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Search Results: 1 - 10 of 191390 matches for " D. Negrea "
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Isovector proton-neutron pairing and Wigner energy in Hartree-Fock mean field calculations
D. Negrea,N. Sandulescu
Physics , 2014, DOI: 10.1103/PhysRevC.90.024322
Abstract: We propose a new approach for the treatment of isovector pairing in self-consistent mean field calculations which conserves exactly the isospin and the particle number in the pairing channel. The mean field is generated by a Skyrme-HF functional while the isovector pairing correlations are described in terms of quartets formed by two neutrons and two protons coupled to the total isospin T=0. In this framework we analyse the contribution of isovector pairing to the symmetry and Wigner energies. It is shown that the isovector pairing provides a good description of the Wigner energy, which is not the case for the mean field calculations in which the isovector pairing is treated by BCS-like models.
Proton-neutron pairing in N=Z nuclei: quartetting versus pair condensation
N. Sandulescu,D. Negrea,D. Gambacurta
Physics , 2015,
Abstract: The isoscalar proton-neutron pairing and isovector pairing, including both isovector proton-neutron pairing and like-particle pairing, are treated in a formalism which conserves exactly the particle number and the isospin. The formalism is designed for self-conjugate (N=Z) systems of nucleons moving in axially deformed mean fields and interacting through the most general isovector and isoscalar pairing interactions. The ground state of these systems is described by a superposition of two types of condensates, i.e., condensates of isovector quartets, built by two isovector pairs coupled to the total isospin T=0, and condensates of isoscalar proton-neutron pairs. The comparison with the exact solutions of realistic isovector-isoscalar pairing Hamiltonians shows that this ansatz for the ground state is able to describe with high precision the pairing correlation energies. It is also shown that, at variance with the majority of Hartree-Fock-Bogoliubov calculations, in the present formalism the isovector and isoscalar pairing correlations coexist for any pairing interactions. The competition between the isovector and isoscalar proton-neutron pairing correlations is studied for N=Z nuclei with the valence nucleons moving in the $sd$ and $pf$ shells and in the major shell above $^{100}$Sn. We find that in these nuclei the isovector pairing prevail over the isoscalar pairing, especially for heavier nuclei. However, the isoscalar proton-neutron correlations are significant in all nuclei and they always coexist with the isovector pairing correlations.
Annals of the University of Oradea : Economic Science , 2010,
Abstract: The main purpose of the paper is to explain what measures can be taken in order to fix the trade deficit, and the pressure that is upon a country by imposing such measures. The international and the national supply and demand conditions change rapidly, and if a country doesn’t succeed in keeping a tight control over its deficit, a lot of factors will affect its wellbeing. In order to reduce the external trade deficit, the government needs to resort to several techniques. The desired result is to have a balanced current account, and therefore, the government is free to use measures such as fixing its exchange rate, reducing government spending etc. We have shown that all these measures will have a certain impact upon an economy, by allowing its exports to thrive and eliminate the danger from excessive imports, or vice-versa. The main conclusion our paper is that government intervention is allowed in order to maintain the balance of the current account.
Annals of the University of Oradea : Economic Science , 2010,
Abstract: The main purpose of the balance of payments (BoP) is identified as representing the long term need of equilibrium and stability of the international payments and revenues. The purpose of this paper is to determine the factors that influence the balance of payments of a certain country, by using a rigorous classification that reveals the complexity of these factors. Our conclusions are very relevant, especially for countries like Romania, because, in order to achieve the external equilibrium, it seems that every county must adopt a mix of internal economic policies, and although theoretically this can be realised, sometimes in practice it can prove to be impossible on account of inability or refusing to combine the appropriate economic policies.
Pairing and alpha-like quartet condensation in N=Z nuclei
N. Sandulescu,J. Dukelsky,D. Negrea
Physics , 2011, DOI: 10.1088/1742-6596/321/1/012001
Abstract: We discuss the treatment of isovector pairing by an alpha-like quartet condensate which conserves exactly the particle number, the spin and the isospin. The results show that the quartet condensate describes accurately the isovector pairing correlations in the ground state of systems with an equal number of protons and neutrons
Four-nucleon alpha-type correlations and proton-neutron pairing away of N=Z line
N. Sandulescu,D. Negrea,C. W. Johnson
Physics , 2012, DOI: 10.1103/PhysRevC.86.041302
Abstract: We study the competition between alpha-type and conventional pair condensation in the ground state of nuclei with neutrons and protons interacting via a charge-independent pairing interaction. The ground state is described by a product of two condensates, one of alpha-like quartets and the other one of pairs in excess relative to the isotope with N=Z. It is shown that this ansatz for the ground state gives very accurate pairing correlation energies for nuclei with the valence nucleons above the closed cores 16O, 40Ca and 100Sn. These results indicate that alpha-type correlations are important not only for the self-conjugate nuclei but also for nuclei away of N=Z line. In the latter case alpha-like quartets coexist with the collective Cooper pairs formed by the nucleons in excess.
Effects of valsartan and nebivolol on blood pressure, QT dispersion and left ventricular hypertrophy in hypertensive patients
Luminita L??ea,?tefania L. Negrea,Sorana D. Bolboac?
