Evaluation of sustainability-oriented transversal competencies in engineering postgraduate studies

[EN] In recent times, education for sustainability is gaining more and more relevance in the field of engineering. One of the recently established Sustainable Development Goals explicitly calls for the achievement of sustainable infrastructures by 2030. Infrastructures are recognised as a crucial element towards a sustainable future, as they are responsible for a vast amount of environmental damages and economic expenses, but also are considered to be essential to achieve social welfare and the economic development of regions. Sustainable design of infrastructures requires a paradigm shift in the way engineering students are taught how to face design problems. The complex relation that exists between the conflicting dimensions in which sustainability is founded, namely economy, environment and society, requires of future engineers to develop a series of transversal competencies during their postgraduate studies. However, there are no objective criteria on which to base the assessment of the degree of acquisition of these skills. This paper presents an objective methodology for the evaluation of one of the key competencies required for sustainability-oriented future engineers, namely critical thinking. The proposed methodology is based on the evaluation of the coherency expressed by the students when dealing with a sustainability-related design problem. Such consistency shall be mathematically quantified by means of the Analytic Hierarchy Process. Through the resolution of a particular case study, where students are required to complete a survey comparing different sustainability criteria pairwise, the professor is able to obtain a consistency index from the comparison matrices derived from the survey results of each student. Such indicator is a valuable tool to assess both the clarity with which students perceive sustainability as well as their ability to meet the new challenges that the society will face in the near future.The authors acknowledge the financial support of the Spanish Ministry of Economy and Competitiveness, along with FEDER funding (Project: BIA2017-85098-R).Navarro, I.; Sánchez-Garrido, A.; Yepes, V. (2020). Evaluation of sustainability-oriented transversal competencies in engineering postgraduate studies. IATED Academy. 2181-2187. https://doi.org/10.21125/iceri.2020.0522S2181218

Supersymmetric codimension-two branes in six-dimensional gauged supergravity

We consider the six-dimensional Salam-Sezgin supergravity in the presence of codimension-2 branes. In the case that the branes carry only tension, we provide a way to supersymmetrise them by adding appropriate localised Fayet-Iliopoulos terms and localised corrections to the Chern-Simons term and modifying accordingly the fermionic supersymmetry transformations. The resulting brane action has N=1 supersymmetry (SUSY). We find the axisymmetric vacua of the system and show that one has unwarped background solutions with "football"-shaped extra dimensions which always respect N=1 SUSY for any value of the equal brane tensions, in contrast with the non-supersymmetric brane action background. Finally, we generically find multiple zero modes of the gravitino in this background and discuss how one could obtain a single chiral zero mode present in the low energy spectrum.Comment: 21 pages, no figures, A sign error in the gauge potential at the lower brane corrected and its consequent effect discusse

Intrinsic Moment of Inertia of Membranes as bounds for the mass gap of Yang-Mills Theories

We obtain the precise condition on the potentials of Yang-Mills theories in 0+1 dimensions and D0 brane quantum mechanics ensuring the discretness of the spectrum. It is given in terms of a moment of inertia of the membrane. From it we obtain a bound for the mass gap of any D+1 Yang-Mills theory in the slow-mode regime. In particular we analyze the physical case D=3. The quantum mechanical behavior of the theories, concerning its spectrum, is determined by harmonic oscillators with frequencies given by the inertial tensor of the membrane. We find a class of quantum mechanic potential polynomials of any degree, with classical instabilities that at quantum level have purely discrete spectrum.Comment: 12pages, Latex, minor changes, more explanatory comment

Lupinus mariae-josphi, a new lupin endemic of soils with active lime and high pH in South Eastern Spain, is nodulated by a new bacterial lineage within Bradyrhizobium genus

