery). Prolonged survival is expected after metastasectomy (even if repeated metastasectomies are required), if the number of the metastases to be resected is low (<3), if complete eradication of the metastatic deposits can be achieved during surgery and if mediastinal lymph nodes are not involved by the tumor. Limited pulmonary resection with the form of wedge resection or enucleation or typical segmentectomy is the standard surgical in­tervention for pulmonary metastases. Major lung parenchyma resection such as lobectomy, bilobectomy or pneumonectomy at instances required in larger, deeply situated within the lung parenchyma, metastases. Formal thoracotomy is the access of choice, while thoracoscopic resection can be applied in selected patients with solitary, peripherally located metastases. Enucleation of the metastatic deposits can be performed using the cautery or preferably using the new generation Nd:YAG lasers. Sparing lung parenchyma is crucial during pulmonary metastasectomy