Simulation of a complete reflected shock tunnel showing a vortex mechanism for flow contamination

Simulations of a complete reflected shock tunnel facility have been performed with the aim of providing a better understanding of the flow through these facilities. In particular, the analysis is focused on the premature contamination of the test flow with the driver gas. The axisymmetric simulations model the full geometry of the shock tunnel and incorporate an iris-based model of the primary diaphragm rupture mechanics, an ideal secondary diaphragm and account for turbulence in the shock tube boundary layer with the Baldwin-Lomax eddy viscosity model. Two operating conditions were examined: one resulting in an over-tailored mode of operation and the other resulting in approximately tailored operation. The accuracy of the simulations is assessed through comparison with experimental measurements of static pressure, pitot pressure and stagnation temperature. It is shown that the widely-accepted driver gas contamination mechanism in which driver gas 'jets' along the walls through action of the bifurcated foot of the reflected shock, does not directly transport the driver gas to the nozzle at these conditions. Instead, driver gas laden vortices are generated by the bifurcated reflected shock. These vortices prevent jetting of the driver gas along the walls and convect driver gas away from the shock tube wall and downstream into the nozzle. Additional vorticity generated by the interaction of the reflected shock and the contact surface enhances the process in the over-tailored case. However, the basic mechanism appears to operate in a similar way for both the over-tailored and the approximately tailored conditions.

Modern developments in hypersonic wind tunnels

The development of new methods of producing hypersonic wind-tunnel flows at increasing velocities during the last few decades is reviewed with attention to airbreathing propulsion, hypervelocity aerodynamics and superorbital aerodynamics. The role of chemical reactions in these flows leads to use of a binary scaling simulation parameter, which can be related to the Reynolds number, and which demands that smaller wind tunnels require higher reservoir pressure levels for simulation of flight phenomena. The use of combustion heated vitiated wind tunnels for propulsive research is discussed, as well as the use of reflected shock tunnels for the same purpose. A flight experiment validating shock-tunnel results is described, and relevant developments in shock tunnel instrumentation are outlined. The use of shock tunnels for hypervelocity testing is reviewed, noting the role of driver gas contamination in determining test time, and presenting examples of air dissociation effects on model flows. Extending the hypervelocity testing range into the superorbital regime with useful test times is seen to be possible by use of expansion tube/tunnels with a free piston driver.

Implementação da técnica de difração de elétrons de baixa energia

The purpose of this study is to describe the implementation of the Low Energy Electron Diffaction (LEED) technique in the Laboratory of Magnetic Nanostructures and Semiconductors of the Department of Theoretical and Experimental Physics of the Universidade Federal do Rio Grande do Norte (UFRN), Natal, Brazil. During this work experimental apparatus were implemented for a complete LEED set-up. A new vacuum system was also set up. This was composed of a mechanical pump, turbomolecular pump and ionic pump for ultra-high vacuum and their respective pressure measurement sensors (Pirani gauge for low vacuum measures and the wide range gauge -WRG); ion cannon maintenance, which is basically mini-sputtering, whose function is sample cleaning; and set-up, maintenance and handling of the quadrupole mass spectrometer, whose main purpose is to investigate gas contamination inside the ultra-high vacuum chamber. It should be pointed out that the main contribution of this Master's thesis was the set-up of the sample heating system; that is, a new sample holder. In addition to the function of sample holder and heater, it was necessary to implement the function of sustaining the ultra-high vacuum environment. This set of actions is essential for the complete functioning of the LEED technique

Light noble gases in 12 meteorites from the Omani desert, Australia, Mauritania, Canada, and Sweden

