Folding Potential Research Articles

Effects of a chiral three-nucleon force on nucleus-nucleus scattering

We investigate the effects of chiral NNLO three-nucleon force (3NF) on nucleus-nucleus elastic scattering, using a standard prescription based on the Brueckner-Hartree-Fock method and the g-matrix folding model. The g-matrix calculated in nuclear matter from the chiral N3LO two-nucleon forces (2NF) is close to that from the Bonn-B 2NF. Because the Melbourne group have already developed a practical g-matrix interaction by localizing the nonlocal g-matrix calculated from the Bonn-B 2NF, we consider the effects of chiral 3NF, in this first attempt to study the 3NF effects, by modifying the local Melbourne g-matrix according to the difference between the g-matrices of the chiral 2NF and 2NF+3NF. For nucleus-nucleus elastic scattering, the 3NF corrections make the folding potential less attractive and more absorptive. The latter novel effect is due to the enhanced tensor correlations in triplet channels. These changes reduce the differential cross section at the middle and large angles, improving the agreement with the experimental data for 16O-16O scattering at 70 MeV/nucleon and 12C-12C scattering at 85 MeV/nucleon.

Complete and incomplete fusion in theBe9+Ta181reaction

Complete and incomplete fusion cross sections for the $^{9}\mathrm{Be}$ $+\phantom{\rule{0.16em}{0ex}}^{181}\mathrm{Ta}$ system were measured at near barrier energies, using the offline gamma ray spectroscopy method. The results were compared with coupled channel calculations that do not take into account the coupling of the breakup channel, using a double folding potential as bare potential. A complete fusion suppression of the order of 35% was found, at energies above the barrier, whereas the total fusion cross sections are in agreement with the calculations. The ratio between incomplete fusion and total fusion at energies above the Coulomb barrier was found to be $32\ifmmode\pm\else\textpm\fi{}1%$. At sub-barrier energies one observes some enhancement of total fusion cross section.

AIDA: ab initio domain assembly server.

AIDA: ab initio domain assembly server, available at http://ffas.burnham.org/AIDA/ is a tool that can identify domains in multi-domain proteins and then predict their 3D structures and relative spatial arrangements. The server is free and open to all users, and there is an option for a user to provide an e-mail to get the link to result page. Domains are evolutionary conserved and often functionally independent units in proteins. Most proteins, especially eukaryotic ones, consist of multiple domains while at the same time, most experimentally determined protein structures contain only one or two domains. As a result, often structures of individual domains in multi-domain proteins can be accurately predicted, but the mutual arrangement of different domains remains unknown. To address this issue we have developed AIDA program, which combines steps of identifying individual domains, predicting (separately) their structures and assembling them into multiple domain complexes using an ab initio folding potential to describe domain–domain interactions. AIDA server not only supports the assembly of a large number of continuous domains, but also allows the assembly of domains inserted into other domains. Users can also provide distance restraints to guide the AIDA energy minimization.

Evidence for a secondary bow in Newton's zero-order nuclear rainbow

Rainbows are generally considered to be caused by static refraction and reflection. A primary and a secondary rainbow appear due to refraction and internal reflection in a raindrop as explained by Newton. The quantum nuclear rainbow, which is generated by refraction in the nucleus droplet, only has a "primary" rainbow. Here we show for the first time evidence for the existence of a secondary nuclear rainbow generated dynamically by coupling to an excited state without internal reflection. This has been demonstrated for experimental $^{16}$O+$^{12}$C scattering using the coupled channel method with an extended double folding potential derived from microscopic realistic wave functions for $^{12}$C and $^{16}$O.

Accuracy of simple folding model in the calculation of the direct part of real α−α interaction potential

The direct part of real α−α interaction potential is calculated in the simple folding model using density-dependent Brink–Boeker effective interaction. The simple folding potentials calculated from the short- and finite-range components of this effective interaction are compared with their corresponding double folding results obtained from the oscillator model wave function to establish the relative accuracy of the model. It is found that the direct part of real α−α interaction potential calculated in the simple folding model is reliable.

