3,971 research outputs found
Efficient Bayesian-based Multi-View Deconvolution
Light sheet fluorescence microscopy is able to image large specimen with high
resolution by imaging the sam- ples from multiple angles. Multi-view
deconvolution can significantly improve the resolution and contrast of the
images, but its application has been limited due to the large size of the
datasets. Here we present a Bayesian- based derivation of multi-view
deconvolution that drastically improves the convergence time and provide a fast
implementation utilizing graphics hardware.Comment: 48 pages, 20 figures, 1 table, under review at Nature Method
Case study in six sigma methadology : manufacturing quality improvement and guidence for managers
This article discusses the successful implementation of Six Sigma methodology in a high precision and critical process in the manufacture of automotive products. The Six Sigma define–measure–analyse–improve–control approach resulted in a reduction of tolerance-related problems and improved the first pass yield from 85% to 99.4%. Data were collected on all possible causes and regression analysis, hypothesis testing, Taguchi methods, classification and regression tree, etc. were used to analyse the data and draw conclusions. Implementation of Six Sigma methodology had a significant financial impact on the profitability of the company. An approximate saving of US$70,000 per annum was reported, which is in addition to the customer-facing benefits of improved quality on returns and sales. The project also had the benefit of allowing the company to learn useful messages that will guide future Six Sigma activities
Composite-pulse magnetometry with a solid-state quantum sensor
The sensitivity of quantum magnetometers is challenged by control errors and,
especially in the solid-state, by their short coherence times. Refocusing
techniques can overcome these limitations and improve the sensitivity to
periodic fields, but they come at the cost of reduced bandwidth and cannot be
applied to sense static (DC) or aperiodic fields. Here we experimentally
demonstrate that continuous driving of the sensor spin by a composite pulse
known as rotary-echo (RE) yields a flexible magnetometry scheme, mitigating
both driving power imperfections and decoherence. A suitable choice of RE
parameters compensates for different scenarios of noise strength and origin.
The method can be applied to nanoscale sensing in variable environments or to
realize noise spectroscopy. In a room-temperature implementation based on a
single electronic spin in diamond, composite-pulse magnetometry provides a
tunable trade-off between sensitivities in the microT/sqrt(Hz) range,
comparable to those obtained with Ramsey spectroscopy, and coherence times
approaching T1
A single low-energy, iron-poor supernova as the source of metals in the star SMSS J 031300.36-670839.3
The element abundance ratios of four low-mass stars with extremely low
metallicities indicate that the gas out of which the stars formed was enriched
in each case by at most a few, and potentially only one low-energy, supernova.
Such supernovae yield large quantities of light elements such as carbon but
very little iron. The dominance of low-energy supernovae is surprising, because
it has been expected that the first stars were extremely massive, and that they
disintegrated in pair-instability explosions that would rapidly enrich galaxies
in iron. What has remained unclear is the yield of iron from the first
supernovae, because hitherto no star is unambiguously interpreted as
encapsulating the yield of a single supernova. Here we report the optical
spectrum of SMSS J031300.36- 670839.3, which shows no evidence of iron (with an
upper limit of 10^-7.1 times solar abundance). Based on a comparison of its
abundance pattern with those of models, we conclude that the star was seeded
with material from a single supernova with an original mass of ~60 Mo (and that
the supernova left behind a black hole). Taken together with the previously
mentioned low-metallicity stars, we conclude that low-energy supernovae were
common in the early Universe, and that such supernovae yield light element
enrichment with insignificant iron. Reduced stellar feedback both chemically
and mechanically from low-energy supernovae would have enabled first-generation
stars to form over an extended period. We speculate that such stars may perhaps
have had an important role in the epoch of cosmic reionization and the chemical
evolution of early galaxies.Comment: 28 pages, 6 figures, Natur
Preferential Paths of Air-water Two-phase Flow in Porous Structures with Special Consideration of Channel Thickness Effects.
