Scanning tunneling spectroscopy of layers of superconducting 2H-TaSe2_\textbf{2}: Evidence for a zero bias anomaly in single layers

We report a characterization of surfaces of the dichalcogenide TaSe$_2$ using scanning tunneling microscopy and spectroscopy (STM/S) at 150 mK. When the top layer has the 2H structure and the layer immediately below the 1T structure, we find a singular spatial dependence of the tunneling conductance below 1 K, changing from a zero bias peak on top of Se atoms to a gap in between Se atoms. The zero bias peak is additionally modulated by the commensurate $3a_0 \times 3a_0$ charge density wave of 2H-TaSe$_2$. Multilayers of 2H-TaSe$_2$ show a spatially homogeneous superconducting gap with a critical temperature also of 1 K. We discuss possible origins for the peculiar tunneling conductance in single layers.Comment: 10 pages, 10 figure

Estudio de la biónica como metodología aplicable en ingeniería de diseño de producto y su formalización a través de una propuesta de investigación del semillero HECAS-ID de la Universidad Eafit

La biónica es reconocida como una herramienta garante para la definición de nuevos conceptos. Esta metodología puede ser abordada desde la investigación, o desde un problema previamente definido, para esto se vale de un análisis de la relación del usuario con el producto, dentro de un contexto especifico, con base en el estudio de unos elementos de análisis definidos como: forma, estructura, mecanismo y entorno, en este estudio vinculados con la función de los mismos.263 p.Contenido parcial: Fundamentos y teorías de la biónica -- Definición de biónica -- Forma, estructura, mecanismos y contexto como elementos de análisis funcional -- Planteamiento de la biónica como metodología -- Análisis de elementos finitos de la estructura -- Resultados estructura convencional -- Diseño de montajes

Parameter Identification in a Probabilistic Setting

Parameter identification problems are formulated in a probabilistic language, where the randomness reflects the uncertainty about the knowledge of the true values. This setting allows conceptually easily to incorporate new information, e.g. through a measurement, by connecting it to Bayes's theorem. The unknown quantity is modelled as a (may be high-dimensional) random variable. Such a description has two constituents, the measurable function and the measure. One group of methods is identified as updating the measure, the other group changes the measurable function. We connect both groups with the relatively recent methods of functional approximation of stochastic problems, and introduce especially in combination with the second group of methods a new procedure which does not need any sampling, hence works completely deterministically. It also seems to be the fastest and more reliable when compared with other methods. We show by example that it also works for highly nonlinear non-smooth problems with non-Gaussian measures.Comment: 29 pages, 16 figure

Influencia del cloruro de calcio en la conservación del mango (mangifera indica l.) variedad tommy atkins

En la actualidad, existen numerosas pérdidas en la poscosecha de productos perecederos, debidas, principalmente, al manejo inadecuado de éstos y a la poca atención que se les suministra después de su recolección. El mango, una de las frutas de mayor importancia para elmercado internacional, no escapa a esta situación; por lo cual, se hacen necesarios estudios que permitan su conservación después de la recolección. Por ésto, en el presente estudio, se empleó en la conservación del mangovariedad Tommy Atkins un retardante de maduración, el cloruro de calcio (CaCl2) a baja temperatura (10°C), con 90% de humedad relativa (H. R.), encontrándose que la inmersión de la fruta en una solución de concentración del 15% de CaCl2 permite su conservación por un espaciode 38 días con un buen comportamiento de las características lisicoquímicas de °Brix, acidez y pH del producto y alcanzado su completa madurez fisiológica.In our country, it exists a lot of postharvest losses caused by inadequate handling of perishable products. The mango, a very important fruit for exportation, has similar problems and it is necessary to solve them. This study was carry out in order to determine the incidence of CaCl2 in the maintenance of the mango variety Tommy Atkinsstored at 1O°C and 90% R.H. lt was lound  that the fruit treated with a solution of 15% ofCaCl2 reached the best devolpement of its phycochemical characteristics of pH, brix and acidity and its madurity process was complete

Scale-invariant magnetoresistance in a cuprate superconductor

The anomalous metallic state in high-temperature superconducting cuprates is masked by the onset of superconductivity near a quantum critical point. Use of high magnetic fields to suppress superconductivity has enabled a detailed study of the ground state in these systems. Yet, the direct effect of strong magnetic fields on the metallic behavior at low temperatures is poorly understood, especially near critical doping, $x=0.19$. Here we report a high-field magnetoresistance study of thin films of \LSCO cuprates in close vicinity to critical doping, $0.161\leq x\leq0.190$. We find that the metallic state exposed by suppressing superconductivity is characterized by a magnetoresistance that is linear in magnetic field up to the highest measured fields of $80$T. The slope of the linear-in-field resistivity is temperature-independent at very high fields. It mirrors the magnitude and doping evolution of the linear-in-temperature resistivity that has been ascribed to Planckian dissipation near a quantum critical point. This establishes true scale-invariant conductivity as the signature of the strange metal state in the high-temperature superconducting cuprates.Comment: 10 pages, 3 figure

