Particle-size characteristics of the vertical dust profiles of two contrasting dust events in the Channel Country of western Queensland, Australia

Spatial and temporal variations in vegetation and soil surface conditions of rangelands add a level of complexity to wind erosion processes which is often difficult to model or measure. Butler and colleagues have developed a methodology which combines computer simulation and experimental measurement to analyse how spatial and temporal changes in dust source area emission rates and atmospheric conditions affect vertical dust concentration profiles during wind erosion events in the Queensland Channel Country. This methodology has not, however, taken into account how variations in dust source area particle-size can affect vertical dust concentration profiles. The present paper examines how the particle-size characteristics of dust source soils affect both vertical dust concentration profiles and the vertical distribution of particle-sizes in two contrasting wind erosion events in the Queensland Channel Country. Comparisons are made between computer simulations of these events and the results of field measurements (of vertical dust concentration profiles) and laboratory measurements (of dust particle-size). Computer simulations of the particle-size emissions from the different dust source areas during the two events produce vertical distributions of dust particle-sizes which are similar to the measured dust particle-sizes for these events. These results indicate that erodibility-induced spatial and temporal variations in particle-size emissions of dust source areas have important influences upon: dust fluxes, vertical dust concentration profiles and the vertical distribution of dust particle-sizes within these profile

Impulsivity and Symptoms of Nicotine Dependence in a Young Adult Population

Introduction: Impulsivity is widely regarded as a risk factor for drug dependence. However, its relationship with the symptomatology of nicotine dependence is poorly understood. Methods: To examine the nature of these relationships, we recruited 404 daily and occasional smokers from a predominantly student population and assessed the association between impulsivity, as measured by the Barratt Impulsiveness Scale (BIS-11) and several self-reported measures of smoking rate and nicotine dependence, including the Diagnostic and Statistical Manual’s (DSM-IV) criteria. Results: Overall, impulsivity was high throughout the entire sample but only modestly associated with nicotine dependence. Within the diagnostic criteria of nicotine dependence, two symptoms, which reflect automatized or habitual smoking, were most strongly associated with impulsivity. Conclusion: These data support recent human and animal work, which suggests that impulsivity is linked to the formation of habitual drug use, and are discussed within the framework of a dual-system account of drug seeking

Twin Paradox and the logical foundation of relativity theory

We study the foundation of space-time theory in the framework of first-order logic (FOL). Since the foundation of mathematics has been successfully carried through (via set theory) in FOL, it is not entirely impossible to do the same for space-time theory (or relativity). First we recall a simple and streamlined FOL-axiomatization SpecRel of special relativity from the literature. SpecRel is complete with respect to questions about inertial motion. Then we ask ourselves whether we can prove usual relativistic properties of accelerated motion (e.g., clocks in acceleration) in SpecRel. As it turns out, this is practically equivalent to asking whether SpecRel is strong enough to "handle" (or treat) accelerated observers. We show that there is a mathematical principle called induction (IND) coming from real analysis which needs to be added to SpecRel in order to handle situations involving relativistic acceleration. We present an extended version AccRel of SpecRel which is strong enough to handle accelerated motion, in particular, accelerated observers. Among others, we show that the Twin Paradox becomes provable in AccRel, but it is not provable without IND.Comment: 24 pages, 6 figure

Approximate analytical solution of the Boussinesq equation

A new approximate solution of the one-dimensional Boussinesq equation is presented for a semi-infinite aquifer when the hydraulic head at the source is an arbitrary function of time. Estimates for recharge, discharge, and elevation of the water table are given. The simplicity and accuracy of the approximation are compared with 'exact' numerical and analytical solutions. The method of solution is illustrated with several examples including the commonly treated case of a constant boundary head and a nonmonotonically varying boundary head

On an exact analytical solution of the Boussinesq equation

A useful exact analytical solution of the Boussinesq equation is discussed and is the most general solution presently available, and in particular yields a solution for a finite aquifer. It provides insight into the physical processes arising during the exchange of water between an aquifer and a free body of water of varying height as an application and extension of Barenblatt’s solution. We also illustrate the value of such a solution to check numerical and approximate schemes

A Survey on Continuous Time Computations

We provide an overview of theories of continuous time computation. These theories allow us to understand both the hardness of questions related to continuous time dynamical systems and the computational power of continuous time analog models. We survey the existing models, summarizing results, and point to relevant references in the literature

Limitation of the transport capacity approach in sediment transport modeling

In a recent paper by Polyakov and Nearing (2003) it was shown experimentally that the sediment transport capacity in a rill is not unique for a given soil type, slope, and flow rate. Indeed, they found that the transport capacity was dependent on whether sediment transport in the rill was occurring under net erosion or net deposition conditions. They concluded that this nonuniqueness in transport capacity is a discrepancy that needs addressing in soil erosion models. Here we postulate that this behavior occurs as a result of defining transport capacity as an model input to distinguish between net erosion and net deposition regimes, instead of determining it as an outcome between the separate but continuous rate processes of deposition and entrainment such as is the case for the multisize class erosion model of Hairsine and Rose (1992a, 1992b). This model is used to reinterpret and reproduce the results of Polyakov and Nearing (2003). The analysis shows that the transport capacity cannot be unique for a soil composed of a range of size classes and that uniqueness only occurs for the exceptional case of single size class soil. Consequently, when used as a model input, the transport capacity concept is deficient in modeling sediment transport of real soils across different flow conditions

Analytical approximation for the recession of a sloping aquifer

An approximation is obtained for the recession of a sloping aquifer. The analytical approximation can provide a useful tool to analyze data and obtain physical properties of the aquifer. In contrast to the case of a horizontal aquifer, when plotting the time derivative of the flux versus the flux on a log scale, the result shows that the flux derivative reaches a minimum value and that the curve can have a slope of unity as often observed. Illustration of the application of the analytical results to the Mahantango Creek data is also discussed