Supersymmetry and Polytopes

We make an imaginative comparison between the Minimal Supersymmetric Standard Model and the 24-cell polytope in four dimensions, the Octacube.Comment: Presented to the Workshop on Geometry and Physics: Supersymmetry. Bilbao, Spain. May 200

Gauge theory in dimension 77

We first review the notion of a $G_2$-manifold, defined in terms of a principal $G_2$ ("gauge") bundle over a $7$-dimensional manifold, before discussing their relation to supergravity. In a second thread, we focus on associative submanifolds and present their deformation theory. In particular, we elaborate on a deformation problem with coassociative boundary condition. Its space of infinitesimal deformations can be identified with the solution space of an elliptic equation whose index is given by a topological formula.Comment: 15 page

The Classification of Highly Supersymmetric Supergravity Solutions

The spinorial geometry method is an effective method for constructing systematic classifications of supersymmetric supergravity solutions. Recent work on analysing highly supersymmetric solutions in type IIB supergravity using this method is reviewed [arXiv:hep-th/0606049, arXiv:0710.1829]. It is shown that all supersymmetric solutions of IIB supergravity with more than 28 Killing spinors are locally maximally supersymmetric.Comment: 23 pages, latex. To appear in the proceedings of the Special Metrics and Supersymmetry conference at Universidad del Pais Vasco, May 2008. References correcte

Graded geometry and Poisson reduction

The main result of [2] extends the Marsden-Ratiu reduction theorem [4] in Poisson geometry, and is proven by means of graded geometry. In this note we provide the background material about graded geometry necessary for the proof in [2]. Further, we provide an alternative algebraic proof for the main result. ©2009 American Institute of Physic

Mono‑, Bi‑, and Trinuclear Bis-Hydrated Mn²⁺ Complexes as Potential MRI Contrast Agents

We report a series of ligands containing pentadentate 6,6′-((methylazanediyl)­bis­(methylene))­dipicolinic acid binding units that form mono- (H₂dpama), di- (<i>m</i>X­(H₂dpama)₂), and trinuclear (<i>m</i>X­(H₂dpama)₃) complexes with Mn²⁺ containing two coordinated water molecules per metal ion, which results in pentagonal bipyramidal coordination around the metal ions. In contrast, the hexadentate ligand 6,6′-((ethane-1,2-diylbis­(azanediyl))­bis­(methylene))­dipicolinic acid (H₂bcpe) forms a complex with distorted octahedral coordination around Mn²⁺ that lacks coordinated water molecules. The protonation constants of the ligands and the stability constants of the Mn²⁺, Cu²⁺, and Zn²⁺ complexes were determined using potentiometric and spectrophotometric titrations in 0.15 M NaCl. The pentadentate dpama^2– ligand and the di- and trinucleating mX­(dpama)₂^4– and mX­(dpama)₃^6– ligands provide metal complexes with stabilities that are very similar to that of the complex with the hexadentate ligand bcpe^2–, with log β₁₀₁ values in the range 10.1–11.6. Cyclic voltammetry experiments on aqueous solutions of the [Mn­(bcpe)] complex reveal a quasireversible system with a half-wave potential of +595 mV versus Ag/AgCl. However, [Mn­(dpama)] did not suffer oxidation in the range 0.0–1.0 V, revealing a higher resistance toward oxidation. A detailed ¹H NMRD and ¹⁷O NMR study provided insight into the parameters that govern the relaxivity for these systems. The exchange rate of the coordinated water molecules in [Mn­(dpama)] is relatively fast, <i>k</i>_ex²⁹⁸ = (3.06 ± 0.16) × 10⁸ s^–1. The trinuclear [mX­(Mn­(dpama)­(H₂O)₂)₃] complex was found to bind human serum albumin with an association constant of 1286 ± 55 M^–1 and a relaxivity of the adduct of 45.2 ± 0.6 mM^–1 s^–1 at 310 K and 20 MHz

Stabilizing Divalent Europium in Aqueous Solution Using Size-Discrimination and Electrostatic Effects

