5,772 research outputs found
Hot new directions for quasi-Monte Carlo research in step with applications
This article provides an overview of some interfaces between the theory of
quasi-Monte Carlo (QMC) methods and applications. We summarize three QMC
theoretical settings: first order QMC methods in the unit cube and in
, and higher order QMC methods in the unit cube. One important
feature is that their error bounds can be independent of the dimension
under appropriate conditions on the function spaces. Another important feature
is that good parameters for these QMC methods can be obtained by fast efficient
algorithms even when is large. We outline three different applications and
explain how they can tap into the different QMC theory. We also discuss three
cost saving strategies that can be combined with QMC in these applications.
Many of these recent QMC theory and methods are developed not in isolation, but
in close connection with applications
Cyanobacterial life at low O 2 : community genomics and function reveal metabolic versatility and extremely low diversity in a Great Lakes sinkhole mat
Cyanobacteria are renowned as the mediators of Earth’s oxygenation. However, little is known about the cyanobacterial communities that flourished under the low‐O 2 conditions that characterized most of their evolutionary history. Microbial mats in the submerged Middle Island Sinkhole of Lake Huron provide opportunities to investigate cyanobacteria under such persistent low‐O 2 conditions. Here, venting groundwater rich in sulfate and low in O 2 supports a unique benthic ecosystem of purple‐colored cyanobacterial mats. Beneath the mat is a layer of carbonate that is enriched in calcite and to a lesser extent dolomite. In situ benthic metabolism chambers revealed that the mats are net sinks for O 2 , suggesting primary production mechanisms other than oxygenic photosynthesis. Indeed, 14 C‐bicarbonate uptake studies of autotrophic production show variable contributions from oxygenic and anoxygenic photosynthesis and chemosynthesis, presumably because of supply of sulfide. These results suggest the presence of either facultatively anoxygenic cyanobacteria or a mix of oxygenic/anoxygenic types of cyanobacteria. Shotgun metagenomic sequencing revealed a remarkably low‐diversity mat community dominated by just one genotype most closely related to the cyanobacterium Phormidium autumnale , for which an essentially complete genome was reconstructed. Also recovered were partial genomes from a second genotype of Phormidium and several Oscillatoria . Despite the taxonomic simplicity, diverse cyanobacterial genes putatively involved in sulfur oxidation were identified, suggesting a diversity of sulfide physiologies. The dominant Phormidium genome reflects versatile metabolism and physiology that is specialized for a communal lifestyle under fluctuating redox conditions and light availability. Overall, this study provides genomic and physiologic insights into low‐O 2 cyanobacterial mat ecosystems that played crucial geobiological roles over long stretches of Earth history.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90535/1/j.1472-4669.2012.00322.x.pd
Pyrolysis of waste tyre for high-quality fuel products: A review
Pyrolysis is a thermal conversion of materials at high temperatures in an inert atmosphere.
Pyrolysis can be obtained through thermal or catalytic pathways. Thermal pyrolysis is known for its
high operating temperature, reaction time, and low oil quality. To subdue these challenges associated
with thermal pyrolysis, catalytic pyrolysis of the waste tyre has materialized with the use of a
catalyst. Catalytic pyrolysis can convert 60–80% of the waste tyre into pyro-oil having close
similarities with diesel fuel. Thus the produced pyro-oil is of better quality and could yield useful
chemicals as feedstock in chemical processes and energy-related applications such as electricity
generation, transport fuel, and heating source. Therefore, this review reports the advancement and
limitations of catalytic pyrolysis of the waste tyre and its future perception when compared to
thermal pyrolysis. Factors affecting pyrolysis, cons, and limitations of thermal pyrolysis were
discussed. These limitations led to the discussion of catalytic pyrolysis, the effects of catalysts on the
product yield, composition, and physical properties. Although the catalytic pyrolysis has advantages
over thermal pyrolysis, it has few shortcomings which were presented. Some recommendations to
address these shortcomings were also stated
A re-analysis of the three-year WMAP temperature power spectrum and likelihood
We analyze the three-year WMAP temperature anisotropy data seeking to confirm
the power spectrum and likelihoods published by the WMAP team. We apply five
independent implementations of four algorithms to the power spectrum estimation
and two implementations to the parameter estimation. Our single most important
result is that we broadly confirm the WMAP power spectrum and analysis. Still,
we do find two small but potentially important discrepancies: On large angular
scales there is a small power excess in the WMAP spectrum (5-10% at l<~30)
primarily due to likelihood approximation issues between 13 <= l <~30. On small
angular scales there is a systematic difference between the V- and W-band
spectra (few percent at l>~300). Recently, the latter discrepancy was explained
by Huffenberger et al. (2006) in terms of over-subtraction of unresolved point
sources. As far as the low-l bias is concerned, most parameters are affected by
a few tenths of a sigma. The most important effect is seen in n_s. For the
combination of WMAP, Acbar and BOOMERanG, the significance of n_s =/ 1 drops
from ~2.7 sigma to ~2.3 sigma when correcting for this bias. We propose a few
simple improvements to the low-l WMAP likelihood code, and introduce two
important extensions to the Gibbs sampling method that allows for proper
sampling of the low signal-to-noise regime. Finally, we make the products from
the Gibbs sampling analysis publically available, thereby providing a fast and
simple route to the exact likelihood without the need of expensive matrix
inversions.Comment: 14 pages, 7 figures. Accepted for publication in ApJ. Numerical
results unchanged, but interpretation sharpened: Likelihood approximation
issues at l=13-30 far more important than potential foreground issues at l <=
12. Gibbs products (spectrum and sky samples, and "easy-to-use" likelihood
module) available from http://www.astro.uio.no/~hke/ under "Research
Supervision and Scholarly Writing: Writing to Learn - Learning to Write
This paper describes an action research project on postgraduate students’ scholarly writing in which I employed reflective approaches to examine and enhance my postgraduate supervisory practice. My reflections on three distinct cycles of supervision illustrate a shift in thinking about scholarly writing and an evolving understanding of how to support postgraduate students’ writing. These understandings provide the foundation for a future-oriented fourth cycle of supervisory practice, which is characterised by three principles, namely the empowerment of students as writers, the technological context of contemporary writing, and ethical issues in writing
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