Selective catalysts for the hydrogen oxidation and oxygen reduction reactions by patterning of platinum with calix[4]arene molecules

The design of new catalysts for polymer electrolyte membrane fuel cells must be guided by two equally important fundamental principles: optimization of their catalytic behaviour as well as the long-term stability of the metal catalysts and supports in hostile electrochemical environments. The methods used to improve catalytic activity are diverse, ranging from the alloying and de-alloying of platinum to the synthesis of platinum core-shell catalysts. However, methods to improve the stability of the carbon supports and catalyst nanoparticles are limited, especially during shutdown (when hydrogen is purged from the anode by air) and startup (when air is purged from the anode by hydrogen) conditions when the cathode potential can be pushed up to 1.5 V (ref. 11). Under the latter conditions, stability of the cathode materials is strongly affected (carbon oxidation reaction) by the undesired oxygen reduction reaction (ORR) on the anode side. This emphasizes the importance of designing selective anode catalysts that can efficiently suppress the ORR while fully preserving the Pt-like activity for the hydrogen oxidation reaction. Here, we demonstrate that chemically modified platinum with a self-assembled monolayer of calix[4]arene molecules meets this challenging requirement.     

Monitoring for exposures to TENORM sources in Vojvodina region

TENORM are found in a wide variety of waste materials, some raw mineral ores and in some consumer products (in trace amounts) where molecules of radionuclides may be bound to specific minerals used in the manufacturing process and can result in increases in radiation exposures to workers and the public. The aim of this paper is to understand this problem and to develop effective ways to protect humans and the environment from harmful exposure to the radiation in TENORM materials in the Vojvodina region. The results of measurement of indoor radon concentration in schools and kindergartens and dose-rate and gamma-spectrometry measurements of the workplace with TENORM materials are presented.     

Versatile gradients of chemistry, bound ligands and nanoparticles on alumina nanopore arrays

Nanoporous alumina (PA) arrays produced by self-ordering growth, using electrochemical anodization, have been extensively explored for potential applications based upon the unique thermal, mechanical and structural properties, and high surface-to-volume ratio of these materials. However, the potential applications and functionality of these materials may be further extended by molecular-level engineering of the surface of the pore rims. In this paper we present a method for the generation of chemical gradients on the surface of PA arrays based upon plasma co-polymerization of two monomers. We further extend these chemical gradients, which are also gradients of surface charge, to those of bound ligands and number density gradients of nanoparticles. The latter represent a highly exotic new class of materials, comprising aligned PA, capped by gold nanoparticles around the rim of the pores. Gradients of chemistry, ligands and nanoparticles generated by our method retain the porous structure of the substrate, which is important in applications that take advantage of the inherent properties of these materials. This method can be readily extended to other porous materials.     

Wetting Kinetics of Eutectic Lead and Lead-Free Solders: Spreading over the Cu Surface

Wetting kinetics of Sn, eutectic Sn-Ag, eutectic Sn-Cu, and eutectic Pb-Sn was studied using real-time in situ monitoring of the triple-line movement, facilitated by a hot-stage microscopy system under a controlled atmosphere. Significantly different kinetics of lead versus lead-free solders is documented. In case of the eutectic lead solder, four characteristic spreading stages were identified. Spreading of lead-free solders features two stages with a sharp change of the spreading rate at the early stages of rather insignificant spreading. Scanning electron microscopy and energy-dispersive x-ray spectroscopy analysis of the resolidified solder surface within a halo region is discussed.     

Preparation and physical characteristics of a lithium-beryllium-substituted fluorapatite

A lithium-beryllium-substituted fluorapatite, Li_0.50Be_0.25Ca_4.50(PO₄)₃F, has been prepared by means of a high-temperature reaction between lithium beryllium fluoride, Li₂BeF₄, and tricalcium phosphate, Ca₃(PO₄)₂. This material has potential application as a waste form for radioactive and toxic fluoride salts. Monitoring of the reaction progress by differential scanning calorimetry indicated that the reaction was initiated by melting of the fluoride salt and that it was fast and complete. While reactive sintering of lithium beryllium fluoride with tricalcium phosphate led to a rather porous product, melting of the reactants with subsequent solidification readily produced a substituted fluorapatite with a near-theoretical bulk density.     