Lupinus mariae-josephi is a recently described species (Pascual, 2004) able to grow in soils with high pH and active lime content in the Valencia province (Spain). L. mariae-josephi endosymbionts are extremely slowgrowing bacteria with genetic and symbiotic characteristics that differentiate them from Bradyrhizobium strains nodulating Lupinus spp. native of the Iberian Peninsula and adapted to grow in acid soils. Cross-inoculation experiments revealed that all the endosymbiotic isolates from L. mariae-josephi tested are legume-host selective and are unable to nodulate species such as L. angustifolius, and L. luteus. In contrast, Bradyrhizobium strains from Lupinus spp. tested were able to nodulate L. mariae-josephi, although the nodules fixed nitrogen inefficiently. Phylogenetic analysis was performed with housekeeping genes (rrn, glnII, recA, atpD) and nodulation gene nodC. Housekeeping gene phylogeny revealed that L. mariae-josephi rhizobia form a strongly supported monophyletic group within Bradyrhizobium genus. This cluster also includes B. jicamae and certain strains of B. elkanii. Contrarily, isolates from other Lupinus spp. native of the Iberian Peninsula were grouped mainly within B. canariense and two B. japonicum lineages. Phylogenetic analysis of L. mariae-josephi isolates based on the nodC symbiotic gene defined a solid clade close to isolates from Algerian Retama spp. and to fast-growing rhizobia

Volume stabilization in a warped flux compactification model

We investigate the stability of the extra dimensions in a warped, codimension two braneworld that is based upon an Einstein-Maxwell-dilaton theory with a non-vanishing scalar field potential. The braneworld solution has two 3-branes, which are located at the positions of the conical singularities. For this type of brane solution the relative positions of the branes (the shape modulus) is determined via the tension-deficit relations, if the brane tensions are fixed. However, the volume of the extra dimensions (the volume modulus) is not fixed in the context of the classical theory, implying we should take quantum corrections into account. Hence, we discuss the one-loop effective potential of the volume modulus for a massless, minimally coupled scalar field.Comment: 25 pages, 8 figures, typos correcte

Exact Black Holes and Gravitational Shockwaves on Codimension-2 Branes

We derive exact gravitational fields of a black hole and a relativistic particle stuck on a codimension-2 brane in $D$ dimensions when gravity is ruled by the bulk $D$-dimensional Einstein-Hilbert action. The black hole is locally the higher-dimensional Schwarzschild solution, which is threaded by a tensional brane yielding a deficit angle and includes the first explicit example of a `small' black hole on a tensional 3-brane. The shockwaves allow us to study the large distance limits of gravity on codimension-2 branes. In an infinite locally flat bulk, they extinguish as $1/r^{D-4}$, i.e. as $1/r^2$ on a 3-brane in $6D$, manifestly displaying the full dimensionality of spacetime. We check that when we compactify the bulk, this special case correctly reduces to the 4D Aichelburg-Sexl solution at large distances. Our examples show that gravity does not really obstruct having general matter stress-energy on codimension-2 branes, although its mathematical description may be more involved.Comment: 18 pages, LaTeX; v2: added references, version to appear in JHE

Phenotypic and phylogenetic characterization of endosymbiotic bacteria from Lupinus mariae-josephi

Lupinus mariae-josephi is a Lupinus species that thrives in a Southeastern area of Spain (Valencia) in soils of singularly high pH and active lime content. It is nodulated by extra-slow growing bacteria symbiotically and phylogenetically distant to endosymbiotic strains nodulating other Lupinus sp. native of the Iberian Peninsula and adapted to growth in acid soils. Cross-inoculation experiments revealed that the L. mariae-josephi endosymbiotic bacteria are unable to nodulate or efficiently fix nitrogen with well-known Lupinus spp. Their species affiliation was examined by a multilocus sequence analysis of four housekeeping genes (16S rDNA, glnII, recA, atpD) and the symbiotic nodC gene. Single and concatenated phylogenetic analyses of these genes consistently revealed that L. mariae-josephi endosymbiotic bacteria belong to a clade, within the Bradyrhizobium genus, highly differentiated from the Bradyrhizobium clade that includes currently named Bradyrhizobium species as well as the endosymbiotic bacteria from Lupinus species tested in this study. Within this new clade the L. mariae-josephi bacteria nested in several subgroup that may correspond to novel sister species. The phylogenetic analysis based on the nodC gene showed that L. mariae-josephi endosymbiotic bacteria define a novel branch of the nodC Bradyrhizobium tree and likely have a common unique ancestor for the symbiotic genes with nodule isolates from Retama spp

