Crystallisation of amorphous Al-Y-Ni-(Cu)alloys

The nanocrystallisation behaviour and subsequent intermetallics formation of an amorphous Al88-Y4-Ni8 alloy has been studied. A 1 at% of Al or Ni was also substituted by Cu and its effect studied. Differential scanning calorimetry has been used to measure the thermal stability of these amorphous alloys. Transmission electron microscopy showed the smaller size of the nanocrystals obtained during primary crystallisation when Cu is added. Using three-dimensional atom probe, it has been checked that Cu is homogeneously distributed in the amorphous matrix, not contributing to a heterogeneous nucleation around Cu clusters during the formation of nanocrystals. Transmission electron microscopy and X-rays diffraction are used to study the controversial intermetallics occurrence at higher temperatures. The sequence and characteristics of the intermetallics appearing in these alloys were sensitive to the presence of Cu. The evolution of these intermetallics, up to 600 ºC, has been studied. Findings are compared with previous studies.Ministerio de Economía y Competitividad DPI2015-69550-C2-2-

The role of metal ions in the electron transport through azurin-based junctions

We studied the coherent electron transport through metal–protein–metal junctions based on a blue copper azurin, in which the copper ion was replaced by three different metal ions (Co, Ni and Zn). Our results show that neither the protein structure nor the transmission at the Fermi level change significantly upon metal replacement. The discrepancy with previous experimental observations suggests that the transport mechanism taking place in these types of junctions is probably not fully coherent

Trend changes of African airmass intrusions in the marine boundary layer over the subtropical Eastern North Atlantic region in winter

African dust intrusions in the marine mixing layer of the Eastern North Atlantic subtropical region (23.5°N to 35°N) are favoured in winter when the eastern edge of the Azores High covers Southwestern Europe and North Africa. In situ ground pressure observations and reanalysis from National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) and European Centre for Medium-Range Weather Forecasts (ECMWF) indicate that the Azores High has strengthened and shifted eastward in winter over the last three decades. This is evidenced by the increase over time of the Madrid–Tenerife Index which is defined as the geopotential height anomaly difference at 1000 mb between Tenerife (28.5°N; 16.3°W) and Madrid (40.5°N; 3.5°W) in winter and of the African Index which is defined as the residence time over Africa of air mass trajectories entering the subtropical Eastern North Atlantic Ocean. Barcelona Supercomputing Center/Dust Regional Atmospheric Model (BSC-DREAM) dust regional model simulations from 1958 to 2006 were performed, assuming that the soil characteristics of dust sources remained unchanged over time. Simulated winter dust concentration levels are well correlated (0.67) with the available background observations for the 1998–2004 period. The model results show a two-fold increase in winter dust concentrations over the 1980–2006 period with respect to the 1958–1979 period, corresponding to the strengthening and eastward shift of the Azores High

Plan de exportación de trajes de baño Kan by Paulina

El proyecto realizado durante el semestre buscó que la empresa Kan by Paulina tuviera un plan de exportación enfocado en un mercado meta. Como objetivo se buscó analizar la empresa en ámbitos empresariales y exportador. Se realizaron dos diagnósticos diferentes para analizarlos y así obtener resultados de cómo se encontraba la empresa actualmente. Otro objetivo, fue analizar el producto escogido por la empresa el cual fue el traje de baño artesanal femenino, a partir de la ficha técnica dada por la empresa se obtuvo la fracción arancelaria. Como objetivo principal se planteó la búsqueda de un mercado potencial que pudiera ser el ideal para el traje de baño femenino. Para lograr esto, se buscó a los países con mayor cantidad de importaciones del producto como lo son Alemania, Francia, Reino Unido y China. Una vez teniendo a los principales países, se realizó un análisis PESTEL analizando variables como lo son la política, economía, demografía, geografía entre otros más. Finalmente, se escogió como país meta a Francia. Otro objetivo esencial fue la búsqueda de ferias de promoción en las cuales la empresa pudiera participar, para esto se realizó una investigación de distintas ferias en el país seleccionado, dando como resultados las ferias de: Foire International Bordeux, Who´s next, Les Puces du Design. Estas ferias serian útiles para la empresa ya que son del giro en el cual Kan busca desarrollarse. Otro objetivo importante, fue la cotización de una ruta de logística y la selección del transporte, para lograr esto se analizaron los diferentes transportes que podrían llegar al país y tomando en cuenta la cantidad de volumen que se enviaría (una caja de 25 trajes de baños) se escogió el transporte aéreo como la mejor opción. Como parte del objetivo se cotizó la ruta para analizar los diferentes costos, se cotizó con empresas de logística como lo son: ISCL, TL Pacífico, Link and Trade. Además de empresas de logística se cotizó con una paquetería la cual fue FedEx. Una vez analizando las diferentes cotizaciones se decidió por seleccionar la paquetería de FedEx, ya que por el momento el costo es menor a las de logística y el proceso resultaría más sencillo para una primera exportación. Como último objetivo esencial del proyecto fue la consulta de las regulaciones arancelarias y no arancelarias, se encontró que México y la unión europea tienen un tratado de libre comercio el cual se denomina “La Decisión”. Con este tratado la empresa Kan puede solicitar un certificado de origen EUR1 para poder comprobar que su mercancía proviene de México y así evitar los aranceles; además se encontró que el tratado tiene el complemento EUR1, el cual menciona que si la mercancía es menor a seis mil euros la empresa podría evitar solicitar el certificado de origen y colocar una leyenda en la factura comercial o digital, la cual se encuentra en el tratado. Se concluye que la empresa tiene un producto innovador y con mucho potencial para que pueda ser vendido en Francia y posteriormente en otras partes del mundo. Kan tiene un producto que representa de gran manera la cultura Wixárika y en otras palabras la cultura mexicana, además de que la empresa tiene el potencial para crecer de manera importante y tener un impacto positivo en la sociedad indígena.ITESO, A.C

