Effects of an induced three-body force in the incident channel of (d,p) reactions

A widely accepted practice for treating deuteron breakup in $A(d,p)B$ reactions relies on solving a three-body $A+n+p$ Schr\"odinger equation with pairwise $A$-$n$, $A$-$p$ and $n$-$p$ interactions. However, it was shown in [Phys. Rev. C \textbf{89}, 024605 (2014)] that projection of the many-body $A+2$ wave function into the three-body $A+n+p$ channel results in a complicated three-body operator that cannot be reduced to a sum of pairwise potentials. It contains explicit contributions from terms that include interactions between the neutron and proton via excitation of the target $A$. Such terms are normally neglected. We estimate the first order contribution of these induced three-body terms and show that applying the adiabatic approximation to solving the $A+n+p$ model results in a simple modification of the two-body nucleon optical potentials. We illustrate the role of these terms for the case of $^{40}$Ca($d,p$)$^{41}$Ca transfer reactions at incident deuteron energies of 11.8, 20 and 56 MeV, using several parameterisations of nonlocal optical potentials.Comment: 7 pages, 2 figures. Publication due in Phys. Rev.

Three-nucleon force contribution to the deuteron channel in (d,p)(d,p) reactions

The contribution of a three-nucleon (3N) force, acting between the neutron and proton in the incoming deuteron with a target nucleon, to the deuteron-target potential in the entrance channel of the $A(d,p)B$ reaction has been calculated within the adiabatic distorted wave approximation (ADWA). Four different 3N interaction sets from local chiral effective field theory ($\chi$EFT) at next-to-next-to-leading order (N2LO) were used. Strong sensitivity of the adiabatic deuteron-target potential to the choice of the 3N force format has been found, which originates from the enhanced sensitivity to the short-range physics of nucleon-nucleon (NN) and 3N interactions in the ADWA. Such a sensitivity is reduced when a Watanabe folding model is used to generate $d$-$A$ potential instead of ADWA. The impact of the 3N force contribution on $(d,p)$ cross sections depends on assumptions made about the $p$-$A$ and $n$-$A$ optical potentials used to calculate the distorted $d$-$A$ potential in the entrance channel. It is different for local and nonlocal optical potentials and depends on whether the induced three-body force arising due to neglect of target excitations is included or not.Comment: Accepted for publication in Physical Review

Three-body optical potentials in (d,p) reactions and their influence on indirect study of stellar nucleosynthesis

Model uncertainties arising due to suppression of target excitations in the description of deuteron scattering and resulting in a modification of the two-body interactions in a three-body system are investigated for several (d,p) reactions serving as indirect tools for studying the astrophysical (p,γ) reactions relevant to rp process. The three-body nature of the deuteron-target potential is treated within the adiabatic distorted-wave approximation (ADWA) which relies on a dominant contribution from the components of the three-body deuteron-target wave function with small n−p separations. This results in a simple prescription for treating the explicit energy dependence of two-body optical potentials in a three-body system requiring nucleon optical potentials to be evaluated at a shifted energy with respect to the standard value of half the deuteron incident energy. In addition, the ADWA allows for leading-order multiple-scattering effects to be estimated, which leads to a simple renormalization of the adiabatic potential's imaginary part by a factor of two. These effects are assessed using both nonlocal and local optical potential systematics for 26Al, 30P, 34Cl, and 56Ni targets at a deuteron incident energy of 12 MeV, which is typical for experiments with radioactive beams in inverse kinematics. The model uncertainties induced by the three-body nature of deuteron-target scattering are found to be within 40% both in the main peak of angular distributions and in total (d,p) cross sections. At higher deuteron energies, around 60 MeV, model uncertainties can reach 100% in the total cross sections. A few examples of application to astrophysically interesting proton resonances in 27Si and 57Cu obtained using (d,p) reactions and mirror symmetry are given

Improving the track friendliness of a four-axle railway vehicle using an inertance-integrated lateral primary suspension

