Resource
2015 EN
Ubertino Battisti · Michele Berra
We show the existence of a family of frames of $L^2(\mathbb{R})$ which dependon a parameter $\alpha\in [0,1]$. If $\alpha=0$, we recover the usual Gaborframe, if $\alpha=1$ we obtain a frame system which is closely related to theso called DOST basis, first introduced by Stockwell and then analyzed byBattisti and Riba. If $\alpha\in (0,1)$, the frame system is associated to a socalled $\alpha$-partitioning of the frequency domain. Restricting to the case$\alpha=1$, we provide a truly $n$-dimensional version of the DOST basis and anassociated frame of $L^2(\mathbb{R}^d)$.
Resource
2015 EN
for the CTA Consortium Laura Valore · for the CTA Consortium Carla Aramo · for the CTA Consortium Michele Doro
+4 more
The Cherenkov Telescope Array (CTA) is the next generation of ground-basedvery high energy gamma-ray instruments; the facility will be organized in twoarrays, one for each hemisphere. The atmospheric calibration of the CTAtelescopes is a critical task. The atmosphere affects the measured Cherenkovyield in several ways: the air-shower development itself, the variation of theCherenkov angle with altitude, the loss of photons due to scattering andabsorption of Cherenkov light out of the camera field-of-view and thescattering of photons into the camera. In this scenario, aerosols are the mostvariable atmospheric component in time and space and therefore need acontinuous monitoring. Lidars are among the most used instruments inatmospheric physics to measure the aerosol attenuation profiles of light. TheARCADE Lidar system is a very compact and portable Raman Lidar system that hasbeen built within the FIRB 2010 grant and is currently taking data in Lamar,Colorado. The ARCADE Lidar is proposed to operate at the CTA sites with thegoal of making a first survey of the aerosol conditions of the selected siteand to use it as a calibrated benchmark for the other Lidars that will beinstalled on site. It is proposed for CTA that the ARCADE Lidar will be firstupgraded in Italy and then tested in parallel to a Lidar of the EARLINETnetwork in L'Aquila. Upgrades include the addition of the water vapour Ramanchannel to the receiver and the use of new and better performing electronics.It is proposed that the upgraded system will travel to and characterize bothCTA sites, starting from the first selected site in 2016.
Resource
2015 EN
Andrea Bussone · Michele Della Morte · Martin Hansen
+1 more
Imposing twisted boundary conditions on the fermionic fields is a procedureextensively used when evaluating, for example, form factors on the lattice.Twisting is usually performed for one flavour and only in the valence, and thiscauses a breaking of unitarity. In this work we explore the possibility ofrestoring unitarity through the reweighting method. We first study someproperties of the approach at tree level and then we stochastically evaluateratios of fermionic determinants for different boundary conditions in order toinclude them in the gauge averages, avoiding in this way the expensivegeneration of new configurations for each choice of the twisting angle,$\theta$. As expected the effect of reweighting is negligible in the case oflarge volumes but it is important when the volumes are small and the twistingangles are large. In particular we find a measurable effect for the plaquetteand the pion correlation function in the case of $\theta=\pi/2$ in a volume$16\times 8^3$, and we observe a systematic upward shift in the pion dispersionrelation.
Resource
2015 EN
Massimiliano Bonomi · Carlo Camilloni · Andrea Cavalli
+1 more
Modelling a complex system is almost invariably a challenging task. Theincorporation of experimental observations can be used to improve the qualityof a model, and thus to obtain better predictions about the behavior of thecorresponding system. This approach, however, is affected by a variety ofdifferent errors, especially when a system populates simultaneously an ensembleof different states and experimental data are measured as averages over suchstates. To address this problem we present a Bayesian inference method, calledmetainference, that is able to deal with errors in experimental measurements aswell as with experimental measurements averaged over multiple states. Toachieve this goal, metainference models a finite sample of the distribution ofmodels using a replica approach, in the spirit of the replica-averagingmodelling based on the maximum entropy principle. To illustrate the method wepresent its application to a heterogeneous model system and to thedetermination of an ensemble of structures corresponding to the thermalfluctuations of a protein molecule. Metainference thus provides an approach tomodel complex systems with heterogeneous components and interconverting betweendifferent states by taking into account all possible sources of errors.
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2015 EN
Michele Caselle · Alessandro Nada · Marco Panero
We present a novel lattice calculation of the equation of state of SU(2)Yang-Mills theory in the confining phase. We show that a gas of massive,non-interacting glueballs describes remarkably well the results, provided thata bosonic closed-string model is used to derive an exponentially growingHagedorn spectrum for the heavy glueball states with no free parameters. Thiseffective model can be applied to SU(3) Yang-Mills theory and the theoreticalprediction agrees nicely with the lattice results reported by Bors\'anyi et al.in JHEP 07 (2012) 056.
