Aerodynamic performance of a bypass engine with fan nozzle exit area change by warped chevrons

Variation of the bypass nozzle exit area enables optimization of the turbofan engine operating cycle over a wider range of operational conditions resulting in improved thrust and/or fuel consumption. Two mechanisms for varying the nozzle area have been investigated. The first uses an array of chevrons which when closed, form a full body of revolution and when warped/curved, increase the exit area while forming a serrated trailing edge. The second technique incorporates an axially translating section of the nacelle shroud and uses the change in the nozzle boat-tail radial location with the axial location as a means to vary the nozzle exit area. To analyse the effects on a typical rotor/stator stage, computational fluid dynamics simulations of the NASA Rotor 67, Stator 67A stage integrated into a custom-built nacelle were performed. Nozzles with 8, 12, and 16 chevrons were simulated to evaluate the impact of the variation in geometry upon the nacelle wake and local forces. Gross thrust of the nacelle and the turbulent kinetic energy (TKE) variation through the wake is compared. The chevron nozzle attains a nearly 2 per cent maximum thrust improvement over the translating nozzle technique. The chevron nozzle also has significantly lower (nearly 8 per cent) peak TKE levels in the jet plume.

Three-dimensional electron number densities in a titanium PLD plasma using interferometry

Interferometry has been used to investigate the spatio-temporal evolution of the electron number density in the initial stages of expansion following 248 nm ablation of a titanium target. Three-dimensional electron number densities are obtained from an interferogram of the plasma plume using the Abel inversion technique.

IR laser desorption of oligonucleotides A novel gas phase target for radiation damage studies

The desorption of oligonucleotides by 3 mu m laser irradiation has been studied by laser induced fluorescence imaging of the resulting gas phase plumes. Fitting of the plume data has been achieved by using a modified Maxwell Boltzmann distribution which incorporates a range of stream velocities. Spatial density profiles, velocities and temperature variation have been determined from these fits indicating that the oligonucleotide plume only achieves a partial thermal relaxation. This laser desorption technique may provide a means of overcoming the limited mass range of gas phase biomolecules available from thermal evaporation techniques.

Two-dimensional imaging of low temperature laser produced plasmas

Laser induced fluorescence images of a low temperature laser-produced plasma expanding into vacuum are presented and compared to a computer simulation. The complex nature of a plume expanding into background gas is highlighted, along with a potential means of simplifying the study of such systems.

A technique for mapping three-dimensional number densities of species in laser produced plumes

The potential of a diagnostic technique to provide quantitative three-dimensional (3D) density distributions of species in a low temperature laser-produced plume is shown. An expanded, short pulse, tunable dye laser is used to probe the plume at a set time during the expansion. Simultaneous recording of two-dimensional in-line absorbance maps and orthogonal recording of laser induced fluorescence permits the 3D density mapping by scanning the dye laser frequency. Preliminary data, supported by a simple model, is presented for the case of Ba II ions in a YBCO plume heated by a KrF laser. (C) 1996 American Institute of Physics.

THE ROLE OF GAS-PHASE OXIDATION AND COMBINATION DURING LASER DEPOSITION OF YBA2CU3O7-X IN AMBIENT OXYGEN

Spectroscopic absorption and emission measurements have been used to study laser deposition of YBCO films. They show that >95% of the monatomic Y and Ba initially ablated from the target undergo gas-phase chemical combination before film deposition. In contrast, considerable monatomic Cu persists into the deposition region. in this region, equilibrated gas temperatures are of the order of 2700 K. It is suggested that this high temperature facilitates film crystallization and epitaxial growth. The survival of monatomic Cu in the plume to the site of deposition is a manifestation of its endothermic reaction with O-2.

YBACUO PRBACUO MULTILAYERS BY EXCIMER LASER ABLATION

YBaCuO films with (001) orientation have been deposited on MgO by laser ablation at 248 and 193 nm wavelengths. Transitions to zero resistance at 87 K and 90 K have been reproducibly achieved in the respective cases. Optical spectroscopic studies of the plume show the importance of molecular species in the ablation if good superconducting films are to be formed. The substrate position in the plume and substrate temperature are important in determining film quality. The influence of oxygen gas pressure can be significant. SEM studies show the occurrence of second-phase outcrops with a needle-like morphology aligned over the whole area of the film along two mutually perpendicular directions on the film surface. Film orientation is determined by XRD and R against T is measured down to 80 K in a hydrogen exchange gas cryostat. Characterization studies of device-related multilayer YBaCuO/PrBaCuO structures by XRD are presented.

