3,496 research outputs found
Effect of flow on the acoustic reflection coefficient at a duct inlet
The effect of duct Mach number upon the acoustic reflection coefficient at the inlet of a duct with mean
flow is investigated. An analysis, which models the duct inlet as a very short, one-dimensional nozzle over
which the mean flow is accelerated from rest, gives good agreement with some recent experimental results.
Discrepancies between the analysis and the experimental results are discussed in terms of radiation losses at
the inlet and real fluid-flow effects within the duct
Simulation and control engineering studies of NASA-Ames 40 foot by 80 foot/80 foot by 120 foot wind tunnels
The development and use of a digital computer simulation of the proposed wind tunnel facility is described. The feasibility of automatic control of wind tunnel airspeed and other parameters was examined. Specifications and implementation recommendations for a computer based automatic control and monitoring system are presented
Unified model of ultracold molecular collisions
A scattering model is developed for ultracold molecular collisions, which
allows inelastic processes, chemical reactions, and complex formation to be
treated in a unified way. All these scattering processes and various
combinations of them are possible in ultracold molecular gases, and as such
this model will allow the rigorous parametrization of experimental results. In
addition we show how, once extracted, these parameters can be related to the
physical properties of the system, shedding light on fundamental aspects of
molecular collision dynamics.Comment: 16 Pages, 5 Figure
Radial and angular rotons in trapped dipolar gases
We study Bose-Einstein condensates with purely dipolar interactions in oblate
(pancake) traps. We find that the condensate always becomes unstable to
collapse when the number of particles is sufficiently large. We analyze the
instability, and find that it is the trapped-gas analogue of the
``roton-maxon'' instability previously reported for a gas that is unconfined in
two dimensions. In addition, we find that under certain circumstances, the
condensate wave function attains a biconcave shape, with its maximum density
away from the center of the gas. These biconcave condensates become unstable
due to azimuthl excitation - an angular roton.Comment: 4 pages, 3 figure
Industrial response to spot electricity prices: some empirical evidence
Time of day prices for electricity are usually preferable to
constant rates, as the true cost of generating energy varies over the
course of a day. But time of day rates are still inefficient,
because prices do not change in step with day by day random fluctuations
in actual generating costs. Spot prices, which change every five minutes,
can avoid this inefficiency by tracking actual marginal cost.
This paper empirically estimates the ability of industrial
customers to respond to rapidly varying prices. The conclusion is
that some customers will be able to react quickly to such prices.
Because the estimates were made from a rate structure which is not
a full spot pricing system, the magnitude of customer response
remains problematic. Also, it appears that the utility in questions
could make a minor change to its rate structure which would help
both it and its customers
Dynamical pattern formation during growth of a dual-species Bose-Einstein condensate
We simulate the growth of a dual species Bose-Einstein condensate using a
Gross-Pitaevskii equation with an additional gain term giving rise to the
growth. Such growth occurs during simultaneous evaporative cooling of a mixture
of two gases. The ground state of a dual condensate is normally either a
miscible mixture, or an immiscible phase with two spatially separated
components. In a cigar trap the ground state typically consists of one
component in the center, and the other component flanking it. Our simulations
show that when the condensates are formed in a cigar trap and the mixture is
phase separated, then the final state upon the end of the growth is generally
far from the true ground state of the system. Instead it consists of multiple,
interleaved bubbles of the two species. Such a pattern was observed recently in
an experiment by Wieman's group at JILA, and our simulations are in good
qualitative agreement with the experiment. We explain the pattern formation as
due to the onset of modulation instability during growth, and study the
dependence of the final state pattern on various parameters of the system
ASSESSING THE RISKS OF A FUTURE RAPID LARGE SEA LEVEL RISE: A REVIEW
Our aim is to make an appropriate characterization and interpretation of the risk problem of rapid large sea level rise that reflects the very large uncertainty in present day knowledge concerning this possibility, and that will be useful in informing discussion about risk management approaches. We consider mainly the potential collapse of the West Antarctic ice sheet as the source of such a sea level rise. Our review, characterization and interpretation of the risk makes us conclude that the risk of a rapid large sea level rise is characterized by potentially catastrophic consequences and high epistemic uncertainty; effective risk management must involve highly adaptive management regimes, vulnerability reduction, and prompt development of capabilities for precautionary reduction of climate change forcings.sea level rise, West Antarctic ice sheet, climate change, adaptive management, epistemic uncertainty, risk management arenas, vulnerability
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