Quantification of channel planform change on the lower Rangitikei River, New Zealand, 1949-2007: response to management?

The Rangitikei River, a large gravel‐bed wandering river located in the North Island of New Zealand, has outstanding scenic characteristics, recreational, fisheries and wildlife habitat features. Recently concerns have been raised over the potential negative impact that perceived channel changes in the latter part of the 20th century may be having on the Rangitikei River recreational fishery. This study describes and quantifies the large‐scale morphological changes that have occurred in selected reaches of the lower Rangitikei River between 1949 and 2007. This research utilised historical aerial photography and analysis in ArcGIS® to quantify channel planform change in three reaches, encompassing ~18 km of the lower Rangitikei River. This showed that the lower Rangitikei was transformed from a multi‐channelled planform to a predominantly single‐thread wandering planform, with an associated reduction in morphological complexity and active channel width of up to 74%, between 1949 and 2007. Bank protection measures instigated under the Rangitikei River Scheme have primarily driven these changes. Gravel extraction has also contributed by enhancing channel‐floodplain disconnection and exacerbating sediment deficits. The findings of this study have implications for future management of the Rangitikei. Previous lower Rangitikei River management schemes have taken a reach‐based engineering approach with a focus on bank erosion protection and flood mitigation. This study has confirmed the lower river has responded geomorphologically to these goals of river control. However questions as to the economic and ecological sustainability of this management style may encourage river managers to consider the benefits of promoting a self‐adjusting fluvial system within a catchment‐framed management approach

Prospects for Detecting Supernova Neutrino Flavor Oscillations

The neutrinos from a Type II supernova provide perhaps our best opportunity to probe cosmologically interesting muon and/or tauon neutrino masses. This is because matter enhanced neutrino oscillations can lead to an anomalously hot nu_e spectrum, and thus to enhanced charged current cross sections in terrestrial detectors. Two recently proposed supernova neutrino observatories, OMNIS and LAND, will detect neutrons spalled from target nuclei by neutral and charged current neutrino interactions. As this signal is not flavor specific, it is not immediately clear whether a convincing neutrino oscillation signal can be extracted from such experiments. To address this issue we examine the responses of a series of possible light and heavy mass targets, 9Be, 23Na, 35Cl, and 208Pb. We find that strategies for detecting oscillations which use only neutron count rates are problematic at best, even if cross sections are determined by ancillary experiments. Plausible uncertainties in supernova neutrino spectra tend to obscure rate enhancements due to oscillations. However, in the case of 208Pb, a signal emerges that is largely flavor specific and extraordinarily sensitive to the nu_e temperature, the emission of two neutrons. This signal and its flavor specificity are associated with the strength and location of the first-forbidden responses for neutral and charge current reactions, aspects of the 208Pb neutrino cross section that have not been discussed previously. Hadronic spin transfer experiments might be helpful in confirming some of the nuclear structure physics underlying our conclusions.Comment: 27 pages, RevTeX, 2 figure

Neutrino Capture and r-Process Nucleosynthesis

We explore neutrino capture during r-process nucleosynthesis in neutrino-driven ejecta from nascent neutron stars. We focus on the interplay between charged-current weak interactions and element synthesis, and we delineate the important role of equilibrium nuclear dynamics. During the period of coexistence of free nucleons and light and/or heavy nuclei, electron neutrino capture inhibits the r-process. At all stages, capture on free neutrons has a larger impact than capture on nuclei. However, neutrino capture on heavey nuclei by itself, if it is very strong, is also detrimental to the r-process until large nuclear equilibrium clusters break down and the classical neutron-capture phase of the r-process begins. The sensitivity of the r-process to neutrino irradiation means that neutrino-capture effects can strongly constrain the r-process site, neutrino physics, or both. These results apply also to r-process scenarios other than neutrino-heated winds.Comment: 20 pages, 17 figures, Submitted to Physical Review

The Influence of Nuclear Composition on the Electron Fraction in the Post-Core-Bounce Supernova Environment

