55,985 research outputs found
Design and testing of liquid hydrogen-cooled, ultrahigh-speed ball bearings
Large-bore, liquid hydrogen-cooled, ultrahigh-speed, rolling contact bearings of an optimum design allow optimization of large rocket engine turbopumps in which bearing speed is a limiting factor. Optimum design for the bearings resulted from an application of liquid hydrogen used as a coolant
Trajectory-Based Dynamic Map Labeling
In this paper we introduce trajectory-based labeling, a new variant of
dynamic map labeling, where a movement trajectory for the map viewport is
given. We define a general labeling model and study the active range
maximization problem in this model. The problem is NP-complete and W[1]-hard.
In the restricted, yet practically relevant case that no more than k labels can
be active at any time, we give polynomial-time algorithms. For the general case
we present a practical ILP formulation with an experimental evaluation as well
as approximation algorithms.Comment: 19 pages, 7 figures, extended version of a paper to appear at ISAAC
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A foam model highlights the differences of the macro- and microrheology of respiratory horse mucus
Native horse mucus is characterized with micro- and macrorheology and
compared to hydroxyethylcellulose (HEC) gel as a model. Both systems show
comparable viscoelastic properties on the microscale and for the HEC the
macrorheology is in good agreement with the microrheology. For the mucus, the
viscoelastic moduli on the macroscale are several orders of magnitude larger
than on the microscale. Large amplitude oscillatory shear experiments show that
the mucus responds nonlinearly at much smaller deformations than HEC. This
behavior fosters the assumption that the mucus has a foam like structure on the
microscale compared to the typical mesh like structure of the HEC, a model that
is supported by cryogenic-scanning-electron-microscopy (CSEM) images. These
images allow also to determine the relative amount of volume that is occupied
by the pores and the scaffold. Consequently, we can estimate the elastic
modulus of the scaffold. We conclude that this particular foam like
microstructure should be considered as a key factor for the transport of
particulate matter which plays a central role in mucus function with respect to
particle penetration. The mesh properties composed of very different components
are responsible for macroscopic and microscopic behavior being part of
particles fate after landing.Comment: Accepted for publication in the Journal of the Mechanical Behavior of
Biomedical Material
Reducing sample variance: halo biasing, non-linearity and stochasticity
Comparing clustering of differently biased tracers of the dark matter
distribution offers the opportunity to reduce the cosmic variance error in the
measurement of certain cosmological parameters. We develop a formalism that
includes bias non-linearities and stochasticity. Our formalism is general
enough that can be used to optimise survey design and tracers selection and
optimally split (or combine) tracers to minimise the error on the
cosmologically interesting quantities. Our approach generalises the one
presented by McDonald & Seljak (2009) of circumventing sample variance in the
measurement of . We analyse how the bias, the noise,
the non-linearity and stochasticity affect the measurements of and explore
in which signal-to-noise regime it is significantly advantageous to split a
galaxy sample in two differently-biased tracers. We use N-body simulations to
find realistic values for the parameters describing the bias properties of dark
matter haloes of different masses and their number density.
We find that, even if dark matter haloes could be used as tracers and
selected in an idealised way, for realistic haloes, the sample variance limit
can be reduced only by up to a factor .
This would still correspond to the gain from a three times larger survey volume
if the two tracers were not to be split. Before any practical application one
should bear in mind that these findings apply to dark matter haloes as tracers,
while realistic surveys would select galaxies: the galaxy-host halo relation is
likely to introduce extra stochasticity, which may reduce the gain further.Comment: 21 pages, 13 figures. Published version in MNRA
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