Study of the ground-state energy of 40Ca with the CD-Bonn nucleon-nucleon potential

We have calculated the ground-state energy of the doubly-magic nucleus 40Ca within the framework of the Goldstone expansion using the CD-Bonn nucleon-nucleon potential. The short-range repulsion of this potential has been renormalized by integrating out its high-momentum components so as to derive a low-momentum potential V-low-k defined up to a cutoff momentum Lambda. A simple criterion has been employed to establish a connection between this cutoff momentum and the size of the two-nucleon model space in the harmonic oscillator basis. This model-space truncation approach provides a reliable way to renormalize the free nucleon-nucleon potential preserving its many-body physics. The role of the 3p-3h and 4p-4h excitations in the description of the ground state of 40Ca is discussed.Comment: 4 pages, 1 figure, 1 table, to be published in Physical Review

Numerical investigation of oxy-natural-gas combustion in a semi-industrial furnace: Validation of CFD sub-models

The modeling through computational fluid dynamics of oxy-natural-gas combustion experimental tests in a 3 MW semi-industrial furnace equipped with a low NOx burner is discussed. Since the complex geometry of the burner and the size of the furnace, a modeling strategy has been adopted to diminish the computational time and thus to make the simulations affordable. The model aims at validating different sub-models (e.g. combustion/kinetics, radiation/spectral) for oxy-natural-gas fired conditions through the comparison of predictions and in-flame measurements of temperature and chemical species. It is found that fast chemistry approaches are unable to predict the temperature field. The spectral model was also found to play a fundamental role for the correct analysis of such scale devices. Uncertainties in experimental and modeling results are discussed and compared

Analysis of oxy-coal combustion through measurements in a pilot-scale entrained flow reactor

Coal combustion is investigated in both air and oxy-fuel conditions in a pilot-scale entrained flow reactor able to provide high temperatures, heating rates and residence times. Measurements are carried out with different levels of complexity and are aimed at: assessing the thermal field inside the reactor; evaluating conversions of devolatilization or char combustion tests; identifying phenomena such as volatiles ignition and measuring the ignition delay time. Computational Fluid Dynamics was also used in order to provide a better understanding of the experimental evidences. Among the results, the ignition delay time was found to be larger in oxy-fuel conditions than in air, mainly because of the larger specific heat of the oxy-fuel environment. The proposed investigation may help the qualification of advanced experimental apparatus as entrained flow reactors, with the purpose to make them suitable for heterogeneous kinetics studies in oxy-fuel conditions

Analysis of Coal Combustion in Oxy-fuel Conditions through Pulsed Feeding Experiments in an Entrained Flow Reactor

Coal combustion is investigated in both air and oxy-fuel conditions in a pilot-scale entrained flow reactor able to provide high temperatures, heating rates and residence times. Measurements are carried out with different levels of complexity and are aimed at: assessing the thermal field inside the reactor; evaluating conversions of devolatilization or char combustion tests; identifying phenomena such as volatiles ignition and measuring the ignition delay time. Computational Fluid Dynamics was also used in order to provide a better understanding of the experimental evidences. Among the results, the ignition delay time was found to be larger in oxy-fuel conditions than in air, mainly because of the larger specific heat of the oxy-fuel environment. The proposed investigation may help the qualification of advanced experimental apparatus as entrained flow reactors, with the purpose to make them suitable for heterogeneous kinetics studies in oxy-fuel conditions

Nuclear Structure Calculations with Low-Momentum Potentials in a Model Space Truncation Approach

We have calculated the ground-state energy of the doubly magic nuclei 4He, 16O and 40Ca within the framework of the Goldstone expansion starting from various modern nucleon-nucleon potentials. The short-range repulsion of these potentials has been renormalized by constructing a low-momentum potential V-low-k. We have studied the connection between the cutoff momemtum Lambda and the size of the harmonic oscillator space employed in the calculations. We have found a fast convergence of the results with a limited number of oscillator quanta.Comment: 6 pages, 8 figures, to be published on Physical Review

Shell-model study of the N=82 isotonic chain with a realistic effective hamiltonian

