Resource
2015 EN
Alvise Raccanelli · Maresuke Shiraishi · Nicola Bartolo
+5 more
We investigate how well future large-scale radio surveys could measuredifferent shapes of primordial non-Gaussianity; in particular we focus onangle-dependent non-Gaussianity arising from primordial anisotropic sources,whose bispectrum has an angle dependence between the three wavevectors that ischaracterized by Legendre polynomials $\mathcal{P}_L$ and expansioncoefficients $c_L$. We provide forecasts for measurements of galaxy powerspectrum, finding that Large-Scale Structure (LSS) data could allowmeasurements of primordial non-Gaussianity competitive or improving uponcurrent constraints set by CMB experiments, for all the shapes considered. Weargue that the best constraints will come from the possibility to assignredshift information to radio galaxy surveys, and investigate a few possiblescenarios for the EMU and SKA surveys. A realistic (futuristic) modeling couldprovide constraints of $f_{\rm NL}^{\rm loc} \approx 1 (0.5)$ for the localshape, $f_{\rm NL}$ of $\mathcal{O}(10) (\mathcal{O}(1))$ for the orthogonal,equilateral and folded shapes, and $c_{L=1} \approx 80 (2)$, $c_{L=2} \approx400 (10)$ for angle-dependent non-Gaussianity. The more futuristic forecastsshow the potential of LSS analyses to considerably improve current constraintson non-Gaussianity, and so on models of the primordial Universe. Finally, wefind the minimum requirements that would be needed to reach$\sigma(c_{L=1})=10$, which can be considered as a typical (lower) valuepredicted by some (inflationary) models.
Resource
2015 EN
Davide Mandelli · Andrea Vanossi · Michele Invernizzi
+3 more
Two-dimensional (2D) crystalline colloidal monolayers sliding over alaser-induced optical lattice recently emerged as a new tool for the study offriction between ideal crystal surfaces. Here we focus in particular on staticfriction, the minimal sliding force necessary to depin one lattice from theother. If the colloid and the optical lattices are mutually commensurate, thecolloid sliding is always pinned by static friction; but when they areincommensurate the presence or absence of pinning can be expected to dependupon the system parameters. If a 2D analogy to the mathematically establishedAubry transition of one-dimensional systems were to hold, an increasingperiodic corrugation strength $U_0$ should turn an initially free-slidingmonolayer into a pinned state through a well-defined dynamical phasetransition. We address this problem by the simulated sliding of a realisticmodel 2D colloidal lattice, confirming the existence of a clear and sharpsuperlubric-pinned transition for increasing corrugation strength. Unlike the1D Aubry transition which is continuous, the 2D transition exhibits a definitefirst-order character. With no change of symmetry, the transition entails astructural character, with a sudden increase of the colloid-colloid interactionenergy, accompanied by a compensating downward jump of the colloid-corrugationenergy. The transition value for the corrugation amplitude $U_0$ depends uponthe misalignment angle $\theta$ between the optical and the colloidal lattices,superlubricity surviving until larger corrugations for angles away from theenergetically favored orientation, which is itself generally slightlymisaligned, as shown in recent work. The observability of thesuperlubric-pinned colloid transition is proposed and discussed.
Resource
2015 EN
Francesca Arrigo · Michele Benzi
We introduce new broadcast and receive communicability indices that can beused as global measures of how effectively information is spread in a directednetwork. Furthermore, we describe fast and effective criteria for the selectionof edges to be added to (or deleted from) a given directed network so as toenhance these network communicability measures. Numerical experimentsillustrate the effectiveness of the proposed techniques.
Resource
2015 EN
Justin F. Brunelle · Michele C. Weigle · Michael L. Nelson
Web resources are increasingly interactive, resulting in resources that areincreasingly difficult to archive. The archival difficulty is based on the useof client-side technologies (e.g., JavaScript) to change the client-side stateof a representation after it has initially loaded. We refer to theserepresentations as deferred representations. We can better archive deferredrepresentations using tools like headless browsing clients. We use 10,000 seedUniversal Resource Identifiers (URIs) to explore the impact of includingPhantomJS -- a headless browsing tool -- into the crawling process by comparingthe performance of wget (the baseline), PhantomJS, and Heritrix. Heritrixcrawled 2.065 URIs per second, 12.15 times faster than PhantomJS and 2.4 timesfaster than wget. However, PhantomJS discovered 531,484 URIs, 1.75 times morethan Heritrix and 4.11 times more than wget. To take advantage of theperformance benefits of Heritrix and the URI discovery of PhantomJS, werecommend a tiered crawling strategy in which a classifier predicts whether arepresentation will be deferred or not, and only resources with deferredrepresentations are crawled with PhantomJS while resources without deferredrepresentations are crawled with Heritrix. We show that this approach is 5.2times faster than using only PhantomJS and creates a frontier (set of URIs tobe crawled) 1.8 times larger than using only Heritrix.
Resource
2015 EN
Pablo Ramos · Marc Mankarious · Michele Pavanello
We present here a short and subjective review of methods for calculatingcharge transfer couplings. Although we mostly focus on Density FunctionalTheory, we discuss a small subset of semiempirical methods as well as theadiabatic-to-diabatic transformation methods typically coupled withwavefunction-based electronic structure calculations. In this work, we willpresent the reader with a critical assessment of the regimes that can bemodeled by the various methods their strengths and weaknesses. In order to givea feeling about the practical aspects of the calculations, we also provide thereader with a practical protocol for running coupling calculations with therecently developed FDE-ET method.
