Abstract
Few questions in condensed matter science have proven as difficult to unravel as the interplay between structure and dynamics in supercooled liquids. To explore this link, much research has ...been devoted to pinpointing local structures and order parameters that correlate strongly with dynamics. Here we use an unsupervised machine learning algorithm to identify structural heterogeneities in three archetypical glass formers—without using any dynamical information. In each system, the unsupervised machine learning approach autonomously designs a purely structural order parameter within a single snapshot. Comparing the structural order parameter with the dynamics, we find strong correlations with the dynamical heterogeneities. Moreover, the structural characteristics linked to slow particles disappear further away from the glass transition. Our results demonstrate the power of machine learning techniques to detect structural patterns even in disordered systems, and provide a new way forward for unraveling the structural origins of the slow dynamics of glassy materials.
Abstract
It is commonly believed that the most efficient way to pack a finite number of equal-sized spheres is by arranging them tightly in a cluster. However, mathematicians have conjectured that a ...linear arrangement may actually result in the densest packing. Here, our combined experimental and simulation study provides a physical realization of the finite sphere packing problem by studying arrangements of colloids in a flaccid lipid vesicle. We map out a state diagram displaying linear, planar, and cluster conformations of spheres, as well as bistable states which alternate between cluster-plate and plate-linear conformations due to membrane fluctuations. Finally, by systematically analyzing truncated polyhedral packings, we identify clusters of 56 ≤
N
≤ 70 number of spheres, excluding
N
= 57 and 63, that pack more efficiently than linear arrangements.
The manipulation of nano-objects through heating is an effective strategy for inducing structural modifications and therefore changing the optoelectronic properties of semiconducting materials. ...Despite its potential, the underlying mechanism of the structural transformations remains elusive, largely due to the challenges associated with their in situ observations. To address these issues, we synthesize temperature-sensitive CsPbBr3 perovskite nanoplatelets and investigate their structural evolution at the nanoscale using in situ heating transmission electron microscopy. We observe the morphological changes that start from the self-assembly of the nanoplatelets into ribbons on a substrate. We identify several paths of merging nanoplates within ribbons that ultimately lead to the formation of nanosheets dispersed randomly on the substrate. These observations are supported by molecular dynamics simulations. We correlate the various paths for merging to the random orientation of the initial ribbons along with the ligand mobility (especially from the edges of the nanoplatelets). This leads to the preferential growth of individual nanosheets and the merging of neighboring ones. These processes enable the creation of structures with tunable emission, ranging from blue to green, all from a single material. Our real-time observations of the transformation of perovskite 2D nanocrystals reveal a route to achieve large-area nanosheets by controlling the initial orientation of the self-assembled objects with potential for large-scale applications.
Duodenal diverticular bleeding: an endoscopic challenge Valdivielso Cortázar, Eduardo; Madarnás Alonso, Lucía; Ortíz Marín, Susana ...
Revista española de enfermedades digestivas,
06/2017, Letnik:
109, Številka:
6
Journal Article
Recenzirano
Odprti dostop
Duodenal diverticula are an uncommon cause of upper gastrointestinal bleeding. Until recently, it was primarily managed with surgery, but advances in the field of endoscopy have made management ...increasingly less invasive. We report a case of duodenal diverticular bleeding that was endoscopically managed, and review the literature about the various endoscopic therapies thus far described.
El epitafio que Ovidio compone para sí mismo (Trist. III 3.73-76) comienza con el adverbio hic, una posición que atrae inmediatamente la atención sobre la deixis. El hecho de tratarse de una ...inscripción no real sino literaria determina el análisis de este aspecto tanto en este caso como en otros epitafios de poetas elegíacos; pero Ovidio complica la cuestión atribuyendo a este texto tres situaciones enunciativas distintas: la de un epitafio que figuraría exento en su futuro monumento funerario; la de la carta desde el exilio que dirige a su esposa, donde le comunica sus disposiciones fúnebres; y la de un poema dentro de un libro dirigido a su lector. El solapamiento de las tres situaciones multiplica las posibilidades de identificar los referentes de los deícticos. El resultado es la comprobación de que probablemente Ovidio explotó esta multirreferencialidad, lo que, además de mostrar su sofisticación, refuerza el carácter metapoético del epitafio.