We measured the concentrations and isotopic compositions of He, Ne, and Ar in 14 fragments from 12 different meteorites: three carbonaceous chondrites, six L chondrites (three most likely paired), one H chondrite, one R chondrite, and one ungrouped chondrite. The data obtained for the CV3 chondrites Ramlat as Sahmah (RaS) 221 and RaS 251 support the hypothesis of exposure age peaks for CV chondrites at approximately 9 Ma and 27 Ma. The exposure age for Shişr 033 (CR chondrite) of 7.3 Ma is also indicative of a possible CR chondrite exposure age peak. The three L chondrites Jiddat al Harasis (JaH) 091, JaH 230, and JaH 296, which are most likely paired, fall together with Hallingeberg into the L chondrite exposure age peak of approximately 15 Ma. The two L chondrites Shelburne and Lake Torrens fall into the peaks at approximately 40 Ma and 5 Ma, respectively. The ages for Bassikounou (H chondrite) and RaS 201 (R chondrite) are approximately 3.5 Ma and 5.8 Ma, respectively. Six of the studied meteorites show clear evidence for 3He diffusive losses, the deficits range from approximately 17% for one Lake Torrens aliquot to approximately 45% for RaS 211. The three carbonaceous chondrites RaS 221, RaS 251, and Shişr 033 all have excess 4He, either of planetary or solar origin. However, very high 4He/20Ne ratios occur at relatively low 20Ne/22Ne ratios, which is unexpected and needs further study. The measured 40Ar ages fit well into established systematics. They are between 2.5 and 4.5 Ga for the carbonaceous chondrites, older than 3.6 Ga for the L and H chondrites, and about 2.4 Ga for the R chondrite as well as for the ungrouped chondrite. Interestingly, none of our studied L chondrites has been degassed in the 470 Ma break-up event. Using the amount of trapped 36Ar as a proxy for noble gas contamination due to terrestrial weathering we are able to demonstrate that the samples studied here are not or only very slightly affected by terrestrial weathering (at least in terms of their noble gas budget).

Multiresidue determination of pesticides in honey samples by gas chromatography-mass spectrometry and application in environmental contamination

A simple and fast multiresidue method has been developed to determine 48 pesticides within the major groups of pesticides (organohalogen, organophosphorous, pyrethroids and organonitrogen) in representative samples of locally produced honey, in Bauru (State of São Paulo, Brazil) during 2003-2004. The recovery results found ranged from 76% to 95% and the limits of detection were lower than 0.01 mg/kg for gas chromatography with electron impact mass spectrometric detection in the selected ion monitoring mode (GC-MS-SIM). The results indicated that most pesticides found in the samples belonged to the organohalogen and organophosphorous groups and lower levels of residues of some organonitrogen and pyretroids were also detected. Malathion residues were detected in all the samples, in a high concentration, owing to its applications to control dengue mosquitoes in the area studied. (c) 2005 Elsevier Ltd. All rights reserved.

The use of radon (Rn-222) and volatile organic compounds in monitoring soil gas to localize NAPL contamination at a gas station in Rio Claro, Sao Paulo State, Brazil

This study focuses on the presence of radon (Rn-222) and volatile organic compounds (VOCs) in soil gases at a gas station located in the city of Rio Claro, Sao Paulo, Brazil, where a fossil fuel leak occurred. The spatial distribution results show a correlation between Rn-222 and VOCs, consistent with the fact that radon gas has a greater chemical affinity with organic phases than with water. This finding demonstrates that the presence of a residual hydrocarbon phase in an aquifer can retain radon, leading to a reduced radon content in the soil gas. The data in this study confirm the results of previous investigations, in which the method used in this study provided a preliminary fingerprint of a contaminated area. Furthermore, the data analysis time is brief, and only simple equipment is required. (C) 2014 Published by Elsevier Ltd.

Chronic Polyaromatic Hydrocarbon (PAH) Contamination Is a Marginal Driver for Community Diversity and Prokaryotic Predicted Functioning in Coastal Sediments

Benthic microorganisms are key players in the recycling of organic matter and recalcitrant compounds such as polyaromatic hydrocarbons (PAHs) in coastal sediments. Despite their ecological importance, the response of microbial communities to chronic PAH pollution, one of the major threats to coastal ecosystems, has received very little attention. In one of the largest surveys performed so far on coastal sediments, the diversity and composition of microbial communities inhabiting both chronically contaminated and non-contaminated coastal sediments were investigated using high-throughput sequencing on the 18S and 16S rRNA genes. Prokaryotic alpha-diversity showed significant association with salinity, temperature, and organic carbon content. The effect of particle size distribution was strong on eukaryotic diversity. Similarly to alpha-diversity, beta-diversity patterns were strongly influenced by the environmental filter, while PAHs had no influence on the prokaryotic community structure and a weak impact on the eukaryotic community structure at the continental scale. However, at the regional scale, PAHs became the main driver shaping the structure of bacterial and eukaryotic communities. These patterns were not found for PICRUSt predicted prokaryotic functions, thus indicating some degree of functional redundancy. Eukaryotes presented a greater potential for their use as PAH contamination biomarkers, owing to their stronger response at both regional and continental scales.

