5,145 research outputs found
Consistency of Bayesian procedures for variable selection
It has long been known that for the comparison of pairwise nested models, a
decision based on the Bayes factor produces a consistent model selector (in the
frequentist sense). Here we go beyond the usual consistency for nested pairwise
models, and show that for a wide class of prior distributions, including
intrinsic priors, the corresponding Bayesian procedure for variable selection
in normal regression is consistent in the entire class of normal linear models.
We find that the asymptotics of the Bayes factors for intrinsic priors are
equivalent to those of the Schwarz (BIC) criterion. Also, recall that the
Jeffreys--Lindley paradox refers to the well-known fact that a point null
hypothesis on the normal mean parameter is always accepted when the variance of
the conjugate prior goes to infinity. This implies that some limiting forms of
proper prior distributions are not necessarily suitable for testing problems.
Intrinsic priors are limits of proper prior distributions, and for finite
sample sizes they have been proved to behave extremely well for variable
selection in regression; a consequence of our results is that for intrinsic
priors Lindley's paradox does not arise.Comment: Published in at http://dx.doi.org/10.1214/08-AOS606 the Annals of
Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical
Statistics (http://www.imstat.org
Surges and Si IV bursts in the solar atmosphere. Understanding IRIS and SST observations through RMHD experiments
Surges often appear as a result of the emergence of magnetized plasma from
the solar interior. Traditionally, they are observed in chromospheric lines
such as H 6563 \AA and Ca II 8542 \AA. However, whether there is a
response to the surge appearance and evolution in the Si IV lines or, in fact,
in many other transition region lines has not been studied. In this paper we
analyze a simultaneous episode of an H surge and a Si IV burst that
occurred on 2016 September 03 in active region AR12585. To that end, we use
coordinated observations from the Interface Region Imaging Spectrograph (IRIS)
and the Swedish 1-m Solar Telescope (SST). For the first time, we report
emission of Si IV within the surge, finding profiles that are brighter and
broader than the average. Furthermore, the brightest Si IV patches within the
domain of the surge are located mainly near its footpoints. To understand the
relation between the surges and the emission in transition region lines like Si
IV, we have carried out 2.5D radiative MHD (RMHD) experiments of magnetic flux
emergence episodes using the Bifrost code and including the non-equilibrium
ionization of silicon. Through spectral synthesis we explain several features
of the observations. We show that the presence of Si IV emission patches within
the surge, their location near the surge footpoints and various observed
spectral features are a natural consequence of the emergence of magnetized
plasma from the interior to the atmosphere and the ensuing reconnection
processes.Comment: 13 pages, 8 figures. The Astrophysical Journal (Accepted
Shedding light on the chromatin changes that modulate shade responses
Altres ajuts: COST-Action INDEPTH CA16212; Generalitat de Catalunya/CERCA programmePerception of vegetation proximity or plant shade informs of potential competition for resources by the neighboring vegetation. As vegetation proximity impacts on both light quantity and quality, perception of this cue by plant photoreceptors reprograms development to result in responses that allow plants to compete with the neighboring vegetation. Developmental reprogramming involves massive and rapid changes in gene expression, with the concerted action of photoreceptors and downstream transcription factors. Changes in gene expression can be modulated by epigenetic processes that alter chromatin compaction, influencing the accessibility and binding of transcription factors to regulatory elements in the DNA. However, little is known about the epigenetic regulation of plant responses to the proximity of other plants. In this manuscript, we review what is known about plant shade effects on chromatin changes at the cytological level, that is, changes in nuclear morphology and high order chromatin density. We address which are the specific histone post-transcriptional modifications that have been associated with changes in shade-regulated gene expression, such as histone acetylation and histone methylation. Furthermore, we explore the possible mechanisms that integrate shade signaling components and chromatin remodelers to settle epigenetic marks at specific loci. This review aims to be a starting point to understand how a specific environmental cue, plant shade, integrates with chromatin dynamics to implement the proper acclimation responses
Twisted flux tube emergence from the convection zone to the corona
3D numerical simulations of a horizontal magnetic flux tube emergence with
different twist are carried out in a computational domain spanning the upper
layers of the convection zone to the lower corona. We use the Oslo Staggered
Code to solve the full MHD equations with non-grey and non-LTE radiative
transfer and thermal conduction along the magnetic field lines. The emergence
of the magnetic flux tube input at the bottom boundary into a weakly magnetized
atmosphere is presented. The photospheric and chromospheric response is
described with magnetograms, synthetic images and velocity field distributions.
