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.
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.
Cadmium is a widespread carcinogen. We previously showed that the administration of low CdCl2 doses for 24 h to healthy C3H10T1/2Cl8 mouse embryonic fibroblast cell line at the beginning of Cell ...Transformation Assay (CTA), up regulates genes involved in metal scavenging and antioxidant defense, like metallothioneines, glutathione S-transferases and heat shock proteins. Still, although most cells thrive normally in the following weeks, malignancy is triggered by CdCl2 and leads to the appearance of foci of transformed cells at the end of the CTA. In this work we aim at elucidating the early metabolic deregulation induced by cadmium, underlying healthy cell transformation into malignant cells.
Respiratory metabolism was investigated through Seahorse Agilent assays, while oxidative stress level was assessed through fluorescent probes; DNA damage was evaluated by Comet assay, and mitochondrial morphology was analyzed in confocal microscopy.
Results show that the initial response to CdCl2 involves mitochondria rearrangement into a perinuclear network. However, SOD1 and SOD2 activities are inhibited, leading to increased superoxide anion level, which in turn causes DNA strand breaks. From the metabolic point of view, cells increase their glycolytic flux, while all extra NADH produced is still efficiently reoxidized by mitochondria.
Our results confirm previously shown response against cadmium toxicity; new data about glycolytic increase and mitochondrial rearrangements suggest pathways leading to cell transformation.
In this work we exploit the widely used, well known CTA, which allows following healthy cells transformation into a malignant phenotype, to understand early events in cadmium-induced carcinogenesis.
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•Mitochondria are key targets in cadmium-induced carcinogenicity.•Cellular response to cadmium toxicity involves up-regulation of glycolysis.•Cadmium inhibits SOD1 activity, raising superoxide anion (O2−) intracellular concentration.
Purpose
Patients with oligo-metastatic disease (OMD) can be safely treated with Stereotactic Radiation Therapy (SRT). Further disease progression is common in these patients. In most cases, patients ...relapse again with oligo-metastases, however some can experience a poly-progression after a local ablative treatment (LAT). The purpose of this study was to retrospectively identify factors associated with poly-progression in patients receiving SRT for OMD.
Methods
Data from a monocentric database were retrospectively analyzed. Patients treated with SRT for OMD and who developed progression after LAT were selected. Patients were categorized as oligo- or poly-progressive according to the number of new/progressing metastases (≤ or > 5). Herein, we analyzed data about patients’ characteristics, oligo-metastatic presentation and radiation treatment characteristics to evaluate their relationship with progression type.
Results
From 2013 to 2021, data on 700 patients progressing after LAT were analyzed. Among them, 227 patients (32.4%) experienced a poly-progression; the median time to poly-progression was 7.72 months (range 1–79.6). Five variables associated with poly-progression were found to be statistically significant in the univariate analysis: performance status (
p
< 0.001), site of the primary tumor (
p
= 0.016), ablative dose (
p
= 0.002), treated site (
p
= 0.002), single or double organ (
p
= 0.03). Of those, all but the number of involved organs retained their significant predictive value on the multivariate analysis.
Conclusion
Our study identified four independent factors associated with poly-progression in patients with OMD receiving SRT. Our data may support comprehensive characterization of OMD, better understanding of factors associated with progression.
Cockayne syndrome (CS) is a rare genetic disease characterized by severe growth, mental retardation and pronounced cachexia. CS is most frequently due to mutations in either of two genes, CSB and ...CSA. Evidence for a role of CSB protein in the repair of oxidative DNA damage has been provided recently. Here, we show that CSA is also involved in the response to oxidative stress. CS-A human primary fibroblasts and keratinocytes showed hypersensitivity to potassium bromate, a specific inducer of oxidative damage. This was associated with inefficient repair of oxidatively induced DNA lesions, namely 8-hydroxyguanine (8-OH-Gua) and (5'S)-8,5'-cyclo 2'-deoxyadenosine. Expression of the wild-type CSA in the CS-A cell line CS3BE significantly decreased the steady-state level of 8-OH-Gua and increased its repair rate following oxidant treatment. CS-A cell extracts showed normal 8-OH-Gua cleavage activity in an in vitro assay, whereas CS-B cell extracts were confirmed to be defective. Our data provide the first in vivo evidence that CSA protein contributes to prevent accumulation of various oxidized DNA bases and underline specific functions of CSB not shared with CSA. These findings support the hypothesis that defective repair of oxidative DNA damage is involved in the clinical features of CS patients.
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
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.
MEASURING BARRIERS TO FUSION Dasgupta, M.; Hinde, D. J.; Rowley, N. ...
Annual review of nuclear and particle science,
01/1998, Letnik:
48, Številka:
1
Journal Article
Recenzirano
Odprti dostop
▪ 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.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
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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