15,704 research outputs found
What gross weight and range for an advanced HSCT?
A review of studies conducted in 1986 indicates that a 300 passenger, 5500 nautical mile range aircraft should weigh less than 400,000 pounds. Some data from a British Aerospace Society of Automotive Engineers (SAE) paper will be shown that purport to be an advanced Concorde that meets the range payload specifications at a gross weight of 360,000 pounds. Previous studies by Peter Coen of Langley Research Center support these results. The weight of a supersonic transport is important from the point of view of how much effort should be expended in developing lower sonic boom technologies. It is obvious that a 360,000 pound aircraft can be modified to a more acceptable boom level than a 700,000 pound one
The Evolution of Ellipticals, Spirals and Irregulars: Overcoming Selection Bias
The Hubble Deep Fields represent our best opportunity for probing galaxy
evolution over a substantive look-back time. However as with any dataset the
HDFs are prone to selection biases. These biases are extremely severe beyond z
\~1.25 such that a meaningful interpretation of generic galaxy evolution is not
possible. We can however extract well defined volume-limited samples at z < 1.
The data are entirely consistent with passive/null-evolution for ellipticals,
spirals and irregulars however this concluion is tempered by small number
statistics. Alas stringent constraints on galaxy evolution await an order of
magnitude increase in the number of HDFs.Comment: To appear in Proc. of the ESO/ECF/STSCI workshop on Deep Fields,
Garching Oct 2000, (Publ: Springer
Riemann-Hilbert analysis for Jacobi polynomials orthogonal on a single contour
Classical Jacobi polynomials , with , have a number of well-known properties, in particular the location
of their zeros in the open interval . This property is no longer valid
for other values of the parameters; in general, zeros are complex. In this
paper we study the strong asymptotics of Jacobi polynomials where the real
parameters depend on in such a way that with . We
restrict our attention to the case where the limits are not both positive
and take values outside of the triangle bounded by the straight lines A=0, B=0
and . As a corollary, we show that in the limit the zeros distribute
along certain curves that constitute trajectories of a quadratic differential.
The non-hermitian orthogonality relations for Jacobi polynomials with varying
parameters lie in the core of our approach; in the cases we consider, these
relations hold on a single contour of the complex plane. The asymptotic
analysis is performed using the Deift-Zhou steepest descent method based on the
Riemann-Hilbert reformulation of Jacobi polynomials.Comment: 37 pages, 10 figure
The decade of galaxy formation: pitfalls in the path ahead
At the turn of the decade we arguably move from the era of precision
cosmology to the era of galaxy formation. One approach to this problem will be
via the construction of comprehensive galaxy samples. In this review I take the
opportunity to highlight a number of challenges which must be overcome before
we can use such data to construct a robust empirical blueprint of galaxy
evolution. The issues briefly highlighted here are: the Hubble tuning fork
versus galaxy components, the hierarchy of structure, the accuracy of
structural decompositions, galaxy photometry, incompleteness, cosmic variance,
photometric versus spectroscopic redshifts, wavelength bias, dust attenuation,
and the disconnect with theory. These concerns essentially form one of the key
motivations of the GAMA survey which, as one of its goals, will establish a
complete comprehensive kpc-resolution 3D multi-wavelength (UV-Opt-IR-Radio)
database of 250k galaxy systems to z <0.5.Comment: Review paper (12 pages, 11 figures) in "Hunting for the Dark: The
Hidden Side of Galaxy Formation", Malta, 19-23 Oct. 2009, eds. V.P.Debattista
& C.C.Popescu, AIP Conf. Ser., in pres
Understanding Equitable Assessment: How Preservice Teachers Make Meaning of DisAbility
Disproportionality of historically marginalized populations in special education continues to be a critical concern. The identification of students with disabilities is reliant on valid and reliable assessment that is free of bias. The extent to which this is possible given measurement constraints and an increasingly diverse student population is unclear. How teachers are trained to design, select, administer, score, and interpret assessment data related to the identification of students with disabilities is vastly under-researched considering the significant implications of assessment practices. In this study, six special education preservice teachers engaged in an assessment methods course during their second semester of an initial certification program. This study focuses on shifts in preservice teacher understanding and the associated learning experiences in the course. Findings from this study have the potential to inform general and special education teacher preparation coursework
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