The emergence of a magnetic flux tube into such an atmosphere results in varied
atmospheric responses. In the photosphere the granular size increases when the
flux tube approaches from below. In the convective overshoot region some 200km
above the photosphere adiabatic expansion produces cooling, darker regions with
the structure of granulation cells. We also find collapsed granulation in the
boundaries of the rising flux tube. Once the flux tube has crossed the
photosphere, bright points related with concentrated magnetic field, vorticity,
high vertical velocities and heating by compressed material are found at
heights up to 500km above the photosphere. At greater heights in the magnetized
chromosphere, the rising flux tube produces a cool, magnetized bubble that
tends to expel the usual chromospheric oscillations. In addition the rising
flux tube dramatically increases the chromospheric scale height, pushing the
transition region and corona aside such that the chromosphere extends up to 6Mm
above the photosphere. The emergence of magnetic flux tubes through the
photosphere to the lower corona is a relatively slow process, taking of order 1
hour.Comment: 53 pages,79 figures, Submitted to Ap
Solar Flux Emergence Simulations
We simulate the rise through the upper convection zone and emergence through
the solar surface of initially uniform, untwisted, horizontal magnetic flux
with the same entropy as the non-magnetic plasma that is advected into a domain
48 Mm wide from from 20 Mm deep. The magnetic field is advected upward by the
diverging upflows and pulled down in the downdrafts, which produces a hierarchy
of loop like structures of increasingly smaller scale as the surface is
approached. There are significant differences between the behavior of fields of
10 kG and 20 or 40 kG strength at 20 Mm depth. The 10 kG fields have little
effect on the convective flows and show little magnetic buoyancy effects,
reaching the surface in the typical fluid rise time from 20 Mm depth of 32
hours. 20 and 40 kG fields significantly modify the convective flows, leading
to long thin cells of ascending fluid aligned with the magnetic field and their
magnetic buoyancy makes them rise to the surface faster than the fluid rise
time. The 20 kG field produces a large scale magnetic loop that as it emerges
through the surface leads to the formation of a bipolar pore-like structure.Comment: Solar Physics (in press), 12 pages, 13 figur
Cooperation in costly-access environments
Understanding cooperative behavior in biological and social systems constitutes a scientific challenge, being the object of intense research over the past decades. Many mechanisms have been proposed to explain the presence and persistence of cooperation in those systems, showing that there is no unique explanation, as different scenarios have different possible driving forces. In this paper, we propose a model to study situations in which voluntary participation involves an access cost to the cooperative interaction, besides the cost associated with cooperation. The proposed costly-access prisoner’s dilemma (PD), a symmetric donation game with voluntary and costly participation, breaks the symmetry between abstainers and participants of the voluntary PD. A mean-field approach shows that, in well-mixed populations, the dynamic always leads the system to abstention. However, depending on the return parameter, numerical simulations in structured populations display an alternating behavior between mono-strategic, multi-stable, and coexistence phases. This behavior is fully explained through a theoretical analysis of the strategic motifs, the transitions being determined by the change in stability of those motifs
Late Protein Synthesis-Dependent Phases in CTA Long-Term Memory: BDNF Requirement
It has been proposed that long-term memory (LTM) persistence requires a late protein synthesis-dependent phase, even many hours after memory acquisition. Brain-derived neurotrophic factor (BDNF) is an essential protein synthesis product that has emerged as one of the most potent molecular mediators for long-term synaptic plasticity. Studies in the rat hippocampus have been shown that BDNF is capable to rescue the late-phase of long-term potentiation as well as the hippocampus-related LTM when protein synthesis was inhibited. Our previous studies on the insular cortex (IC), a region of the temporal cortex implicated in the acquisition and storage of conditioned taste aversion (CTA), have demonstrated that intracortical delivery of BDNF reverses the deficit