OPTICAL-ABSORPTION SPECTROSCOPY STUDY OF THE ROLE OF PLASMA CHEMISTRY IN YBA2CU3O7 PULSED LASER DEPOSITION

Time-resolved optical absorption spectroscopy techniques were used to study Ba, metastable Ba+, and YO absorptions in the laser-produced plasma plume from a YBa2Cu3O7 target. Results obtained indicate an initial explosive removal of material from the target sur-face followed by a subsequent evaporation process. Some YO is ejected from the target in molecular form, particularly at laser fluence

SUPERCONDUCTING YBA2CU3O7 THIN-FILMS ON MGO BY KRF LASER ABLATION - OPTIMIZATION OF DEPOSITION PARAMETERS

The optimization of interrelated deposition parameters during deposition of in situ YBa2Cu3O7 thin films on MgO substrates by KrF laser ablation was systematically studied in a single experimental chamber. The optimum condition was found to be a substrate temperature of 720-degrees-C and a target-substrate distance of 5 cm in an oxygen partial pressure of 100 mTorr. These conditions produced films with T(c) = 87 K. The presence of YO in the plasma plume was found to be important in producing good quality films. The films were characterized by resistance-temperature measurements, energy dispersive x-ray analyses, scanning electron microscopy, and x-ray-diffraction measurements, and the physical reasons underlying film quality degradation at parameter values away from optimal are discussed.

Polycyclic aromatic hydrocarbon (PAH) dispersion and deposition to vegetation and soil following a large scale chemical fire

Polycyclic aromatic hydrocarbons (PAHs) were determined in soil and vegetation following a large scale chemical fire involving 10,000 ton of polypropylene. In comparison with sites outside the plume from the fire, PAH concentrations were elevated in grass shoots (by up to 70-fold) and in soil (by up to 370-fold). The pattern of PAH dispersion under the plume was dependent on the physical-chemical properties of individual PAHs. The lighter, least hydrophobic PAHs were dispersed into the environment at greater distances than heavier, more hydrophobic PAHs. At the most distant sampling point (4.5 km) under the plume, the low molecular weight PAHs were still considerably elevated in vegetation samples compared to control sites. Dispersion appeared to be regulated by the compounds partitioning between the vapour and particulate phase, with dry particulate deposition occurring closer to the fire source than gaseous deposition. For all PAHs, the fire resulted in greater contamination of soils compared to grasses, with the relative ratio of plant/soil contamination decreasing as hydrophobicity increased.

Investigation of magnesium laser ablated plumes with Thomson scattering

Optical Thomson scattering has been implemented as a diagnostic of laser ablated plumes generated with second harmonic Nd:YAG laser radiation at 532 nm. Thomson scattering data with both spatial and temporal resolution has been collected, giving both electron density, and temperature distributions within the plume as a function of time. Although the spatial profiles do not match very well for simple models assuming either isothermal or isentropic expansion, consideration of the measured ablated mass indicates an isothermal expansion fits better than an isentropic expansion and indeed, at late time, the spatial profile of temperature is almost consistent with an isothermal approximation.

Le survivant de la Shoah face au texte de fiction: un écran protecteur ou un écran projecteur? L’exemple d’Anna Langfus

La terminologie ‘écriture écran’ est souvent utilisée dans un sens proche de celui que lui donne Annie Ernaux lorsqu’elle écrit que ‘la fiction protège’ en permettant à un auteur de dire tout en gardant le lecteur à distance. Pourtant, de Blanchot à Genette, de nombreux critiques ont souligné que le texte est par essence un espace qui n’existe que dans et par cet échange, le lecteur – surtout dans le cas des textes de fiction – devant s’investir, se projeter dans le texte lu. Le texte de fiction serait-il donc un écran protecteur pour celui qui tient la plume et un écran projecteur pour celui qui tient le livre ? En nous basant principalement sur des textes de la psychanalyste Rachel Rosenblum et de l’auteure et survivante de la Shoah Anna Langfus, nous suggèrerons que, pour l’auteur comme pour le lecteur, le texte de fiction est à la fois un écran protecteur et un écran projecteur, ces deux fonctions étant étroitement liées et nullement contradictoires. Nous montrerons en effet qu’aucun genre n’est a priori protecteur puisque c’est l’acte de lecture ou d’écriture qui peut se transformer en morbide compulsion de répétition quand la mémoire d’un lecteur ou d’un auteur est devenue pathologique.

