Abstract Quantum tunnelling plays a crucial role in heavy-ion fusion reactions at sub-barrier energies, especially in the context of nuclear physics and astrophysics. The nuclear structure of the ...colliding nuclei and nucleon transfer processes represent intrinsic degrees of freedom. They are coupled to the relative ion motion and, in general, increase the probability of tunnelling. The influence of couplings to nucleon transfer channels relatively to inelastic excitations, on heavy-ion fusion cross sections, is one of the still open problems in this field. We present a new analysis of several systems, based on the combined observation of the energy-weighted excitation functions $$E\sigma $$ E σ in relation to their first energy derivatives $$d(E\sigma )/dE$$ d ( E σ ) / d E . The relation between $$d(E\sigma )/dE$$ d ( E σ ) / d E and $$E\sigma $$ E σ removes the basic differences due to the varying Coulomb barrier when comparing different systems. We show that, depending on the nuclear structure and/or the presence of strong transfer channels, this representation reveals characteristic features below the barrier. The possible presence of cross section oscillations makes this analysis less clear for light- or medium-light systems.
Recent major health shocks, such as the 2014-16 Ebola, the Zika outbreak, and, last but not least, the COVID-19 pandemic, have strongly contributed to drawing attention to the issue of resilience in ...the healthcare domain. Nevertheless, the scientific literature appears fragmented, creating difficulties in developing incremental research in this relevant managerial field.To fill this gap, this systematic literature review aims to provide a clear state of the art of the literature dealing with resilience in healthcare. Specifically, from the analysis of the theoretical articles and reviews, the key dimensions of resilience are identified, and a novel classification framework is proposed. The classification framework is then used to systematize extant empirical contributions. Two main dimensions of resilience are identified: the approach to resilience (reactive vs. proactive) and the type of crisis to deal with (acute shocks vs. chronic stressors). Four main streams of research are thus identified: (i) proactive approaches to acute shocks; (ii) proactive approaches to chronic stressors; (iii) reactive approaches to acute shocks; and (iv) reactive approaches to chronic stressors. These are scrutinised considering three additional dimensions: the level of analysis, the resources to nurture resilience, and the country context. The classification framework and the associated mapping contribute to systematising the fragmented literature on resilience in healthcare, providing a clear picture of the state of the art in this field and drawing a research agenda that opens interesting paths for future research.
The study of fusion reactions at extreme sub-barrier energies has seen an increased interest in recent years, although difficult to measure due to their very small cross sections. Such reactions are ...extremely important for our understanding of the production of heavy elements in various environments. In this article, the status of the field is reviewed covering the experimental techniques, the available data, and the theoretical approaches used to describe such reactions. The fusion hindrance effect, first discovered in medium-mass systems, has been found to be relevant also for lighter systems. In some light systems, resonance structures are found to be important, while for heavy systems, the fission process plays an important role. In the near barrier region, couplings to collective excitations in the fusion participants and transfer reactions have been found to give a good description of the measured fusion cross sections and it results in a distribution of fusion barrier heights. New physics ingredients, related to the overlap process of the two projectiles, have to be introduced to describe the hindrance behavior. In addition, it has recently been found that the fusion cross section in both near-barrier and sub-barrier regions can be described very well in many cases using simple, analytical forms of the barrier-height distributions or a modified version of the classic Wong formula.
Measurements of the excitation function for the fusion of Mg-24 + Si-30 (Q = 17.89 MeV)have been extended toward lower energies with respect to previous experimental data. The S-factor maximum ...observed in this large, positive-Q-value system is the most pronounced among such systems studied thus far. The significance and the systematics of an S-factor maximum in systems with positive fusion Q values are discussed. This result would strongly impact the extrapolated cross sections and reaction rates in the carbon and oxygen burnings and, thus, the study of the history of stellar evolution.
Spiders have recently emerged as important diversity hot spots for endosymbiotic bacteria, but the consequences of these symbiotic interactions are largely unknown. In this article, we examined the ...evolutionary history and effect of the intracellular bacterium Cardinium hertigii in the marbled cellar spider Holocnemus pluchei. We showed that Cardinium infection is primarily transmitted in spider populations maternally via egg cytoplasm, with 100% of the progeny from infected mothers being also infected. Examination of a co‐inherited marker, mitochondrial DNA (mtDNA), revealed that Cardinium infection is associated with a wide diversity of mtDNA haplotypes, showing that the interaction between Cardinium and H. pluchei has a long‐term evolutionary dimension and that horizontal transmission among individuals could also occur. Although Cardinium is well known to exert sex ratio distortion or cytoplasmic incompatibility in various arthropod hosts, we show, however, that Cardinium does not interact with the reproductive biology of H. pluchei. A field survey shows a clear geographical structuring of Cardinium infection, with a marked gradual variation of infection frequencies from ca. 0.80 to 0. We discuss different mechanistic and evolutionary explanations for these results as well as their consequences for spider phenotypes. Notably, we suggest that Cardinium can either behave as a neutral cytoplasmic element within H. pluchei or exhibit a context‐dependent effect, depending on the environmental conditions.