3-Form Flux Compactification of Salam-Sezgin Supergravity

The compactification of 6 dimensional Salam-Sezgin model in the presence of 3-form flux H is investigated. We find a torus topology for this compactification with two cusps which are the places of branes, while at the limit of large size L of the compact direction we also obtain sphere topology. This resembles the Randall-Sundrum I,II model. The branes at one of the cusps can be chosen to be 3- and 4-branes which fill our 4-dimensional space together with the fact that H=0 at this position restores the Lorentz symmetry. This compactification also provides an example for the so-called `time warp' solution, [0812.5107 [hep-th]]. According to a no-go theorem in $d\ne 6$, the time warp compactification violates the null energy condition. While the theorem is quiet for d=6, our model gives a time warp compactification which satisfies the null energy condition. We also derive the four dimensional effective Planck mass which is not obvious due to the time warp nature of the solution.Comment: 19 pages, 5 fig

Sculpting the Extra Dimensions: Inflation from Codimension-2 Brane Back-reaction

We construct an inflationary model in 6D supergravity that is based on explicit time-dependent solutions to the full higher-dimensional field equations, back-reacting to the presence of a 4D inflaton rolling on a space-filling codimension-2 source brane. Fluxes in the bulk stabilize all moduli except the `breathing' modulus (that is generically present in higher-dimensional supergravities). Back-reaction to the inflaton roll causes the 4D Einstein-frame on-brane geometry to expand, a(t) ~ t^p, as well as exciting the breathing mode and causing the two off-brane dimensions to expand, r(t) ~ t^q. The model evades the general no-go theorems precluding 4D de Sitter solutions, since adjustments to the brane-localized inflaton potential allow the power p to be dialed to be arbitrarily large, with the 4D geometry becoming de Sitter in the limit p -> infinity (in which case q = 0). Slow-roll solutions give accelerated expansion with p large but finite, and q = 1/2. Because the extra dimensions expand during inflation, the present-day 6D gravity scale can be much smaller than it was when primordial fluctuations were generated - potentially allowing TeV gravity now to be consistent with the much higher gravity scale required at horizon-exit for observable primordial gravity waves. Because p >> q, the 4 on-brane dimensions expand more quickly than the 2 off-brane ones, providing a framework for understanding why the observed four dimensions are presently so much larger than the internal two. If uplifted to a 10D framework with 4 dimensions stabilized, the 6D evolution described here could describe how two of the six extra dimensions evolve to become much larger than the others, as a consequence of the enormous expansion of the 4 large dimensions we can see.Comment: 27 pages + appendices, 2 figure

Galactic stellar haloes in the CDM model

We present six simulations of galactic stellar haloes formed by the tidal disruption of accreted dwarf galaxies in a fully cosmological setting. Our model is based on the Aquarius project, a suite of high-resolution N-body simulations of individual dark matter haloes. We tag subsets of particles in these simulations with stellar populations predicted by the galform semi-analytic model. Our method self-consistently tracks the dynamical evolution and disruption of satellites from high redshift. The luminosity function (LF) and structural properties of surviving satellites, which agree well with observations, suggest that this technique is appropriate. We find that accreted stellar haloes are assembled between 1 < z < 7 from less than five significant progenitors. These progenitors are old, metal-rich satellites with stellar masses similar to the brightest Milky Way dwarf spheroidals (107–108 M⊙). In contrast to previous stellar halo simulations, we find that several of these major contributors survive as self-bound systems to the present day. Both the number of these significant progenitors and their infall times are inherently stochastic. This results in great diversity among our stellar haloes, which amplifies small differences between the formation histories of their dark halo hosts. The masses (∼ 108–109 M⊙) and density/surface-brightness profiles of the stellar haloes (from 10 to 100 kpc) are consistent with expectations from the Milky Way and M31. Each halo has a complex structure, consisting of well-mixed components, tidal streams, shells and other subcomponents. This structure is not adequately described by smooth models. The central regions (<10 kpc) of our haloes are highly prolate (c/a∼ 0.3), although we find one example of a massive accreted thick disc. Metallicity gradients in our haloes are typically significant only where the halo is built from a small number of satellites. We contrast the ages and metallicities of halo stars with surviving satellites, finding broad agreement with recent observations