585 research outputs found
High Temperature Photochemistry in the Atmosphere of HD189733b
Recent infrared spectroscopy of hot exoplanets is beginning to reveal their
atmospheric composition. Deep with in the planetary atmosphere, the composition
is controlled by thermochemical equilibrium. Photochemistry becomes important
higher in the atmosphere, at levels above ~1 bar. These two chemistries compete
between ~1-10 bars in hot Jupiter-like atmospheres, depending on the strength
of the eddy mixing and temperature. HD189733b provides an excellent laboratory
in which to study the consequences of chemistry of hot atmospheres. The recent
spectra of HD189733b and HD209458b contain signatures of CH4, CO2, CO and H2O.
Here we identify the primary chemical pathways that govern the abundances of
CH4, CO2, CO and H2O in the cases of thermochemical equilibrium chemistry,
photochemistry, and their combination. Our results suggest that the abundance
of these species can be photochemically enhanced above or below the
thermochemical equilibrium value, so some caution must be taken when assuming
that an atmosphere is in strict thermochemical equilibrium
Impact of Donor Lung Gram Stain on Post-Transplant Pneumonia and Mortality: More Lungs Can Be Used to Save Lives
Microstructural differences in white matter tracts across middle to late adulthood : a diffusion MRI study on 7167 UK Biobank participants
Acknowledgements This research was approved by the UK Biobank (application number: 24089) and was supported by the Roland Sutton Academic Trust (grant number: 0039/R/16) and Taiwan National Health Research Institute (NHRI-EX109-10928NI). We acknowledge the valuable contributions of members of the UK Biobank Imaging Working Group and the UK Biobank coordinating center. The UK Biobank (including the imaging enhancement) was supported by the UK Medical Research Council and the Wellcome Trust. The authors are grateful for the provision of simultaneous multislice (multiband) pulse sequence and reconstruction algorithms by the Center for Magnetic Resonance Research, University of Minnesota. Finally, the authors are extremely grateful to all UK Biobank study participants, who have generously donated their time to make this resource possible. This article was edited by Wallace Academic Editing.Peer reviewedPostprin
Simulating chemistry efficiently on fault-tolerant quantum computers
Quantum computers can in principle simulate quantum physics exponentially
faster than their classical counterparts, but some technical hurdles remain.
Here we consider methods to make proposed chemical simulation algorithms
computationally fast on fault-tolerant quantum computers in the circuit model.
Fault tolerance constrains the choice of available gates, so that arbitrary
gates required for a simulation algorithm must be constructed from sequences of
fundamental operations. We examine techniques for constructing arbitrary gates
which perform substantially faster than circuits based on the conventional
Solovay-Kitaev algorithm [C.M. Dawson and M.A. Nielsen, \emph{Quantum Inf.
Comput.}, \textbf{6}:81, 2006]. For a given approximation error ,
arbitrary single-qubit gates can be produced fault-tolerantly and using a
limited set of gates in time which is or ; with sufficient parallel preparation of ancillas, constant average
depth is possible using a method we call programmable ancilla rotations.
Moreover, we construct and analyze efficient implementations of first- and
second-quantized simulation algorithms using the fault-tolerant arbitrary gates
and other techniques, such as implementing various subroutines in constant
time. A specific example we analyze is the ground-state energy calculation for
Lithium hydride.Comment: 33 pages, 18 figure
Exploratory Analysis of the Copy Number Alterations in Glioblastoma Multiforme
The Cancer Genome Atlas project (TCGA) has initiated the analysis of multiple samples of a variety of tumor types, starting with glioblastoma multiforme. The analytical methods encompass genomic and transcriptomic information, as well as demographic and clinical data about the sample donors. The data create the opportunity for a systematic screening of the components of the molecular machinery for features that may be associated with tumor formation. The wealth of existing mechanistic information about cancer cell biology provides a natural reference for the exploratory exercise.Glioblastoma multiforme DNA copy number data was generated by The Cancer Genome Atlas project for 167 patients using 227 aCGH experiments, and was analyzed to build a catalog of aberrant regions. Genome screening was performed using an information theory approach in order to quantify aberration as a deviation from a centrality without the bias of untested assumptions about its parametric nature. A novel Cancer Genome Browser software application was developed and is made public to provide a user-friendly graphical interface in which the reported results can be reproduced. The application source code and stand alone executable are available at (http://code.google.com/p/cancergenome) and (http://bioinformaticstation.org), respectively.The most important known copy number alterations for glioblastoma were correctly recovered using entropy as a measure of aberration. Additional alterations were identified in different pathways, such as cell proliferation, cell junctions and neural development. Moreover, novel candidates for oncogenes and tumor suppressors were also detected. A detailed map of aberrant regions is provided
