Direct neutron capture of 48Ca at kT = 52 keV

The neutron capture cross section of 48Ca was measured relative to the known gold cross section at kT = 52 keV using the fast cyclic activation technique. The experiment was performed at the Van-de-Graaff accelerator, Universitaet Tuebingen. The new experimental result is in good agreement with a calculation using the direct capture model. The 1/v behaviour of the capture cross section at thermonuclear energies is confirmed, and the adopted reaction rate which is based on several previous experimental investigations remains unchanged.Comment: 9 pages (uses Revtex), 2 postscript figures, accepted for publication as Brief Report in Phys. Rev.

Universal Cubic Eigenvalue Repulsion for Random Normal Matrices

Random matrix models consisting of normal matrices, defined by the sole constraint $[N^{\dag},N]=0$, will be explored. It is shown that cubic eigenvalue repulsion in the complex plane is universal with respect to the probability distribution of matrices. The density of eigenvalues, all correlation functions, and level spacing statistics are calculated. Normal matrix models offer more probability distributions amenable to analytical analysis than complex matrix models where only a model wth a Gaussian distribution are solvable. The statistics of numerically generated eigenvalues from gaussian distributed normal matrices are compared to the analytical results obtained and agreement is seen.Comment: 15 pages, 2 eps figures. to appar in Physical Review

A new ghost cell/level set method for moving boundary problems:application to tumor growth

In this paper, we present a ghost cell/level set method for the evolution of interfaces whose normal velocity depend upon the solutions of linear and nonlinear quasi-steady reaction-diffusion equations with curvature-dependent boundary conditions. Our technique includes a ghost cell method that accurately discretizes normal derivative jump boundary conditions without smearing jumps in the tangential derivative; a new iterative method for solving linear and nonlinear quasi-steady reaction-diffusion equations; an adaptive discretization to compute the curvature and normal vectors; and a new discrete approximation to the Heaviside function. We present numerical examples that demonstrate better than 1.5-order convergence for problems where traditional ghost cell methods either fail to converge or attain at best sub-linear accuracy. We apply our techniques to a model of tumor growth in complex, heterogeneous tissues that consists of a nonlinear nutrient equation and a pressure equation with geometry-dependent jump boundary conditions. We simulate the growth of glioblastoma (an aggressive brain tumor) into a large, 1 cm square of brain tissue that includes heterogeneous nutrient delivery and varied biomechanical characteristics (white matter, gray matter, cerebrospinal fluid, and bone), and we observe growth morphologies that are highly dependent upon the variations of the tissue characteristics—an effect observed in real tumor growth

Non-resonant direct p- and d-wave neutron capture by 12C

Discrete gamma-rays from the neutron capture state of 13C to its low-lying bound states have been measured using pulsed neutrons at En = 550 keV. The partial capture cross sections have been determined to be 1.7+/-0.5, 24.2+/-1.0, 2.0+/-0.4 and 1.0+/-0.4 microb for the ground (1/2-), first (1/2+), second (3/2-) and third (5/2+) excited states, respectively. From a comparison with theoretical predictions based on the non-resonant direct radiative capture mechanism, we could determine the spectroscopic factor for the 1/2+ state to be 0.80 +/- 0.04, free from neutron-nucleus interaction ambiguities in the continuum. In addition we have detected the contribution of the non-resonant d-wave capture component in the partial cross sections for transitions leading to the 1/2- and 3/2- states. While the s-wave capture dominates at En < 100 keV, the d-wave component turns out to be very important at higher energies. From the present investigation the 12C(n,gamma)13C reaction rate is obtained for temperatures in the range 10E+7 - 10E+10 K.Comment: Accepted for publication in Phys. Rev. C. - 16 pages + 8 figure

