Kinetics of the NO + H2 reaction over supported noble metal based catalysts: Support effect on their adsorption properties

This paper reports a kinetic investigation of the global reduction of NO by H₂ which has been considered as a probe reaction for characterising the adsorption properties of supported palladium based catalysts. A particular attention has been paid towards the influence of the support on the catalytic properties of Pd, particularly towards the production of undesirable by-products such as nitrous oxide (N₂O) and ammonia (NH₃). It has been found that the kinetics of the overall NO + H₂ reaction on Pd/Al₂O₃ can be correctly depicted according to a Langmuir–Hinshelwood mechanism involving the dissociation of nitrosyl species assisted by chemisorbed hydrogen atoms. On the other hand, Pd/LaCoO₃ exhibits a different kinetic behaviour towards the adsorption of hydrogen depending on the pre-activation thermal treatment. In that case, different mechanisms may occur.     

Revealing the Dynamics of Hybrid Metal Halide Perovskite Formation via Multimodal In Situ Probes

The exploration of the synthetic space of halide perovskites hinges on an enormous number of parameters requiring time‐consuming experimentation to decouple and optimize. Here, the formation of the prototype material CH₃NH₃PbI₃ (MAPbI₃) is investigated at different time and length scales using multimodal in situ measurements to monitor the evolution of crystalline phases, morphology, and photoluminescence as a function of the lead precursors. Kinetically fast formation of crystalline precursor phases already during the spin‐coat deposition is observed using lead iodide (PbI₂) or lead chloride (PbCl₂) routes. These precursor phases most likely template final MAPbI₃ film morphology. In particular, the emergence of the “needle‐like” structure is shown to appear before film annealing. In situ photoluminescence measurements suggest nanoscale nucleation followed by rapid nuclei densification and growth. Using this multimodal in situ approach, different formation pathways can be identified either via precursor phases in the PbI₂ and PbCl₂ routes or direct perovskite formation from molecular building blocks as observed in the lead acetate (PbAc₂) route. Correlation of in situ results with photovoltaic device performance demonstrates the power of in situ multimodal techniques, paves the way to a fast screening of synthetic parameters, and ultimately leads to controlled synthetic procedures that yield high‐efficiency devices.     

ICT for development in the context of the closure of Chernobyl nuclear power plant: an activity theory perspective

This paper provides an analysis of a broadband implementation in the town of Slavutych, Ukraine. Slavutych was purposefully built 50 km from Chernobyl shortly after the Chernobyl Nuclear Power Plant (ChNPP) disaster in 1986 to house personnel of ChNPP and their families evacuated from the city of Prip'yat. Drawing on activity theory, and in particular the notion of activity systems, we demonstrate how an activity system approach can be used to frame Information and Communication Technology for Development (ICTD) intervention. We highlight the tools used to mediate the activity, the activity motivation and the relevant stakeholders and examine the role of ‘contradictions’. Using the notion of connected activities, we also provide some theoretical basis for understanding the emergence of activities and conceptualising the impact of development projects, arguing that the outcome of an activity leads to/is consumed by other related activities. This paper contributes to scholarship in the field of ICTD using an empirical case in a complex setting and furthers theoretical development by advancing an activity system perspective for understanding and theorising ICTD interventions.     

Thermal resistance of steam‐generator tube deposits under single‐phase forced convection and flow‐boiling heat transfer

Measurements were made of the thermal resistance of porous deposits of various thicknesses under both single‐phase forced convection and flow‐boiling conditions. Both synthetic deposits and deposits on tubes removed from operating steam generators were used in this investigation. The thermal resistance was modeled as the sum of two components: one associated with conduction through the porous deposit and a second associated with the effect of surface roughness. The conductive component of the thermal resistance was always positive, whereas surface roughness made a negative contribution to the thermal resistance, i.e., roughness enhanced the rate of heat transfer. Thermal conductivity of the porous deposits was higher for single‐phase forced convection, whereas the effect of deposit roughness on thermal resistance was higher under flow‐boiling conditions. The results are discussed in terms of the effect of composition, morphology, surface roughness, and the mode of heat transfer on the thermal resistance of porous deposit.     

Modeling and fabrication of three-dimensional silicon substrates with tailored shape and microtopography parameters for CdTe films

Seven models were constructed for the surface of three-dimensional silicon substrates. We proposed models of upright and inverted pyramids (and frusta) and models of substrates with triangular and prismatic cross sections. In modeling, we took into account the capabilities of photolithography and anisotropic etching of silicon wafers. We modeled the light ray trajectory in a thin-film three-dimensional CdS/CdTe solar cell with a large surface area. Three-dimensional microtextured substrates were fabricated using photomasks and modeling and calculation results. Their surface morphology was studied by scanning electron microscopy. The elemental composition of the microtextured silicon substrates was determined.     

