On measurement of carbon content in retained austenite in a nanostructured bainitic steel

In this study, the carbon content of retained austenite in a nanostructured bainitic steel was measured by atom probe tomography and compared with data derived from the austenite lattice parameter determined by X-ray diffraction. The results provide new evidence about the heterogeneous distribution of carbon in austenite, a fundamental issue controlling ductility in this type of microstructure.     

Numerical Characterization of Particle Beam Collimation: Part II Integrated Aerodynamic-Lens–Nozzle System

As a sequel to our previous effort on the modeling of particle motion through a single lens or nozzle, flows of gas–particle suspensions through an integrated aerodynamic-lens–nozzle inlet have been investigated numerically. It is found that the inlet transmission efficiency (η_t) is unity for particles of intermediate diameters (D_p ～ 30–500 nm). The transmission efficiency gradually diminishes to ～40% for large particles (D_p > 2500 nm) because of impact losses on the surface of the first lens. There is a catastrophic reduction of η_t to almost zero for very small particles (D_p ≤ 15 nm) because these particles faithfully follow the final gas expansion. We found that, for very small particles, particle transmission is mainly controlled by nozzle geometry and operating conditions. A lower upstream pressure or a small inlet can be used to improve transmission of very small particles, but at the expense of sampling rate, or vice versa. Brownian motion exacerbates the catastrophic reduction in η_t for small particles; we found that the overall particle transmission efficiency can be roughly calculated as the product of the aerodynamic and the purely Brownian efficiencies. For particles of intermediate diameters, Brownian motion is irrelevant, and the modeling results show that the transmission efficiency is mainly controlled by the lenses. Results for an isolated lens or nozzle are used to provide guidance for the design of alternative inlets. Several examples are given, in which it is shown that one can configure the inlet to preferentially sample large particles (with η_t > 50% for D_p = 50–2000 nm) or ultrafine particles (with η_t > 50% for D_p = 20–1000 nm). Some of the results have been compared with experimental data, and reasonable agreement has been demonstrated.     

Chitosan-grafted nonwoven geotextile for heavy metals sorption in sediments

Functionalized polypropylene nonwoven (PP) geotextiles can be used as a new eco-friendly way to trap heavy metals in sediments. Chitosan was chosen as sorbent because of its ability to trap heavy metals, its natural origin (from shells) and its low cost. PP was first functionalized with acrylic acid using a low pressure cold plasma process, in order to bring reactive carboxylic functions onto the surface. Chitosan was then covalently grafted on the acrylic acid modified PP. The functionalized surfaces were characterized by Fourier Transform Infrared Spectroscopy–Attenuated Total Reflectance (FTIR–ATR) and X-ray Photoelectron Spectroscopy (XPS) and evidence of chitosan grafting was given. The ability of the functionalized geotextile to trap heavy metals was then investigated. Copper was chosen as a model heavy metal, and artificial solutions of CuSO₄ were prepared for the experiments. Sorption studies were carried out at 20 °C with Polypropylene-grafted-Acrylic acid-Chitosan (PP-g-AA-chitosan) varying the concentration of copper in polluted solutions to evaluate the maximum of adsorption of the surface: the textile can chelate copper increasingly as a function of the initial copper concentration until 830 ppm. At this concentration, it reaches a plateau at about 30 mg of trapped copper per gram of geotextile. The effects of pH and of the ionic strength (adsorption in a NaCl containing solution) were finally investigated. The trapping of Cu²⁺ decreases slowly when the ionic strength increases. When there are 30 g/L NaCl in the artificial polluted solution (like in seawater), only 20 mg of Cu²⁺ can be trapped per g of geotextile. Finally, the optimum pH to trap the maximum amount of copper was determined to be 4.8, which corresponds to the optimum pH for the chitosan solubility.     

Kinetic analysis of the thermal degradation of PVC plastisols

The thermal degradation of plasticized polyvinyl chloride (plastisol) is reported here. Plastisols used in the present work were prepared with the plasticizer diethylhexyl phthalate in different proportions. Thermogravimetric analysis has been applied to study the behavior of plastisols at high temperatures and to evaluate their degradation kinetics. Several tests were carried out at different heating rates and the variation of the degree of reaction with time and temperature was calculated. The influence of the heating rate in dynamic measurements (5–40°C/min) on kinetic parameters, such as activation energies and reaction orders, has also been studied. These parameters were calculated from dynamic thermogravimetric analysis tests using Friedman analysis and a kinetic model for the degradation of poly(vinyl chloride) and plastisols has been then developed. The obtained model was able to simulate the thermal degradation process of plastisols in dynamic conditions and was used to evaluate the effects of additives in the degradation. The results of this study can be used to optimize the concentration of plasticizers and stabilizers in poly(vinyl chloride) formulations. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1069–1079, 1999     

Activated sludge model (ASM) based modelling of membrane bioreactor (MBR) processes: A critical review with special regard to MBR specificities

Membrane bioreactors (MBRs) have been increasingly employed for municipal and industrial wastewater treatment in the last decade. The efforts for modelling of such wastewater treatment systems have always targeted either the biological processes (treatment quality target) as well as the various aspects of engineering (cost effective design and operation). The development of Activated Sludge Models (ASM) was an important evolution in the modelling of Conventional Activated Sludge (CAS) processes and their use is now very well established. However, although they were initially developed to describe CAS processes, they have simply been transferred and applied to MBR processes. Recent studies on MBR biological processes have reported several crucial specificities: medium to very high sludge retention times, high mixed liquor concentration, accumulation of soluble microbial products (SMP) rejected by the membrane filtration step, and high aeration rates for scouring purposes. These aspects raise the question as to what extent the ASM framework is applicable to MBR processes. Several studies highlighting some of the aforementioned issues are scattered through the literature. Hence, through a concise and structured overview of the past developments and current state-of-the-art in biological modelling of MBR, this review explores ASM-based modelling applied to MBR processes. The work aims to synthesize previous studies and differentiates between unmodified and modified applications of ASM to MBR. Particular emphasis is placed on influent fractionation, biokinetics, and soluble microbial products (SMPs)/exo-polymeric substances (EPS) modelling, and suggestions are put forward as to good modelling practice with regard to MBR modelling both for end-users and academia. A last section highlights shortcomings and future needs for improved biological modelling of MBR processes.     

Computer-aided band gap engineering and experimental verification of amorphous silicon–germanium solar cells

A new band gap profile (exponential profile) for the active layer of the a-SiGe:H single junction cell has been designed and experimentally demonstrated. By computer simulations we show how bending the grading of the band gap in the i-layer contributes to the enhancement of the carrier collection, improving the fill factor and efficiency. The differences observed between experiments and simulations are studied using Rutherford Backscattering Spectrometry (RBS). The results highlight weak points during the deposition process, whose control enables us to bring together experimental and computational results.     

A robotic vehicle for disabled children

One of the most frequent effects of physical disability is reduced or impaired mobility. There are a number of technical aids for all the cases of physical impairment but none of the systems described in the literature address the particular problems of children affected by neuromotor disorders accompanied by mental retardation. The following addresses the development of the PALMA [(plataforma de apoyo ludico a la movilidad alternative) (assistive platform for alternative mobility)] system as a tool to assist the mobility of children affected by cerebral palsy. PALMA is specifically adapted to a personalized and early cognitive development of children affected by severe neuromotor problems. The rehabilitation process based on PALMA has an impact on the interaction between children and environment, on their motor dexterity, and on decision-making ability.