1,721,452 research outputs found
Bayesian nonparametric clustering as a community detection problem
Full text linkA wide class of Bayesian nonparametric priors leads to the representation of the distribution of the observable variables as a mixture density with an infinite number of components. Such a representation induces a clustering structure in the data. However, due to label switching, cluster identification is not straightforward a posteriori and some post-processing of the MCMC output is usually required. Alternatively, observations can be mapped on a weighted undirected graph, where each node represents a sample item and edge weights are given by the posterior pairwise similarities. It is shown how, after building a particular random walk on such a graph, it is possible to apply a community detection algorithm, known as map equation, leading to the minimisation of the expected description length of the partition. A relevant feature of this method is that it allows for the quantification of the posterior uncertainty of the classification
Identifiability Conditions for Spatio-Temporal Bayesian Dynamic Linear Models
No full textIn this paper a class of models for Gaussian space-time processes is considered in a state--space setup. The observed process is assumed to be the sum of unobservable components, such as a trend, a periodic component, a stationary autoregressive component and a measurement error. Although only the space--time structure of the stationary component is treated explicitly, it can\ud
be shown that it is possible to deal with spatial interaction among nonstationary components too. The inclusion of explanatory variables is considered, which can be suitable for both control policies and spatial prediction. Since in real applications such models can be considerably complex, our attention focuses on identifiability conditions
Random field priors for spectral density functions
No full textIn this paper we discuss how a Gaussian random field with Matérn covariance function can represent our prior uncertainty about the log-spectral density, , of a Gaussian, short memory time series. Hyperparameters can be suitably tuned in order to determine the mean square differentiability and the range of autocorrelation of the random field . However, Bayesian computations cannot be easily performed under such prior elicitations. We suggest therefore to approximate the Gaussian random field priors with a class of Gaussian Markov random fields which preserve the main features of the genuine prior distributions
A multivariate time series model for the analysis and prediction of carbon monoxide atmospheric concentrations
No full textJournal of the Royal Statistical Society, Series C: Applied Statistic
CXCR4 in neurophysiology and neurodegeneration
No full textRegeneration of the peripheral nervous system (PNS) relies on an orchestrated response involving not only motor neurons (MNs), but also other type of cells, and a plethora of mediators, with central and peripheral contributions. Axonal injury activates a transcriptional programming in neuronal cell bodies in the spinal cord that drives a polarized axon regrowth over long distances, to reconnect damaged axons with their original targets. This process is coordinated by different peripheral glial cells holding key roles in promoting re-innervation, which localize along the nerve - myelinating Schwann cells (mSCs) – or at the neuromuscular junction (NMJ) - perysinaptic Schwann cells (PSCs).
Our research group has helped to identify the molecular components of the crosstalk driving neurotransmission recovery at the regenerating NMJ following an acute presynaptic injury. By exploiting the presynaptic neurotoxin α-LTx, which causes the reversible degeneration of the motor axon terminal (MAT) at the NMJ, the reviving of the developmental axis Cxcl12α-Cxcr4 and its role in the rescue of synaptic functionality were recently highlighted. Indeed, upon injury the receptor becomes re-expressed by the axonal stump, and its activation by the natural ligand, the chemokine Cxcl12α, as well as by the agonist NUCC-390, promotes a faster recovery of function of the NMJ. These findings suggest that Cxcr4 is potential pharmacological target to counteract nerve degeneration and promote neurotransmission rescue.
Given the role of this molecular axis in peripheral nerve repair, my PhD project aims at elucidating the dynamics of Cxcr4 in PNS physiology and upon injury. To achieve this goal, I investigated Cxcr4 transcription, expression and localization in time and space by employing in vivo models of acute nerve injuries, and by detecting Cxcr4 protein and transcript through immunostaining and RNAscope technology, respectively. I discovered that Cxcr4 re-expression following injury is driven by both central and peripheral mechanisms, which come into play at distinct temporal stages. The early expression of the receptor at the injury site upon a sciatic nerve damage, and even much more distally,
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at the NMJ, together with the axonal localization of CXCR4 transcripts, speak in favor of a local translation of CXCR4 mRNA as an early response to nerve damage. Moreover, our preliminary results point to mSCs and the muscle as possible sources of CXCR4 transcripts for the axon and at the NMJs, respectively.
Furthermore, I explored the impact of Cxcr4 agonists on axonal growth and cAMP levels - being cAMP a major signaling pathway downstream of Cxcr4 engagement - in search of the most effective activator of Cxcr4 in a therapeutic perspective
Photoinitiated Olefin Epoxidation with Molecular Oxygen, Sensitized by Free Base Porphyrins and Promoted by Hexacarbonylmolybdenum in Homogeneous Solution
No full textThe photooxidation of various olefins in homogeneous solution under an oxygen atmosphere, using visible light, a dye sensitizer, and an oxygen-transfer catalyst has been investigated. The oxygen transfer from molecular oxygen to olefin involves the following steps: i) photoinduced singlet-oxygen formation, ii) alkylhydroperoxide formation through ene-reaction, iii) intermediacy of a reactive molybdenum-peroxide, and iv) olefin epoxidation of the remaining substrate or of a second olefin. Among the various sensitizers and catalysts tested, electron deficient free base porphyrin 5,10,15,20-tetrakis(2’,6’-dichlorophenyl)-b-octabromoporphyrin and molybdenum hexacarbonyl showed the best performances in terms of robustness and activity. Under proper conditions, a complete olefin conversion may be obtained, adopting molar ratios of sensitizer/catalyst/substrate=1/50/2000, with the formation of the corresponding epoxide up to 38% yield, which corresponds to 77% of the theoretical maximum. Quite interestingly, olefins reluctant to undergo ene-reaction may be epoxidized in the presence of a second sacrificial olefin yielding the corresponding epoxides with up to 80% total selectivity
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