7,944 research outputs found
Bias and uncertainty in the absorption emission measurement of atomic sodium density in the SSME exit plane
The measurement of atomic sodium concentration in the TTB 019 firing of April 1990 is significant in that it represents the first measurement of density at the exit plane of the space shuttle main engine. The knowledge of the sodium density, combined with the certainty that the exit plane of the plume is optically thin at the sodium D-line wavelengths, provides essential information for evaluation of diagnostic techniques using sodium atoms, such as resonant Doppler velocimetry for temperature, pressure, and velocity through high resolution fluorescent lineshape analysis. The technique used for the sodium atom line transmission (SALT) measurements is that of resonant absorption emission using a hollow cathode lamp as the reference source. Through the use of two-dimensional kinetic (TDK) predictions of temperature and density for the flight engine case and radiative transfer calculations, this line-of-sight spectrally integrated transmission indicates a sodium atom concentration, i.e., mole fraction, of 0.91e-10. The subject of this paper is the assumptions and measurement uncertainties tied into the calculation. Because of the narrow shape of the source emission, the uncertainties in the absorption profile could introduce considerable bias in the measurement. The following were investigated: (1) the inclusion of hyperfine splitting of the D-lines in the calculation; (2) the use of the flight engine predictions of plume temperature and density versus those for the large throat engine; (3) the assumption of a Gaussian, i.e., Doppler, distribution for the source radiance with a temperature of 400 K; (4) the use of atomic collisional shift and width values for the work by Jongerius; and (5) a Doppler shift for a 7 degree outward velocity vector at the plume edge. Also included in the study was the bias introduced by an uncertainty in the measurement of the D1/D2 line ratio in the source
Tissue culture studies of human lymphocyte transformation and DNA synthesis utilizing tritiated deoxycytidine as specific DNA precursor
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'We're not like that': Crusader and Maverick Occupational Identity Resistance
This article explores the occupational identities of hairdressers and vehicle mechanics working in small and micro-firms. Using qualitative interview data from two UK cities, it examines the ways that workers expounded, reflected on and discursively reframed public perceptions of their occupation. A novel distinction between two types of identity reframing is proposed. âCrusadersâ are workers who reject characterisations as inappropriate for the occupation at large, whereas âmavericksâ accept that popular characterisations apply to other workers but differentiate themselves. The analysis identifies differences in occupational identity resistance strategies (crusader or maverick) when workers interact with two different publics: customers and trainees
Some recent results in aerospace vehicle trajectory optimization techniques
Algorithms and computation techniques for solving trajectory optimization problem
Educational Entrepreneurship: A New Challenge to Fiscal Equity?
The search for equity in public elementary and secondary education funding in the United States continues into the twenty-first century
New Regulators for Quantum Field Theories with Compactified Extra Dimensions. I: Fundamentals
In this paper, we propose two new regulators for quantum field theories in
spacetimes with compactified extra dimensions. We refer to these regulators as
the ``extended hard cutoff'' (EHC) and ``extended dimensional regularization''
(EDR). Although based on traditional four-dimensional regulators, the key new
feature of these higher-dimensional regulators is that they are specifically
designed to handle mixed spacetimes in which some dimensions are infinitely
large and others are compactified. Moreover, unlike most other regulators which
have been used in the extra-dimension literature, these regulators are designed
to respect the original higher-dimensional Lorentz and gauge symmetries that
exist prior to compactification, and not merely the four-dimensional symmetries
which remain afterward. This distinction is particularly relevant for
calculations of the physics of the excited Kaluza-Klein modes themselves, and
not merely their radiative effects on zero modes. By respecting the full
higher-dimensional symmetries, our regulators avoid the introduction of
spurious terms which would not have been easy to disentangle from the physical
effects of compactification. As part of our work, we also derive a number of
ancillary results. For example, we demonstrate that in a gauge-invariant
theory, analogues of the Ward-Takahashi identity hold not only for the usual
zero-mode (four-dimensional) photons, but for all excited Kaluza-Klein photons
as well.Comment: 47 pages, LaTeX, 3 figure
Holidaying with the family pet: No dogs allowed!
This paper assesses the extent to which dog owners located in Brisbane, Australia, wish to holiday with their pets, and whether there is a gap between this desire and reality. The paper also examines the extent to which this demand is being catered for by the tourism accommodation sector. The need for this study reflects the increasingly significant role dogs are playing in the lives of humans, and the scale
of the dog-owning population. The results suggest that, although there is a strong desire among dog owners to take holidays with their pets, the actualisation of this
desire is comparatively low. A significant obstacle to the realisation of this desire appears to be a dearth of pet-friendly accommodation. This has implications for the
ability of the tourism industry to benefit from this potentially lucrative market, that is, the dog-owning population
Design considerations for CELT adaptive optics
California Institute of Technology and University of California have begun conceptual design studies for a new telescope for astronomical research at visible and infrared wavelengths. The California Extremely Large Telescope (CELT) is currently envisioned as a filled-aperture, steerable, segmented telescope of approximately 30 m diameter. The key to satisfying many of the science goals of this observatory is the availability of diffraction-limited wavefront control. We describe potential observing modes of CELT, including a discussion of the several major outstanding AO system architectural design issues to be resolved prior to the initiation of the detailed design of the adaptive optics capability
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