We study the early evolution of the electron fraction (or, alternatively, the neutron-to-proton ratio) in the region above the hot proto-neutron star formed after a supernova explosion. We study the way in which the electron fraction in this environment is set by a competition between lepton (electron, positron, neutrino, and antineutrino) capture processes on free neutrons and protons and nuclei. Our calculations take explicit account of the effect of nuclear composition changes, such as formation of alpha particles (the alpha effect) and the shifting of nuclear abundances in nuclear statistical equilibrium associated with cooling in near-adiabatic outflow. We take detailed account of the process of weak interaction freeze-out in conjunction with these nuclear composition changes. Our detailed treatment shows that the alpha effect can cause significant increases in the electron fraction, while neutrino and antineutrino capture on heavy nuclei tends to have a buffering effect on this quantity. We also examine the effect on weak rates and the electron fraction of fluctuations in time in the neutrino and antineutrino energy spectra arising from hydrodynamic waves. Our analysis is guided by the Mayle & Wilson supernova code numerical results for the neutrino energy spectra and density and velocity profiles.Comment: 38 pages, AAS LaTeX, 8 figure

Probing neutrino physics with a self-consistent treatment of the weak decoupling, nucleosynthesis, and photon decoupling epochs

We show that a self-consistent and coupled treatment of the weak decoupling, big bang nucleosynthesis, and photon decoupling epochs can be used to provide new insights and constraints on neutrino sector physics from high-precision measurements of light element abundances and cosmic microwave background observables. Implications of beyond-standard-model physics in cosmology, especially within the neutrino sector, are assessed by comparing predictions against five observables: the baryon energy density, helium abundance, deuterium abundance, effective number of neutrinos, and sum of the light neutrino mass eigenstates. We give examples for constraints on dark radiation, neutrino rest mass, lepton numbers, and scenarios for light and heavy sterile neutrinos.Comment: 29 pages, 10 figure

Three dimensional laser Doppler velocimeter turbulence measurements in a pipe flow

The mean and turbulent u, v, and w components of a gaseous fully developed turbulent pipe flow were measured with a laser Doppler velocimeter system. Measurements of important system parameters are presented and discussed in relation to the measurement accuracy. Simultaneous comparisons of the laser Doppler and hot wire anemometer measurements in the turbulent flow provided evidence that the two systems were responding to the same flow phenomena

Evidence for an Intense Neutrino Flux during rr-Process Nucleosynthesis?

We investigate the possibility that neutrino capture on heavy nuclei competes with beta decay in the environment where the $r$-Process elements are synthesized. We find that such neutrino capture is not excluded by existing abundance determinations. We show that inclusion of significant neutrino capture on the (neutron number) N=82 waiting point nuclei can allow the inferred abundances of these species to provide a good fit to steady weak (beta decay plus neutrino capture) flow equilibrium. In fact, for particular choices of neutrino flux conditions, this fit is improved over the case where nuclei change their charge by beta decay alone. However, this improved fit can be realized only if neutrino capture plays a negligible role in nuclear decay back toward stability. We discuss the implications of these considerations for current proposed sites and models for $r$-Process nucleosynthesis.Comment: 10 pages, plain tex, submitted to ApJ

Neutrino-Accelerated Hot Hydrogen Burning

We examine the effects of significant electron anti-neutrino fluxes on hydrogen burning. Specifically, we find that the bottleneck weak nuclear reactions in the traditional pp-chain and the hot CNO cycle can be accelerated by anti-neutrino capture, increasing the energy generation rate. We also discuss how anti-neutrino capture reactions can alter the conditions for break out into the rp-process. We speculate on the impact of these considerations for the evolution and dynamics of collapsing very- and super- massive compact objects.Comment: 14 pages, 6 figures, submitted to ApJ; minor content chang

An Active-Sterile Neutrino Transformation Solution for r-Process Nucleosynthesis

We discuss how matter-enhanced active-sterile neutrino transformation in both neutrino and antineutrino channels could enable the production of the rapid neutron capture (r-process) nuclei in neutrino-heated supernova ejecta. In this scheme the lightest sterile neutrino would be heavier than the electron neutrino and split from it by a vacuum mass-squared difference roughly between 3 and 70 eV$^2$ and vacuum mixing angle given by $\sin^2 2\theta_{es} > 10^{-4}$.Comment: 27 pages plus twelve figures. Submitted to Phys. Rev.