Background:
Recent measurements of fusion cross sections for the
28
Si
+
28
Si system revealed a rather
unsystematic behavior; i.e., they drop faster near the barrier than at lower energies. This was ...tentatively attributed
to the large oblate deformation of
28
Si because coupled-channels (CC) calculations largely underestimate the
28
Si
+
28
Si cross sections at low energies, unless a weak imaginary potential is applied, probably simulating
the deformation.
30
Si has no permanent deformation and its low-energy excitations are of a vibrational nature.
Previous measurements of this system reached only 4 mb, which is not sufficient to obtain information on effects
that should show up at lower energies.
Purpose:
The aim of the present experiment was twofold: (i) to clarify the underlying fusion dynamics by
measuring the symmetric case
30
Si
+
30
Si in an energy range from around the Coulomb barrier to deep sub-barrier
energies, and (ii) to compare the results with the behavior of
28
Si
+
28
Si involving two deformed nuclei.
Methods:
30
Si beams from the XTU tandem accelerator of the Laboratori Nazionali di Legnaro of the Istituto
Nazionale di Fisica Nucleare were used, bombarding thin metallic
30
Si targets (50
µ
g
/
cm
2
) enriched to 99
.
64%
in mass 30. An electrostatic beam deflector allowed the detection of fusion evaporation residues (ERs) at very
forward angles, and angular distributions of ERs were measured.
Results:
The excitation function of
30
Si
+
30
Si was measured down to the level of a few microbarns. It has a
regular shape, at variance with the unusual trend of
28
Si
+
28
Si. The extracted logarithmic derivative does not
reach the
L
CS
limit at low energies, so that no maximum of the
S
factor shows up. CC calculations were performed
including the low-lying 2
+
and 3
-
excitations.
Conclusions:
Using a Woods-Saxon potential the experimental cross sections at low energies are overpredicted,
and this is a clear sign of hindrance, while the calculations performed with a M3Y + repulsion potential nicely
fit the data at low energies, without the need of an imaginary potential. The comparison with the results for
28
Si
+
28
Si strengthens the explanation of the oblate shape of
28
Si being the reason for the irregular behavior of
that system.
Peer Reviewed
MEASURING BARRIERS TO FUSION Dasgupta, M.; Hinde, D. J.; Rowley, N. ...
Annual review of nuclear and particle science,
01/1998, Volume:
48, Issue:
1
Journal Article
Peer reviewed
Open access
▪ Abstract The experimental extraction of detailed barrier distributions has brought a significant advance in the study of the fusion of heavy nuclei, and indeed in the entire heavy-ion reaction ...process. A quantitative understanding of the entrance-channel effects induced by target and projectile structure has emerged, based on recent high-precision measurements of fusion excitation functions. These distributions show clearly whether the experimental data are good enough to give the information required. They are also the functions best suited to the theoretical interpretation of the reaction dynamics—often presenting an unambiguous “fingerprint” of the target and projectile structure. We are now at the stage where we can start to exploit the insights gained in order to understand properties of the compound nucleus created: its spin distribution and evaporation residues, perhaps its possible shapes, and, in the case of heavy systems, its subsequent fission.
In the present work the fusion cross section of the 12C+24Mg system has been measured down to energies far below the coulomb barrier around 4μb. This system is slightly heavier than those of ...astrophysical interest, like 12C+12C and 16O+16O. The data points highlight the presence of hindrance in 12C+24Mg because the excitation function is over-estimated by standard Coupled-Channels calculations, and a clear maximum of the S factor has been observed. The cross section at hindrance threshold is found to be remarkably large (σ ≈0.75mb). The S-factor maximum is nicely fitted using both an empirical interpolation in the spirit of the adiabatic model, and the hindrance parametrisation. The data far below the barrier may suggest that the coupling strengths gradually decrease and vanish, so that the excitation function seems to be well reproduced by a simple one-dimensional tunnelling through the potential barrier in that energy range. On the other hand, the equally good fit obtained with the hindrance model, indicates that discriminating between the two approaches would require further precise measurements at slightly lower energies.
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