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Observation and Numerical Simulation of Melt Pool Dynamic and Beam Powder Interaction During Selective Electron Beam Melting
Selective electron beam melting (SEBM) is an additive manufacturing method used to
produce complex parts in a layer-by-layer process utilizing Ti6Al4V powder. To improve the
very good properties of built parts even more and to use the full capacity of the process, the
fundamental understanding of the beam powder interaction is of essential relevance.
Numerical simulations and observation with a high speed camera of powder melting show the
strong melt pool dynamic and its lateral extent clearly. Furthermore, the immediate effect of
beam parameters, e.g. beam current and velocity, on the melting behavior of the powder can
be resolved in time steps of a few milliseconds.Mechanical Engineerin
Equivalence between Zwanziger's horizon function and Gribov's no-pole ghost form factor
The ghost form factor entering the Gribov no-pole condition is evaluated till
the third order in the gauge fields. The resulting expression turns out to
coincide with Zwanziger's horizon function implementing the restriction to the
Gribov region in the functional integral.Comment: 9 pp. No figures. Final version to appear in Physics Letters
On the topological reduction from the affine to the orthogonal gauge theory of gravity
Making use of the fibre bundle theory to describe metric-affine gauge
theories of gravity we are able to show that metric-affine gauge theory can be
reduced to the Riemann-Cartan one. The price we pay for simplifying the
geometry is the presence of matter fields associated with the nonmetric degrees
of freedom of the original setup. Also, a possible framework for the
construction of a quantum gravity theory is developed along the text.Comment: 22 pages, no figures. V2: Title changed, Small changes on the text,
references added. Final version to appear in Journal Of Geometry and Physic
A study of the zero modes of the Faddeev-Popov operator in Euclidean Yang-Mills theories in the Landau gauge in d=2,3,4 dimensions
Examples of normalizable zero modes of the Faddeev-Popov operator in SU(2)
Euclidean Yang-Mills theories in the Landau gauge are constructed in d=2,3,4
dimensions.Comment: 18 pages. Text modifications. References added. Version accepted for
publication in the EPJ
The Gribov-Zwanziger action in the presence of the gauge invariant, nonlocal mass operator in the Landau gauge
We prove that the nonlocal gauge invariant mass dimension two operator
can be consistently added to the
Gribov-Zwanziger action, which implements the restriction of the path
integral's domain of integration to the first Gribov region when the Landau
gauge is considered. We identify a local polynomial action and prove the
renormalizability to all orders of perturbation theory by employing the
algebraic renormalization formalism. Furthermore, we also pay attention to the
breaking of the BRST invariance, and to the consequences that this has for the
Slavnov-Taylor identity.Comment: 30 page
Infinitesimal Gribov copies in gauge-fixed topological Yang-Mills theories
We study the Gribov problem in four-dimensional topological Yang-Mills
theories following the Baulieu-Singer approach in the (anti-)self-dual Landau
gauges. This is a gauge-fixed approach that allows to recover the topological
spectrum, as first constructed by Witten, by means of an equivariant (or
constrained) BRST cohomology. As standard gauge-fixed Yang-Mills theories
suffer from the gauge copy (Gribov) ambiguity, one might wonder if and how this
has repercussions for this analysis. The resolution of the small
(infinitesimal) gauge copies, in general, affects the dynamics of the
underlying theory. In particular, treating the Gribov problem for the standard
Landau gauge condition in non-topological Yang-Mills theories strongly affects
the dynamics of the theory in the infrared. In the current paper, although the
theory is investigated with the same gauge condition, the effects of the copies
turn out to be completely different. In other words: in both cases, the copies
are there, but the effects are very different. As suggested by the tree-level
exactness of the topological model in this gauge choice, the Gribov copies are
shown to be inoffensive at the quantum level. To be more precise, following
Gribov, we discuss the path integral restriction to the Gribov horizon. The
associated gap equation, which fixes the so-called Gribov parameter, is however
shown to only possess a trivial solution, making the restriction obsolete. We
relate this to the absence of radiative corrections in both gauge and ghost
sectors. We give further evidence by employing the renormalization group which
shows that, for this kind of topological model, the gap equation indeed forbids
the introduction of a massive Gribov parameter.Comment: 21 pages. Final version accepted for publication in Physics Letters
Degassing Behavior of Nanostructured Al and Its Composites
The synthesis of bulk ultrafine-grained (UFG) and nanostructured Al via cryomilling can frequently require a degassing step prior to consolidation, partly due to the large surface area of the as-milled powders. The objective of this study is to investigate the effects associated with cryomilling with stearic acid additions (as a process-control agent) on the degassing behavior of Al powders. This objective was accomplished by completing select experiments with Al-7.5Mg, Al-6.4 wt pct Al85Ni10La5, and Al-14.3 wt pct B4C. The interaction between Al and stearic acid was determined using thermal analysis combined with Fourier transform infrared spectroscopy (FTIR). The degassing experiments were carried out under high vacuum (10−4 to ~10−6 torr) in a range from room temperature to 400 °C, with the pressure of the released gases monitored using a digital vacuum gage. The results showed that the liberation of chemisorbed water was suppressed in cryomilled Al powders and both the chemisorbed water and stearic acid were primarily released in the form of hydrogen. It was also demonstrated that under certain conditions, a nanostructure (grain size ~100 nm) can be retained following the hot vacuum degassing of cryomilled Al
The Plasma and Suprathermal Ion Composition (PLASTIC) Investigation on the STEREO Observatories
Doenças cardiovasculares ateroscleróticas, dislipidemias, hipertensão, obesidade e diabetes melito em população da área metropolitana da região sudeste do Brasil: I - Metodologia da pesquisa
Sq and EEJ—A Review on the Daily Variation of the Geomagnetic Field Caused by Ionospheric Dynamo Currents
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