121 research outputs found
On a vector-valued generalisation of viscosity solutions for general PDE systems
We propose a theory of non-differentiable solutions which applies to fully
nonlinear PDE systems and extends the theory of viscosity solutions of
Crandall-Ishii-Lions to the vectorial case. Our key ingredient is the discovery
of a notion of extremum for maps which extends min-max and allows "nonlinear
passage of derivatives" to test maps. This new PDE approach supports certain
stability and convergence results, preserving some basic features of the scalar
viscosity counterpart. In this first part of our two-part work we introduce and
study the rudiments of this theory, leaving applications for the second part.Comment: 34 pages, 6 figure
Properties of components with incrementally formed gears
The process class of sheet-bulk metal forming (SBMF) involves several advantages for the manufacture of functional components. Its incremental variant (iSBMF) enables a very flexible dimensioning of components. To treat the unfavorable manufacturing time of the incremental approach, this investigation is focused on an alternative process route using rotating forming tools, which decrease the process time significantly. After an analysis of the mechanical properties as well as the micro- and macroscopic surface quality, a quasi-static benchmark test was performed. Normalized by the weight of the component, gears manufactured by iSBMF and BS600 steel presented the same load capacity as gears manufactured by blanking with subsequent hardening. Here, using innovative high strength steels with a significant strain hardening behavior like high manganese steels enables for weight-reduced gears
N-body simulations of stars escaping from the Orion nebula
We study the dynamical interaction in which the two single runaway stars AE
Aurigae and mu Columbae and the binary iota Orionis acquired their unusually
high space velocity. The two single runaways move in almost opposite directions
with a velocity greater than 100 km/s away from the Trapezium cluster. The star
iota Ori is an eccentric (e=0.8) binary moving with a velocity of about 10 km/s
at almost right angles with respect to the two single stars. The kinematic
properties of the system suggest that a strong dynamical encounter occurred in
the Trapezium cluster about 2.5 Myr ago. Curiously enough, the two binary
components have similar spectral type but very different masses, indicating
that their ages must be quite different. This observation leads to the
hypothesis that an exchange interaction occurred in which an older star was
swapped into the original iota Orionis binary. We test this hypothesis by a
combination of numerical and theoretical techniques, using N-body simulations
to constrain the dynamical encounter, binary evolution calculations to
constrain the high orbital eccentricity of iota Orionis and stellar evolution
calculations to constrain the age discrepancy of the two binary components. We
find that an encounter between two low eccentricity (0.4<e<0.6) binaries with
comparable binding energy, leading to an exchange and the ionization of the
wider binary, provides a reasonable solution to this problem.Comment: 14 pages, 13 figures, 5 tables, accepted for publication in MNRA
Comparing the effects of sun exposure and vitamin D supplementation on vitamin D insufficiency, and immune and cardio-metabolic function: the Sun Exposure and Vitamin D Supplementation (SEDS) Study
BACKGROUND Adults living in the sunny Australian climate are at high risk of skin cancer, but vitamin D deficiency (defined here as a serum 25-hydroxyvitamin D (25(OH)D) concentration of less than 50 nmol/L) is also common. Vitamin D deficiency may be a risk factor for a range of diseases. However, the optimal strategies to achieve and maintain vitamin D adequacy (sun exposure, vitamin D supplementation or both), and whether sun exposure itself has benefits over and above initiating synthesis of vitamin D, remain unclear. The Sun Exposure and Vitamin D Supplementation (SEDS) Study aims to compare the effectiveness of sun exposure and vitamin D supplementation for the management of vitamin D insufficiency, and to test whether these management strategies differentially affect markers of immune and cardio-metabolic function. METHODS/DESIGN The SEDS Study is a multi-centre, randomised controlled trial of two different daily doses of vitamin D supplementation, and placebo, in conjunction with guidance on two different patterns of sun exposure. Participants recruited from across Australia are aged 18-64 years and have a recent vitamin D test result showing a serum 25(OH)D level of 40-60 nmol/L. DISCUSSION This paper discusses the rationale behind the study design, and considers the challenges but necessity of data collection within a non-institutionalised adult population, in order to address the study aims. We also discuss the challenges of participant recruitment and retention, ongoing engagement of referring medical practitioners and address issues of compliance and participant retention. TRIAL REGISTRATION Australia New Zealand Clinical Trials Registry: ACTRN12613000290796 Registered 14 March 2013