Electrochemical Biosensors Featuring Oriented Antibody Immobilization via Electrografted and Self-Assembled Hydrazide Chemistry

Appropriate site-directed chemistry is essential to maximize the performance of immunosensors. We present two new functionalization strategies that preserve proper folding and binding potential of antibodies by forcing their oriented immobilization. Both strategies are based on the formation of hydrazone bonds between aldehyde groups on the Fc moieties of periodate-oxidized antibodies and hydrazide groups on functionalized gold electrodes. Those hydrazide groups are introduced by electrografting of diazonium salts or by self assembly of mono- and dithiolated hydrazide linkers, resulting in films with tailored functional groups and, thus, antibody distribution and spacing. Their barrier properties and permeability toward electroactive species are evaluated. To demonstrate the potential of these new functionalization strategies, detection of bacteriophage MS2 is performed through either a direct assay using electrochemical impedance spectroscopy (EIS) or through a sandwich assay using differential pulse voltammetry (DPV). Diazonium and monothiolated self-assembled monolayer-modified electrodes enable the detection of less than 1 plaque forming unit (pfu)/mL in a direct EIS assay. However, nonspecific adsorption renders measurements in river water samples difficult. In contrast, sandwich-assays on electrodes with electrografted diazonium salts and monothiolated self-assembled monolayers do not show significant matrix effects using river water samples, but the limits of detection are 10(8) times higher than those of the direct assay. Best results are achieved for immunosensors based on mixed monolayers of hydrazide and hydroxyl diothiolated linkers (15 pfu/mL). These new functionalization techniques are facile to implement. They afford the possibility to tune the surface composition and tailor the electrochemical properties of electrochemical sensors. These advantages should translate into broad interest in this type of surface chemistry for biosensor development.

Projectile structure effects in the collisions6,7Li+64Zn around the Coulomb barrier.

We measured elastic scattering angular distributions and cross sections for heavy residue production for the systems 6,7Li+64Zn at different energies around the Coulomb barrier. The elastic scattering angular distributions have been reproduced by optical model fits using a renormalized double folding potential for the real and imaginary parts. Absence of usual threshold anomaly in the optical potential was found. The excitation functions for heavy residue production were measured using an activation technique. Comparison with different calculations suggest that complete fusion is the dominant reaction mechanism above the barrier whereas, below the Coulomb barrier, incomplete fusion and transfer dominate.

Semimicroscopic Dispersive Analysis of Nuclear-Nuclear Collisions on the Basis of Folding Potential

A semimicroscopic analysis of a set of experimental data of elastic α + 12C scattering was performed at several laboratory energies. The Woods-Saxon parameters were adjusted to obtain the best χ2 fit to the scattering data. The energy systematics of the positions of Airy minima was constructed, and it was shown that their positions depend linearly on the inverse center of mass energy. The parameters of the model potential have been determined unambiguously. It has been shown that the energy dependence of the volume integrals satisfies the dispersion relation and agrees well with the results obtained within a phenomenological analysis. Also, it has been shown that the found positions of the Airy minima satisfy the rule of the quadratical dependence of the position of the Airy minima on the reduced mass of the colliding nuclei.

Open shell effects in a microscopic optical potential for elastic scattering of6(8)He

Elastic scattering observables (differential cross section and analyzing power) are calculated for the reaction ${}^{6}$He($p,p$)${}^{6}$He at projectile energies starting at 71 MeV/nucleon. The optical potential needed to describe the reaction is based on a microscopic Watson first-order folding potential, which explicitly takes into account that the two neutrons outside the ${}^{4}$He core occupy an open $p$ shell. The folding of the single-particle harmonic oscillator density matrix with the nucleon-nucleon $t$ matrix leads for this case to new terms not present in traditional folding optical potentials for closed shell nuclei. The effect of those new terms on the elastic scattering observables is investigated. Furthermore, we study the influence of an exponential tail of the $p$-shell wave functions on the scattering observables, as well as the sensitivity of the observables to variations of matter and charge radius. Finally, elastic scattering observables for the reaction ${}^{8}$He($p,p$)${}^{8}$He are presented at selected projectile energies.

Unification of Airy structure in inelasticα+16O scattering andα-cluster structure with core excitation in20Ne

The Airy structure of the nuclear rainbow and prerainbow in inelastic and elastic $\alpha+^{16}$O scattering is studied with the coupled channel method using a folding potential derived from the microscopic wave functions of $^{16}$O. The theoretical calculations reproduce the characteristic energy evolution of the Airy minimum of the experimental angular distributions. The energy levels with $\alpha$-cluster structure in $^{20}$Ne are reproduced well using the potentials determined from the analysis of scattering. It is shown that the emergence of the $K=0_3^+$ $\alpha$-cluster band with core excitation at 7.19 MeV in $^{20}$Ne is intimately related to the emergence of the prerainbow and rainbow in inelastic scattering to the $^{16}$O($0^+_2$). It is found that the $\alpha$-cluster states with core excitation, the prerainbow and the rainbow in inelastic scattering are understood in a unified way as well as in the case of elastic scattering.

