Sublinear algorithms for local graph centrality estimation

We study the complexity of local graph centrality estimation, with the goal of approximating the centrality score of a given target node while exploring only a sublinear number of nodes/arcs of the graph and performing a sublinear number of elementary operations. We develop a technique, that we apply to the PageRank and Heat Kernel centralities, for building a low-variance score estimator through a local exploration of the graph. We obtain an algorithm that, given any node in any graph of $m$ arcs, with probability $(1-\delta)$ computes a multiplicative $(1\pm\epsilon)$-approximation of its score by examining only $\tilde{O}(\min(m^{2/3} \Delta^{1/3} d^{-2/3},\, m^{4/5} d^{-3/5}))$ nodes/arcs, where $\Delta$ and $d$ are respectively the maximum and average outdegree of the graph (omitting for readability $\operatorname{poly}(\epsilon^{-1})$ and $\operatorname{polylog}(\delta^{-1})$ factors). A similar bound holds for computational complexity. We also prove a lower bound of $\Omega(\min(m^{1/2} \Delta^{1/2} d^{-1/2}, \, m^{2/3} d^{-1/3}))$ for both query complexity and computational complexity. Moreover, our technique yields a $\tilde{O}(n^{2/3})$ query complexity algorithm for the graph access model of [Brautbar et al., 2010], widely used in social network mining; we show this algorithm is optimal up to a sublogarithmic factor. These are the first algorithms yielding worst-case sublinear bounds for general directed graphs and any choice of the target node.Comment: 29 pages, 1 figur

On Approximating the Stationary Distribution of Time-reversible Markov Chains

Approximating the stationary probability of a state in a Markov chain through Markov chain Monte Carlo techniques is, in general, inefficient. Standard random walk approaches require tilde{O}(tau/pi(v)) operations to approximate the probability pi(v) of a state v in a chain with mixing time tau, and even the best available techniques still have complexity tilde{O}(tau^1.5 / pi(v)^0.5); and since these complexities depend inversely on pi(v), they can grow beyond any bound in the size of the chain or in its mixing time. In this paper we show that, for time-reversible Markov chains, there exists a simple randomized approximation algorithm that breaks this "small-pi(v) barrier"

Decellularization and Delipidation Protocols of Bovine Bone and Pericardium for Bone Grafting and Guided Bone Regeneration Procedures

The combination of bone grafting materials with guided bone regeneration (GBR) membranes seems to provide promising results to restore bone defects in dental clinical practice. In the first part of this work, a novel protocol for decellularization and delipidation of bovine bone, based on multiple steps of thermal shock, washes with detergent and dehydration with alcohol, is described. This protocol is more effective in removal of cellular materials, and shows superior biocompatibility compared to other three methods tested in this study. Furthermore, histological and morphological analyses confirm the maintenance of an intact bone extracellular matrix (ECM). In vitro and in vivo experiments evidence osteoinductive and osteoconductive properties of the produced scaffold, respectively. In the second part of this study, two methods of bovine pericardium decellularization are compared. The osmotic shock-based protocol gives better results in terms of removal of cell components, biocompatibility, maintenance of native ECM structure, and host tissue reaction, in respect to the freeze/thaw method. Overall, the results of this study demonstrate the characterization of a novel protocol for the decellularization of bovine bone to be used as bone graft, and the acquisition of a method to produce a pericardium membrane suitable for GBR applications

Methane-Assisted Iron Oxides Chemical Looping in a Solar Concentrator: A Real Case Study

Recent interest in hydrogen as an alternative fuel for lowering carbon emissions is funding the exploration of new ways to cleanly produce this molecule. Iron oxides can be used within a process of chemical looping. More specifically, they can lose oxygens at extremely high temperature in an inert atmosphere. An alumina receiver could not stand the extreme thermal stress, while steel (AISI 316 and Inconel Hastelloy c-276) lasted enough for the reaction to start, even if at the end of the process the receiver melted. Operating at a temperature above 1000 K helped the reaction switch from methane chemical looping combustion to chemical looping reforming, thus favouring H2 and CO yields. The gas flow outlet from the reactor reached a percentage up to 45% of H2 and 10% of CO. Carbon dioxide instead reached very low concentrations. While CO and CO2 reached a peak at the beginning of the experiment and then decreased, H2 was oscillating around a stable value. Unreacted methane was detected. The temperatures recorded in the reactor and the gas mixture obtained were used to validate a multiphysical model. The heat transfer and the chemistry of the experiment were simulated

Chemical evolution of disc galaxies from cosmological simulations

We perform a suite of cosmological hydrodynamical simulations of disc galaxies, with zoomedin initial conditions leading to the formation of a halo of mass M-halo, DM similar or equal to 2 x 10(12) M-circle dot at redshift z = 0. These simulations aim at investigating the chemical evolution and the distribution of metals in a disc galaxy, and at quantifying the effect of (i) the assumed IMF, (ii) the adopted stellar yields, and (iii) the impact of binary systems originating SNe Ia on the process of chemical enrichment. We consider either a Kroupa, Tout & Gilmore (1993) or a more top-heavy Kroupa (2001) IMF, two sets of stellar yields and different values for the fraction of binary systems suitable to give rise to SNe Ia. We investigate stellar ages, SN rates, stellar and gas metallicity gradients, and stellar alpha-enhancement in simulations, and compare predictions with observations. We find that a Kroupa et al. (1993) IMF has to be preferred when modelling late-type galaxies in the local Universe. On the other hand, the comparison of stellar metallicity profiles and alpha-enhancement trends with observations of Milky Way stars shows a better agreement when a Kroupa (2001) IMF is assumed. Comparing the predicted SN rates and stellar alpha-enhancement with observations supports a value for the fraction of binary systems producing SNe Ia of 0.03, at least for late-type galaxies and for the considered IMFs. Adopted stellar yields are crucial in regulating cooling and star formation, and in determining patterns of chemical enrichment for stars, especially for those located in the galaxy bulge

