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The Effects of Specimen Dimensions on the Mechanical Behavior of EBM Produced Ti6Al4V Alloys
There are several published studies investigating the microstructures and mechanical
properties obtained during additive manufacturing of Ti6Al4V alloys utilizing the Electron Beam
Melting (EBM) technique. These studies have concentrated on conventional testing coupon sizes
and configurations which allowed for a direct comparison to the properties of conventionally
produced Ti6Al4V alloys. One of the many benefits of the EBM process is that it allows the
manufacturer to produce components in sizes and configurations unachievable by conventional
methods. It becomes important to understand and verify the microstructures and mechanical
performance of these smaller components in a manufacturing environment, requiring the use of
nonâconventional testing configurations. This paper presents case-studies involving the
production and testing of non-standard samples and how these samples compare to conventional
E8 testing coupons. Differences in mechanical performance were observed and are most likely
due to the unique characteristics of EBM produced materials.Mechanical Engineerin
Effect of anti-icing chemicals on stripping of asphalt concrete mixtures for airport runway wearing courses
As part of a wider research project for the study and development of a system for the prediction, monitoring and management of meteorological winter emergencies in airports (Airport Weather Information System, AWIS), the experimental investigation reported in this paper focused on damage phenomena caused by antiicing chemicals on asphalt concrete mixtures for airport runway surface courses, with an emphasis placed upon stripping. Asphalt mixtures derived from the combination of aggregates of two different mineralogical types (basaltic and siliceous) and two bituminous binders (one neat bitumen and one SBS polymer modified binder). The testing program included determination of aggregate-binder affinity, indirect tensile strength and fracture properties. A potassium formate solution was employed as antiicer. Obtained results indicated that anti-icing treatments may promote stripping phenomena to an extent which depends on aggregate and binder typ
Life cycle modelling of environmental impacts of application of processed organic municipal solid waste on agricultural land (EASEWASTE)
A model capable of quantifying the potential environmental impacts of agricultural application of composted or anaerobically digested source-separated organic municipal solid waste (MSW) is presented. In addition to the direct impacts, the model accounts for savings by avoiding the production and use of commercial fertilizers. The model is part of a larger model, Environmental Assessment of Solid Waste Systems and Technology (EASEWASTE), developed as a decisionsupport model, focusing on assessment of alternative waste management options. The environmental impacts of the land application of processed organic waste are quantified by emission coefficients referring to the composition of the processed waste and related to specific crop rotation as well as soil type. The model contains several default parameters based on literature data, field experiments and modelling by the agro-ecosystem model, Daisy. All data can be modified by the user allowing application of the model to other situations. A case study including four scenarios was performed to illustrate the use of the model. One tonne of nitrogen in composted and anaerobically digested MSW was applied as fertilizer to loamy and sandy soil at a plant farm in western Denmark. Application of the processed organic waste mainly affected the environmental impact categories global warming (0.4â0.7 PE), acidification (â0.06 (saving)â1.6 PE), nutrient enrichment (â1.0 (saving)â3.1 PE), and toxicity. The main contributors to these categories were nitrous oxide formation (global warming), ammonia volatilization (acidification and nutrient enrichment), nitrate losses (nutrient enrichment and groundwater contamination), and heavy metal input to soil (toxicity potentials). The local agricultural conditions as well as the composition of the processed MSW showed large influence on the environmental impacts. A range of benefits, mainly related to improved soil quality from long-term application of the processed organic waste, could not be generally quantified with respect to the chosen life cycle assessment impact categories and were therefore not included in the model. These effects should be considered in conjunction with the results of the life cycle assessment
Scaling Behavior of Ricci Curvature at Short Distance near Two Dimensions
We study the renormalization of the Ricci curvature as an example of
generally covariant operators in quantum gravity near two dimensions. We find
that it scales with a definite scaling dimension at short distance. The Ricci
curvature singularity at the big bang can be viewed as such a scaling
phenomenon. The problem of the spacetime singularity may be resolved by the
scale invariance of the spacetime at short distance.Comment: 9pages, LaTe
Quantum field aspect of Unruh problem
It is shown using both conventional and algebraic approach to quantum field
theory that it is impossible to perform quantization on Unruh modes in
Minkowski spacetime. Such quantization implies setting boundary condition for
the quantum field operator which changes topological properties and symmetry
group of spacetime and leads to field theory in two disconnected left and right
Rindler spacetimes. It means that "Unruh effect" does not exist.Comment: LaTeX, 13 pages, 1 figur
Conservation Laws and 2D Black Holes in Dilaton Gravity
A very general class of Lagrangians which couple scalar fields to gravitation
and matter in two spacetime dimensions is investigated. It is shown that a
vector field exists along whose flow lines the stress-energy tensor is
conserved, regardless of whether or not the equations of motion are satisfied
or if any Killing vectors exist. Conditions necessary for the existence of
Killing vectors are derived. A new set of 2D black hole solutions is obtained
for one particular member within this class of Lagrangians. One such solution
bears an interesting resemblance to the 2D string-theoretic black hole, yet
contains markedly different thermodynamic properties.Comment: 11 pgs. WATPHYS-TH92/0
Reissner-Nordstrom Black Holes and Thick Domain Walls
We solve numerically equations of motion for real self-interacting scalar
fields in the background of Reissner-Nordstrom black hole and obtained a
sequence of static axisymmetric solutions representing thick domain walls
charged black hole systems. In the case of extremal Reissner-Nordstrom black
hole solution we find that there is a parameter depending on the black hole
mass and the width of the domain wall which constitutes the upper limit for the
expulsion to occur.Comment: 18 pages, 10 figures, accepted for Phys. Rev.