Elastic alpha scattering experiments and the alpha-nucleus optical potential at low energies

High precision angular distribution data of (α,α) elastic scattering are presented for the nuclei 89Y, 92Mo, 106,110,116Cd, 112,124Sn, and 144Sm at energies around the Coulomb barrier. Such data with small experimental uncertainties over the full angular range (20–170°) are the indispensable prerequisite for the extraction of local optical potentials and for the determination of the total reaction cross section σreac. A systematic fitting procedure was applied to the experimental scattering data presented to obtain comprehensive local potential parameter sets that are composed of a real folding potential and an imaginary potential of Woods–Saxon surface type. The potential parameters obtained were used in turn to construct a new systematic α-nucleus potential with very few parameters. Although this new potential cannot reproduce the angular distributions with the same small deviations as the local potential, the new potential is able to predict the total reaction cross sections for all cases under study.

Energy dependence of the 6Li + 16O elastic scattering versus that of 7Li + 16O

Existing data for the 6Li + 16O elastic scattering at $ E_{c.m.}=3.27$ -36.8MeV were analyzed within the optical model and coupled-reaction-channels method. The 6Li + 16O elastic and inelastic scattering as well as the reorientation of 6Li and the simplest transfer reactions were included in the coupled-channels scheme. The 6Li + 16O potential parameters at different energies as well as their energy dependence were deduced by the use of the dispersion relation between the real and imaginary parts of the potential. The contributions of the 6Li reorientation and transfer reactions to the 6Li + 16O elastic scattering channel were estimated at the different energies. It is found that the potential scattering dominates the interaction at smaller angles for all energies, with the transfers contributing significantly at larger angles at the highest energies studied. The real part of the 6Li + 16O deduced potential is in reasonable agreement with that of a corresponding folding potential. The isotopic difference between the 6Li + 16O and 7Li + 16O optical potentials is larger for the imaginary potentials.

Observation of an Airy minimum in elastic and inelastic scattering of3He from12C at 50.5 and 60 MeV, andα-particle condensation in12C

Angular distributions for elastic and inelastic scattering of $^3$He from $^{12}$C were measured at energies 50.5 and 60 MeV. The Airy minimum of the prerainbow scattering was clearly observed in the angular distributions for the 0$_2^+$ (7.65 MeV) state of $^{12}$C (Hoyle state). The experimental results were analyzed with a coupled channels method with double folding potentials derived from the microscopic wave functions for the ground 0$_1^+$, 2$^+$ (4.44 MeV), 3$^-$ (9.64 MeV) and 0$_2^+$ states. The analysis supports the view that the Hoyle state is a three alpha particle condensate with a large radius of dilute matter distribution.

$${\Xi}$$ Hypernucler States Predicted by the New Interaction Model ESC08c

The features of the new interaction model ESC08c in \({\Lambda N}\), \({\Sigma N}\) and \({\Xi N}\) channels are demonstrated single hyperon potentials \({U_Y(Y=\Lambda, \Sigma, \Xi)}\) in nuclear matter on the basis of the G-matrix theory. (K−, K+) productions of \({\Xi}\) hypernuclei are studied with \({\Xi}\)-nucleus folding potentials.

Refractive Features and Diffraction Scattering Patterns Observed in the Elastic Scattering of <sup>12</sup>C from <sup>12</sup>C at Various Energies

We have measured the angular distributions for 12C ion beam elastically scattered from 12C target of thickness 17.4 μg/cm2 at energies 15, 18 and 21 MeV which is close to the Coulomb barrier energy for 12C + 12C nuclear system. The elastic scattering of 12C beam on 12C was analysed also at different energies (139.5, 158.8, 180, 240, 288.6, 300, 360 and 420 MeV) from literature in order to obtain the global optical potential parameters, which could fairly reproduce the experimental data. The experimental results were analysed within the framework of both the optical model and the double folding potential obtained with different density-dependent NN interactions which give the corresponding values of the nuclear incompressibility K in the Hartree-Fock calculation of nuclear matter. The agreement between the experimental results and the theoretical predictions in the whole angular range is fairly good.