An analysis of the sustainability index of micro- and small-sized furniture industries

The measurement of the sustainability level can bring benefits to organizations, particularly in integrating traditional and sustainable management. Thus, the scope of this study is to structure a process to measure the sustainability level, specifically in micro- and small-sized enterprises that belong to the furniture industry, providing them the possibility to measure and monitor their sustainability level through indicators, subindices and a sustainability index. Currently, there is no system for measuring the level of sustainability and its integration in the management of furniture industries. Thus, the system proposed in this article can be considered unprecedented. This measurement system comprises the equations of measurement, standardization, weighting and aggregation of indicators in a sustainability index. The practical application was carried out in nine furniture industries. The results demonstrate that the indicators, subindices and index of sustainability are adequate to diagnose their sustainability level, revealing negligence with environmental aspects. Our conclusion is that the proposed method to measure the sustainability level of micro- and small-sized industries is consistent and reflects the reality of the furniture industry. Furthermore, its efficient use should consider a joint analysis of indicators and subindices. Finally, its integration with the management process of the industries enables a diagnosis, without additional information efforts, of the strengths and weaknesses of environmental, social and economic aspects.     

Fluorescence study of the dynamics of a star-shaped poly(?-caprolactone)s in THF: A comparison with a star-shaped poly(l-lactide)s

Molecular dynamics of 2-, 4- and 6-arm star-shaped poly(?-caprolactone)s (PCLs) functionalized with pyrene at all chain ends followed by excimer formation were investigated in THF as a solvent. Dilute solutions (10⁻⁸ to 10⁻⁶ mol L⁻¹) of these polymers revealed excimer emission due to the intramolecular cyclization, proceeding via chain end interaction. Time-resolved fluorescence measurements of star-shaped PCLs showed complex decay profiles of monomer and excimer fluorescence. An intensity rise component of decay profiles monitored in excimer region (500 nm) was observed for star-shaped polymers due to dynamic formation of excimers. Dipyrene-PCL (2-arm) also showed partial formation of static pyrene excimers as followed from measurement of excitation spectra at ambient temperature in THF. Excimer intensity of di- and four pyrene-telechelic PCLs was found to be comparable with that of di- and four pyrene-telechelic polylactide (PLA) polyesters having similar molar masses. 6-Arm PCL showed depressed excimer formation with regard to 6-arm PLA under the otherwise identical conditions contrary to the conclusion expected from the higher flexibility of the PCL chain. Eventually, molecular dynamic simulations showed that possible explanation can be related to different conformations of 6-arm PLA versus PCL stars.     

Numerical solution of the dynamic stability problems

A novel integral equation technique is employed for the analysis of dynamic stability problems. The governing equation of the linearized parametric resonance problem is transformed into an integral equation. The kernel of the integral equation is computed as the influence function for the deflection and/or bending moment of a corresponding beam. The highest derivative of the governing function (in our case fourth derivative of the displacement function) is chosen as the basic unknown. Using the formal analogy with the differential equation of the beam flexure this highest derivative is comprehended as some unknown transverse ‘load’. The distribution of this ‘load’ is a priori assumed to be polygonal. Using elementary methods of structural analysis, the displacements due to the assumed ‘load’ are determined. These displacements, arrayed into a square matrix, approximate the kernel of the governing integral equation. The subsequent procedure via Hill's determinant is a conventional one. The results prove to be accurate enough even for a very modest number of points of integration. This reflects the fact that the method is based on numerical integration rather than on numerical differentiation.     

Thermoplastic-thermosetting hybrid polymer systems as gap-filling adhesives

The most important requirement for a hot melt adhesive to perform well in gap-filling applications is the ability to yield or flow under shrinkage tension which develops in the adhesives during cooling, while maintaining a satisfactory bond to the substrate. In addition, such an adhesive must have a high room temperature viscosity and high green strength to effect an acceptable bond before curing. We found that the required combination of properties for the gap-filling applications can be achieved with interpenetrating networks of selected thermoset-thermoplastic polymers. The best results were obtained with systems consisting of an amorphous polyester and an epoxy blend. The properties of these adhesives depend on numerous variables. This study concerns the three composition variables which appeared particularly important in the performance of these adhesives: (1) epoxy-polyester ratio, (2) molecular weight of the epoxy system, and (3) the quality of dispersion.