Improving the track friendliness of a railway vehicle can benefit the railway industry significantly. Rail surface damage in curves can be reduced by using vehicles with a lower Primary Yaw Stiffness (PYS); however, this can reduce high-speed stability and worsen ride comfort. Previous studies have shown that this trade-off between track friendliness and passenger comfort can be successfully combated by using an inerter in the primary suspension; however, these utilise simplified vehicle models, contact models, and track inputs. Considering a realistic four-axle passenger vehicle model, this paper investigates the extent to which the PYS can be reduced with inertance-integrated primary lateral suspensions without increasing root-mean-square (RMS) carbody lateral accelerations. The vehicle model, with these enhanced suspensions, has been created in VAMPIRE (Formula presented.), with the dynamics being captured over a range of vehicle velocities and equivalent conicities. Based on systematic optimisations using network-synthesis theory, several beneficial inertance-integrated configurations are identified, and the PYS can be reduced by up to 47% compared to the default vehicle (a potential Network Rail Variable Usage Charge saving of 26%), without increasing RMS carbody lateral accelerations. Further simulations are performed to investigate the vehicle's performance in curve transitions and when subject to one-off peak lateral track irregularities

Inertance-Integrated Primary Suspension Optimisation on an Industrial Railway Vehicle Model

Improving the track friendliness of a railway vehicle is highly beneficial to the rail industry, as it substantially increases its cost effectiveness. Rail surface damage under curving conditions can be reduced by using vehicles with a reduced Primary Yaw Stiffness (PYS); however, a lower PYS often leads to a reduction in high-speed stability and can negatively impact ride comfort. Previous studies have suggested that this trade-off, between track friendliness and passenger comfort, can be successfully improved by using an inerter in the primary suspension; however, these studies used simplified two-axle vehicles and simplified contact models, and track inputs. Considering a more realistic four-axle passenger vehicle model, this paper investigates the extent to which the PYS can be reduced using inertance-integrated primary lateral suspensions without increasing Root Mean Square (RMS) lateral carbody accelerations when running over a 5 km example track (with a number of vertical, lateral and longitudinal irregularities, and gauge variations). The vehicle, with inertance-integrated primary lateral suspensions, has been modelled in$$\mathrm{VAMPIRE}^{\textregistered }$$, and the vehicle dynamics are captured over a range of different velocities and wheel-rail equivalent conicities. Several inertance-integrated suspensions are optimised, leading to permissible PYS reductions of up to 47% compared to the original vehicle, whilst lateral carbody accelerations remain at acceptable levels. This level of PYS reduction would result in a potential Network Rail Variable Usage Charge saving of 26%

Indicators of the ecological impact of bottom-trawl disturbance on seabed communities

The Ecosystem Approach to Fisheries requires that managers take account of the environmental impacts of fishing. We develop linked state and pressure indicators that show the impact of bottom-trawling on benthic communities. The state indicator measures the proportion of an area where benthic invertebrate biomass (B) or production (P) is more than 90% of pristine benthic biomass (B 0.9) or production (P0.9). The pressure indicator measures the proportion of the area where trawling frequency is sufficiently high to prevent reaching predicted B0.9 or P0.9. Time to recovery to B0.9 and P0.9 after trawling, depending on the habitat, was estimated using a validated size-based model of the benthic community. Based on trawling intensity in 2003, 53.5% of the southern North Sea was trawled too frequently for biomass to reach B0.9, and 27.1% was trawled too frequently for production to reach P0.9. As a result of bottom-trawling in 2003, in 56% of the southern North Sea benthic biomass was below B0.9, whereas in 27% of the southern North Sea benthic production was below P0.9. Modeled recovery times were comparable to literature estimates (2.5 to more than 6 years). The advantages of using the area with an ecological impact of trawling as a pressure indicator are that it is conceptually easy to understand, it responds quickly to changes in management action, it can be implemented at a relevant scale for fisheries management, and the necessary effort distribution data are centrally collected. One of this approach's greatest utilities, therefore, will be to communicate to policy makers and fishing enterprises the expected medium- to long-term ecological benefits that will accrue if the frequency of trawling in particular parts of fishing grounds is reduced