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 water vapour visualization in porous packing by near-infrared diffuse transmittance tomography

Near-infrared diffuse tomography was used in order to observe dynamic behaviour of flowing gases by measuring the 3D distributions of composition and temperature in a weakly scattering packed bed reactor, subject to wall effects and non-isothermal conditions. The technique was applied to the vapour phase hydrogen isotopic exchange reaction in a hydrophobic packing of low aspect ratio made of platinum on styrene divinyl benzene sulphonate copolymer resin. The results of tomography revealed uneven temperature and composition maps of water and deuterated water vapours in the core-packed bed and in the vicinity of the wall owing to flow maldistribution. The dynamic lag between the near-wall water vapour and deuterated water vapour compositions were observed suggesting that the convective transfer which was significant near the wall at the start, owing to high porosity, was also effective at large conversions.

Stellar jitter from variable gravitational redshift: implications for radial velocity confirmation of habitable exoplanets

A variation of gravitational redshift, arising from stellar radius fluctuations, will introduce astrophysical noise into radial velocity measurements by shifting the centroid of the observed spectral lines. Shifting the centroid does not necessarily introduce line asymmetries. This is fundamentally different from other types of stellar jitter so far identified, which do result from line asymmetries. Furthermore, only a very small change in stellar radius, ˜0.01 per cent, is necessary to generate a gravitational redshift variation large enough to mask or mimic an Earth-twin. We explore possible mechanisms for stellar radius fluctuations in low-mass stars. Convective inhibition due to varying magnetic field strengths and the Wilson depression of starspots are both found to induce substantial gravitational redshift variations. Finally, we investigate a possible method for monitoring/correcting this newly identified potential source of jitter and comment on its impact for future exoplanet searches.

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.

The blue supergiant Sher 25 and its intriguing hourglass nebula

The blue supergiant Sher 25 is surrounded by an asymmetric, hourglass-shaped circumsteller nebula. Its structure and dynamics have been studied previously through high-resolution imaging and spectroscopy, and it appears dynamically similar to the ring structure around SN 1987A. Here, we present long-slit spectroscopy of the circumstellar nebula around Sher 25, and of the background nebula of the host cluster NGC 3603. We perform a detailed nebular abundance analysis to measure the gas-phase abundances of oxygen, nitrogen, sulphur, neon and argon. The oxygen abundance in the circumstellar nebula (12 + log O/H = 8.61 +/- 0.13 dex) is similar to that in the background nebula (8.56 +/- 0.07), suggesting that the composition of the host cluster is around solar. However, we confirm that the circumsteller nebula is very rich in nitrogen, with an abundance of 8.91 +/- 0.15, compared to the background value of 7.47 +/- 0.18. A new analysis of the stellar spectrum With the FASTWIND model atmosphere code suggests that the photospheric nitrogen and oxygen abundances in Sher 25 are consistent with the nebular results. While the nitrogen abundances are high, when compared to stellar evolutionary models, they do not unambiguously confirm that the star has undergone convective dredge-up during a previous red supergiant phase. We suggest that the more likely scenario is that the nebula was ejected from the star while it was in the blue supergiant phase. The star's initial mass was around 50 M-circle dot which is rather too high for it to have had a convective envelope stage as a red supergiant. Rotating stellar models that lead to mixing of core-processed material to the stellar surface during core H-burning can quantitatively match the stellar results with the nebula abundances.

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.

Influence of Different European Cements (CEM) on the Hydration of Cover-Zone Concrete during the Curing and Post Curing Periods

The durability of reinforced concrete structures depends, in the main, on the performance of the cover-zone concrete as it is this which protects the steel from the external environment. This paper focusses on the use of discretised electrical property measurements to study depth-related features during both the curing and post-curing period thereby allowing an integrated assessment of the protective properties of the cover region. In the current work, use is made of a small, multi-electrode array embedded within the surface 75mm of concrete specimens. Concretes were manufactured with different European cements (CEM) and water/binder ratios representing mixes which satisfied the minimum requirements for a range of environmental exposure classes including exposure to chlorides. Electrical resistance measurements were taken over a period in excess of 300 days which showed on-going hydration, pozzolanic reaction and pore-structure refinement; in addition, in the post-curing period, when exposed to a cyclic chloride ponding regime, measurements could be used to study the convective zone and ionic enrichment of the surface layer.

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.

Stellar Surface Magneto-Convection as a Source of Astrophysical Noise. I. Multi-component Parameterisation of Absorption Line Profiles

We outline our techniques to characterise photospheric granulation as an astrophysical noise source. A four component parameterisation of granulation is developed that can be used to reconstruct stellar line asymmetries and radial velocity shifts due to photospheric convective motions. The four components are made up of absorption line profiles calculated for granules, magnetic intergranular lanes, non-magnetic intergranular lanes, and magnetic bright points at disc centre. These components are constructed by averaging Fe I $6302 \mathrm{\AA}$ magnetically sensitive absorption line profiles output from detailed radiative transport calculations of the solar photosphere. Each of the four categories adopted are based on magnetic field and continuum intensity limits determined from examining three-dimensional magnetohydrodynamic simulations with an average magnetic flux of $200 \mathrm{G}$. Using these four component line profiles we accurately reconstruct granulation profiles, produced from modelling 12 x 12 Mm$^2$ areas on the solar surface, to within $\sim \pm$ 20 cm s$^{-1}$ on a $\sim$ 100 m s$^{-1}$ granulation signal. We have also successfully reconstructed granulation profiles from a $50 \mathrm{G}$ simulation using the parameterised line profiles from the $200 \mathrm{G}$ average magnetic field simulation. This test demonstrates applicability of the characterisation to a range of magnetic stellar activity levels.