Dicle Medical Journal , 2010,
Abstract: Objectives: The aim of this study was to analyze the antihypertensiveeffect of Valsartan and Nebivolol and their effects on QT dispersion and left ventricular hypertrophy (LVH) in the treatment of naive hypertensive patients.Methods: A prospective study with a six-month follow-up was conducted on hypertensive patients with LVH and mild/ moderate essential hypertension. The patients were randomly assigned to Valsartan (80 to 160 mg/day) or Nebivolol (5 to 10 mg/day) groups. The study group consistedof 108 patients, 55 in the Valsartan group and 53 in the Nebivolol group.Results: The range of mean systolic blood pressure (SBP) varied from 152±17 (baseline) to 132±17 mmHg (follow-up) in the Valsartan group (p<0.001); from 146±13 to 125±14 mmHg in the Nebivolol group (p<0.001). The decrease in mean diastolic blood pressure (DBP) was 9.5±2.5 mmHg in the Valsartan group and 12.3±5.0 mmHg in the Nebivolol group. A significant reduction in QT and corrected QT (Bazett’s formula) dispersion was observed in both groups, with a slightly higher reduction in the Valsartan group. Echocardiography showed a decreasein the left ventricle mass (LVM) indices (p<0.05) in both groups with a greater reduction in the Valsartan group.Conclusion: Valsartan treatment was as effective as Nebivolol in reducing the 24 hour- SBP after a 6 month treatment. Nebivolol treatment proved to be superior to Valsartan in reducing DBP. Both therapies were effective in reducing the LVH; Valsartan proved to be superior to Nebivolol in reducing the QT interval indexes in relation to blood pressure and LVM reduction.
Alpha-like quartet condensation and isovector pairing correlations in N=Z nuclei
N. Sandulescu,D. Negrea,J. Dukelsky,C. W. Johnson
Physics , 2012, DOI: 10.1103/PhysRevC.85.061303
Abstract: We propose a simple quartet condensation model (QCM) which describes with very high accuracy the isovector pairing correlations in self-conjugate nuclei. The quartets have an alpha-like structure and are formed by collective isovector pairs. The accuracy of the QCM is tested for N=Z nuclei for which exact shell model diagonalizations can be performed. The calculations are done with two isovector pairing forces, one extracted from standard shell model interactions and the other of seniority type, acting, respectively, upon spherical and axially-deformed single-particle states. It is shown that for all calculated nuclei the QCM gives very accurate values for the pairing correlations energies, with errors which do not exceed 1%. These results show clearly that the correlations induced by the isovector pairing in self-conjugate nuclei are of quartet type and also indicate that QCM is the proper tool to calculate the isovector proton-neutron correlations in mean field pairing models.
On the specimens of Eupolybothrus (Leptopolybothrus) tridentinus (Fanzago, 1874) (Chilopoda: Lithobiidae) from the "Z. Matic" and " t. Negrea" collections (Romania)
tefan Negrea
Travaux du Muséum National d'Histoire Naturelle "Grigore Antipa" , 2010, DOI: 10.2478/v10191-010-0010-y
Abstract: This work is the second of the series dedicated to the critical evaluation of the Chilopod specimens from the "Z. Matic" and " t. Negrea" collections - the only ones existing in Romania (vide "Literature cited"). The history of the study of Eupolybothrus tridentinus (Fanzago, 1874), the synonymies, the examined material, the redescription of the species based on specimens found in the two collections are presented. A nomenclatural updating of two old records is proposed: Eupolybothrus tridentinus (Fanzago) = Polybothrus leptopus sensu Matic, 1958; Eupolybothrus tridentinus (Fanzago) = Eupolybothrus leptopus f. brolemanni sensu Negrea, 1964. The paper concludes on some taxonomical and ecological remarks regarding the Eupolybothrus tridentinus (Fanzago) species.
Critical evaluation of the specimens of Lithobius validus Meinert - species group (Chilopoda: Lithobiidae) from the "Z. Matic" and " t. Negrea" collections (Romania)
tefan Negrea
Travaux du Muséum National d'Histoire Naturelle "Grigore Antipa" , 2010, DOI: 10.2478/v10191-010-0009-4
Abstract: Z. Matic's collection, preserved at the Zoological Museum of the "Babe -Bolyai" University of Cluj-Napoca, and t. Negrea's collection, preserved at the "Emil Racovitza" Speleological Institute of Bucharest (the only chilopod collections existing in Romania) are containing three species of the Lithobius validus Meinert group: L. (L.) validus Meinert, 1872 (sensu Eason, 1974 a), L. (L.) moldavicus Prunesco, 1966 (sensu Negrea, in the present paper) and L. (L.) matici Prunesco, 1966. New synonymies are proposed: Lithobius punctulatus moldavicus Prunesco, 1966 = Lithobius moldavicus Negrea in this work = Lithobius validus Zapparoli, 1994 nov. syn.; Lithobius matici Prunesco, 1966 = Lithobius matici biharicus Prunesco, 1966 nov. syn. The subspecies Lithobius punctulatus moldavicus Prunesco, 1966 is elevated to the taxonomical rank of species, Lithobius moldavicus Prunesco, establishing its geographical area as it is currently known. The following species are redescribed: Lithobius validus Meinert, 1872, based on the Romanian Carpathians populations; Lithobius moldavicus Prunesco, 1966 based on the specimens of the Eastern Carpathians - including the type series, establishing a lectotypus and an allolectotypus; Lithobius matici Prunesco, 1966 based on populations from the Eastern Carpathians and the Western Carpathians.
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