Universal conductivity and dimensional crossover in multi-layer graphene

We show, by exact Renormalization Group methods, that in multi-layer graphene the dimensional crossover energy scale is decreased by the intra-layer interaction, and that for temperatures and frequencies greater than such scale the conductivity is close to the one of a stack of independent layers up to small corrections

Extended scaling relations for planar lattice models

It is widely believed that the critical properties of several planar lattice models, like the Eight Vertex or the Ashkin-Teller models, are well described by an effective Quantum Field Theory obtained as formal scaling limit. On the basis of this assumption several extended scaling relations among their indices were conjectured. We prove the validity of some of them, among which the ones by Kadanoff, [K], and by Luther and Peschel, [LP].Comment: 32 pages, 7 fi

Ward Identities and chiral anomalies for coupled fermionic chains

Coupled fermionic chains are usually described by an effective model written in terms of bonding and anti-bonding spinless fields with linear dispersion in the vicinities of the respective Fermi points. We derive for the first time exact Ward Identities (WI) for this model, proving the existence of chiral anomalies which verify the Adler-Bardeen non-renormalization property. Such WI are expected to play a crucial role in the understanding of the thermodynamic properties of the system. Our results are non-perturbative and are obtained analyzing Grassmann functional integrals by means of Constructive Quantum Field Theory methods.Comment: TeX file, 26 pages, 7 figures. Published version, new section added to answer referee remarks and derive the Ward Identites, no modifications in the main resul

Spin Hall insulators beyond the Helical Luttinger model

We consider the interacting, spin-conserving, extended Kane-Mele-Hubbard model, andwe rigorously establish the exact quantization of the edge spin conductance and the validity of the helical Luttinger liquid relations for Drude weights and susceptibilities. Our analysis takes fully into account lattice effects, typically neglected in the helical Luttinger model approximation, which play an essential role for universality. The analysis is based on exact renormalization-group methods and on a combination of lattice and emergent Ward identities, which enable the emergent chiral anomaly to be related with the finite renormalizations due to lattice corrections

Conductivity between Luttinger liquids: coupled chains and bilayer graphene

The conductivity properties between Luttinger liquids are analyzed by exact Renormalization Group methods. We prove that in a two chain system or in a model of bilayer graphene, described by two coupled fermionic honeycomb lattices interacting with a gauge field, the transverse optical conductivity at finite temperature is anomalous and decreasing together with the frequency as a power law with Luttinger liquid exponent.Comment: Title changed, new section on bilayer graphene adde

A tale of two tails:Insights from simulations into the formation of the peculiar dwarf galaxy NGC 1427A

We present a scenario for the formation and the morphology of the arrow-shaped dwarf irregular galaxy NGC 1427A in the Fornax Cluster. This galaxy shows intriguing stellar and gaseous tails pointing in different directions for which alternative but not conclusive formation scenarios have been proposed in the literature. We performed N-body/SPH simulations of dwarf galaxies falling into a model of the Fornax cluster, exhibiting a jellyfish-like appearance while undergoing ram-pressure stripping. We noted that some of our models show interesting tail morphologies similar to that of NGC 1427A. In this way, the peculiar NGC 1427A structure can be studied using models whose stellar and neutral gas photometry and kinematics are in good agreement with the observed ones, without the need of invoking an interaction with a nearby galaxy. Thanks to the tails, we can identify the requirements for a galaxy to expose such a structure and assess the possible position and velocity of the galaxy in the cluster. This puts constraints on the orbit of the galaxy, its position in the cluster and the time since its pericentre passage. From the statistics of identified snapshots following our modelling, we found that the most likely position of the galaxy is around 200 kpc in front of the cluster centre, travelling towards the cluster with a velocity angle with respect to the line-of-sight direction of around 50 deg. This analysis can be useful in future observations of similar galaxies in clusters to characterize their position and velocity in the cluster and their formation

Multicenter Validation of the Vasoactive-Ventilation-Renal Score as a Predictor of Prolonged Mechanical Ventilation After Neonatal Cardiac Surgery

Objectives: We sought to validate the Vasoactive-Ventilation-Renal score, a novel disease severity index, as a predictor of outcome in a multicenter cohort of neonates who underwent cardiac surgery. Design: Retrospective chart review. Setting: Seven tertiary-care referral centers. Patients: Neonates defined as age less than or equal to 30 days at the time of cardiac surgery. Interventions: Ventilation index, Vasoactive-Inotrope Score, serum lactate, and Vasoactive-Ventilation-Renal score were recorded for three postoperative time points: ICU admission, 6 hours, and 12 hours. Peak values, defined as the highest of the three measurements, were also noted. Vasoactive-Ventilation-Renal was calculated as follows: ventilation index + Vasoactive-Inotrope Score + Δ creatinine (change in creatinine from baseline × 10). Primary outcome was prolonged duration of mechanical ventilation, defined as greater than 96 hours. Receiver operative characteristic curves were generated, and abilities of variables to correctly classify prolonged duration of mechanical ventilation were compared using area under the curve values. Multivariable logistic regression modeling was also performed. Measurements and Main Results: We reviewed 275 neonates. Median age at surgery was 7 days (25th–75th percentile, 5–12 d), 86 (31%) had single ventricle anatomy, and 183 (67%) were classified as Society of Thoracic Surgeons-European Association for Cardio-Thoracic Surgery Congenital Heart Surgery Mortality Category 4 or 5. Prolonged duration of mechanical ventilation occurred in 89 patients (32%). At each postoperative time point, the area under the curve for prolonged duration of mechanical ventilation was significantly greater for the Vasoactive-Ventilation-Renal score as compared to the ventilation index, Vasoactive-Inotrope Score, and serum lactate, with an area under the curve for peak Vasoactive-Ventilation-Renal score of 0.82 (95% CI, 0.77–0.88). On multivariable analysis, peak Vasoactive-Ventilation-Renal score was independently associated with prolonged duration of mechanical ventilation, odds ratio (per 1 unit increase): 1.08 (95% CI, 1.04–1.12). Conclusions: In this multicenter cohort of neonates who underwent cardiac surgery, the Vasoactive-Ventilation-Renal score was a reliable predictor of postoperative outcome and outperformed more traditional measures of disease complexity and severity