Colloidal molecules are ideal model systems for mimicking real molecules and can serve as versatile building blocks for the bottom-up self-assembly of flexible and smart materials. While most ...colloidal molecules are rigid objects, the development of colloidal joints has made it possible to endow them with conformational flexibility. However, their unrestricted range of motion does not capture the limited movement and bond directionality that is instead typical of real molecules. In this work, we create flexible colloidal molecules with an in situ controllable motion range and bond directionality by assembling spherical particles onto cubes functionalized with complementary surface-mobile DNA. By varying the sphere-to-cube size ratio, we obtain colloidal molecules with different coordination numbers and find that they feature a constrained range of motion above a critical size ratio. Using theory and simulations, we show that the particle shape together with the multivalent bonds creates an effective free-energy landscape for the motion of the sphere on the surface of the cube. We quantify the confinement of the spheres on the surface of the cube and the probability to change facet. We find that temperature can be used as an extra control parameter to switch in situ between full and constrained flexibility. These flexible colloidal molecules with a temperature switching motion range can be used to investigate the effect of directional yet flexible bonds in determining their self-assembly and phase behavior, and may be employed as constructional units in microrobotics and smart materials.
Este artículo forma parte de un estudio de la Universidad de Valencia donde se analiza la percepción que algunos hombres tienen acerca del cuidado de personas adultas (mayores y/o discapacitadas) que ...ellos realizan de manera informal en su entorno familiar en la ciudad de Valencia. A través de entrevistas en profundidad, identificamos, la responsabilidad que estos hombres se toman con la persona cuidada a través del establecimiento de procesos de reciprocidad. Dicha reciprocidad destaca como un elemento positivo a extraer de sus vivencias que permite reivindicar el cuidado como un valor positivo y no exclusivo de ningún género.
En la presente coyuntura socioeconómica, la posibilidad de inclusión a través del empleo de las personas con discapacidad es importante no solo por las posibilidades de autonomía económica, sino ...también por las oportunidades de socialización. Sobre esta base, y considerando que las empresas socialmente responsables asumen la inclusión de estas personas en sus plantillas como una posibilidad de crecimiento y de diferenciación, en el texto se analiza, de manera descriptiva, el papel que las administraciones públicas (AA. PP.) autonómicas, con competencias en la materia, pueden, deben y están haciendo para fomentar la responsabilidad social corporativa (RSC) y la gestión de la inclusión laboral de las personas con discapacidad. A partir de la discusión teórica y de la revisión de las políticas desarrolladas, se pretende dar respuesta a las siguientes cuestiones de fondo: ¿Cómo se está atendiendo la pluralidad en las empresas desde las administraciones públicas? ¿Son la RSC y la gestión de las personas con discapacidad modas pasajeras o por el contrario pueden resultar un instrumento válido de inclusión de estas personas dentro de los espacios de trabajo? Llegando a la conclusión de que esto solo será posible desde una RSC estratégica e integradora.
Display omitted
Colloidal molecules with anisotropic shapes and interactions are powerful model systems for deciphering the behavior of real molecules and building units for creating materials with ...designed properties. While many strategies for their assembly have been developed, they typically yield a broad distribution or are limited to a specific type. We hypothesize that the shape and relative sizes of colloidal particles can be exploited to efficiently direct their assembly into colloidal molecules of desired valence.
We exploit electrostatic self-assembly of negatively charged spheres made from either polystyrene or silica onto positively charged hematite cubes. We thoroughly analyze the role of the shape and size ratio of particles on the cluster size and yield of colloidal molecules.
Using a combination of experiments and simulations, we demonstrate that cubic particle shape is crucial to generate high yields of distinct colloidal molecules over a wide variety of size ratios. We find that electrostatic repulsion between the satellite spheres is important to leverage the templating effect of the cubes, leading the spheres to preferentially assemble on the facets rather than the edges and corners of the cube. The sixfold symmetry of cubes favors the assembly of molecules with six, four, and two satellite spheres at appropriate size ratios and interaction strength.
Furthermore, we reveal that our protocol is not affected by the specific choice of the material of the colloidal particles. Finally, we show that the permanent magnetic dipole moment of the hematite cubes can be utilized to separate colloidal molecules from non-assembled satellite particles. Our simple and effective strategy might be extended to other templating particle shapes, thereby greatly expanding the library of colloidal molecules that can be achieved with high yield and purity.
PDF
