Quantification of particle morphologies in view of quality control of the thermal spray process

The relationships between processing parameters, deposit microstructures, and deposit properties are not well understood, mainly due, on the one hand, to the numerous parameters governing the thermal spray process and, on the other, to the random mode of deposition of the material (for example, individual impacts of molten particles). The interactions are mainly related to the impact, spreading, and solidification of the material droplets onto the substrate, or previously deposited layers. A methodology was implemented to quantify individual splat morphologies using size and shape factors referring to an equivalent diameter, an elongation factor, and a degree of splashing, and also three-dimensional profilometry and stereology. This approach is mainly based on the use of an image analysis system and statistical tools. A few examples of the potential of this method are given. Such a lowcost and low-time-consuming protocol could be easily implemented for an optimization purpose.     

On the simulation of the flaking paint due to internal stresses: A simple model

We present a simple theoretical and experimental model to explain the flaking off of paints, from a pre-existing defect, due to the influence of internal stresses provoked by the variation of ambient temperature and a long or strong illumination. The experimental model is made of two superimposed rubber strips, one of them being submitted to an instantaneous elongation or to a constant speed of strain. The detachment of the other strip, that represents the peeling and the flaking off of the paint layer, is measured and analyzed using concepts of the fracture mechanics, such as the strain energy release rate, in order to determine the conditions of stability and propagation of a crack at the interface, and to draw a master curve representing the dissipation function as a function of the crack propagation speed.     

A numerical investigation of three different thermosyphon solar water heating systems

This work presents a theoretical evaluation of the performance of three types of thermosyphon solar water heating (TSWH) systems with flat-plate collectors considering different weather conditions. The flat-plate solar collectors considered are the absorber–pipe lower bond configuration (Type I), the absorber–pipe side bond configuration (Type II) and the absorber–pipe upper bond configuration (Type III). The performance of the three heaters have been investigated numerically under the same conditions. The average values of the energetic and exergetic efficiencies, for one of the weather conditions are: 39.47% and 18.21% for Type I, 34.86% and 15.45% for Type II, 32.28% and 13.8% for Type III. This study reveals that, the thermal performances obtained with Type I TSWH is always greater than the two others, and that this configuration leads to an improvement in the efficiency–temperature rise couple, followed by Type II TSWH system.     

Synthesis of carboxy‐terminated telechelic oligostyrenes by Dead End Polymerization

Styrene was polymerized with 4,4′‐azobiscyanovaleric acid (ACVA) in order to obtain carboxy‐telechelic polystyrene (CTPS) using the Dead‐End Polymerization (DEP) conditions. First, we focused on experimental conditions leading to oligomers with molecular weights about 2000 g mol^?1. Second, we demonstrated by‐products of ACVA radicals are also synthesized in the DEP conditions by combination or by disproportionation. The purification of CTPS was investigated in order to extract the by‐products of ACVA. An extraction of these by‐products in H₂O pH 7 is suggested. Finally, the acid functionality of oligostyrene is evaluated by ¹H NMR and conductimetric titrations. A functionality about 2 is obtained that confirmed the synthesis of CTPS. Copyright © 2002 Society of Chemical Industry     

Effect of aeration and pH on gramicidin S production by Bacillus brevis

Although the biosynthesis of the antibiotic gramicidin S (GS) by Bacillus brevis ATCC 9999 has been studied extensively, almost no attention has been given to environmental control of its fermentation process. In this respect, GS fermentations conducted in a 7.5 dm³ fermentor in complex (YP) medium revealed that a high aeration rate resulted in a high biomass yield (12 g DCW dm^?3) with very low GS levels (170 mg GS dm^?3). Lowering the aeration rate (5 dm³ air min^?1 at 300 rev min^?1) caused a dramatic increase in GS formation (2100 mg GS dm^?3) and comparable but slower biomass formation. In chemically-defined (F3/6) medium fermentations, an aeration rate of 5 dm³ air min^?1 at 300 rev min^?1 was apparently too high as only 0.104 mg GS mg^?1 DCW was produced. A much lower aeration rate (2 dm³ air min^?1 at 250 rev min^?1) was needed to arrive at a higher specific antibiotic level: 0.130 mg GS mg^?1 DCW. These data seem compatible with the finding that oxygen is known to inactivate the GS-synthetases. Furthermore, keeping the pH constant at 7.3 under low aeration conditions increased specific GS production up to 0.220 mg GS mg^?1 DCW in YP, as well as in F3/6 fermentations. Both environmental pH and dissolved oxygen tension clearly affect growth pattern, growth extent and GS production in these high yielding media. These data stress the importance of controlling pH and aeration rate during GS fermentations.     

Methods to explore design space for MPEG RMC codec specifications

The recent MPEG Reconfigurable Media Coding (RMC) standard aims at defining media processing specifications (e.g. video codecs) in a form that abstracts from the implementation platform, but at the same time is an appropriate starting point for implementation on specific targets. To this end, the RMC framework has standardized both an asynchronous dataflow model of computation and an associated specification language. Either are providing the formalism and the theoretical foundation for multimedia specifications. Even though these specifications are abstract and platform-independent the new approach of developing implementations from such initial specifications presents obvious advantages over the approaches based on classical sequential specifications. The advantages appear particularly appealing when targeting the current and emerging homogeneous and heterogeneous manycore or multicore processing platforms. These highly parallel computing machines are gradually replacing single-core processors, particularly when the system design aims at reducing power dissipation or at increasing throughput. However, a straightforward mapping of an abstract dataflow specification onto a concurrent and heterogeneous platform does often not produce an efficient result. Before an abstract specification can be translated into an efficient implementation in software and hardware, the dataflow networks need to be partitioned and then mapped to individual processing elements. Moreover, system performance requirements need to be accounted for in the design optimization process. This paper discusses the state of the art of the combinatorial problems that need to be faced at this design space exploration step. Some recent developments and experimental results for image and video coding applications are illustrated. Both well-known and novel heuristics for problems such as mapping, scheduling and buffer minimization are investigated in the specific context of exploring the design space of dataflow program implementations.     

Identification and functional analysis of the Saccharomyces cerevisiae nicotinamidase gene, PNC1

Nicotinamidase (NAMase) from the budding yeast, Saccharomyces cerevisiae, was purified by Ni(2+) affinity chromatography and gel filtration. N-terminal microsequencing revealed sequence identity with a hypothetical polypeptide encoded by the yeast YGL037C open reading frame sharing 30% sequence identity with Escherichia coli pyrazinamidase/nicotinamidase. A yeast strain in which the NAMase gene, hereafter named PNC1, was deleted shows a decreased intracellular NAD(+) concentration, consistent with the loss of NAMase activity in the null mutant. In wild-type strains, NAMase activity is stimulated during the stationary phase of growth, by various hyperosmotic shocks or by ethanol treatment. Using a P(PNC1)::lacZ gene fusion, we have shown that this stimulation of NAMase activity results from increased levels of the protein and requires stress response elements in the 5'non-coding region of PNC1. These results suggest that NAMase helps yeast cells to adapt to various stress conditions and nutrient depletion, most likely via the activation of NAD-dependent biological processes.