Contemporary environmental issues of landfill leachate: assessment & remedies

Landfills are the primary option for waste disposal all over the world. Most of the landfill sites across the world are old and are not engineered to prevent contamination of the underlying soil and groundwater by the toxic leachate. The pollutants from landfill leachate have accumulative and detrimental effect on the ecology and food chains leading to carcinogenic effects, acute toxicity and genotoxicity among human beings. Management of this highly toxic leachate presents a challenging problem to the regulatory authorities who have set specific regulations regarding maximum limits of contaminants in treated leachate prior to disposal into the environment to ensure minimal environmental impact. There are different stages of leachate management such as monitoring of its formation and flow into the environment, identification of hazards associated with it and its treatment prior to disposal into the environment. This review focuses on: (i) leachate composition, (ii) Plume migration, (iii) Contaminant fate, (iv) Leachate plume monitoring techniques, (v) Risk assessment techniques, Hazard rating methods, mathematical modeling, and (vi) Recent innovations in leachate treatment technologies. However, due to seasonal fluctuations in leachate composition, flow rate and leachate volume, the management approaches cannot be stereotyped. Every scenario is unique and the strategy will vary accordingly. This paper lays out the choices for making an educated guess leading to the best management option.

Geophysical and hydrogeological characterisation of the impacts of on-site wastewater treatment discharge to groundwater in a poorly productive bedrock acquifer

Contaminants discharging from on-site wastewater treatment systems (OSWTSs) can impact groundwater quality, threatening human health and surface water ecosystems. Risk of negative impacts becomes elevated in areas of extreme vulnerability with high water tables, where thin unsaturated intervals limit vadose zone attenuation. A combined geophysical/hydrogeological investigation into the effects of an OSWTS, located over a poorly productive aquifer (PPA) with thin subsoil cover, aimed to characterise effluent impacts on groundwater. Groundwater, sampled from piezometers down-gradient of the OSWTS percolation area displayed spatially erratic, yet temporally consistent, contaminant distributions. Electrical resistivity tomography identified an area of gross groundwater contamination close to the percolation area and, when combined with seismic refraction and water quality data, indicated that infiltrating effluent reaching the water table discharged to a deeper more permeable zone of weathered shale resting on more competent bedrock. Subsurface structure, defined by geophysics, indicated that elevated chemical and microbiological contaminant levels encountered in groundwater samples collected from piezometers, down-gradient of sampling points with lower contaminant levels, corresponded to those locations where piezometers were screened close to the weathered shale/competent rock interface; those immediately up-gradient were too shallow to intercept this interval, and thus the more impacted zone of the contaminant plume. Intermittent occurrence of faecal indicator bacteria more than 100 m down gradient of the percolation area suggested relatively short travel times. Study findings highlight the utility of geophysics as part of multidisciplinary investigations for OSWTS contaminant plume characterisation, while also demonstrating the capacity of effluent discharging to PPAs to impact groundwater quality at distance. Comparable geophysical responses observed in similar settings across Ireland suggest the phenomena observed in this study are more widespread than previously suspected.

Numerical modelling of low temperature laser produced magnesium plasma

The two-dimensional laser-plasma-interaction hydrodynamic code POLLUX has been used to simulate the ablation of a magnesium target by a 30-ns, 248-nm KrF excimer laser at low laser fluences of ≤10 J cm2. This code, originally written for much higher laser intensities, has been recently extended to include a detailed description of the equation of state in order to treat changes of phase within the target material, and also includes a Thomas Fermi description of the electrons. The simulated temporal and spatial evolution of the plasma plume in the early phase of the expansion (≤100 ns) is compared with experimental interferometric measurements of electron density. The expansion dynamics are in good agreement, although the simulated electron number density is about 2.5 times higher than the experimental values.