Satellite protection and drag reduction using a purging gas flow

We have used the DSMC method to determine contamination (impingement of atmospheric molecules) and the aerodynamic forces on a cold satellite when a protective “purge gas” is ejected from a sting protruding ahead of the satellite. Forward ejection of the purge gas provides the greatest protection for a given mass of purge gas and the aerodynamic drag can be significantly reduced, thus compensating for the backward reaction from the forward ejection. If the purge gas is ejected backward from the sting (towards the satellite) the ejection provides thrust and the net retarding force can be reduced to zero. Contamination can be reduced and the mass of purging gas is less than the mass of conventional rocket propellant required to maintain the orbit of an unprotected satellite.

Implications of specimen preparation and of surface contamination for the measurement of the grain boundary carbon concentration of steels using x-ray microanalysis in an UHVFESTEM

The purpose of the present investigation was to gain an understanding of the nature of the carbon contamination on the surface of standard steel transmission electron spectroscopy (TEM) specimens, the effect of exposure of a clean specimen to normal laboratory air, and the efficacy of plasma-cleaning treatments. This knowledge is a necessary prerequisite to the development of appropriate specimen preparation and/or specimen cleaning methods. X-ray photoelectron spectroscopy in combination with argon ion beam profiling was used to characterize the specimen surfaces of X65 steel and 316 stainless steel. The only clean carbon-free surface obtained was that during argon etching of the sample in the surface analysis chamber. Any exposure of a previously cleaned sample to laboratory air resulted in a rapid carbon (hydrocarbon) contamination of the sample surface and the development of surface oxidation, Plasma cleaning with subsequent exposure of the specimen to the laboratory air also resulted in a carbon-contaminated surface. This suggests that procedures of preparation of TEM specimens of steels outside an ultrahigh vacuum chamber are unlikely to result in the lowering of contamination rates on specimens to levels where measurements for carbon in the grain boundaries are possible. What is needed is a cleaning system as an integral part of the specimen insertion system into the field-emission scanning transmission electron microscope. This cleaning could be carried out by argon ion etching. Copyright (C) 2000 John Wiley & Sons, Ltd.

Determination of total petroleum hydrocarbons in soil from different locations using infrared spectrophotometry and gas chromatography

Total petroleum hydrocarbons (TPH) are important environmental contaminants which are toxic to human and environmental receptors. Several analytical methods have been used to quantify TPH levels in contaminated soils, specifically through infrared spectrometry (IR) and gas chromatography (GC). Despite being two of the most used techniques, some issues remain that have been inadequately studied: a) applicability of both techniques to soils contaminated with two distinct types of fuel (petrol and diesel), b) influence of the soil natural organic matter content on the results achieved by various analytical methods, and c) evaluation of the performance of both techniques in analyses of soils with different levels of contamination (presumably non-contaminated and potentially contaminated). The main objectives of this work were to answer these questions and to provide more complete information about the potentials and limitations of GC and IR techniques. The results led us to the following conclusions: a) IR analysis of soils contaminated with petrol is not suitable due to volatilisation losses, b) there is a significant influence of organic matter in IR analysis, and c) both techniques demonstrated the capacity to accurately quantify TPH in soils, irrespective of their contamination levels.

Distribution of artifactual gas on post-mortem multidetector computed tomography (MDCT)