Fullerene-based molecular nanobridges: A first-principles study

Building upon traditional quantum chemistry calculations, we have implemented an {\em ab-initio} method to study the electrical transport in nanocontacts. We illustrate our technique calculating the conductance of C$_{60}$ molecules connected in various ways to Al electrodes characterized at the atomic level. Central to a correct estimate of the electrical current is a precise knowledge of the local charge transfer between molecule and metal which, in turn, guarantees the correct positioning of the Fermi level with respect to the molecular orbitals. Contrary to our expectations, ballistic transport seems to occur in this system.Comment: 4 pages in two-column forma

Localization of nonlinear excitations in curved waveguides

Motivated by the example of a curved waveguide embedded in a photonic crystal, we examine the effects of geometry in a ``quantum channel'' of parabolic form. We study the linear case and derive exact as well as approximate expressions for the eigenvalues and eigenfunctions of the linear problem. We then proceed to the nonlinear setting and its stationary states in a number of limiting cases that allow for analytical treatment. The results of our analysis are used as initial conditions in direct numerical simulations of the nonlinear problem and localized excitations are found to persist, as well as to have interesting relaxational dynamics. Analogies of the present problem in contexts related to atomic physics and particularly to Bose-Einstein condensation are discussed.Comment: 14 pages, 4 figure

Sharp increase in Saharan dust intrusions over the western Euro-Mediterranean in February–March 2020–2022 and associated atmospheric circulation

During the months of February–March (FM) of the 2020–2022 period, several intense dust intrusions from northern Africa affected Europe. The frequency of dust events was exceptional, considering that wintertime is the season with minimum dust activity in the Mediterranean, and some episodes displayed a duration and/or intensity never recorded before, affecting large areas of the western Euro-Mediterranean (WEM) region. The main objective of this work is to construct a catalogue of FM dust events over the WEM for the 2003–2022 period based on satellite aerosol retrievals and to analyse their atmospheric drivers at the synoptic and large scales, paying special attention to the recent 2020–2022 period of high dust activity. Overall, our results indicate large intraseasonal and interannual variability in the occurrence of wintertime dust events over the WEM. Dust events of FM 2020–2022 were characterized by enhanced dust concentration and high maximum altitudes in comparison with those of previous years (2003–2019). WEM dust events are associated with enhanced activity of high-pressure systems over the Euro-Atlantic sector, which favour the obstruction of the westerlies and the occurrence of cut-off lows at subtropical latitudes. However, these high-pressure systems can exhibit a large variety of configurations, including meridional dipole blocking patterns with poleward shifted jets or Mediterranean subtropical ridges with an intensified mid-latitude jet. The former is the dominant favourable pattern for WEM dust occurrence, but the latter was relatively common during the 2020–2022 period.</p

Macrocyclic colibactin induces DNA double-strand breaks via copper-mediated oxidative cleavage.

Colibactin is an assumed human gut bacterial genotoxin, whose biosynthesis is linked to the clb genomic island that has a widespread distribution in pathogenic and commensal human enterobacteria. Colibactin-producing gut microbes promote colon tumour formation and enhance the progression of colorectal cancer via cellular senescence and death induced by DNA double-strand breaks (DSBs); however, the chemical basis that contributes to the pathogenesis at the molecular level has not been fully characterized. Here, we report the discovery of colibactin-645, a macrocyclic colibactin metabolite that recapitulates the previously assumed genotoxicity and cytotoxicity. Colibactin-645 shows strong DNA DSB activity in vitro and in human cell cultures via a unique copper-mediated oxidative mechanism. We also delineate a complete biosynthetic model for colibactin-645, which highlights a unique fate of the aminomalonate-building monomer in forming the C-terminal 5-hydroxy-4-oxazolecarboxylic acid moiety through the activities of both the polyketide synthase ClbO and the amidase ClbL. This work thus provides a molecular basis for colibactin's DNA DSB activity and facilitates further mechanistic study of colibactin-related colorectal cancer incidence and prevention