NPARSEC : NTT Parallaxes of Southern Extremely Cool objects. Goals, targets, procedures and first results

The discovery and subsequent detailed study of T dwarfs have provided many surprises and pushed the physics and modelling of cool atmospheres in unpredicted directions. Distance is a critical parameter for studies of these objects to determine intrinsic luminosities, test binarity and measure their motion in the Galaxy. We describe a new observational programme to determine distances across the full range of T-dwarf subtypes using the New Technology Telescope (NTT)/SOFI telescope/instrument combination. We present preliminary results for ten objects, five of which represent new distances.Peer reviewe

Brane Inflation, Solitons and Cosmological Solutions: I

In this paper we study various cosmological solutions for a D3/D7 system directly from M-theory with fluxes and M2-branes. In M-theory, these solutions exist only if we incorporate higher derivative corrections from the curvatures as well as G-fluxes. We take these corrections into account and study a number of toy cosmologies, including one with a novel background for the D3/D7 system whose supergravity solution can be completely determined. This new background preserves all the good properties of the original model and opens up avenues to investigate cosmological effects from wrapped branes and brane-antibrane annihilation, to name a few. We also discuss in some detail semilocal defects with higher global symmetries, for example exceptional ones, that could occur in a slightly different regime of our D3/D7 model. We show that the D3/D7 system does have the required ingredients to realise these configurations as non-topological solitons of the theory. These constructions also allow us to give a physical meaning to the existence of certain underlying homogeneous quaternionic Kahler manifolds.Comment: Harvmac, 115 pages, 9 .eps figures; v2: typos corrected, references added and the last section expanded; v3: Few minor typos corrected and references added. Final version to appear in JHE

Normal mode analysis for scalar fields in BTZ black hole background

We analyze the possibility of inequivalent boundary conditions for a scalar field propagating in the BTZ black hole space-time. We find that for certain ranges of the black hole parameters, the Klein-Gordon operator admits a one-parameter family of self-adjoint extensions. For this range, the BTZ space-time is not quantum mechanically complete. We suggest a physically motivated method for determining the spectra of the Klein-Gordon operator.Comment: 6 pages, no figure, late

Fracture envelope estimation of a structural adhesive by dedicated fracture tests

Cohesive zone modelling (CZM) is widespread for the strength analysis of bonded joints. The fracture toughness (GC) is required to use CZM. A scarcely studied mixed-mode test is the Asymmetric Tapered Double-Cantilever Beam (ATDCB), which merges a Tapered Double-Cantilever Beam (TDCB) adherend with a Double-Cantilever Beam (DCB) adherend. This work addresses the ATDCB test to estimate the fracture envelope of a structural adhesive. TDCB and End-Notched Flexure (ENF) tests were also performed to acquire the tensile (GIC) and shear fracture toughness (GIIC), respectively. Numerically, mixed-mode CZM laws were constructed based on the obtained data, and the results were compared with experiments, to validate the CZM laws and the mixed mode propagation criterion. As a result, the best damage propagation criterion for mixed mode was estimated and validated.info:eu-repo/semantics/publishedVersio

Evaluation of T-joints in aluminium structures under different geometries

30th International Conference on Flexible Automation and Intelligent Manufacturing (FAIM2021) -15-18 June 2021, Athens, GreeceThe adhesive bonding technique is nowadays very popular in industrial applications, and is gradually replacing other more traditional bonding methods (fastened, welded and riveted joints) due to some advantages. However, its application supposes accurate methods for strength prediction. As a result, the techniques to predict the strength of adhesive joints has highly evolved. The eXtended Finite Element Method (XFEM) is a recent innovation implemented over the (Finite Element Method) FEM that enables crack growth to be modelled. However, its application to adhesive joints is still scarce. This work consists of an experimental and XFEM analysis of aluminium alloy T-joints, adhesively-bonded with three adhesive types. A parametric study is undertaken regarding the curved adherends’ thickness (tP2), with values between 1 and 4 mm. The adhesives Araldite® AV138 (strong but brittle), Araldite® 2015 (less strong but moderately ductile) and the Sikaforce® 7752 (with the smallest strength but highly ductile) were tested. A comparative analysis between the different joints conditions was undertaken by plotting peel (σу) and shear (τxy) stresses. The XFEM predictive capabilities were tested with different damage initiation criteria. It was found that, provided that the modelling conditions are properly set, accurate numerical results can be found.info:eu-repo/semantics/publishedVersio