Inverse Problems in a Bayesian Setting

In a Bayesian setting, inverse problems and uncertainty quantification (UQ) --- the propagation of uncertainty through a computational (forward) model --- are strongly connected. In the form of conditional expectation the Bayesian update becomes computationally attractive. We give a detailed account of this approach via conditional approximation, various approximations, and the construction of filters. Together with a functional or spectral approach for the forward UQ there is no need for time-consuming and slowly convergent Monte Carlo sampling. The developed sampling-free non-linear Bayesian update in form of a filter is derived from the variational problem associated with conditional expectation. This formulation in general calls for further discretisation to make the computation possible, and we choose a polynomial approximation. After giving details on the actual computation in the framework of functional or spectral approximations, we demonstrate the workings of the algorithm on a number of examples of increasing complexity. At last, we compare the linear and nonlinear Bayesian update in form of a filter on some examples.Comment: arXiv admin note: substantial text overlap with arXiv:1312.504

Failure detection in a pressure vessel using acoustic emissions technology

The acoustic emission (AE) technique was implemented to monitor different failure stages in steel cylinders used to store Liquefied Petroleum Gas (LPG). Experiments in two containers with external and internal defects subjected to a hydrostatic test were carried out. The severity of the faults was progressively increasing through the different stages to study the microseismic activity. The experimental tests allowed checking the Kaiser and Felicity effects. Additionally, it was observed that an increase in the severity of the failure depicts an increase in the number of hits, counts and energy values detected. The evolution of the acoustic activity for the different failure stages established the container's structural integrity, proving that AE allows evaluating its entire condition.En este artículo se implementó la técnica de emisiones acústicas (EA) para monitorear diferentes escenarios de falla en cilindros de acero usados para almacenar gas licuado del petróleo (GLP). Los experimentos se llevaron a cabo en dos recipientes con defectos externos e internos sometidos a una prueba hidrostática. La severidad de las fallas fue aumentando progresivamente a través de los distintos escenarios con el fin de estudiar la actividad microsísmica. Las pruebas experimentales permitieron comprobar los efectos Káiser - Felicity y se observó que un aumento en la severidad de la falla representaba un incremento en la cantidad de hits detectados, cuentas y valores de energía. La evolución de la actividad acústica para los diferentes escenarios de falla determinó la integridad estructural de los contenedores, demostrándose que las EA permiten evaluar la condición global de los cilindros

Subsurface bending and reorientation of tilted vortex lattices in bulk isotropic superconductors due to Coulomb-like repulsion at the surface

We study vortex lattices (VLs) in superconducting weak-pinning platelet-like single crystals of β-Bi2Pd in tilted magnetic fields with a scanning tunneling microscope. We show that vortices exit the sample perpendicular to the surface and are thus bent beneath the surface. The structure and orientation of the tilted VLs in the bulk are, for large tilt angles, strongly affected by Coulomb-type intervortex repulsion at the surface due to stray magnetic fieldsThe authors are grateful to P. C. Canfield for discussions, for having proposed the growth of single crystals of β-Bi2 Pd, and for having shown how to do that. E.H. was supported by the Departamento Administrativo de Ciencia, Tecnología e Innovación, COLCIENCIAS (Colombia) Programa Doctorados en el Exterior Convocatoria Program No. 568-2012 and the Universidad Nacional de Colombia, División de Investigación y Extensión sede Bogotá (DIEB) Project No. 35615. I.G. was supported by the ERC (Grant Agreement No. 679080 and the Ramón y Cajal Program through Grant No. RyC-2014-15093). This work also was supported by the Spanish MINECO (Grants No. FIS2014-54498-R and No. MAT2014-52405-C2-02), by the Comunidad de Madrid through Program NANOFRONTMAG-CM (Program No. S2013/MIT-2850), and by Axa Research Funds. We also acknowledge the SEGAINVEX workshop of UAM, Banco Santander and COST Grant No. CA16128 action, the EU through Grant Agreements No. FP7-PEOPLE-2013-CIG 618321 and No. 604391, and Nanopyme Grant No. FP7-NMP-2012-SMALL-6 NMP3-SL 2012-310516. V.G.K. was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division. The Ames Laboratory is operated for the U.S. DOE by Iowa State University under Contract No. DE-AC02-07CH1135

Influencia de la rugosidad en la micrudureza y en la resistencia al desgaste de recubrimientos aplicados mediante proyeción térmica

En los recubrimientos depositados por rociado térmico, la rugosidad superficial puede reflejar el grado de fusión y la fuerza con que llegan las partículas al sustrato durante la formación de la capa. Una alta unión de las partículas puede permitir baja porosidad del recubrimiento, lo que se puede traducir en un aumento de sus propiedades mecánicas. Es por esto que el interés de este trabajo se centra en el estudio de la influencia que tiene la rugosidad superficial sobre las propiedades mecánicas y tribológicas de recubrimientos de Níquel, Níquel - Carburo de Tungsteno, Níquel – Carburo de Silicio y Carburo de silicio, con el fin de establecer si los resultados de la medida del perfil de rugosidad superficial ueden reflejar el comportamiento de las propiedades mecánicas y tribológicas de estos recubrimiento