We report two macrocyclic ligands containing a 1,10-diaza-18-crown-6 fragment functionalized with either two picolinamide pendant arms (bpa18c6) or one picolinamide and one picolinate arm (ppa18c6^–). The X-ray structure of [La­(ppa18c6)­(H₂O)]²⁺ shows that the ligand binds to the metal ion using the six donor atoms of the crown moiety and the four donor atoms of the pendant arms, 11-coordination being completed by the presence of a coordinated water molecule. The X-ray structure of the [Sr­(bpa18c6)­(H₂O)]²⁺ was also investigated due to the very similar ionic radii of Sr²⁺ and Eu²⁺. The structure of this complex is very similar to that of [La­(ppa18c6)­(H₂O)]²⁺, with the metal ion being 11-coordinated. Potentiometric measurements were used to determine the stability constants of the complexes formed with La³⁺ and Eu³⁺. Both ligands present a very high selectivity for the large La³⁺ ion over the smaller Eu³⁺, with a size-discrimination ability that exceeds that of the analogous ligand containing two picolinate pendant arms reported previously (bp18c6^2–). DFT calculations using the TPSSh functional and the large-core pseudopotential approximation provided stability trends in good agreement with the experimental values, indicating that charge neutral ligands derived from 1,10-diaza-18-crown-6 enhance the selectivity of the ligand for the large Ln³⁺ ions. Cyclic voltammetry measurements show that the stabilization of Eu²⁺ by these ligands follows the sequence bp18c6^2– < ppa18c6^– < bpa18c6 with half-wave potentials of −753 mV (bp18c6^2–), −610 mV (ppa18c6^–), and −453 mV (bpa18c6) versus Ag/AgCl. These values reveal that the complex of bpa18c6 possesses higher stability against oxidation than the aquated ion, for which an <i>E</i>_1/2 value of −585 mV has been measured

Memorias I Congreso Internacional. Universidad, desarrollo y cooperación

La participación de la Universidad Politécnica Salesiana, representada por su Rector, en el III Congreso sobre Universidad, Cooperación y Desarrollo, en Madrid, abril de 2006, la publicación n. 8 de la revista Universitas dedicada al tema ¿Qué cooperación para qué desarrollo? y una experiencia generalizada tanto en Ecuador como en América latina de la urgente necesidad de repensar y replantear la Cooperación Internacional desde los Desarrollos Nacionales, fueron los tres precedentes principales para la organización del I Congreso sobre Uni-versidad, Desarrollo y Cooperación. A la iniciativa de organizar dicho Congreso en Cuenca, con motivo de las celebraciones de los 450 años de fundación de la ciudad, junto con la Universidad Politécnica Salesiana, se unieron la Universidad de Cuenca, Universidad del Azuay, Universidad Particular Técnica de Loja, Universidad Santa María de Guayaquil y el Fondo Ecuatoriano Populorum Progressio FEPP. Todo el proyecto contó con el apoyo financiero del Municipio de Cuenca, del Consejo Provincial del Azuay, la Agencia Española de Cooperación Internacional, y de las Universidades participantes. Así mismo el Congreso se benefició del apoyo académico de la Universidad de Murcia. Las tres Conferencias que enmarcaron el Congreso, coincidieron desde enfoques diferentes en una misma estimación de las relaciones entre Cooperación Internacional y Desarrollo Nacional. José de Souza, a partir de la problemática y experiencia de un desarrollo posible en América Latina, hizo un balance crítico no sólo de la Cooperación Internacional respecto de dicho desarrollo, sino también de las relaciones entre países desarrollados y subdesarrollados. Alfonso Moro, tomando como referencia principal las políticas y programas de la cooperación europea con América Latina, puso de manifiesto las relaciones de desigualdad y dependencia impuestas por dicha cooperación, las cuales condicionan y limitan las reales posibilidades de desarrollos autónomos y sostenidos en los países latinoamericanos

Extreme blazars under the eyes of MAGIC

Extreme high-frequency-peaked BL Lac objects (EHBLs) are the most energetic persistent sources in the universe. This contribution reports on long-term observing campaigns of tens of EHBLs that have been organized by the MAGIC collaboration to enlarge their population at VHE and understand the origin of their extreme properties. EHBLs are characterized by a spectral energy distribution (SED) featuring a synchrotron peak energy above 1 keV. Several EHBLs display a hard spectral index at very high energies (VHE; E &gt; 100 GeV), suggesting a gamma-ray SED component peaking significantly above 1 TeV. Such extreme properties are challenging current standard emission and acceleration mechanisms. Recent studies have also unveiled intriguing disparities in the temporal characteristics of EHBLs. Some sources seem to display a persistent EHBL behaviour, while others belong to the EHBL family only temporarily. Here, we present recent results of the first hard-TeV EHBL catalog. The MAGIC observations are accompanied by an extensive multiwavelength coverage to obtain an optimal determination of the SED. This allow us to investigate leptonic and hadronic scenarios for the emission. We also present the recent detection of the EHBL RX J0812.0+0237 in the VHE band by MAGIC. Finally, we discuss a broad multiwavelength campaign on the BL Lac type object 1ES 2344+514, which showed intermittent EHBL characteristics in August 2016