On the phase structure of five-dimensional SU(2) gauge theories with anisotropic couplings
The phase diagram of five-dimensional SU(2) gauge theories is explored using
Monte Carlo simulations of the theory discretized on a Euclidean lattice using
the Wilson plaquette action and periodic boundary conditions. We simulate
anisotropic gauge couplings which correspond to different lattice spacings a_4
in the four dimensions and a_5 along the extra dimension. In particular we
study the case where a_5>a_4. We identify a line of first order phase
transitions which separate the confined from the deconfined phase. We perform
simulations in large volume at the bulk phase transition staying in the
confined vacuum. The static potential measured in the hyperplanes orthogonal to
the extra dimension hint at dimensional reduction. We also locate and analyze
second order phase transitions related to breaking of the center along one
direction.Comment: 28 pages, 22 figures, 4 tables; few explanations and references
added; version accepted for publication in Nucl. Phys.
A Quintessential Axion
The model independent axion of string theory has a decay constant of order of
the Planck scale. We explore the properties of this quintessence candidate
(quintaxion) in the scheme of hidden sector supergravity breakdown. In models
allowing for a reasonable term, the hidden sector dynamics may lead to an
almost flat potential responsible for the vacuum energy of . A solution to the strong CP-problem is provided by an additional
hidden sector pseudoscalar (QCD axion) with properties that make it an
acceptable candidate for cold dark matter of the universe.Comment: 11 pages, Revtex, 1 figur
Fixed points of quantum gravity in extra dimensions
We study quantum gravity in more than four dimensions with renormalisation
group methods. We find a non-trivial ultraviolet fixed point in the
Einstein-Hilbert action. The fixed point connects with the perturbative
infrared domain through finite renormalisation group trajectories. We show that
our results for fixed points and related scaling exponents are stable. If this
picture persists at higher order, quantum gravity in the metric field is
asymptotically safe. We discuss signatures of the gravitational fixed point in
models with low-scale gravity and compact extra dimensions.Comment: Wording sharpened, refs added, to appear in PL
The Antarctic ozone hole during 2015 and 2016
We reviewed the 2015 and 2016 Antarctic ozone holes, making use of a variety of ground-based and spacebased measurements of ozone and ultraviolet radiation, supplemented by meteorological reanalyses. The ozone hole of 2015 was one of the most severe on record with respect to maximum area and integrated deficit and was notably longlasting, with many values above previous extremes in October, November and December. In contrast, all assessed metrics for the 2016 ozone hole were at or below their median values for the 37 ozone holes since 1979 for which adequate satellite observations exist. The 2015 ozone hole was influenced both by very cold conditions and enhanced ozone depletion caused by stratospheric aerosol resulting from the April 2015 volcanic eruption of Calbuco (Chile)
The Antarctic ozone hole during 2014
We review the 2014 Antarctic ozone hole, making use of a variety of ground-based and space-based measurements of ozone and ultra-violet radiation, supplemented by meteorological reanalyses. Although the polar vortex was relatively stable in 2014 and persisted some weeks longer into November than was the case in 2012 or 2013, the vortex temperature was close to the long-term mean in September and October with modest warming events occurring in both months, preventing severe depletion from taking place. Of the seven metrics reported here, all were close to their respective median values of the 1979–2014 record, being ranked between 16th and 21st of the 35 years for which adequate satellite observations exist
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