in CTA memory caused by the inhibition of IC protein synthesis due to anisomycin administration during early acquisition. In this work, we first analyze whether CTA memory storage is protein synthesis-dependent in different time windows. We observed that CTA memory become sensible to protein synthesis inhibition 5 and 7 h after acquisition. Then, we explore the effect of BDNF delivery (2 μg/2 μl per side) in the IC during those late protein synthesis-dependent phases. Our results show that BDNF reverses the CTA memory deficit produced by protein synthesis inhibition in both phases. These findings support the notion that recurrent rounds of consolidation-like events take place in the neocortex for maintenance of CTA memory trace and that BDNF is an essential component of these processes
Development of type 2 diabetes mellitus thirty-one years after Billroth II in a patient asking for diabetes surgery
Introduction: Diabetes surgery in obese and slim patients seems to be a superior alternative to the current medical treatment. Gastric bypass is an alternative treat- ment for diabetes. Nevertheless, there are still doubts whether diabetes can recur if you gain weight or if the effects are maintained over time. Other questions refer to the type of surgery to make the bypass limb length or reservoir size for the resolution of the Diabetes Mellitus. Presentation of case: Male patient 69-year-old came to us in order to perform tailored One Anastomosis Gastric Bypass (BAGUA) to treat his type 2 diabetes mellitus and metabolic syndrome. He has a history of peptic ulcer treated with subtotal gastrectomy and Billroth II recons- truction 49 years ago. He currently is not obese and deve- loped diabetes 31 years after surgery. Discussion: Globally there are no reports of patients with normal BMI that after performing gastric bypass developed diabetes mellitus. There are cases where obese diabetic patients after gastric bypass improve or remits the T2DM, but it relapses due to insufficient weight loss or gain it. The patient with gastric bypass Billroth II type, should not developed diabetes. He is normal weight and not had weight gain that could be linked to the develop- ment of diabetes. Conclusions: The results generated by bariatric surgery are encouraging, but still do not clarify the precise way how surgery produces rapid improvement of systemic metabolism as in diabetes, but in our patient, the effect was quite different because the gastric bypass had no protective effect against diabetes
Characterization and improvement of rheological properties of sodium caseinate glycated with galactose, lactose and dextran
10 páginas, 7 figuras, 2 tablas.-- El pdf del artículo es la versión de autor.The aim of this work was to investigate the effect of non-enzymatic glycosylation with galactose, lactose, and 10 kDa dextran on the rheological properties of sodium caseinate. To promote the formation of covalent complexes, the reaction was done in solid state (aw = 0.67), pH 7.0 (0.1 M sodium phosphate buffer), and temperature set at 50 and 60 °C. The progress of Maillard reaction was indirectly traced by measuring the formation of the Amadori compound, through furosine (2-furoylmethyl-lysine) analysis, and brown polymers, and the resulting glycoconjugates were characterized by LC/ESI-MS and SEC. Results showed a higher reactivity of galactose than lactose and dextran to form the glycoconjugates, due to its smaller molecular weight. Glycation with galactose and lactose increased the viscosity of caseinate and also altered its flow characteristics from Newtonian to shear-thinning. Oscillatory testing showed a higher elastic modulus (G′) in glycoconjugates when compared to non-glycated caseinate, especially with galactose, where a gel-like behaviour was observed after long incubation times. Glycation with dextran did not produce substantial improvements in the rheological properties of caseinate, probably due to the limited extent of the reaction. Our results show that by controlling the rate and extent of the Maillard reaction is a technologically feasible operation to improve the viscosity and gelling properties of sodium caseinate-based ingredients.This work was supported by projects Consolider Ingenio 2010
FUN-C-FOOD CSD2007-00063 (Ministerio de Educación y Ciencia),
ALIBIRD S-0505/AGR/000153 (Comunidad de Madrid) and Hatch
project TEN00332 (University of Tennessee Institute of Agriculture).
M. Corzo-Martínez thanks the CSIC for an I3P PhD-grant.Peer reviewe
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