Robust Henderson III estimators of variance components in the nested error model
Common methods for estimating variance components in Linear Mixed Models include Maximum Likelihood (ML) and Restricted Maximum Likelihood (REML). These methods are based on the strong assumption of multivariate normal distribution and it is well know that they are very sensitive to outlying observations with respect to any of the random components. Several robust altematives of these methods have been proposed (e.g. Fellner 1986, Richardson and Welsh 1995). In this work we present several robust alternatives based on the Henderson method III which do not rely on the normality assumption and provide explicit solutions for the variance components estimators. These estimators can later be used to derive robust estimators of regression coefficients. Finally, we describe an application of this procedure to small area estimation, in which the main target is the estimation of the means of areas or domains when the within-area sample sizes are small
Stellar evolution and modelling stars
In this chapter I give an overall description of the structure and evolution
of stars of different masses, and review the main ingredients included in
state-of-the-art calculations aiming at reproducing observational features. I
give particular emphasis to processes where large uncertainties still exist as
they have strong impact on stellar properties derived from large compilations
of tracks and isochrones, and are therefore of fundamental importance in many
fields of astrophysics.Comment: Lecture presented at the IVth Azores International Advanced School in
Space Sciences on "Asteroseismology and Exoplanets: Listening to the Stars
and Searching for New Worlds" (arXiv:1709.00645), which took place in Horta,
Azores Islands, Portugal in July 201
Constructing and Characterising Solar Structure Models for Computational Helioseismology
In this paper, we construct background solar models that are stable against
convection, by modifying the vertical pressure gradient of Model S
(Christensen-Dalsgaard et al., 1996, Science, 272, 1286) relinquishing
hydrostatic equilibrium. However, the stabilisation affects the eigenmodes that
we wish to remain as close to Model S as possible. In a bid to recover the
Model S eigenmodes, we choose to make additional corrections to the sound speed
of Model S before stabilisation. No stabilised model can be perfectly
solar-like, so we present three stabilised models with slightly different
eigenmodes. The models are appropriate to study the f and p1 to p4 modes with
spherical harmonic degrees in the range from 400 to 900. Background model CSM
has a modified pressure gradient for stabilisation and has eigenfrequencies
within 2% of Model S. Model CSM_A has an additional 10% increase in sound speed
in the top 1 Mm resulting in eigenfrequencies within 2% of Model S and
eigenfunctions that are, in comparison with CSM, closest to those of Model S.
Model CSM_B has a 3% decrease in sound speed in the top 5 Mm resulting in
eigenfrequencies within 1% of Model S and eigenfunctions that are only
marginally adversely affected. These models are useful to study the interaction
of solar waves with embedded three-dimensional heterogeneities, such as
convective flows and model sunspots. We have also calculated the response of
the stabilised models to excitation by random near-surface sources, using
simulations of the propagation of linear waves. We find that the simulated
power spectra of wave motion are in good agreement with an observed SOHO/MDI
power spectrum. Overall, our convectively stabilised background models provide
a good basis for quantitative numerical local helioseismology. The models are
available for download from http://www.mps.mpg.de/projects/seismo/NA4/.Comment: 35 pages, 23 figures Changed title Updated Figure 1
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