Resource
2015 EN
Hossein Shokri-Ghadikolaei · Carlo Fischione · Petar Popovski
+1 more
Increased density of wireless devices, ever growing demands for extremelyhigh data rate, and spectrum scarcity at microwave bands make the millimeterwave (mmWave) frequencies an important player in future wireless networks.However, mmWave communication systems exhibit severe attenuation, blockage,deafness, and may need microwave networks for coordination and fall-backsupport. To compensate for high attenuation, mmWave systems exploit highlydirectional operation, which in turn substantially reduces the interferencefootprint. The significant differences between mmWave networks and legacycommunication technologies challenge the classical design approaches,especially at the medium access control (MAC) layer, which has receivedcomparatively less attention than PHY and propagation issues in the literatureso far. In this paper, the MAC layer design aspects of short range mmWavenetworks are discussed. In particular, we explain why current mmWave standardsfail to fully exploit the potential advantages of short range mmWavetechnology, and argue for the necessity of new collision-aware hybrid resourceallocation frameworks with on-demand control messages, the advantages of acollision notification message, and the potential of multihop communication toprovide reliable mmWave connections.
Resource
2015 EN
Nicolo Michelusi · Petar Popovski · Michele Zorzi
This paper introduces a novel technique that enables access by a cognitivesecondary user (SU) to a spectrum occupied by an incumbent primary user (PU)that employs Type-I Hybrid ARQ. The technique allows the SU to performselective retransmissions of SU data packets that have not been successfullydecoded in the previous attempts. The temporal redundancy introduced by the PUARQ protocol and by the selective retransmission process of the SU can beexploited by the SU receiver to perform interference cancellation (IC) overmultiple transmission slots, thus creating a "clean" channel for the decodingof the concurrent SU or PU packets. The chain decoding technique is initiatedby a successful decoding operation of a SU or PU packet and proceeds by aniterative application of IC in order to decode the buffered signals thatrepresent packets that could not be decoded before. Based on this scheme, anoptimal policy is designed that maximizes the SU throughput under a constrainton the average long-term PU performance. The optimality of the chain decodingprotocol is proved, which determines which packet the SU should send at a giventime. Moreover, a decoupling principle is proved, which establishes theoptimality of decoupling the secondary access strategy from the chain decodingprotocol. Specifically, first, the SU access policy, optimized via dynamicprogramming, specifies whether the SU should access the channel or not, basedon a compact state representation of the protocol; and second, the chaindecoding protocol embeds four basic rules that are used to determine whichpacket should be transmitted by the SU. Chain decoding provably yields themaximum improvement that can be achieved by any scheme under our assumptions,and thus it is the ultimate scheme, which completely closes the gap betweenprevious schemes and optimality.
Resource
2015 EN
Michele Scaraggi · Davide Comingio
We present a numerical model for the prediction of the rough contactmechanics of a viscoelastic block, with graded rheology, in steady slidingcontact with a randomly rough rigid surface. In particular, we derive theeffective surface response of a stepwise or continuously-graded block in theFourier domain, which is then embedded in a Fourier-based residuals moleculardynamic formulation of the contact mechanics. Finally we discuss on the role ofsmall-scale wavelengths on rubber friction and contact area, and we demonstratethat the rough contact mechanics exhibits effective interface properties whichconverge to asymptotes upon increase of the small-scale roughness content, whena realistic rheology of the confinement is taken into account.
Resource
2015 EN
St. Anthony Falls Laboratory, UMN Michele Guala · St. Anthony Falls Laboratory, UMN Jiarong Hong
A simple theory, based on observations of snowflake distribution in aturbulent flow, is proposed to model the growth of inertial particles as aresult of dynamic clustering at scales larger than the Kolmogorov length scale.Particles able to stick or coalesce are expected to grow in size in flowregions where preferential concentration is predicted by a critical Stokesnumber $St=\tau_p/\tau_f \simeq 1 $. We postulate that, during growth, $St$remains critical, with the particle response time $\tau_p$ evolving accordingto the specific flow time scale $\tau_f$ defined by the vortices around whichprogressively larger particles end up orbiting. This mechanism leads to theprediction of the limiting size of aggregating particles in a turbulent flow.Such limit is determined by the extent of the turbulent inertial range, whichcan be formulated as a function of accessible integral-scale quantities. Theproposed dynamically critical Stokes growth provides a framework to interpretparticle aggregation, size growth and particle cluster growth in variousgeophysical multi-phase flows.
Resource
2015 EN
INFN, Milan Bicocca Michele Pepe · Milan Bicocca U.
INFN, Milan Bicocca Leonardo Giusti
We present the calculation of the non-perturbative renormalization constantsof the energy-momentum tensor in the SU(3) Yang-Mills theory. That computationis carried out in the framework of shifted boundary conditions, where a thermalquantum field theory is formulated in a moving reference frame. Thenon-perturbative renormalization factors are then used to measure the Equationof State of the SU(3) Yang-Mills theory. Preliminary numerical results arepresented and discussed.