Calculations of binding energies and masses of heavy quarkonia using renormalon cancellation

We use various methods of Borel integration to calculate the binding ground energies and masses of b-bbar and t-tbar quarkonia. The methods take into account the leading infrared renormalon structure of the hard+soft part of the binding energies E(s), and of the corresponding quark pole masses m_q, where the contributions of these singularities in M(s) = 2 m_q + E(s) cancel. Beforehand, we carry out the separation of the binding energy into its hard+soft and ultrasoft parts. The resummation formalisms are applied to expansions of m_q and E(s) in terms of quantities which do not involve renormalon ambiguity, such as MSbar quark mass, and alpha_s. The renormalization scales are different in calculations of m_q, E(s) and E(us). The MSbar mass of b quark is extracted, and the binding energies of t-tbar and the peak (resonance) energies for (t+tbar) production are obtained.Comment: 23 pages, 8 double figures, revtex4; the version to appear in Phys.Rev.D; extended discussion between Eqs.(25) and (26); the paragraph between Eqs.(32) and (33) is new and explains the numerical dependence of the residue parameter on the factorization scale; several new references were added; acknowledgments were modified; the numerical results are unchange

Stellar structure and compact objects before 1940: Towards relativistic astrophysics

Since the mid-1920s, different strands of research used stars as "physics laboratories" for investigating the nature of matter under extreme densities and pressures, impossible to realize on Earth. To trace this process this paper is following the evolution of the concept of a dense core in stars, which was important both for an understanding of stellar evolution and as a testing ground for the fast-evolving field of nuclear physics. In spite of the divide between physicists and astrophysicists, some key actors working in the cross-fertilized soil of overlapping but different scientific cultures formulated models and tentative theories that gradually evolved into more realistic and structured astrophysical objects. These investigations culminated in the first contact with general relativity in 1939, when J. Robert Oppenheimer and his students George Volkoff and Hartland Snyder systematically applied the theory to the dense core of a collapsing neutron star. This pioneering application of Einstein's theory to an astrophysical compact object can be regarded as a milestone in the path eventually leading to the emergence of relativistic astrophysics in the early 1960s.Comment: 83 pages, 4 figures, submitted to the European Physical Journal

N2O decomposition catalysed by transition metal ions

The direct N2O decomposition catalysed by 5-coordinated transition metal ions Fe, Co, and Rh was studied using the DFT method. The cluster model has the formula M(OH)(3) (H2O)(2). Energies of intermediates and transition states were computed. The results show that Co and Rh sites are more active than Fe, the former two being very simila

DFT calculations on N2O decomposition by binuclear Fe complexes in Fe/ZSM-5

N2O decomposition catalyzed by oxidized Fe clusters localized in the micropores of Fe/ZSM-5 has been studied using the DFT approach and a binuclear cluster model of the active site. Three different reaction routes were found, depending on temperature and water pressure. The results show that below 200 degreesC the binuclear cluster is hydroxylated and is probably inactive. Above this temperature and up to 500 degreesC the catalytic site has the [HO-Fe-O-Fe-OH](2+) structure, and above 500 degreesC the site is predominantly [Fe-O-Fe](2+). The reaction paths on the latter two forms of the site are similar. N2O dissociates on each of the Fe ions with subsequent oxygen recombination and desorption. Some of the side reactions including NO formation are also considere

N2O decomposition catalysed by transition metal ions

The direct N2O decomposition catalysed by 5-coordinated transition metal ions Fe, Co, and Rh was studied using the DFT method. The cluster model has the formula M(OH)(3) (H2O)(2). Energies of intermediates and transition states were computed. The results show that Co and Rh sites are more active than Fe, the former two being very simila

DFT study of oxygen-bridged Zn2+ ion pairs in Zn/ZSM-5 zeolites

A cluster model for Zn/ZSM-5 zeolite is proposed, which consists of an oxygen-bridged [Zn-O-Zn](2+) moiety attached to two framework aluminum ions of two adjacent ZSM-5 5-rings. Its stability and catalytic activity in ethane dehydrogenation were considered using the DFT method and compared with those for single Zn2+ ions in the same rings. It is shown that the oxygen-bridged Zn2+ pair is rather reactive towards ethane dissociation and that the rate-limiting step is release of hydroge

Comparative quantum chemical study of stabilization energies of Zn²⁺ ions in different zeolite structures

Cluster model quantum chemical calculations have been performed to compare stabilization energies (E-st) of Zn2+ ions in four-, five-, and six-membered zeolitic rings. E-st was evaluated as energy of the reaction Zn2+/Z + H-2 double right arrow 2H(+)/Z + Zn-0. It was found that E-st substantially decreases in the series six-, five-, and four-membered ring, and this trend is essential to the understanding of the comparative adsorption ability and reactivity of Zn2+ in cationic sites of different zeolites. This conclusion was proved in calculations of the heterolytic dissociation of ethane, The molecular structure of active sites in ZnHY and ZnHZSM-5 zeolites and the question of the stability of small intrazeolite zinc oxide species are discusse

Effects of Homocysteine and its Derivatives on Spontaneous Network Activity in the Hippocampus of Neonatal Rat Pups

© 2020, Springer Science+Business Media, LLC, part of Springer Nature. Homocysteine is a sulfur-containing amino acid, which at high concentrations has neurotoxic effects and induces impairments to the development of the nervous system. Homocysteine is rapidly oxidized in the plasma, forming disulfide bonds with proteins and other low molecular weight thiols; it also undergoes transformation into the into homocysteine thiolactone. On chronic exposure, the neurotoxicity of homocysteine is therefore mediated mainly by its derivatives. The aim of the present work was to investigate the effects of homocysteine and its derivatives – homocystine and homocysteine thiolactone – on spontaneous network activity in the hippocampus of rats in the first week after birth. Giant depolarizing potentials (GDP) and multiple action potentials (MAP) were recorded using an extracellular electrode in hippocampal field CA3. All three study compounds were found to induce increases in the frequency of GDP and MAP at concentrations of 100 and 500 μM, homocystine producing the most significant increase in neuron network activity. The effects of homocysteine, homocystine, and homocysteine thiolactone on the spontaneous network activity of neurons were completely eliminated on blockade of NMDA and AMPA receptors. Thus, homocysteine and its derivatives lead to increased spontaneous network activity of hippocampal neurons in neonatal rats, which can induce impairments to the formation of the neural networks of the hippocampus in conditions of chronic hyperhomocysteinemia, and could also induce hyperexcitability and the risk of developing epilepsy in the postnatal period