Effect of material hybridization on the strength of scarf adhesive joints

Adhesively-bonded joints have become more efficient due to the improvement of adhesives’ characteristics. On the other hand, with the use of composites in structures it is possible to reduce weight. Due to this, new techniques are being explored, including adhesively-bonding different materials. Nowadays, in many high performance structures, it is necessary to combine composite materials with other light-weighted metals such as aluminium or titanium. This work reports on an experimental and numerical study for hybrid scarf joints between composite and aluminium adherends, and considering different values of the scarf angle (α). The numerical analysis by Finite Elements (FE), using the software Abaqus®, enabled the obtainment of peel (σy) and shear stresses (τxy), which are then used to discuss the strength between different joint configurations. Cohesive zone modelling (CZM) was used to predict the joint strength and the results were compared to the experiments for validation. The joints’ behaviour was highly dependent on α, and CZM were validated for the design process of hybrid scarf joints.info:eu-repo/semantics/publishedVersio

A new structural two-component epoxy adhesive: Strength and fracture characterization

30th International Conference on Flexible Automation and Intelligent Manufacturing (FAIM2021) -15-18 June 2021, Athens, GreeceIn the past decades, adhesive technology has been useful in order to solve numerous issues related with conventional joining techniques (bolting, riveting and welding). Several advantages of adhesive bonding can be pointed out, such as low weight (relevant in the automotive and aeronautical industries), capability to resist to adverse environmental conditions, lower manufacturing costs and possibility to join different materials. To predict crack propagation of an adhesive joint by advanced fracture mechanics-based techniques such as cohesive zone models (CZM) it is not enough to know the traditional mechanical properties, such as Young’s modulus (E), shear modulus (G), tensile strength (σf) and shear strength (τf). Actually, it is also mandatory to estimate the tensile (GIC) and shear fracture energies (GIIC). The purpose of this work is to carry out the mechanical and fracture property characterization of a new structural two-component epoxy adhesive. With this purpose, four tests which were conducted: tensile testing to bulk specimens, shear testing with thick adherend shear tests (TAST), double-cantilever beam (DCB) and end-notched flexure (ENF). With these tests, it was possible to determine the mechanical and fracture properties of the adhesive in tension and shear. Different data reduction methods were evaluated for the fracture properties. The test results agreed with the data provided by the manufacturer and will enable the design of bonded structures with this adhesive.The authors would like to thank Sika® Portugal for supplying the adhesive SikaPower® 1277info:eu-repo/semantics/publishedVersio

The Influence of Civil Works on Heritage Architecture, El Vergel, Cuenca - Ecuador

In urban and rural areas of the Andean cities of Ecuador, construction based on earthen technologies has been an important alternative, which are carried out through ancestral customs, such as the minga, which benefit the cohesion of the community. Against this background, the World Heritage City Project of the University of Cuenca (Ecuador) has since the year 2011 undertaken interventions in heritage buildings inspired by the minga, so called Maintenance Campaigns, where the collective efforts of various actors (community, academy and organizations) are joined to recover buildings in highly vulnerable heritage neighborhoods, promoting preventive conservation, maintenance and monitoring of vernacular buildings. The fourth campaign, which was carried out in 2018, took place in the Las Herrerias Street in the historical El Vergel neighborhood of Cuenca, a World Heritage City since 1999. The methodology applied in the previous campaigns was essentially maintained, gaining experience and innovating at every opportunity. As a special aspect, the Las Herrerias Campaign was characterized by the existence of buildings with structures that were already affected by civil works previously carried out, such as re-pavements, drinking water installations, various services, etc. This research proposes to establish conservation strategies of vernacular heritage buildings and to mitigate the effects of poorly carried out civil works. The buildings intervened in the 2018 campaign are taken as reference, specifically those whose damages are the result of civil works. First, a review of bibliographic sources is undertaken to reveal historical data about the neighborhood and the civil works that have been carried out. The research continues with a diagnosis of the condition of the buildings before the Maintenance Campaign. Next, the daily maintenance records and the experience of the participants of the Campaign are investigated to identify and analyze those buildings affected by bad civil works practices and their impact on the damages of their structures. Subsequently, the condition of the buildings after the Campaign is evaluated. Finally, strategies are proposed that must be considered for the interventions of vernacular heritage architecture, built with traditional earth and wood systems. Furthermore, civil works guidelines are defined for these types of interventions. Accordingly, the preservation for future generations of the wealth of material as well as immaterial heritage is encouraged