II. Combined numerical model of ion and neutral composition above 120 km

A coupled neutral-ionic photochemical model has been used to interpret the ionic composition of the Venusian dayside ionosphere measured by the orbiter retarding potential analyser (ORPA) experiment on board the NASA Pioneer-Venus orbiter spacecraft. The electron and ion temperatures also measured by the ORPA are used for calculating the plasma-diffusion coefficients and scale heights for ions. The neutral temperature profiles and the densities of neutral constituents, particularly CO₂ and O, play key roles in the determination of the height profiles of the ionic constituents. All these quantities vary substantially in the Venusian thermosphere near the terminator; the models presented are representatives of the solar zenith angle ～65°. The predicted O₂⁺ densities below ～200km agree particularly well with observations by the ORPA, but the model values are significantly less than those measured by the orbiter ion mass spectrometer (OIMS). Models predict much smaller densities than observed values for all molecular ions above ～200km. The reason for the turn-up trend of the concentration gradient of molecular ions observed at these heights by both ORPA and OIMS is unknown. One of the models can predict O⁺ ion densities above ～200km compatible with observations, if an effective vertical escape flux (φ10⁸cm^?2sec^?1) is assumed at the ionopause. The neutral air density required to explain the observed ion composition is about 1.4 times larger than the values measured by the orbiter neutral mass spectrometer (ONMS).     

A unified presentation of the Voigt functions

This paper aims at presenting a unified study of the Voigt functionsK(x,y) andL(x,y) which play a rather important role in several diverse fields of physics such as astrophysical spectroscopy and the theory of neutron reactions. Explicit expressions for these functions are given in terms of relatively more familiar special functions of one and two variables; indeed, each of these representations will naturally lead to various other needed properties of the Voigt functions.     

User Assessment as Input for Useful Geospatial Representations within Mobile Location-Based Services

Mobile Location‐Based Services (mLBS) are an increasingly consumer‐based concept borne from, and continually driven by, technology‐centred development; as opposed to the needs of end users. Where users have been made a focus, the research generally concerns issues of overall system appearance, functionality, information content and interaction methods, with little emphasis on the component geospatial representations. This paper describes the initial stages of a research project aimed at filling this void through the application of a qualitative User‐Centred Design (UCD) methodology for optimising geospatial representations within mLBS applications, in order to support a selected user group: Australian ‘leisure‐based travellers’. Presented in this paper is an account of two UCD activities adopted for the research. The first, user profiling, served to define the target user population in terms of their technological, geospatial and travel experiences, using an online questionnaire. The second, user task analysis, involved in‐depth interviews with a subset of users in order to obtain a deeper understanding of the geospatial goals, tasks, needs and preferences within the population, as well as the range of user differences and variability in tasks present. An overall user assessment, through combined analysis of the two result sets, highlighted considerations for the ongoing research, including a set of specific implications for the design of alternative models for geospatial services, representations and interactions. The themes described in this paper represent an initial and necessary component of UCD, which has been largely overlooked in research relating to mLBS. Whilst the focus here is on a specific user group and context of use, it is envisaged that many of the concepts tested and ratified by the resulting models will be relevant to mLBS applications in general.     

Seasonal variations in pore water and sediment geochemistry of littoral lake sediments (Asylum Lake, MI, USA)

Background  

Seasonal changes in pore water and sediment redox geochemistry have been observed in many near-surface sediments. Such changes have the potential to strongly influence trace metal distribution and thus create seasonal fluctuations in metal mobility and bioavailability.     

Pore-scale simulation of entrapped non-aqueous phase liquid dissolution

We investigated the dissolution of non-aqueous phase liquids (NAPLs) in a three-dimensional random sphere-pack medium using a pore-scale modeling approach to advance fundamental understanding and connect rigorously to microscale processes. Residual NAPL distributions were generated using a morphological approach and the entrapped non-wetting phase was quantitatively characterized by calculating volume, orientation, interfacial area, and shape of isolated NAPL regions. With a detailed aqueous-phase flow field obtained by a multiple-relaxation time lattice Boltzmann approach, we solved the advective–diffusive equation in the pore space using a high-resolution, adaptive-stencil finite-volume scheme and an operator-splitting algorithm. We show good agreement between the mass transfer rates predicted in the computational approach and previously published experimental observations. The pore-scale simulations presented in this work provide the first three-dimensional comparison to the considerable experimental work that has been performed to derive constitutive relations to quantify mass transfer from a residual NAPL to a flowing aqueous phase.