On Causal Inference for Data-free Structured Pruning

Neural networks (NNs) are making a large impact both on research and industry. Nevertheless, as NNs' accuracy increases, it is followed by an expansion in their size, required number of compute operations and energy consumption. Increase in resource consumption results in NNs' reduced adoption rate and real-world deployment impracticality. Therefore, NNs need to be compressed to make them available to a wider audience and at the same time decrease their runtime costs. In this work, we approach this challenge from a causal inference perspective, and we propose a scoring mechanism to facilitate structured pruning of NNs. The approach is based on measuring mutual information under a maximum entropy perturbation, sequentially propagated through the NN. We demonstrate the method's performance on two datasets and various NNs' sizes, and we show that our approach achieves competitive performance under challenging conditions

Density Profiles of Cold Dark Matter Substructure: Implications for the Missing Satellites Problem

The structural evolution of substructure in cold dark matter (CDM) models is investigated combining ``low-resolution'' satellites from cosmological N-body simulations of parent halos with N=10^7 particles with high-resolution individual subhalos orbiting within a static host potential. We show that, as a result of mass loss, convergence in the central density profiles requires the initial satellites to be resolved with N=10^7 particles and parsec-scale force resolution. We find that the density profiles of substructure halos can be well fitted with a power-law central slope that is unmodified by tidal forces even after the tidal stripping of over 99% of the initial mass and an exponential cutoff in the outer parts. The solution to the missing-satellites problem advocated by Stoehr et al. in 2002 relied on the flattening of the dark matter (DM) halo central density cusps by gravitational tides, enabling the observed satellites to be embedded within DM halos with maximum circular velocities as large as 60 km/s. In contrast, our results suggest that tidal interactions do not provide the mechanism for associating the dwarf spheroidal satellites (dSphs) of the Milky Way with the most massive substructure halos expected in a CDM universe. We compare the predicted velocity dispersion profiles of Fornax and Draco to observations, assuming that they are embedded in CDM halos. Models with isotropic and tangentially anisotropic velocity distributions for the stellar component fit the data only if the surrounding DM halos have maximum circular velocities in the range 20-35 km/s. If the dSphs are embedded within halos this large then the overabundance of satellites within the concordance LCDM cosmological model is significantly alleviated, but this still does not provide the entire solution.Comment: Accepted for publication in ApJ, 17 pages, 9 figures, LaTeX (uses emulateapj5.sty

ASTRI SST-2M prototype and mini-array simulation chain, data reduction software, and archive in the framework of the Cherenkov Telescope Array

The Cherenkov Telescope Array (CTA) is a worldwide project aimed at building the next-generation ground-based gamma-ray observatory. Within the CTA project, the Italian National Institute for Astrophysics (INAF) is developing an end-to-end prototype of the CTA Small-Size Telescopes with a dual-mirror (SST-2M) Schwarzschild-Couder configuration. The prototype, named ASTRI SST-2M, is located at the INAF "M.C. Fracastoro" observing station in Serra La Nave (Mt. Etna, Sicily) and is currently in the scientific and performance validation phase. A mini-array of (at least) nine ASTRI telescopes has been then proposed to be deployed at the Southern CTA site, by means of a collaborative effort carried out by institutes from Italy, Brazil, and South-Africa. The CTA/ASTRI team is developing an end-to-end software package for the reduction of the raw data acquired with both ASTRI SST-2M prototype and mini-array, with the aim of actively contributing to the global ongoing activities for the official data handling system of the CTA observatory. The group is also undertaking a massive Monte Carlo simulation data production using the detector Monte Carlo software adopted by the CTA consortium. Simulated data are being used to validate the simulation chain and evaluate the ASTRI SST-2M prototype and mini-array performance. Both activities are also carried out in the framework of the European H2020-ASTERICS (Astronomy ESFRI and Research Infrastructure Cluster) project. A data archiving system, for both ASTRI SST-2M prototype and mini-array, has been also developed by the CTA/ASTRI team, as a testbed for the scientific archive of CTA. In this contribution, we present the main components of the ASTRI data handling systems and report the status of their development.Comment: Proceedings of the 35th International Cosmic Ray Conference (ICRC 2017), Bexco, Busan, Korea. All CTA contributions at arXiv:1709.0348