9,356 research outputs found

    An investigation of combustion instability in aircraft-engine reheat systems

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    The principal objective of this study was to examine experimentally the effects of upstream temperature, velocity, gutter blockage, tailpipe length, and main and pilot fuel flows, on the form of combustion instability encountered in aircraft reheat systems which is sometimes referred to as 'buzz'. Tests were carried out at atmospheric pressure for upstream temperatures of between 200 and 500°C, and upstream velocities ranging from 140 to 200 ft/sec. Three values of stabilizer blockage were employed, namely 25, 30 and 35%. The tailpipe length was varied between 9 and 45 inches. Auto-correlation techniques were used in the frequency analysis of the buzz waveforms. It was found that a certain minimum tailpipe length is necessary in order to produce buzz which is then strengthened as the tailpipe length is increased. Buzz also becomes more pronounced with an increase in gas velocity but stabilizer blockage appears to have no discernible effect … [cont.]

    Repetition and difference: Lefebvre, Le Corbusier and modernity's (im)moral landscape: a commentary

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    This article engages with the relationship between social theory, architectural theory and material culture. The article is a reply to an article in a previous volume of the journal in question (Smith, M. (2001) ‘Repetition and difference: Lefebvre, Le Corbusier and modernity’s (im)moral landscape’, Ethics, Place and Environment, 4(1), 31-34) and, consequently, is also a direct engagement with another academic's scholarship. It represents a critique of their work as well as a recasting of their ideas, arguing that the matter in question went beyond interpretative issues to a direct critique of another author's scholarship on both Le Corbusier and Lefebvre. A reply to my article from the author of the original article was carried in a later issue of the journal (Smith, M. (2002) ‘Ethical Difference(s): a Response to Maycroft on Le Corbusier and Lefebvre’, Ethics, Place and Environment, 5(3), 260-269)

    Breakup of diminutive Rayleigh jets

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    Discharging a liquid from a nozzle at sufficient large velocity leads to a continuous jet that due to capillary forces breaks up into droplets. Here we investigate the formation of microdroplets from the breakup of micron-sized jets with ultra high-speed imaging. The diminutive size of the jet implies a fast breakup time scale τc=ρr3/γ\tau_\mathrm{c} = \sqrt{\rho r^3 / \gamma} of the order of 100\,ns{}, and requires imaging at 14 million frames per second. We directly compare these experiments with a numerical lubrication approximation model that incorporates inertia, surface tension, and viscosity [Eggers and Dupont, J. Fluid Mech. 262, 205 (1994); Shi, Brenner, and Nagel, Science 265, 219 (1994)]. The lubrication model allows to efficiently explore the parameter space to investigate the effect of jet velocity and liquid viscosity on the formation of satellite droplets. In the phase diagram we identify regions where the formation of satellite droplets is suppressed. We compare the shape of the droplet at pinch-off between the lubrication approximation model and a boundary integral (BI) calculation, showing deviations at the final moment of the pinch-off. Inspite of this discrepancy, the results on pinch-off times and droplet and satellite droplet velocity obtained from the lubrication approximation agree with the high-speed imaging results

    Zero kinetic energy-pulsed field ionization and resonance enhanced multiphoton ionization photoelectron spectroscopy: Ionization dynamics of Rydberg states in HBr

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    The results of rotationally resolved resonance enhanced multiphoton ionization photoelectron spectroscopy and zero kinetic energy‐pulsed field ionization studies on HBr via various rotational levels of the F^ 1Δ_2 and f^ 3Δ_2 Rydberg states are reported. These studies lead to an accurate determination of the lowest ionization threshold as 94 098.9±1 cm^(−1). Observed rotational and spin–orbit branching ratios are compared to the results of ab initio calculations. The differences between theory and experiment highlight the dominant role of rotational and spin–orbit interactions for the dynamic properties of the high‐n Rydberg states involved in the pulsed field ionization process

