23,665 research outputs found
Technological change and productivity growth in the air transport industry
The progress of the civil air transport industry in the United States was examined in the light of a proposal of Enos who, after examining the growth of the petroleum industry, divided that phenomenon into two phases, the alpha and the beta; that is, the invention, first development and production, and the improvement phase. The civil air transport industry developed along similar lines with the technological progress coming in waves; each wave encompassing several new technological advances while retaining the best of the old ones. At the same time the productivity of the transport aircraft as expressed by the product of the aircraft velocity and the passenger capacity increased sufficiently to allow the direct operating cost in cents per passenger mile to continually decrease with each successive aircraft development
A paradigmatic flow for small-scale magnetohydrodynamics: properties of the ideal case and the collision of current sheets
We propose two sets of initial conditions for magnetohydrodynamics (MHD) in
which both the velocity and the magnetic fields have spatial symmetries that
are preserved by the dynamical equations as the system evolves. When
implemented numerically they allow for substantial savings in CPU time and
memory storage requirements for a given resolved scale separation. Basic
properties of these Taylor-Green flows generalized to MHD are given, and the
ideal non-dissipative case is studied up to the equivalent of 2048^3 grid
points for one of these flows. The temporal evolution of the logarithmic
decrements, delta, of the energy spectrum remains exponential at the highest
spatial resolution considered, for which an acceleration is observed briefly
before the grid resolution is reached. Up to the end of the exponential decay
of delta, the behavior is consistent with a regular flow with no appearance of
a singularity. The subsequent short acceleration in the formation of small
magnetic scales can be associated with a near collision of two current sheets
driven together by magnetic pressure. It leads to strong gradients with a fast
rotation of the direction of the magnetic field, a feature also observed in the
solar wind.Comment: 8 pages, 4 figure
Research on processes for utilization of lunar resources quarterly report, 16 jul. - 15 oct. 1964
Lunar resource utilization - silicate reduction unit and carbon monoxide reduction reacto
Investigation of the fiber reinforcement of a cobalt base alloy for application at elevated temperature
Technique developed for incorporating alumina and silicon carbide fibers in cobalt base alloy for application at high temperature
The Arecibo Dual-Beam Survey: Arecibo and VLA Observations
The Arecibo Dual-Beam Survey is a "blind" 21 cm search for galaxies covering
\~430 deg^2 of sky. We present the data from the detection survey as well as
from the follow-up observations to confirm detections and improve positions and
flux measurements. We find 265 galaxies, many of which are extremely low
surface brightness. Some of these previously uncataloged galaxies lie within
the zone of avoidance where they are obscured by the gas and dust in our
Galaxy. 81 of these sources are not previously cataloged optically and there
are 11 galaxies that have no associated optical counterpart or are only
tentatively associated with faint wisps of nebulosity on the Digitized Sky
Survey images. We discuss the properties of the survey and in particular we
make direct determinations of the completeness and reliability of the sample.
The behavior of the completeness and its dependencies is essential for
determining the HI mass function. We leave the discussion of the mass function
for a later paper, but do note that we find many low surface brightness
galaxies and 7 sources with M_HI < 10^8 Msolar.Comment: 23 pages, 20 figures, accepted ApJS. For tables 2 and 3 only the
first page has been included. ASCII tables are provided separatel
Finite energy shifts in SU(n) supersymmetric Yang-Mills theory on T^3xR at weak coupling
We consider a semi-classical treatment, in the regime of weak gauge coupling,
of supersymmetric Yang-Mills theory in a space-time of the form T^3xR with
SU(n)/Z_n gauge group and a non-trivial gauge bundle. More specifically, we
consider the theories obtained as power series expansions around a certain
class of normalizable vacua of the classical theory, corresponding to isolated
points in the moduli space of flat connections, and the perturbative
corrections to the free energy eigenstates and eigenvalues in the weakly
interacting theory. The perturbation theory construction of the interacting
Hilbert space is complicated by the divergence of the norm of the interacting
states. Consequently, the free and interacting Hilbert furnish unitarily
inequivalent representation of the algebra of creation and annihilation
operators of the quantum theory. We discuss a consistent redefinition of the
Hilbert space norm to obtain the interacting Hilbert space and the properties
of the interacting representation. In particular, we consider the lowest
non-vanishing corrections to the free energy spectrum and discuss the crucial
importance of supersymmetry for these corrections to be finite.Comment: 31 pages, 1 figure, v4 Minor changes, references correcte
Unravelling the Mysteries of the Leo Ring: An Absorption Line Study of an Unusual Gas Cloud
Since the 1980's discovery of the large (2x10^9 Msun) intergalactic cloud
known as the Leo Ring, this object has been the center of a lively debate about
its origin. Determining the origin of this object is still important as we
develop a deeper understanding of the accretion and feedback processes that
shape galaxy evolution. We present HST/COS observations of three sightlines
near the Ring, two of which penetrate the high column density neutral hydrogen
gas visible in 21 cm observations of the object. These observations provide the
first direct measurement of the metallicity of the gas in the Ring, an
important clue to its origins. Our best estimate of the metallicity of the ring
is ~10% Zsun, higher than expected for primordial gas but lower than expected
from an interaction. We discuss possible modifications to the interaction and
primordial gas scenarios that would be consistent with this metallicity
measurement.Comment: 11 pages, 7 figures, accepted Ap
Beta lives - some statistical perspectives on the capital asset pricing model
This note summarizes some technical issues relevant to the use of the idea of excess return in empirical modelling. We cover the case where the aim is to construct a measure of expected return on an asset and a model of the CAPM type is used. We review some of the problems and show examples where the basic CAPM may be used to develop other results which relate the expected returns on assets both to the expected return on the market and other factors
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