Resource
2015 EN
D. Carnevale · B. Esposito · M. Gospodarczyk
+19 more
Experimental results on the position and current control of disruptiongenerated runaway electrons (RE) in FTU are presented. A scanninginterferometer diagnostic has been used to analyze the time evolution of the REbeam radial position and its instabilities. Correspondence of theinterferometer time traces, radial profile reconstructed via magneticmeasurements and fission chamber signals are discussed. New RE controlalgorithms, which define in real-time updated plasma current and positionreferences, have been tested in two experimental scenarios featuring disruptiongenerated RE plateaus. Comparative studies among 52 discharges with disruptiongenerated RE beam plateaus are presented in order to assess the effectivenessof the proposed control strategies as the RE beam interaction with the plasmafacing components is reduced while the current is ramped-down.
Resource
2015 EN
Daniela Bubboloni · Michele Gori
We introduce three different qualifications of the reversal bias in theframework of social choice correspondences. For each of them, we prove that theMinimax social choice correspondence is immune to it if and only if the numberof voters and the number of alternatives satisfy suitable arithmeticalconditions. We prove those facts thanks to a new characterization of theMinimax social choice correspondence and using a graph theory approach. Wediscuss the same issue for the Borda and Copeland social choicecorrespondences.
Resource
2015 EN
Luca Di Persio · Michele Bonollo · Gregorio Pellegrini
The Polynomial Chaos Expansion (PCE) technique recovers a finite second orderrandom variable exploiting suitable linear combinations of orthogonalpolynomials which are functions of a given stochas- tic quantity {\xi}, henceacting as a kind of random basis. The PCE methodology has been developed as amathematically rigorous Uncertainty Quantification (UQ) method which aims atproviding reliable numerical estimates for some uncertain physical quantitiesdefining the dynamic of certain engineering models and their relatedsimulations. In the present paper we exploit the PCE approach to analyze someequity and interest rate models considering, without loss of generality, theone dimensional case. In particular we will take into account those modelswhich are based on the Geometric Brownian Motion (gBm), e.g. the Vasicek model,the CIR model, etc. We also provide several numerical applications and resultswhich are discussed for a set of volatility values. The latter allows us totest the PCE technique on a quite large set of different scenarios, henceproviding a rather complete and detailed investigation on PCE-approximation'sfeatures and properties, such as the convergence of statistics, distributionand quantiles. Moreover we give results concerning both an efficiency and anaccuracy study of our approach by comparing our outputs with the ones obtainedadopting the Monte Carlo approach in its standard form as well as in itsenhanced version.
Resource
2015 EN
for the CTA Consortium Markus Gaug · for the CTA Consortium Michael Daniel · for the CTA Consortium David Berge
+6 more
The construction of the Cherenkov Telescope Array is expected to start soon.We will present the baseline methods and their extensions currently foreseen tocalibrate the observatory. These are bound to achieve the strong requirementson allowed systematic uncertainties for the reconstructed gamma-ray energy andflux scales, as well as on the pointing resolution, and on the overall dutycycle of the observatory. Onsite calibration activities are designed to includea robust and efficient calibration of the telescope cameras, and variousmethods and instruments to achieve calibration of the overall opticalthroughput of each telescope, leading to both inter-telescope calibration andan absolute calibration of the entire observatory. One important aspect of theonsite calibration is a correct understanding of the atmosphere above thetelescopes, which constitutes the calorimeter of this detection technique. Itis planned to be constantly monitored with state-of-the-art instruments toobtain a full molecular and aerosol profile up to the stratosphere. In order toguarantee the best use of the observation time, in terms of usable data, anintelligent scheduling system is required, which gives preference to thosesources and observation programs that can cope with the given atmosphericconditions, especially if the sky is partially covered by clouds, or slightlycontaminated by dust. Ceilometers in combination with all-sky-cameras areplannned to provide the observatory with a fast, online and full-sky knowledgeof the expected conditions for each pointing direction. For a precisecharacterization of the adopted observing direction, wide-field opticaltelescopes and Raman Lidars are planned to provide information about theheight-resolved and wavelength-dependent atmospheric extinction, throughout thefield-of-view of the cameras.
Resource
2015 EN
Peter D. Tovee · Claire Tinker-Mill · Kevin Kjoller
+6 more
Infrared (IR) spectroscopy, a well established tool for chemical analysis ofdiverse materials, has significant potential in biomedical applications. Whilethe spatial resolution of traditional IR spectroscopy is limited by thewavelength of the IR light to the few micrometres, it has been shown thatnanoscale chemical analysis can be obtained by detecting IR induced localheating photothermal response via Scanning Thermal Microscopy (SThM) or localthermomechanical expansion using Atomic Force Microscopy (AFM). This paperexplores the potential of a pulsed ps pulse duration high power free electronlaser (FEL) light source for AFM-IR and SThM-IR spectroscopy employing standardAFM and SThM probes. The SThM-IR response was found to have a detrimentalstrong background signal due to the direct heating of the probe, whereas theAFM IR thermomechanical response allowed to eliminate such a problem for bothtop down and bottom up illuminations with the FEL IR source. The SThM IRcharacteristic response time was approximately half that of AFM-IR, in linewith finite element analysis simulations. Finally, the advantages and drawbacksof AFM-IR wavelength sensitive spectroscopic response using a ps duration FELvs a high repetition quantum cascade laser IR source in studies of nanoscaledimension amyloid peptide fibres were explored both experimentally and viafinite elements analysis.