4,715 research outputs found
Forming circumnuclear disks and rings in galactic nuclei: a competition between supermassive black hole and nuclear star cluster
We investigate the formation of circumnuclear gas structures from the tidal
disruption of molecular clouds in galactic nuclei, by means of smoothed
particle hydrodynamics simulations. We model galactic nuclei as composed of a
supermassive black hole (SMBH) and a nuclear star cluster (NSC) and consider
different mass ratios between the two components. We find that the relative
masses of the SMBH and the NSC have a deep impact on the morphology of the
circumnuclear gas. Extended disks form only inside the sphere of influence of
the SMBH. In contrast, compact rings naturally form outside the SMBH's sphere
of influence, where the gravity is dominated by the NSC. This result is in
agreement with the properties of the Milky Way's circumnuclear ring, which
orbits outside the SMBH sphere of influence. Our results indicate that compact
circumnuclear rings can naturally form outside the SMBH sphere of influence.Comment: Accepted for publication in ApJ. 12 pages, 6 figures, 3 tables.
Comments welcom
Nonparametric Estimators of Dose-Response Functions
We propose two semiparametric estimators of the dose-response function based on spline techniques. Under uncounfoundedness, the generalized propensity score can be used to estimate dose-response functions (DRF) and marginal treatment effect functions. In many observational studies treatment may not be binary or categorical. In such cases, one may be interested in estimating the dose-response function in a setting with a continuous treatment. We evaluate the performance of the proposed estimators using Monte Carlo simulation methods. The simulation results suggested that the estimated DRF is robust to the specific semiparametric estimator used, while the parametric estimates of the DRF were sensitive to model mis-specification. We apply our approach to the problem of evaluating the effect on innovation sales of Research and Development (R&D) financial aids received by Luxembourgish firms in 2004 and 2005.Continuous treatment; Dose-response function; Generalized Propensity Score; Non-parametric methods; R&D investment
Concordance with the British Society of Rheumatology (BSR) 2010 recommendations on eligibility criteria for the first biologic agent
Aims: The aim of this study is to assess concordance with the British Society of Rheumatology (BSR) 2010 recommendations on the use of biologic therapy in Rheumatoid Arthritis (RA). The Disease Activity Score in 28 joints (DAS 28), a composite numerical score is included in these recommendations to assess disease activity and response to treatment.
Methods: Clinical notes of fifty patients who were commenced on biologic treatment between March 2010 and June 2011 were reviewed for documentation of DAS 28 scores at baseline, after approximately 6 months of commencement of treatment and at approximately 6 monthly intervals during treatment.
Results: Twenty two patients were eligible for this audit. Of these patients only half had a DAS 28 score performed prior to starting treatment, four patients had the score performed within 3-9 months of commencement of therapy and only 2 patients had continuous scores performed at six monthly intervals during treatment.
Conclusions: This audit shows that we are not adhering to the BSR recommendations. In order to improve our adherence we plan to train all staff in contact with patients on biologic treatment to perform DAS 28 scores and have a DAS 28 calculator readily available at out patients. A proforma is being developed for patients on biologic therapy to ensure that DAS 28 scores are performed at baseline and during treatment.peer-reviewe
Hierarchical fractional-step approximations and parallel kinetic Monte Carlo algorithms
We present a mathematical framework for constructing and analyzing parallel
algorithms for lattice Kinetic Monte Carlo (KMC) simulations. The resulting
algorithms have the capacity to simulate a wide range of spatio-temporal scales
in spatially distributed, non-equilibrium physiochemical processes with complex
chemistry and transport micro-mechanisms. The algorithms can be tailored to
specific hierarchical parallel architectures such as multi-core processors or
clusters of Graphical Processing Units (GPUs). The proposed parallel algorithms
are controlled-error approximations of kinetic Monte Carlo algorithms,
departing from the predominant paradigm of creating parallel KMC algorithms
with exactly the same master equation as the serial one.
