Is There a Negative Thermal Expansion in Supported Metal Nanoparticles? An In-Situ X-ray Absorption Study Coupled with Neural Network Analysis

Interactions with their support, adsorbates and unique structural motifs are responsible for the many intriguing properties and potential applications of supported metal nanoparticles (NPs). At the same time, they complicate the interpretation of experimental data. In fact, the methods and approaches that work well for the ex situ analysis of bulk materials may be inaccurate or introduce artifacts in the in situ analysis of nanomaterials. Here we revisit the controversial topic of negative thermal expansion and anomalies in the Debye temperature reported for oxide-supported metal NPs. In situ X-ray absorption experimental data collected for Pt NPs in ultrahigh vacuum and an advanced data analysis approach based on an artificial neural network demonstrate that Pt NPs do not exhibit intrinsic negative thermal expansion. Similarly as for bulk materials, in the absence of adsorbates the bond lengths in metal NPs increase with temperature. The previously reported anomalies in particle size-dependent Debye temperatures can also be linked to the artifacts in the interpretation of conventional X-ray absorption data of disordered materials such as NPs

The global forum on migration and development

The paper explores the proposed rationale of the Global Forum on Migration and Development that was launched by Kofi Annan in 2006 as UN Secretary General, as an informal inter-governmental discussion space. First, it identifies the series of claims in Annan’s speech to the High-Level Dialogue that he convened in New York: that international migration must be managed; that to proceed from the present situation of entrenched disagreements and mistrust requires constructive structured communication; that the Global Forum can provide this and is a feasible way forward, unlike proposals for binding international conventions; and that through processes of growing mutual education and mutual acceptance the Forum can be fruitful. Implied are notions of building trust and community amongst the “migro-crats”, the public policymakers in the global networks of migration. Second, the paper monitors how the hypotheses had fared by the time of the second Forum conference, in Manila in 2008, by discourse analysis of its concluding report. The Manila meeting’s declaration of a “focus on the person” appeared in reality to a large extent mean a focus on the “migro-crats” and their interactive processes of mutual education and team-building that are intended to produce practical cooperation. To clarify this strategy and draw out its mindset and assumptions, the paper presents a series of tools for discourse analysis that may be more widely useful in migration studies and for participation in migration policy debate

Operando Insights into Nanoparticle Transformations during Catalysis

Nanostructured materials play an important role in today’s chemical industry acting as catalysts in heterogeneous thermal and electrocatalytic processes for chemical energy conversion and the production of feedstock chemicals. Although catalysis research is a long standing discipline, the fundamental properties of heterogeneous catalysts like atomic structure, morphology and surface composition under realistic reaction conditions, together with insights into the nature of the catalytically active sites, have remained largely unknown. Having access to such information is however of outmost importance in order to understand the rate-determining processes and steps of many heterogeneous reactions and identify important structure-activity/selectivity relationships enabling knowledge-driven improvement of catalysts. In the last decades, in situ and operando methods have become available to identify the structural and morphological properties of the catalysts under working conditions. Such investigations have led to important insights into the catalytically-active state of the materials at different length scales, from the atomic level to the nano-/micrometer scale. The accessible operando methods utilizing photons range from vibrational spectroscopy in the infrared and optical regime to small-angle X-ray scattering (SAXS), diffraction (XRD), absorption spectroscopy (XAFS) and photoelectron spectroscopy (XPS), whereas electron-based techniques include scanning (SEM) and transmission microscopy (TEM) methods. In this work, we summarize recent findings of structural, morphological and chemical nanoparticle transformations during selected heterogeneous and electrochemical reactions, integrate them into the current state of knowledge, and discuss important future developments

Unequal Partnerships in Higher Education: Pedagogic Innovations in an Electronics within Physics Degree Course

This cross-European research partnership reports on supporting pro-active learning and teaching. The two-part project firstly explored student beliefs about electronics within a physics degree and secondly, the use of peer assessment of a Mathematica notebook to develop understandings of standards and quality. Student beliefs were explored because of the negative perceptions tutors thought students brought to the Engineering course within the Physics degree. The results showed that tutors’ fears were unfounded and that the students were highly motivated. Secondly, through peer assessment of a notebook, students developed critical understandings of standards and quality. Generally, students valued the content support and appreciated both the work of their peer and how this helped their own understanding. Esta investigación realizada por un partenariado transeuropeo se centra en el apoyo proactivo de la enseñanza y el aprendizaje en la educación superior. Este proyecto consta de dos partes. Primero se exploraron las creencias de los estudiantes sobre la electrónica en el grado de Física para, después, usar la evaluación por pares del manual Mathematica para desarrollar la comprensión de los estandares y calidad. Las creencias de los estudiantes se exploraron teniendo en cuenta las percepciones negativas que los tutores pensaban que tenían los estudianties del curso de Ingeniería en el grado de Física. Los resultados destacaron que los miedos de los tutores eran infundados y que los estudiantes se mostraban altamente motivados. Segundo, a través de la evaluación a pares del manual, el alumnado desarrolló una comprensión crítica de los estandares y su calidad. Generalmente, el alumnado valoró el apoyo sobre el contenido y apreció tanto el trabajo de sus compañeros y como éste les había ayudado en su comprensión

Comparative analysis of rigidity across protein families

We present a comparative study in which 'pebble game' rigidity analysis is applied to multiple protein crystal structures, for each of six different protein families. We find that the main-chain rigidity of a protein structure at a given hydrogen bond energy cutoff is quite sensitive to small structural variations, and conclude that the hydrogen bond constraints in rigidity analysis should be chosen so as to form and test specific hypotheses about the rigidity of a particular protein. Our comparative approach highlights two different characteristic patterns ('sudden' or 'gradual') for protein rigidity loss as constraints are removed, in line with recent results on the rigidity transitions of glassy networks

Shape-Selection of Thermodynamically Stabilized Colloidal Pd and Pt Nanoparticles Controlled via Support Effects

Colloidal chemistry, in combination with nanoparticle (NP)/support epitaxial interactions is used here to synthesize shape-selected and thermodynamically stable metallic NPs over a broad range of NP sizes. The morphology of three-dimensional palladium and platinum NPs supported on TiO₂(110) was investigated using scanning tunneling microscopy. Well-defined Pd and Pt NPs were synthesized via inverse micelle encapsulation. The initially spherical NPs were found to become faceted and form an epitaxial relationship with the support after high-temperature annealing (e.g., 1100 °C). Shape selection was achieved for almost all Pd NPs, namely, a truncated octahedron shape with (111) top and interfacial facets. The Pt NPs were however found to adopt a variety of shapes. The epitaxial relationship of the NPs with the support was evidenced by the alignment of the cluster’s edges with TiO₂(110)-[001] atomic rows and was found to be responsible for the shape control. The ability of synthesizing thermally stable shape-selected metal NPs demonstrated here is expected to be of relevance for applications in the field of catalysis, since the activity and selectivity of NP catalysts has been shown to strongly depend on the NP shape