    Electronic structure and spectroscopy of O2 and O2+

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    We carried out a comprehensive SCF MRD--CI ab initio study of the electronic structure of O2_2 and O2+_2^+. Potential energy curves (PECs) of about 150 electronic states of O2_2 and about 100 of O2+_2^+, as well as a number of states of O2++_2^{++} were computed. The cc--pVQZ basis set augmented with diffuse functions was employed. Spectroscopic parameters (Te,Tv,ωe,ωexe,Be,T_e, T_v, \omega_e, \omega_ex_e, B_e, De,D0D_e, D_0, μ\mu, IP, etc.) are reported. A preliminary sample of the results will be presented. The electronic absorption spectrum of O2_2 has proved difficult to analyze/interpret due to the unusually large number of electronic states which arise from the peculiar open--shell structure of both the oxygen atomic fragments and the O2_2 molecule. For instance, there are 62 valence molecular electronic states which correlate to the six lowest dissociation limits resulting from the three valence O atom fragment states (3^3P, 1^1D, 1^1S). In addition, there are several nlλnl\lambda Rydberg series converging to the X2Πg^2\Pi_g ground ionic state and to the lowest two excited states of the cation, a4Πu^4\Pi_ui_i and A2Πu^2\Pi_u. Furthermore, a number of interactions of various types among several electronic states result in rovibronic perturbations which manifest themselves, e.g., as irregular vibronic structure, hence severely complicating the assignment of the absorption features and the analysis and interpretation of the spectrum. An overview of the electronic states and spectroscopy of O2_2 will be presented. A chief motivation of this study of O2_2 was to try to provide a theoretical insight on the nature, energetic position, shape, and dissociation asymptotes, of electronic states located in the 4 eV energy region encompassed between the O2+_2^+ ground state X2Πg^2\Pi_g (IP=12.07=12.07 eV) and the first excited state of the cation a4Πu^4\Pi_ui_i (IP=16.10=16.10 eV). This in order to aid in the interpretation of experimental data related to the mechanism(s) of the neutral dissociation of the O2_2^{**} (Rydberg) superexcited states, which competes with autoionization. We are currently striving to compute PECs of relatively highly excited states of O2_2 located in the 12--16 eV energy region which might help to visualize possible pathways for the neutral XUV photodissociation of the I, I^{\prime} and I^{\prime\prime} 3Πu^3\Pi_u superexcited states of O2_2 leading to the O(3^3P) + O^{*}(3^3S, 5^5S) dissociation limits.Ope

    Performing Place: A Rhythmanalysis of the City of London

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    Through its focus on the City of London as a particular work sector and setting, this paper emphasizes the symbolic and material significance of place to understanding the lived experiences of power relations within organizational life. The socio-cultural and material aspects of the City are explored through an analysis of the rhythms of place, as well through interview data. Using a methodological approach based on Lefebvre’s Rhythmanalysis in order to develop an embodied, immersive sense of how the City is experienced as a workplace, the paper makes a methodological, empirical and theoretical contribution to an understanding of the way in which rhythms shape how place is performed. Using rhythmanalysis as a method, the paper shows the relationship between rhythms and the performances of place, foregrounding a subjective, embodied and experiential way of researching the places and spaces of organizing

    The Urban Political Ecology of Post-industrial Scottish Towns: Examining Greengairs and Ravenscraig

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    Urban ecological politics is shaped by both moments of concerted action and more silent perceptions and responses. Instead of only being evident in situations of organised protest, the politics of urban ecology is also manifested, in material and symbolic terms, in the daily life of the residents. The fragmentation of urban political ecology turns out to be an important element in the affirmation of post-political forms of urban governance. Those issues were the object of fieldwork research carried out in Greengairs and Ravenscraig, two towns in North Lanarkshire, near Glasgow, with the goal of unravelling the understanding and the coping mechanisms of environmentally deprived residents. The towns are permeated by a widespread, often dissimulated, political ecology that is nonetheless always present. Empirical results demonstrate that a more comprehensive handling of the political ecology of the urban is crucial in order to halt the sources of marginalisation and ecological degradation

    Observation of Feshbach resonances in an ultracold gas of 52{}^{52}Cr

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    We have observed Feshbach resonances in elastic collisions between ultracold 52{}^{52}Cr atoms. This is the first observation of collisional Feshbach resonances in an atomic species with more than one valence electron. The zero nuclear spin of 52{}^{52}Cr and thus the absence of a Fermi-contact interaction leads to regularly-spaced resonance sequences. By comparing resonance positions with multi-channel scattering calculations we determine the s-wave scattering length of the lowest 2S+1Σg+^{2S+1}\Sigma_{g}^{+} potentials to be \unit[112(14)]{a_0}, \unit[58(6)]{a_0} and -\unit[7(20)]{a_0} for S=6, 4, and 2, respectively, where a_{0}=\unit[0.0529]{nm}.Comment: 4 pages, 2 figures, 1 tabl

    An insight into some innovative cycles for aircraft propulsion

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    Emissions are important drivers in the design and use of aero-engines. This paper presents a part of the work carried out in the VITAL (EnVIronmenTALly aero-engine) project; it consists of a parameter study on the application of three innovative thermodynamic cycles to aircraft propulsion, looking for benefits on fuel consumption, carbon dioxide, nitrogen oxides, and noise. These cycles are intercooler-regenerative, the wave rotor topping, and the constant volume combustor cycles. The work, starting from a next-generation ultra-high bypass ratio turbofan, the baseline, and considering two possible design conditions, presents the influence of the application of these new cycles or design changes to the baseline on emissions and on the required technological level, represented by the turbine entry temperature (TET). VITAL is a project supported by the Sixth Framework Programme of the European Communities. The results showthat some significant benefits on emissions can be achieved although they are linked to significant technology improvements and in-depth studies of the new components involved in cycle implementation