Loss of LHCI system affects LHCII re-distribution between thylakoid domains upon state transitions

LHCI, the peripheral antenna system of Photosystem I, includes four light-harvesting proteins (Lhca1-Lhca4) in higher plants, all of which are devoid in the Arabidopsis thaliana knock-out mutant \u394Lhca. PSI absorption cross-section was reduced in the mutant, thus affecting the redox balance of the photosynthetic electron chain and resulting in a more reduced PQ with respect to the wild type. \u394Lhca plants developed compensatory response by enhancing LHCII binding to PSI. However, the amplitude of state transitions, as measured from changes of chlorophyll fluorescence in vivo, was unexpectedly low than the high level of PSI-LHCII supercomplex established. In order to elucidate the reasons for discrepancy, we further analyzed state transition in \u394Lhca plants. The STN7 kinase was fully active in the mutant as judged from up-regulation of LHCII phosphorylation in state II. Instead, the lateral heterogeneity of thylakoids was affected by lack of LHCI, with LHCII being enriched in stroma membranes with respect to the wild type. Re-distribution of this complex affected the overall fluorescence yield of thylakoids already in state I and minimized changes in RT fluorescence yield when LHCII did connect to PSI reaction center. We conclude that interpretation of chlorophyll fluorescence analysis of state transitions becomes problematic when applied to mutants whose thylakoid architecture is significantly modified with respect to the wild type

A path analysis on the direct and indirect effects of the unit environment on eating dependence among cognitively impaired nursing home residents

BACKGROUND: This study aims to estimate the direct and indirect effects of the unit environment alongside individual and nursing care variables on eating dependence among residents who are cognitively impaired and living in a nursing home. METHOD: A multicentre observational study was carried out in 2017: 13 Italian nursing homes were involved in data collection. Included residents were aged > 65 at baseline, living in the considered facility for the last 6 months and during the entire study period and having received at least one comprehensive assessment. Data were collected (a) at the individual level: eating dependence using the Edinburgh Feeding Evaluation in Dementia Scale and other clinical variables; (b) at the nursing care level with daily interventions to maintain eating independence assessed with a checklist; and (c) at the nursing home level, using the Therapeutic Environment Screening Survey for Nursing Homes. RESULTS: One thousand twenty-seven residents were included with an average age of 85.32 years old (95% CI: 84.74-85.89), mainly female (781; 76%). The path analysis explained the 57.7% variance in eating dependence. Factors preventing eating dependence were: (a) at the individual level, increased functional dependence measured with the Barthel Index (β - 2.374); eating in the dining room surrounded by residents (β - 1.802) as compared to eating alone in bed; and having a close relationship with family relatives (β - 0.854), (b) at the nursing care level, the increased number of interventions aimed at promoting independence (β - 0.524); and (c) at the NH level, high scores in 'Space setting' (β - 4.446), 'Safety' (β - 3.053), 'Lighting' (β - 2.848) and 'Outdoor access' (β - 1.225). However, environmental factors at the unit level were found to have also indirect effects by influencing the degree of functional dependence, the occurrence of night restlessness and the number of daily interventions performed by the nursing staff. CONCLUSION: Eating dependence is a complex phenomenon requiring interventions targeting individual, nursing care, and environmental levels. The NH environment had the largest direct and indirect effect on residents' eating dependence, thus suggesting that at this level appropriate interventions should be designed and implemented

Impact of AGN feedback on galaxies and their multiphase ISM across cosmic time

We present simulations of galaxy formation, based on the GADGET-3 code, in which a sub-resolution model for star formation and stellar feedback is interfaced with a new model for AGN feedback. Our sub-resolution model describes a multiphase ISM, accounting for hot and cold gas within the same resolution element: we exploit this feature to investigate the impact of coupling AGN feedback energy to the different phases of the ISM over cosmic time. Our fiducial model considers that AGN feedback energy coupling is driven by the covering factors of the hot and cold phases. We perform a suite of cosmological hydrodynamical simulations of disc galaxies (Mhalo, DM 43 2 . 1012 M&09, at z = 0), to investigate: (i) the effect of different ways of coupling AGN feedback energy to the multiphase ISM; (ii) the impact of different prescriptions for gas accretion (i.e. only cold gas, both cold and hot gas, with the additional possibility of limiting gas accretion from cold gas with high angular momentum); (iii) how different models of gas accretion and coupling of AGN feedback energy affect the coevolution of supermassive BHs and their host galaxy. We find that at least a share of the AGN feedback energy has to couple with the diffuse gas, in order to avoid an excessive growth of the BH mass. When the BH only accretes cold gas, it experiences a growth that is faster than in the case in which both cold and hot gas are accreted. If the accretion of cold gas with high angular momentum is reduced, the BH mass growth is delayed, the BH mass at z = 0 is reduced by up to an order of magnitude, and the BH is prevented from accreting below z 72 2, when the galaxy disc forms