Exact Results for Hamiltonian Walks from the Solution of the Fully Packed Loop Model on the Honeycomb Lattice
We derive the nested Bethe Ansatz solution of the fully packed O() loop
model on the honeycomb lattice. From this solution we derive the bulk free
energy per site along with the central charge and geometric scaling dimensions
describing the critical behaviour. In the limit we obtain the exact
compact exponents and for Hamiltonian walks, along with
the exact value for the connective constant
(entropy). Although having sets of scaling dimensions in common, our results
indicate that Hamiltonian walks on the honeycomb and Manhattan lattices lie in
different universality classes.Comment: 12 pages, RevTeX, 3 figures supplied on request, ANU preprint
MRR-050-9
Upper limits for undetected trace species in the stratosphere of Titan
In this paper we describe a first quantitative search for several molecules
in Titan's stratosphere in Cassini CIRS infrared spectra. These are: ammonia
(NH3), methanol (CH3OH), formaldehyde (H2CO), and acetonitrile (CH3CN), all of
which are predicted by photochemical models but only the last of which
observed, and not in the infrared. We find non-detections in all cases, but
derive upper limits on the abundances from low-noise observations at 25{\deg}S
and 75{\deg}N. Comparing these constraints to model predictions, we conclude
that CIRS is highly unlikely to see NH3 or CH3OH emissions. However, CH3CN and
H2CO are closer to CIRS detectability, and we suggest ways in which the
sensitivity threshold may be lowered towards this goal.Comment: 11 pages plus 6 figure file
Thermochemistry and Photochemistry in Cooler Hydrogen Dominated Extrasolar Planets: The Case of GJ436b
We introduce a new thermochemical kinetics and photochemical model. We use
high-temperature bidirectional reaction rates for important H, C, O and N
reactions (most importantly for CH to CO interconversion), allowing us to
attain thermochemical equilibrium, deep in an atmosphere, purely kinetically.
This allows ab initio chemical modeling of an entire atmosphere, from
deep-atmosphere thermochemical equilibrium to the photochemically dominated
regime. We use our model to explore the atmospheric chemistry of cooler
( K) extrasolar giant planets. In particular, we choose to
model the nearby hot Neptune GJ436b, the only planet in this temperature regime
for which spectroscopic measurements and estimates of chemical abundances now
exist. Recent {\it Spitzer} measurements with retrieval have shown that methane
is driven strongly out of equilibrium and is deeply depleted on the dayside of
GJ 436b, whereas quenched carbon monoxide is abundant. This is surprising
because GJ 436b is cooler than many of the heavily irradiated hot Jovians and
thermally favorable for CH, and thus requires an efficient mechanism for
destroying it. We include realistic estimates of ultraviolet flux from the
parent dM star GJ 436, to bound the direct photolysis and photosensitized
depletion of CH. While our models indicate fairly rich disequilibrium
conditions are likely in cooler exoplanets over a range of planetary
metallicities, we are unable to generate the conditions for substantial CH
destruction. One possibility is an anomalous source of abundant H atoms between
0.01-1 bars (which attack CH), but we cannot as yet identify an efficient
means to produce these hot atoms
Does Industry-Driven Alcohol Marketing Influence Adolescent Drinking Behaviour? A Systematic Review.
AIM: To systematically review evidence on the influence of specific marketing components (Price, Promotion, Product attributes and Place of sale/availability) on key drinking outcomes (initiation, continuation, frequency and intensity) in young people aged 9–17. METHODS: MEDLINE, EMBASE, SCOPUS, PsychINFO, CINAHL and ProQuest were searched from inception to July 2015, supplemented with searches of Google Scholar, hand searches of key journals and backward and forward citation searches of reference lists of identified papers. RESULTS: Forty-eight papers covering 35 unique studies met inclusion criteria. Authors tended to report that greater exposure to alcohol marketing impacted on drinking initiation, continuation, frequency and intensity during adolescence. Nevertheless, 23 (66%) studies reported null results or negative associations, often in combination with positive associations, resulting in mixed findings within and across studies. Heterogeneity in study design, content and outcomes prevented estimation of effect sizes or exploration of variation between countries or age subgroups. The strength of the evidence base differed according to type of marketing exposure and drinking outcome studied, with support for an association between alcohol promotion (mainly advertising) and drinking outcomes in adolescence, whilst only two studies examined the relationship between alcohol price and the drinking behaviour of those under the age of 18. CONCLUSION: Despite the volume of work, evidence is inconclusive in all four areas of marketing but strongest for promotional activity. Future research with standardized measures is needed to build on this work and better inform interventions and policy responses
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