Elastic scattering and heavy residue production in the collisions6,7Li+64Zn around the Coulomb barrier

Elastic scattering angular distributions and heavy residue production cross sections have been measured at different energies around the Coulomb barrier for the systems 6,7 Li+ 64 Zn. Optical model fits of the elastic angular distributions were performed using a renormalized double folding potential and absence of usual threshold anomaly in the optical potential was found. Excitation functions for heavy residue production have been measured using an activation technique. Comparison of the data with the results of different calculations show that complete fusion is the dominant reaction mechanism above the barrier, whereas the heavy residue yield below the barrier is mainly due to incomplete fusion and transfer.

A theoretical study on 120Sn(6He, 6He)120Sn elastic scattering

In this study, we analyze 120Sn(6He,6He)120Sn elastic scattering with both the phenomenological (WS) and microscopic double folding (DF) potentials. In the phenomenological calculations we use the optical model (OM) parameters acquired from literature. DF potentials have been obtained for no-core shell model (NCSM) density distribution (DD) of 6He nucleus. The phenomenological results is compared with DF model results as well as the experimental data. These comparison provides information about the similarities and differences of the models used in calculations.

Phenomenological and semi-microscopic analysis for 16O and 12C elastically scattering on the nucleus of 16O and 12C at Energies near the Coulomb barrier

The nuclear burning process proceeds from the conservation of the most abundant element hydrogen to helium, then from helium to carbon and oxygen, and then from these to heavier elements. Some of the key reactions for the carbon and oxygen burning stages of the nucleosynthesis are 12C+12C and 16O+16O leading to all possible final states. This paper contains the experimental measurements of 12C+12C and 16O+16O angular distributions performed at the cyclotron DC-60 in Astana, Kazakhstan. The extracted beam of 16O and 12C was accelerated up to two energies 1.75 and 1.5 MeV/n and then directed to an Al2O3 target of thickness 20 μg/cm2 and a carbon self-supporting target of thickness 17.4 μg/cm2. The angular distribution calculations were performed using both the phenomenological optical potential (SPI-GENOA) code and the double folding potential (FRESCO) code.

Werner syndrome protein suppresses the formation of large deletions during the replication of human telomeric sequences

Werner syndrome (WS) is a disorder characterized by features of premature aging and increased cancer that is caused by loss of the RecQ helicase WRN. Telomeres consisting of duplex TTAGGG repeats in humans protect chromosome ends and sustain cellular proliferation. WRN prevents the loss of telomeres replicated from the G-rich strand, which can form secondary G-quadruplex (G4) structures. Here, we dissected WRN roles in the replication of telomeric sequences by examining factors inherent to telomeric repeats, such as G4 DNA, independently from other factors at chromosome ends that can also impede replication. For this we used the supF shuttle vector (SV) mutagenesis assay. We demonstrate that SVs with [TTAGGG]6 sequences are stably replicated in human cells, and that the repeats suppress the frequency of large deletions despite G4 folding potential. WRN depletion increased the supF mutant frequency for both the telomeric and non-telomeric SVs, compared with the control cells, but this increase was much greater (27-fold) for telomeric SVs. The higher SV mutant frequencies in WRN-deficient cells were primarily due to an increase in large sequence deletions and rearrangements. However, WRN depletion caused a more dramatic increase in deletions and rearrangements arising within the telomeric SV (70-fold), compared with non-telomeric SV (8-fold). Our results indicate that WRN prevents large deletions and rearrangements during replication, and that this role is particularly important in templates with telomeric sequence. This provides a possible explanation for increased telomere loss in WS cells.

An Investigation of 4He+12C and 4He+16O Reactions Using the Cluster Model

The α-target semimicroscopic single folding potentials have been derived by folding a composite (repulsive and attractive) effective α-α interaction with the α-cluster distribution density in the target nuclei. The obtained potentials are considered as the real part of the nuclear optical model potentials, while the imaginary parts are phenomenologicaly expressed using the Woods—Saxon form. Nine sets of measured experimental data of the 4He+12C and 4He+16O elastic rainbow scattering over the energy range 80–240 MeV are analyzed using the obtained potentials. The data are successfully reproduced using the extracted potentials. The resulted reaction cross sections are also investigated and compared with the available corresponding data.