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

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

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

Expert Statement:Pneumothorax Associated with One-Way Valve Therapy for Emphysema: 2020 Update

For selected patients with advanced emphysema, bronchoscopic lung volume reduction with one-way valves can lead to clinically relevant improvements of airflow obstruction, hyperinflation, exercise capacity, and quality of life. The most common complication of this procedure is pneumothorax with a prevalence of up to +/- 34% of the treated patients. Patients who develop a pneumothorax also experience meaningful clinical benefits once the pneumothorax is resolved. Timely resolution of a post-valve treatment pneumothorax requires skilled and adequate pneumothorax management. This expert panel statement is an updated recommendation of the 2014 statement developed to help guide pneumothorax management after valve placement. Additionally, mechanisms for pneumothorax development, risk assessment, prevention of pneumothorax, and outcomes after pneumothorax are addressed. This recommendation is based on a combination of the current scientific literature and expert opinion, which was obtained through a modified Delphi method

Can the Universe Create Itself?

The question of first-cause has troubled philosophers and cosmologists alike. Now that it is apparent that our universe began in a Big Bang explosion, the question of what happened before the Big Bang arises. Inflation seems like a very promising answer, but as Borde and Vilenkin have shown, the inflationary state preceding the Big Bang must have had a beginning also. Ultimately, the difficult question seems to be how to make something out of nothing. This paper explores the idea that this is the wrong question --- that that is not how the Universe got here. Instead, we explore the idea of whether there is anything in the laws of physics that would prevent the Universe from creating itself. Because spacetimes can be curved and multiply connected, general relativity allows for the possibility of closed timelike curves (CTCs). Thus, tracing backwards in time through the original inflationary state we may eventually encounter a region of CTCs giving no first-cause. This region of CTCs, may well be over by now (being bounded toward the future by a Cauchy horizon). We illustrate that such models --- with CTCs --- are not necessarily inconsistent by demonstrating self-consistent vacuums for Misner space and a multiply connected de Sitter space in which the renormalized energy-momentum tensor does not diverge as one approaches the Cauchy horizon and solves Einstein's equations. We show such a Universe can be classically stable and self-consistent if and only if the potentials are retarded, giving a natural explanation of the arrow of time. Some specific scenarios (out of many possible ones) for this type of model are described. For example: an inflationary universe gives rise to baby universes, one of which turns out to be itself. Interestingly, the laws of physics may allow the Universe to be its own mother.Comment: 48 pages, 8 figure

Helen Chadwick’s ‘Composite Images’

This article traces the considerations of British artist Helen Chadwick (1953–1996) regarding ‘composite images’ and the potential liberation they opened up in the gap between image and form, surface and spectator. These will be discussed as the author follows two apparently contrasting trajectories of her thought; while her considerations of the image, and her own image-making, tend increasingly towards ‘pure surface’, her ambitions for spectatorial positioning and agency increase. In parallel, while the epistemological underpinnings of her thinking become increasingly complex and dynamic, the role of (self)portraiture in her work moves away from the portrayal of her own, and later the recognisably human, body. These trajectories can be mapped (roughly) onto particular projects, beginning with Ego Geometria Sum (1982–1984), developing through Of Mutability (1984–1986) where she first used the photocopier to produce ‘automatic images’ and into her light-based installations, such as Blood Hyphen (1988)