Making better use of local data in flood frequency estimation

Flood frequency estimates are an essential part of flood risk management. They are an important ingredient of many important decisions, informing the cost-effectiveness, design and operation of flood defences, flood mapping and planning decisions in flood risk areas. They also inform the National Flood Risk Assessment, the setting of insurance premiums and long-term investment planning. Methods described in the Flood Estimation Handbook (FEH) published in 1999, and many subsequent updates, are considered the industry standard for flood estimation in the UK. They are used extensively by hydrologists from both the public and private sectors. Flood frequency estimates – also known as design flood estimates – are associated with many sources of uncertainty. These hydrological uncertainties often constitute the most uncertain component in any flood study. Uncertainty can lead to difficulty in having confidence in the outputs of studies, whether these are for investment planning, insurance, asset design, development planning or other purposes. As a result, there is considerable benefit to be gained from any reduction in the uncertainty of flood frequency estimation. There are many supplementary sources of information that can help to refine estimates of design floods and potentially reduce uncertainty. Examples include long-term flood history, river level records, photographs of floods and information obtained from field visits. These and similar types of information are defined as ‘local data’. The FEH Local research project aimed to: quantify the uncertainty of design floods estimated from FEH methods develop procedures and guidance for incorporating local and historical data into flood estimation to reduce uncertainties The primary objective of this report is to describe the reviews and research carried out during the FEH Local project. Another output from the project was a document giving guidance to practitioners on how to estimate uncertainty in flood frequency and how to find and incorporate local data. The practitioner guidance, ‘Using Local Data to Reduce Uncertainty in Flood Frequency Estimation’, will be disseminated early in 2017. This report aims to avoid duplication with the practitioner guidance and so is intended mainly for those with an interest in the background to the methods presented in the guidance

Recurring flood distribution patterns related to short-term Holocene climatic variability

Received: 01 July 2015, Accepted: 08 October 2015, Published online: 09 November 2015Millennial- and multi-centennial scale climate variability during the Holocene has been well documented, but its impact on the distribution and timing of extreme river floods has yet to be established. Here we present a meta-analysis of more than 2000 radiometrically dated flood units to reconstruct centennial-scale Holocene flood episodes in Europe and North Africa. Our data analysis shows a general increase in flood frequency after 5000 cal. yr BP consistent with a weakening in zonal circulation over the second half of the Holocene, and with an increase in winter insolation. Multi-centennial length phases of flooding in UK and central Europe correspond with periods of minimum solar irradiance, with a clear trend of increasing flood frequency over the last 1000 years. Western Mediterranean regions show synchrony of flood episodes associated with negative phases of the North Atlantic Oscillation that are out-of-phase with those evident within the eastern Mediterranean. This long-term flood record reveals complex but geographically highly interconnected climate-flood relationships, and provides a new framework to understand likely future spatial changes of flood frequency.GB was funded by the Spanish Ministry of Economy and Competitiveness through the research projects CLARIES (CGL2011–29176), and PALEOMED (CGL2014–58127-C3-1-R).Peer reviewe

Habitat Hydrology and Geomorphology Control the Distribution of Malaria Vector Larvae in Rural Africa

Larval source management is a promising component of integrated malaria control and elimination. This requires development of a framework to target productive locations through process-based understanding of habitat hydrology and geomorphology. We conducted the first catchment scale study of fine resolution spatial and temporal variation in Anopheles habitat and productivity in relation to rainfall, hydrology and geomorphology for a high malaria transmission area of Tanzania. Monthly aggregates of rainfall, river stage and water table were not significantly related to the abundance of vector larvae. However, these metrics showed strong explanatory power to predict mosquito larval abundances after stratification by water body type, with a clear seasonal trend for each, defined on the basis of its geomorphological setting and origin. Hydrological and geomorphological processes governing the availability and productivity of Anopheles breeding habitat need to be understood at the local scale for which larval source management is implemented in order to effectively target larval source interventions. Mapping and monitoring these processes is a well-established practice providing a tractable way forward for developing important malaria management tools

Dependence of direct neutron capture on nuclear-structure models

The prediction of cross sections for nuclei far off stability is crucial in the field of nuclear astrophysics. We calculate direct neutron capture on the even-even isotopes $^{124-145}$Sn and $^{208-238}$Pb with energy levels, masses, and nuclear density distributions taken from different nuclear-structure models. The utilized structure models are a Hartree-Fock-Bogoliubov model, a relativistic mean field theory, and a macroscopic-microscopic model based on the finite-range droplet model and a folded-Yukawa single-particle potential. Due to the differences in the resulting neutron separation and level energies, the investigated models yield capture cross sections sometimes differing by orders of magnitude. This may also lead to differences in the predicted astrophysical r-process paths. Astrophysical implications are discussed.Comment: 25 pages including 12 figures, RevTeX, to appear in Phys. Rev.