Iron Powder Treated Gray Irons: Critical Shape Characteristics for Graphite Nuclei

A program was conducted to research how to characterize the size and shape of micro-particles. These can act as graphite nuclei, but are altered by adding a commercial iron powder, or after a similar treatment combined with inoculation. Resin sand mold (RSM) and metal mold (MM) solidified sample structures were subjected to automatic image analysis. In general, a higher cooling rate, typical for MM solidification, favors smaller size and more compact particles, even in RSM media. Iron powder treatment led to the largest particles with unusual morphologies, better defined by complex shape factors, which employ actual perimeters, rather than the simpler median size and aspect ratio method. Conventional inoculation employed after an iron powder treatment altered the particles (smaller and more compact), which benefited their effectiveness to act as graphite nuclei, especially at slower solidification rates in RSMs. The results confirm that promoting more compact micro-inclusions, at smaller sizes, involved in graphite nucleation, reduces the sensitivity to chill and improves the eutectic cell characteristics in gray cast iron.     

Photoluminescent Polymer Composites Based on New Tb(III) and Eu(III): Maleimide Complexes

The paper reports the preparation of two photoluminescent polymer composites by embedding two newly prepared Tb(III) and Eu(III) complexes into poly(4-styrenesulfonic acid) matrices using maleimide as ligand. In the first step, the photoluminescent complexes were prepared at 1:3 metal-to-ligand ratio. Prior to the embedment into the polymer matrix the complexes were investigated by chemical and thermal analysis, FT-IR, powder X-ray diffraction and fluorescence spectroscopy. The prepared composites preserve the photoluminescent properties of the complexes and provide them with long-term stability. Thin films of the composites were spin–coated on glass slides and investigated by SEM and AFM techniques. The remarkable photoluminescent properties of the composites prepared in bulk or deposited in thin films on various substrates recommend them for applications in optical devices as photonic conversion mediums.     

Improving the performance of a quadrupole time-of-flight instrument for macromolecular mass spectrometry

We modified and optimized a first generation quadrupole time-of-flight (Q-TOF) 1 to perform tandem mass spectrometry on macromolecular protein complexes. The modified instrument allows isolation and subsequent dissociation of high-mass protein complexes through collisions with argon molecules. The modifications of the Q-TOF 1 include the introduction of (1) a flow-restricting sleeve around the first hexapole ion bridge, (2) a low-frequency ion-selecting quadrupole, (3) a high-pressure hexapole collision cell, (4) high-transmission grids in the multicomponent ion lenses, and (5) a low repetition rate pusher. Using these modifications, we demonstrate the experimental isolation of ions up to 12 800 mass-to-charge units and detection of product ions up to 38 150 Da, enabling the investigation of the gas-phase stability, protein complex topology, and quaternary structure of protein complexes. Some of the data reveal a so-far unprecedented new mechanism in gas-phase dissociation of protein oligomers whereby a tetramer complex dissociates into two dimers. These data add to the current debate whether gas-phase structures of protein complexes do retain some of the structural features of the corresponding species in solution. The presented low-cost modifications on a Q-TOF 1 instrument are of interest to everyone working in the fields of macromolecular mass spectrometry and more generic structural biology.     

Experimental study of gas flow through a multi-opening orifice

Gas flow through an orifice can be determined with high accuracy based only on the geometrical dimensions of the orifice and the upstream and downstream pressures when the flow is purely molecular. An orifice with a number of smaller openings in parallel can be used to maintain the molecular flow at higher pressure and high total conductance of the orifice. The question of how close such openings can be without influencing each other is important for practical design. This problem was studied experimentally. Changes in the total conductance versus pressure were followed for a set of multi-opening orifices with regularly arranged differently spaced circular openings. The experimental results show that no influence on the flow through a single opening can be observed at sufficiently distant opening, over the entire pressure range. At centre-to-centre distances shorter than approximately three times the diameter of the opening, notable differences in the total conductance can be seen in the pressure range where the transition from the molecular to transitional flow regime occurs.     

Nanoscale mapping of contact stiffness and damping by contact resonance atomic force microscopy

In this work, a new procedure is demonstrated to retrieve the conservative and dissipative contributions to contact resonance atomic force microscopy (CR-AFM) measurements from the contact resonance frequency and resonance amplitude. By simultaneously tracking the CR-AFM frequency and amplitude during contact AFM scanning, the contact stiffness and damping were mapped with nanoscale resolution on copper (Cu) interconnects and low-k dielectric materials. A detailed surface mechanical characterization of the two materials and their interfaces was performed in terms of elastic moduli and contact damping coefficients by considering the system dynamics and included contact mechanics. Using Cu as a reference material, the CR-AFM measurements on the patterned structures showed a significant increase in the elastic modulus of the low-k dielectric material compared with that of a blanket pristine film. Such an increase in the elastic modulus suggests an enhancement in the densification of low-k dielectric films during patterning. In addition, the subsurface response of the materials was investigated in load-dependent CR-AFM point measurements and in this way a depth dimension was added to the common CR-AFM surface characterization. With the new proposed measurement procedure and analysis, the present investigation provides new insights into characterization of surface and subsurface mechanical responses of nanoscale structures and the integrity of their interfaces.