We have performed shell-model calculations for the even- and odd-mass N=82 isotones, focusing attention on low-energy states. The single-particle energies and effective two-body interaction have been both determined within the framework of the time-dependent degenerate linked-diagram perturbation theory, starting from a low-momentum interaction derived from the CD-Bonn nucleon-nucleon potential. In this way, no phenomenological input enters our effective Hamiltonian, whose reliability is evidenced by the good agreement between theory and experiment.Comment: 7 pages, 11 figures, 3 tables, to be published in Physical Review

Low Momentum Nucleon-Nucleon Interactions and Shell-Model Calculations

In the last few years, the low-momentum nucleon-nucleon (NN) interaction V-low-k derived from free-space NN potentials has been successfully used in shell-model calculations. V-low-k is a smooth potential which preserves the deuteron binding energy as well as the half-on-shell T-matrix of the original NN potential up to a momentum cutoff Lambda. In this paper we put to the test a new low-momentum NN potential derived from chiral perturbation theory at next-to-next-to-next-to-leading order with a sharp low-momentum cutoff at 2.1 fm-1. Shell-model calculations for the oxygen isotopes using effective hamiltonians derived from both types of low-momentum potential are performed. We find that the two potentials show the same perturbative behavior and yield very similar results.Comment: 8 pages, 8 figures, to be published in Physical Review

The role of three-nucleon potentials within the shell model: past and present

We survey the impact of nuclear three-body forces on structure properties of nuclei within the shell model. It has long been acknowledged, since the seminal works of Zuker and coworkers, that three-body forces play a fundamental role in making the monopole component of shell-model Hamiltonians, derived from realistic nucleon-nucleon potentials, able to reproduce the observed evolution of the shell structure. In the vast majority of calculations, however, their effects have been taken into account by shell-model practitioners by introducing ad hoc modifications of the monopole matrix elements. During last twenty years, a new theoretical approach, framed within the chiral perturbation theory, has progressed in developing nuclear potentials, where two- and many-body components are naturally and consistently built in. This new class of nuclear forces allows to carry out nuclear structure studies that are improving our ability to understand nuclear phenomena in a microscopic approach. We provide in this work an update on the status of the nuclear shell model based on realistic Hamiltonians that are derived from two- and three-nucleon chiral potentials, focusing on the role of the three-body component to provide the observed shell evolution and closure properties, as well as the location of driplines. To this end, we present the results of shell-model calculations and their comparison with recent experimental measurements, which enlighten the relevance of the inclusion of three-nucleon forces to master our knowledge of the physics of atomic nuclei.Comment: Accepted for publication in Progress in Particle and Nuclear Physic

Effects of the COVID-19 lockdown on glycaemic control in subjects with type 2 diabetes: the glycalock study

Aim: To assess the effect of the coronavirus disease 2019 (COVID-19) lockdown on glycaemic control in subjects with type 2 diabetes (T2D). Materials and Methods: In this observational, multicentre, retrospective study conducted in the Lazio region, Italy, we compared the differences in the HbA1c levels of 141 subjects with T2D exposed to lockdown with 123 matched controls with T2D who attended the study centres 1 year before. Basal data were collected from 9 December to 9 March and follow-up data from 3 June to 10 July in 2020 for the lockdown group, and during the same timeframes in 2019 for the control groups. Changes in HbA1c (ΔHbA1c) and body mass index (ΔBMI) during lockdown were compared among patients with different psychological well-being, as evaluated by tertiles of the Psychological General Well-Being Index (PGWBS). Results: No difference in ΔHbA1c was found between the lockdown and control groups (lockdown group −0.1% [−0.5%−0.3%] vs. control group −0.1% [−0.4%−0.2%]; p =.482). Also, no difference was found in ΔBMI (p =.316) or ΔGlucose (p =.538). In the lockdown group, subjects with worse PGWBS showed a worsening of HbA1c (p =.041 for the trend among PGWBS tertiles) and BMI (p =.022). Conclusions: The COVID-19 lockdown did not significantly impact glycaemic control in people with T2D. People with poor psychological well-being may experience a worsening a glycaemic control because of restrictions resulting from lockdown. These findings may aid healthcare providers in diabetes management once the second wave of COVID-19 has ended