L'imagerie est de plus en plus utilisée en médecine forensique. Actuellement, les connaissances nécessaires pour interpréter les images post mortem sont faibles et surtout celles concernant les artéfacts post mortem. Le moyen radiologique le plus utilisé en médecine légale est la tomodensitométrie multi-coupes (TDMC). Un de ses avantages est la détection de gaz dans le corps. Cette technique est utile au diagnostic d'embolie gazeuse mais sa très grande sensibilité rend visible du gaz présent même en petite quantité. Les premières expériences montrent que presque tous les corps scannés présentent du gaz surtout dans le système vasculaire. Pour cette raison, le médecin légiste est confronté à un nouveau problème : la distinction entre du gaz d'origine post-mortem et une embolie gazeuse vraie. Pour parvenir à cette distinction, il est essentiel d'étudier la distribution de ces gaz en post mortem. Aucune étude systématique n'a encore été réalisée à ce jour sur ce sujet.¦Nous avons étudié l'incidence et la distribution des gaz présents en post mortem dans les vaisseaux, dans les os, dans les tissus sous-cutanés, dans l'espace sous-dural ainsi que dans les cavités crânienne, thoracique et abdominale (82 sites au total) de manière à identifier les facteurs qui pourraient distinguer le gaz post-mortem artéfactuel d'une embolie gazeuse¦Les données TDMC de 119 cadavres ont été étudiées rétrospectivement. Les critères d'inclusion des sujets sont l'absence de lésion corporelle permettant la contamination avec l'air extérieur, et, la documentation du délai entre le moment du décès et celui du CT-scan (p.ex. rapport de police, protocole de réanimation ou témoin). La présence de gaz a été évaluée semi-quantitativement par deux radiologues et codifiée. La codification est la suivante : grade 0 = pas de gaz, grade 1 = une à quelques bulles d'air, grade 2 = structure partiellement remplie d'air, grade 3 = structure complètement remplie d'air.¦Soixante-quatre des 119 cadavres présentent du gaz (62,2%), et 56 (75,7%) ont montré du gaz dans le coeur. Du gaz a été détecté le plus fréquemment dans le parenchyme hépatique (40%); le coeur droit (ventricule 38%, atrium 35%), la veine cave inférieure (infra-rénale 30%, supra-rénale 26%), les veines sus-hépatiques (gauche 26%, moyenne 29%, droite 22 %), et les espaces du porte (29%). Nous avons constaté qu'une grande quantité de gaz liée à la putréfaction présente dans le coeur droit (grade 3) est associée à des collections de gaz dans le parenchyme hépatique (sensibilité = 100%, spécificité = 89,7%). Pour décrire nos résultats, nous avons construit une séquence d'animation qui illustre le processus de putréfaction et l'apparition des gaz à la TDMC post-mortem.¦Cette étude est la première à montrer que l'apparition post-mortem des gaz suit un modèle de distribution spécifique. L'association entre la présence de gaz intracardiaque et dans le parenchyme hépatique pourrait permettre de distinguer du gaz artéfactuel d'origine post-mortem d'une embolie gazeuse vraie. Cette étude fournit une clé pour le diagnostic de la mort due à une embolie gazeuse cardiaque sur la base d'une TDMC post-mortem.¦Abstract¦Purpose: We investigated the incidence and distribution of post-mortem gas detected with multidetector computed tomography (MDCT) to identify factors that could distinguish artifactual gas from cardiac air embolism.¦Material and Methods: MDCT data of 119 cadavers were retrospectively examined. Gas was semiquantitatively assessed in selected blood vessels, organs and body spaces (82 total sites).¦Results: Seventy-four of the 119 cadavers displayed gas (62.2%; CI 95% 52.8 to 70.9), and 56 (75.7%) displayed gas in the heart. Most gas was detected in the hepatic parenchyma (40%); right heart (38% ventricle, 35% atrium), inferior vena cava (30% infrarenally, 26% suprarenally), hepatic veins (26% left, 29% middle, 22% right), and portal spaces (29%). Male cadavers displayed gas more frequently than female cadavers. Gas was detected 5-84 h after death; therefore, the post-mortem interval could not reliably predict gas distribution (rho=0.719, p<0.0001). We found that a large amount of putrefaction-generated gas in the right heart was associated with aggregated gas bubbles in the hepatic parenchyma (sensitivity = 100%, specificity = 89.7%). In contrast, gas in the left heart (sensitivity = 41.7%, specificity = 100%) or in peri-umbilical subcutaneous tissues (sensitivity = 50%, specificity = 96.3%) could not predict gas due to putrefaction.¦Conclusion: This study is the first to show that the appearance of post-mortem gas follows a specific distribution pattern. An association between intracardiac gas and hepatic parenchymal gas could distinguish between post- mortem-generated gas and vital air embolism. We propose that this finding provides a key for diagnosing death due to cardiac air embolism.