Our methodology relies on a spatial decomposition of the Markov operator
underlying the KMC algorithm into a hierarchy of operators corresponding to the
processors' structure in the parallel architecture. Based on this operator
decomposition, we formulate Fractional Step Approximation schemes by employing
the Trotter Theorem and its random variants; these schemes, (a) determine the
communication schedule} between processors, and (b) are run independently on
each processor through a serial KMC simulation, called a kernel, on each
fractional step time-window.
Furthermore, the proposed mathematical framework allows us to rigorously
justify the numerical and statistical consistency of the proposed algorithms,
showing the convergence of our approximating schemes to the original serial
KMC. The approach also provides a systematic evaluation of different processor
communicating schedules.Comment: 34 pages, 9 figure
Exploring the importance of sulfate transporters and ATP sulphurylases for selenium hyperaccumulation\u2014a comparison of Stanleya pinnata and Brassica juncea (Brassicaceae)
Selenium (Se) hyperaccumulation, the capacity of some species to concentrate Se to levels upwards of 0.1% of dry weight, is an intriguing phenomenon that is only partially understood. Questions that remain to be answered are: do hyperaccumulators have one or more Se-specific transporters? How are these regulated by Se and sulfur (S)? In this study, hyperaccumulator Stanleya pinnata was compared with related non-hyperaccumulator Brassica juncea with respect to S-dependent selenate uptake and translocation, as well as for the expression levels of three sulfate/selenate transporters (Sultr) and three ATP sulphurylases (APS). Selenium accumulation went down ~10-fold with increasing sulfate supply in B. juncea, while S. pinnata only had a 2\u20133-fold difference in Se uptake between the highest (5 mM) and lowest sulfate (0 mM) treatments. The Se/S ratio was generally higher in the hyperaccumulator than the non-hyperaccumulator, and while tissue Se/S ratio in B. juncea largely reflected the ratio in the growth medium, S. pinnata enriched itself up to 5-fold with Se relative to S. The transcript levels of Sultr1;2 and 2;1 and APS1, 2, and 4 were generally much higher in S. pinnata than B. juncea, and the species showed differential transcript responses to S and Se supply. These results indicate that S. pinnata has at least one transporter with significant selenate specificity over sulfate. Also, the hyperaccumulator has elevated expression levels of several sulfate/selenate transporters and APS enzymes, which likely contribute to the Se hyperaccumulation and hypertolerance phenotype
Evoluzione, stasi e regressione nei Dubliners di James Joyce
Simbolo della necessitĂ della fuga ma anche della sua
impossibilitĂ concreta e quindi di una ribellione solo
pensata, i personaggi di Dubliners sono spesso stati
definiti esclusivamente dalla loro staticitĂ . Ma mentre
appare senzâaltro vero che Ăš la paralisi di Dublino a costituire
uno dei tratti dominanti, oltre che piĂč evidenti,
dellâambientazione delle storie, una messa a fuoco
piĂč esclusiva della competenza dei personaggi - intesa
come il volere, potere, sapere, essenziali affinché il
personaggio possa attuare la sua performance, il suo/fare/ - rivela invece una rigorosa dinamica trasformazionale,
almeno per quanto riguarda una metĂ dei
racconti che si possono considerare quindi come un
corpus omogeneo e di cui si propone qui un campione
sottoponendolo ad analisi
Effects of selenium biofortification on crop nutritional quality
Selenium (Se) at very low doses has crucial functions in humans and animals. Since plants represent the main dietary source of this element, Se-containing crops may be used as a means to deliver Se to consumers (biofortification). Several strategies have been exploited to increase plant Se content. Selenium assimilation in plants affects both sulphur (S) and nitrogen (N) metabolic pathways, which is why recent research has also focused on the effect of Se fertilization on the production of S- and N- secondary metabolites with putative health benefits. In this review we discuss the function of Se in plant and human nutrition and the progress in the genetic engineering of Se metabolism to increase the levels and bioavailability of this element in food crops. Particular attention is paid to Se biofortification and the synthesis of compounds with beneficial effects on health
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