Experimental ejection angles for oblique impacts: Implications for the subsurface flow‐field

Abstract— A simple analytical solution for subsurface particle motions during impact cratering is useful for tracking the evolution of the transient crater shape at late times. A specific example of such an analytical solution is Maxwell's Z‐Model, which is based on a point‐source assumption. Here, the parameters for this model are constrained using measured ejection angles from both vertical and oblique experimental impacts at the NASA Ames Vertical Gun Range. Data from experiments reveal that impacts at angles as high as 45° to the target's surface generate subsurface flow‐fields that are significantly different from those created by vertical impacts. The initial momentum of the projectile induces a subsurface momentum‐driven flow‐field that evolves in three dimensions of space and in time to an excavation flow‐field during both vertical and oblique impacts. A single, stationary point‐source model (specifically Maxwell's Z‐Model), however, is found inadequate to explain this detailed evolution of the subsurface flow‐field during oblique impacts. Because 45° is the most likely impact angle on planetary surfaces, a new analytical model based on a migrating point‐source could prove quite useful. Such a model must address the effects of the subsurface flow‐field evolution on crater excavation, ejecta deposition, and transient crater morphometry.     

A process‐based transfer function approach to model tile‐drain hydrographs

Tile‐drain response to rainfall events is determined by unsaturated vertical flow to the water table, followed by horizontal saturated water movement. In this study, unsaturated vertical movement from the redistribution of water is modelled using a sharp‐front approximation, and the saturated horizontal flow is modelled by an approximate solution to the Boussinesq equation. The unsaturated flow component models the fast response that is associated with the presence of preferential flow paths. By convoluting the responses of the two components, a transfer function is developed that predicts tile‐drain response to unit amounts of infiltrated water. It is observed that the unsaturated flow component can be cast in a form that is linear in a power function of the infiltrated depth. Since the approach is process based, model parameter definitions are easily identified with soil properties at the field scale. Furthermore, it is demonstrated that the transfer function model parameters can be estimated from moment analysis. Using superposition, the transient tile‐drain response to arbitrary amounts of infiltrated water can be constructed. Comparison with data measured from the Water Quality Field Station show that this approach provides a promising method for generating tile‐drain response to rainfall events. Copyright © 2006 John Wiley & Sons, Ltd.     

[Fe/H] relations for c-type RR Lyrae variables based upon Fourier coefficients

[Fe/H]–φ₃₁– P relations are found for c-type RR Lyrae stars in globular clusters. The relations are analogous to that found by Jurcsik & Kovács for field ab-type RR Lyrae stars, where a longer period correlates with lower metallicity values for similar values of the Fourier coefficient φ₃₁. The relations obtained here are used to determine the metallicity of field c-type RR Lyrae stars, those within ω Cen, the Large Magellanic Cloud and toward the galactic bulge. The results are found to compare favourably to metallicity values obtained elsewhere.     

A thermobarometer for sphene (titanite)

Sphene and zircon are common accessory minerals in metamorphic and igneous rocks of very different composition from many different geological environments. Their essential structural constituents, Ti and Zr, are capable of replacing each other to some degree. In this paper we detail the results of high pressure–temperature experiments as well as analyses of natural sphene crystals that establish a systematic relationship between temperature, pressure and Zr concentration in sphene. Calibrations of the temperature and pressure relationships are presented as a thermobarometer. Synthetic sphene crystals were crystallized in the presence of zircon, quartz and rutile at 1–2.4 GPa and 800–1,000°C from hydrothermal solutions. Crystals were analyzed for Zr by electron microprobe (EMP). The experimental results define a log-linear relationship between equilibrium Zr content (ppm by weight), pressure (GPa) and reciprocal absolute temperature: The incorporation of Zr into sphene was found to be rather sensitive to pressure effects and also to the effects of kinetic disequilibrium and growth entrapment that result in sector zoning. The Zr content of sphene is relatively insensitive to the presence of both REEs and F-Al substitutions in sphene. To supplement and test the experimental data, sphenes from seven rocks of well-constrained origin were analyzed for Zr by both EMP and ion microprobe (IMP). The sphene thermobarometer records crystallization temperatures that are consistent with independent thermometry. When applied to natural sphene of unknown origin or growth conditions, this thermobarometer has the potential to estimate temperatures with an approximate uncertainty of ±20°C over the temperature range of interest (600–1,000°C). The Zr-in-sphene thermobarometer can also be used in conjunction with the Zr-in-rutile thermobarometer to estimate both pressure and temperature of crystallization. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.

