Reporting obstacles

NRC. 2000a. Ixtter Report. Obstacles to Closure of the Johnston Atoll Chemical Agent Disposal System. Washington, D.C. National Academy Press. 

Harris and Wickens (1989) report large-scale tests in an open-sided 45-m-long apparatus incorporating grids and obstructions. Maximum flame speeds were approximately ten times those found in the absence of obstacles. 

Hjertager (1984) reported overpressures of 1.8 bar and 0.8 bar for propane and methane-air explosions, respectively, in a 0.5-m radial disk with repeated obstacles. 

A tube 10 m long and 2.5 m inside diameter was used for experiments with methane (Moen et al. 1982) and propane (Hjertager et al. 1984). These often-cited experiments showed that very intense gas explosions were possible in this tube, which had an aspect ratio of only 4 but which contained internal obstructions. Pressures of up to 4.0 bar for methane and 13.9 bar for propane were reported. Obstruction parameters, for example, blockage ratio and pitch, were varied. As with cylindrical geometry, explosions became more severe with increasing obstacle density. 

Taylor (1987) reports some experiments performed in a horizontal duct (2 m long, 0.05 X 0.05 m cross section). Obstacles were placed in the channel. The top of the duct could be covered by perforated plates with a minimum of 6% open area. Terminal flame speeds of 80 m/s were reported for propane in a channel with a blockage ratio of 50% and a 12% open roof. 

Experiments reported by Harris and Wickens (1989) deserve special attention. They modified the experimental apparatus described in Section 4.1.1—a 45 m long, open-sided apparatus. The first 9 m of the apparatus was modified by the fitting of solid walls to its top and sides in order to produce a confined region. Thus, it was possible to investigate whether a flame already propagating at high speed could be further accelerated in unconfined parts of the apparatus, where obstacles of pipework were installed. The initial flame speed in the unconfined parts of the apparatus could be modified by introduction of obstacles in the confined part. 

Van Wingerden, C. J. M. 1984. Experimental study of the influence of obstacles and partial confinement on flame propagation. Commission of the European Communities for Nuclear Science and Technology, report no. EUR 9541 EN/n. 

Quality Management systems have demonstrated their effectiveness in providing efficient, flexible management processes. However, in many instances they have failed to deliver their promises in full and in some cases have failed completely. These failures have been ascribed to cultural obstacles that were not identified during the design process. In a recent survey of 350 senior executives Arthur D. Little, Inc. found that 68 percent of the companies reported unanticipated problems with their change process. 

Despite its attractions for reducing common-pool losses, use of unitization has been more limited than one would expect. Joe Bain (1947, p. 29) noted It is difficult to understand why in the United States, even admitting all obstacles of law and tradition, not more than a dozen pools are 100 percent unitized (out of some 3,000) and only 185 have even partial unitization. Similarly, in 1985 Wiggins and Libccap reported that as late as 1975, only 38 percent of Oklahoma production and 20 percent of Texas production came from field-wide units. 

Quite recently Yasumori el al. (43) have reported the results of their studies on the effect that adsorbed acetylene had on the reaction of ethylene hydrogenation on a palladium catalyst. The catalyst was in the form of foil, and the reaction was carried out at 0°C with a hydrogen pressure of 10 mm Hg. The velocity of the reaction studied was high and no poisoning effect was observed, though under the conditions of the experiment the hydride formation could not be excluded. The obstacles for this reaction to proceed could be particularly great, especially where the catalyst is a metal present in a massive form (as foil, wire etc.). The internal strains... 

Confusion as to what constitutes municipal waste is presenting an obstacle to the use of packaging waste as a fuel in cement kilns. Whilst cement kilns can bum hazardous waste, they cannot bum a wide range of non-hazardous materials, it is reported. The case of Castle Cement is described which planned to bum a range of non-hazardous commercial and industrial wastes. Some waste-fired combustion processes, however, such as UK Waste s Fibre Fuel operation have been granted derogations where fuel is manufactured by advanced mechanical processes, which includes the production of fuel pellets. This latter process would be pointless for the cement industry since their fuels have to be pulverised. The problems are further discussed with reference to current European legislation. 

The development and reports of methods for colorless chlorophyll derivative (RCCs, FCCs, and NCCs) analysis are relatively recent and the structures of the compounds are being elucidated by deduction from their chromatographic behaviors, spectral characteristics (UV-Vis absorbance spectra), mass spectrometry, and nuclear magnetic resonance analysis. The main obstacle is that these compounds do not accumulate in appreciable quantities in situ and, moreover, there are no standards for them. The determination of the enzymatic activities of red chlorophyll catabolite reductase (RCCR) and pheophorbide a monoxygenase (PAO) also helps to monitor the appearance of colorless derivatives since they are the key enzymes responsible for the loss of green color. ... 

Experimental limitations initially limited the types of molecular systems that could be studied by TRIR spectroscopy. The main obstacles were the lack of readily tunable intense IR sources and sensitive fast IR detectors. Early TRIR work focused on gas phase studies because long pathlengths and/or multipass cells could be used without interference from solvent IR bands. Pimentel and co-workers first developed a rapid scan dispersive IR spectrometer (using a carbon arc broadband IR source) with time and spectral resolution on the order of 10 ps and 1 cm , respectively, and reported the gas phase IR spectra of a number of fundamental organic intermediates (e.g., CH3, CD3, and Cp2). Subsequent gas phase approaches with improved time and spectral resolution took advantage of pulsed IR sources. 

Phycomyces is by no means the only organism that can regulate its own growth with volatile substances. Bonner and Dodd (1962) have reported that Polysphondilium pallidum,Dictyostelium discoideum,D. mucoroides,D. purpureum have the capacity to avoid obstacles. A series of experiments has clearly shown that this orientating effect is due to a gas made by the organism. Attempts to identify this gas have been unsuccessful. 

The synthesis of block copolymers of polysaccharides and aliphatic polyesters has also been tried. But, many successful results were not reported because the reactivity of many hydroxyl groups on polysaccharides was an obstacle to the ROP of cyclic polyester or coupling reactions using terminal-activated polysaccharides. Li and Zhang reported the synthesis of maltoheptaose-b-PCL copolymers by ROP... 

Some earlier developments and applications of various implantable pH sensors or measurement systems have been reported [128, 129, 130, 131]. However, reliable pH sensors for long-term implantations are still not available, and widespread clinical usage of implantable pH sensors has not been reached. Similar to other implantable sensors, the development of implantable pH microelectrodes, either fully implanted in the body or needle type sensors applied through the skin (percutaneous), has faced serious obstacles including sensor stability deterioration, corrosion, and adverse body reactions [48, 132, 133], Among them, encapsulation to prevent corrosion represents a major challenge for the implantable sensor devices [51]. Failure of encapsulation can cause corrosion damage on internal components, substrate materials, and electrical contacts [48], The dissolution of very thin pH sensitive layers will also limit the stability and lifetime of implantable micro pH sensors. 

On September 29, 1942, Dollfus reported to Edsel Ford that the Vichy government had paid French Ford 38,000,000 francs for damages incurred in the bombing of Poissy. Dollfus added that the Ford assets in France had been conserved regardless of various obstacles encountered. 

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