Accurate understanding and predicting the flow paths of immiscible two-phase flow in rocky porous structures are of critical importance for the evaluation of oil or gas recovery and prediction of rock slides caused by gas-liquid flow. A 2D phase field model was established for compressible air-water two-phase flow in heterogenous porous structures. The dynamic characteristics of air-water two-phase interface and preferential paths in porous structures were simulated. The factors affecting the path selection of two-phase flow in porous structures were analyzed. Transparent physical models of complex porous structures were prepared using 3D printing technology. Tracer dye was used to visually observe the flow characteristics and path selection in air-water two-phase displacement experiments. The experimental observations agree with the numerical results used to validate the accuracy of phase field model. The effects of channel thickness on the air-water two-phase flow behavior and paths in porous structures were also analyzed. The results indicate that thick channels can induce secondary air flow paths due to the increase in flow resistance; consequently, the flow distribution is different from that in narrow channels. This study provides a new reference for quantitatively analyzing multi-phase flow and predicting the preferential paths of immiscible fluids in porous structures
The EMBLA survey - metal-poor stars in the Galactic bulge
Cosmological models predict the oldest stars in the Galaxy should be found closest to the centre of the potential well, in the bulge. The Extremely Metal-poor BuLge stars with AAOmega survey (EMBLA) successfully searched for these old, metal-poor stars by making use of the distinctive SkyMapper photometric filters to discover candidate metal-poor stars in the bulge. Their metal-poor nature was then confirmed using the AAOmega spectrograph on the Anglo-Australian Telescope. Here we present an abundance analysis of 10 bulge stars with −2.8 < [Fe/H] < −1.7 from MIKE/Magellan observations, in total determining the abundances of 22 elements. Combining these results with our previous high-resolution data taken as part of the Gaia-ESO Survey, we have started to put together a picture of the chemical and kinematic nature of the most metal-poor stars in the bulge. The currently available kinematic data are consistent with the stars belonging to the bulge, although more accurate measurements are needed to constrain the stars’ orbits. The chemistry of these bulge stars deviates from that found in halo stars of the same metallicity. Two notable differences are the absence of carbon-enhanced metal-poor bulge stars, and the α element abundances exhibit a large intrinsic scatter and include stars which are underabundant in these typically enhanced elements.LMH and MA have been supported by the Australian Research Council (grant FL110100012). ARC acknowledges support from the European Union FP7 programme through ERC grant number 320360. DY is supported through an Australian Research Council Future Fellowship (FT140100554). Research on metal-poor stars with SkyMapper is supported through Australian Research Council Discovery Projects grants DP120101237 and DP150103294 (PI: Da Costa). This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. This paper includes data gathered with the 6.5 metre Magellan Telescopes located at Las Campanas Observatory, Chile.This is the final version of the article. It first appeared from Oxford University Press via http://dx.doi.org/10.1093/mnras/stw100
Evolutionary distances in the twilight zone -- a rational kernel approach
Phylogenetic tree reconstruction is traditionally based on multiple sequence
alignments (MSAs) and heavily depends on the validity of this information
bottleneck. With increasing sequence divergence, the quality of MSAs decays
quickly. Alignment-free methods, on the other hand, are based on abstract
string comparisons and avoid potential alignment problems. However, in general
they are not biologically motivated and ignore our knowledge about the
evolution of sequences. Thus, it is still a major open question how to define
an evolutionary distance metric between divergent sequences that makes use of
indel information and known substitution models without the need for a multiple
alignment. Here we propose a new evolutionary distance metric to close this
gap. It uses finite-state transducers to create a biologically motivated
similarity score which models substitutions and indels, and does not depend on
a multiple sequence alignment. The sequence similarity score is defined in
analogy to pairwise alignments and additionally has the positive semi-definite
property. We describe its derivation and show in simulation studies and
real-world examples that it is more accurate in reconstructing phylogenies than
competing methods. The result is a new and accurate way of determining
evolutionary distances in and beyond the twilight zone of sequence alignments
that is suitable for large datasets.Comment: to appear in PLoS ON
Insights into the regulation of DMSP synthesis in the diatom Thalassiosira pseudonana through APR activity, proteomics and gene expression analyses on cells acclimating to changes in salinity, light and nitrogen
Despite the importance of dimethylsulphoniopropionate (DMSP) in the global sulphur cycle and climate regulation, the biological pathways underpinning its synthesis in marine phytoplankton remain poorly understood. The intracellular concentration of DMSP increases with increased salinity, increased light intensity and nitrogen starvation in the diatom Thalassiosira pseudonana. We used these conditions to investigate DMSP synthesis at the cellular level via analysis of enzyme activity, gene expression and proteome comparison. The activity of the key sulphur assimilatory enzyme, adenosine 5′- phosphosulphate reductase was not coordinated with increasing intracellular DMSP concentration. Under all three treatments coordination in the expression of sulphur assimilation genes was limited to increases in sulphite reductase transcripts. Similarly, proteomic 2D gel analysis only revealed an increase in phosphoenolpyruvate carboxylase following increases in DMSP concentration. Our findings suggest that increased sulphur assimilation might not be required for increased DMSP synthesis, instead the availability of carbon and nitrogen substrates may be important in the regulation of this pathway. This contrasts with the regulation of sulphur metabolism in higher plants, which generally involves upregulation of several sulphur assimilatory enzymes. In T. pseudonana changes relating to sulphur metabolism were specific to the individual treatments and, given that little coordination was seen in transcript and protein responses across the three growth conditions, different patterns of regulation might be responsible for the increase in DMSP concentration seen under each treatment
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