Motores de reacción modernos por turbinas de gas

This Bachelor’s thesis investigates the different types of jet engines used nowadays, their performance and applications. The thesis includes a general study of dynamics of fly, engine thermodynamics and contamination.

The application of gas liquid chromatography to the simultaneous analysis of sugars and sugar phosphates in biological samples /|nby David J. LeBlanc. -- 260 St. Catharines [Ont. : s. n.],

A study was undertaken' to determine the applicability of gas liquid chromatography to the simultaneous analysis of sugars and sugar phosphates from biological samples. A new method of silylation involving dimethylsulfoxide, hexamethyldisilazane, trimethylchlorosilane and cyclohexane (1:0.2:0.1:1) which rapidly silylated sugars and sugar phosphates was developed. Subsequent chromatography on a 5% SE-52 column gave good resolution of the sugar and sugar phosphate samples. Sugar phosphates decomposed during chromatography and were lost at the 7 x 10-3 ~mole level. Acidic ethanol extraction of yeast samples revealed background contamination from the yeast sample, the culture medium and the silylation reagents which would further limit the level of detection obtainable with the glc for sugars in biological samples to the 3 x 10-4 ~mole level.

The use of gaseous ozone and gas packaging to control populations of Salmonella infantis and Pseudomonas aeruginosa on the skin of chicken portions

Chilled breasts of chicken were inoculated with Salmonella infantis or Pseudomonas aeruginosa and then given one of the following treatments: (i) exposure to gaseous ozone (>2000 ppm for up to 30 min); (ii) storage under 70% CO2:30% N-2; and (iii) exposure to gaseous ozone (>2000 ppm for 15 min) followed by storage under 70% CO2:30% N-2; all storage at 7degreesC. Gaseous ozone reduced the counts of samnonellae by 97(Y,, and pseudomonads by 95%, but indigenous coliforms were unaffected. Under the modified atmosphere, the cell count of S. infantis was reduced by 72% following initial exposure and then stabilised, coliforms grew, but Ps. aeruginosa behaved like S. infantis-initial reduction (58%) followed by stability. Exposure to gaseous ozone followed by gas packaging allowed survival of S. infantis, Ps. aeruginosa and coliforms over 9 days at 7degreesC, but there was no evidence of any sensory deterioration. It is proposed that the latter treatment could, in a modified form perhaps, be used to reduce the contamination of chicken carcasses with salmonellae and improve their shelf-life. (C) 2004 Elsevier Ltd. All rights reserved.

Accurate analysis of noble gas concentrations in small water samples and its application to fluid inclusions in stalagmites

The concentrations of dissolved noble gases in water are widely used as a climate proxy to determine noble gas temperatures (NGTs); i.e., the temperature of the water when gas exchange last occurred. In this paper we make a step forward to apply this principle to fluid inclusions in stalagmites in order to reconstruct the cave temperature prevailing at the time when the inclusion was formed. We present an analytical protocol that allows us accurately to determine noble gas concentrations and isotope ratios in stalagmites, and which includes a precise manometrical determination of the mass of water liberated from fluid inclusions. Most important for NGT determination is to reduce the amount of noble gases liberated from air inclusions, as they mask the temperature-dependent noble gas signal from the water inclusions. We demonstrate that offline pre-crushing in air to subsequently extract noble gases and water from the samples by heating is appropriate to separate gases released from air and water inclusions. Although a large fraction of recent samples analysed by this technique yields NGTs close to present-day cave temperatures, the interpretation of measured noble gas concentrations in terms of NGTs is not yet feasible using the available least squares fitting models. This is because the noble gas concentrations in stalagmites are not only composed of the two components air and air saturated water (ASW), which these models are able to account for. The observed enrichments in heavy noble gases are interpreted as being due to adsorption during sample preparation in air, whereas the excess in He and Ne is interpreted as an additional noble gas component that is bound in voids in the crystallographic structure of the calcite crystals. As a consequence of our study's findings, NGTs will have to be determined in the future using the concentrations of Ar, Kr and Xe only. This needs to be achieved by further optimizing the sample preparation to minimize atmospheric contamination and to further reduce the amount of noble gases released from air inclusions.