2,394 research outputs found
Crew egress procedures for Apollo block 1 command module at sea
Crew egress procedures for Apollo block 1 command module at se
Adaptive Multidimensional Integration Based on Rank-1 Lattices
Quasi-Monte Carlo methods are used for numerically integrating multivariate
functions. However, the error bounds for these methods typically rely on a
priori knowledge of some semi-norm of the integrand, not on the sampled
function values. In this article, we propose an error bound based on the
discrete Fourier coefficients of the integrand. If these Fourier coefficients
decay more quickly, the integrand has less fine scale structure, and the
accuracy is higher. We focus on rank-1 lattices because they are a commonly
used quasi-Monte Carlo design and because their algebraic structure facilitates
an error analysis based on a Fourier decomposition of the integrand. This leads
to a guaranteed adaptive cubature algorithm with computational cost ,
where is some fixed prime number and is the number of data points
Probe-based Rapid Hybrid Hyperspectral and Tissue Surface Imaging Aided by Fully Convolutional Networks
Tissue surface shape and reflectance spectra provide rich intra-operative
information useful in surgical guidance. We propose a hybrid system which
displays an endoscopic image with a fast joint inspection of tissue surface
shape using structured light (SL) and hyperspectral imaging (HSI). For SL a
miniature fibre probe is used to project a coloured spot pattern onto the
tissue surface. In HSI mode standard endoscopic illumination is used, with the
fibre probe collecting reflected light and encoding the spatial information
into a linear format that can be imaged onto the slit of a spectrograph.
Correspondence between the arrangement of fibres at the distal and proximal
ends of the bundle was found using spectral encoding. Then during pattern
decoding, a fully convolutional network (FCN) was used for spot detection,
followed by a matching propagation algorithm for spot identification. This
method enabled fast reconstruction (12 frames per second) using a GPU. The
hyperspectral image was combined with the white light image and the
reconstructed surface, showing the spectral information of different areas.
Validation of this system using phantom and ex vivo experiments has been
demonstrated.Comment: This paper has been submitted to MICCAI2016 on 17 March, 2016, and
conditionally accepted on 2 June, 201
Spin Waves in the Ferromagnetic Ground State of the Kagome Staircase System Co3V2O8
Inelastic neutron scattering measurements were performed on single crystal
Co3V2O8 wherein magnetic cobalt ions reside on distinct spine and cross-tie
sites within kagome staircase planes. This system displays a rich magnetic
phase diagram which culminates in a ferromagnetic ground state below Tc~6 K. We
have studied the low-lying magnetic excitations in this phase within the kagome
plane. Despite the complexity of the system at higher temperatures, linear
spin-wave theory describes most of the quantitative detail of the inelastic
neutron measurements. Our results show two spin-wave branches, the higher
energy of which displays finite spin-wave lifetimes well below Tc, and
negligible magnetic exchange coupling between Co moments on the spine sites.Comment: 4 pages and 4 figure
Structural Fluctuations in the Spin Liquid State of Tb2Ti2O7
High resolution X-ray scattering measurements on single crystal Tb2Ti2O7
reveal finite structural correlations at low temperatures. This geometrically
frustrated pyrochlore is known to exhibit a spin liquid, or cooperative
paramagnetic state, at temperatures below ~ 20 K. Parametric studies of
structural Bragg peaks appropriate to the Fdm space group of Tb2Ti2O7
reveal substantial broadening and peak intensity reduction in the temperature
regime 20 K to 300 mK. We also observe a small, anomalous lattice expansion on
cooling below a density maximum at ~ 18 K. These measurements are consistent
with the development of fluctuations above a cooperative Jahn-Teller,
cubic-tetragonal phase transition at very low temperatures.Comment: 5 pages, 4 figures, submitted for publicatio
Magnetoelastics of a spin liquid: X-ray diffraction studies of Tb2Ti2O7 in pulsed magnetic fields
We report high resolution single crystal x-ray diffraction measurements of
the frustrated pyrochlore magnet Tb2Ti2O7, collected using a novel low
temperature pulsed magnet system. This instrument allows characterization of
structural degrees of freedom to temperatures as low as 4.4 K, and in applied
magnetic fields as large as 30 Tesla. We show that Tb2Ti2O7 manifests
intriguing structural effects under the application of magnetic fields,
including strongly anisotropic giant magnetostriction, a restoration of perfect
pyrochlore symmetry in low magnetic fields, and ultimately a structural phase
transition in high magnetic fields. It is suggested that the magnetoelastic
coupling thus revealed plays a significant role in the spin liquid physics of
Tb2Ti2O7 at low temperatures.Comment: 4 pages, 4 figures, submitted for publicatio
- …