Measurements and Computations of Flow in an Urban Street System

We present results from laboratory and computational experiments on the turbulent flow over an array of rectangular blocks modelling a typical, asymmetric urban canopy at various orientations to the approach flow. The work forms part of a larger study on dispersion within such arrays (project DIPLOS) and concentrates on the nature of the mean flow and turbulence fields within the canopy region, recognising that unless the flow field is adequately represented in computational models there is no reason to expect realistic simulations of the nature of the dispersion of pollutants emitted within the canopy. Comparisons between the experimental data and those obtained from both large-eddy simulation (LES) and direct numerical simulation (DNS) are shown and it is concluded that careful use of LES can produce generally excellent agreement with laboratory and DNS results, lending further confidence in the use of LES for such situations. Various crucial issues are discussed and advice offered to both experimentalists and those seeking to compute canopy flows with turbulence resolving models.     

Killing Carp (Cyprinus carpio) as a Volunteer Practice: implications for community involvement in invasive species management and policy

Community engagement is understood to be one of the keys to successful environmental programs—‘the social pillar’ of management. In this paper we examine community engagement where volunteers participate by killing invasive animals. Most research to date focuses on the biological or management implications of volunteer efforts for the invasive species, with little attention to the people involved or the social acceptability of killing animals in this context. Here, we report on a survey and participant observations of community fishing events in south-eastern Australia, where volunteers fish for and kill carp (Cyprinus carpio). We examine who takes part in these events, their motivations for being involved and the implications for ongoing community engagement. Survey respondents were predominantly well-educated Australian-born men, motivated to fish by a desire to spend time in nature. However, we also noted a strong response from overseas-born men with different motivations. Our survey elicited complex responses regarding killing, illustrating contradictory, sometimes conflicted experiences, which jar with personal motivations. The implications are that questions of ethics must extend to the human volunteers, and that more direct communication of program outcomes and the proposed benefits for volunteers be more rigorously assessed. We argue that invasive species management must contend with the experiences of volunteers, otherwise meaningful dialogue and program objectives risk being undermined.     

The Decision‐Making/Accountability Spatial Incongruence Problem for Research Linking Environmental Science and Policy

Increasingly, scholars engage policy makers around fundamental, complex questions on environmental change in interdisciplinary settings. Researchers attempting to develop robust contributions to knowledge that can support policymaker understandings in this context face significant inferential challenges in dealing with the spatial dimension of their phenomenon of interest. In this paper, we extend an understanding of well‐defined methodological challenges familiar to applied spatial scientists by explicitly articulating the Decision‐Making/Accountability, Spatial Incongruence Problem, or DASIP. Three case studies illustrate how spatial incongruences matter to researchers who work on complex, interdisciplinary problems, while seeking to understand decision‐making or policy‐related phenomenon: urban heat‐island mitigation research in Arizona, water transfer conflicts in Kansas, and hydraulic‐fracturing debates in Texas. With such examples, we aim to evoke a deeper understanding of this problem in applied research and also inspire thinking about how scholars might innovate methods for creating knowledge about environmental change that supports spatially accountable decision making.     

Sequential sample reservoirs for Itrax-XRF analysis of discrete samples

Geochemical analysis of sediment samples can be used to characterize between- and within-lake variability and provide insights into lake chemistry, depositional processes and contamination sources. The number of samples for geochemical studies is restricted by cost, sample volume required, and the destructive nature of inductively coupled plasma mass spectrometry, instrumental neutron activation analysis, or wavelength dispersive x-ray fluorescence. Core scanners that incorporate energy dispersive x-ray fluorescence spectrometry, such as the Cox Itrax-XRF core scanner, have high through-put and can be used to produce high-quality geochemical datasets at low cost without destroying sample material. Here we describe a new analysis vessel that enables rapid, non-destructive Itrax-XRF analysis of discrete sediment samples.     

Geological structure and kinematics of normal faults in the Otway Basin,Australia, based on quantitative analysis of 3‐D seismic reflection data

The Otway Basin in the south of Victoria, Australia underwent three phases of deformation during breakup of the southern Australian margin. We assess the geometry and kinematics of faulting in the basin by analysing a 3‐D reflection seismic volume. Eight stratigraphic horizons and 24 SW‐dipping normal faults as well as subordinate antithetic faults were interpreted. This resulted in a high‐resolution geological 3‐D model (ca. 8 km × 7 km × 4 km depth) that we present as a supplementary 3‐D PDF (Data S1). We identified hard‐ and soft‐linking fault connections over the entire area, such as antithetic faults and relay ramps, respectively. Most major faults were continuously active from Early to Late Cretaceous, with two faults in the northern part of the study area active until at least the Oligocene. Allan maps of faults show tectonic activity continuously waned over this time period. Isopach maps of stratigraphic volumes quantify the amount of syn‐sedimentary movement that is characteristic of passive margins, such as the Otway Basin. We show that the faults possess strong corrugations (with amplitudes above the seismic resolution), which we illustrated by novel techniques, such as cylindricity and curvature. We argue that the corrugations are produced by sutures between sub‐vertical fault segments and this morphology was maintained during fault growth. Thus, they can be used to indicate the kinematics vector of the fault movement. This evidences, together with left‐stepping relay ramps, that 40% of the faults had a small component (up to 25°) of dextral oblique slip as well as normal (dip‐slip) movement.