1,646 research outputs found

    Superexpanders from group actions on compact manifolds

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    It is known that the expanders arising as increasing sequences of level sets of warped cones, as introduced by the second-named author, do not coarsely embed into a Banach space as soon as the corresponding warped cone does not coarsely embed into this Banach space. Combining this with non-embeddability results for warped cones by Nowak and Sawicki, which relate the non-embeddability of a warped cone to a spectral gap property of the underlying action, we provide new examples of expanders that do not coarsely embed into any Banach space with nontrivial type. Moreover, we prove that these expanders are not coarsely equivalent to a Lafforgue expander. In particular, we provide infinitely many coarsely distinct superexpanders that are not Lafforgue expanders. In addition, we prove a quasi-isometric rigidity result for warped cones.Comment: 16 pages, to appear in Geometriae Dedicat

    Trasmettitore "ultra-low power" per applicazioni WPAN-RFID

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    In questo lavoro di tesi è stato progettato e simulato un trasmettitore integrato in tecnologia CMOS 0.35 um per applicazioni wireless con particolare interesse verso quelle a bassissimo consumo di potenza, secondo lo standard IEEE 802.15.4. L'ambiente di simulazione principale è stato ADS ma, quando possibile, è stato impiegato anche SpectreRF

    Study of the 14N(p,g)15O reaction in a wide energy range in underground with LUNA

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    openThe 14N+p is the bottleneck of the CNO cycle and determines the CNO neutrinos from the Sun. Those have been recently observed by Borexino and this information can be used to determine the CNO abundances in the Sun core. The new accelerator installed at the Gran Sasso National Laboratory can provide the cross section for this reaction in a wide energy range.The 14N+p is the bottleneck of the CNO cycle and determines the CNO neutrinos from the Sun. Those have been recently observed by Borexino and this information can be used to determine the CNO abundances in the Sun core. The new accelerator installed at the Gran Sasso National Laboratory can provide the cross section for this reaction in a wide energy range

    An experimental and theoretical investigation of particle–wall impacts in a T-junction

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    Understanding the behaviour of particles entrained in a fluid flow upon changes in flow direction is crucial in problems where particle inertia is important, such as the erosion process in pipe bends.We present results on the impact of particles in a T-shaped channel in the laminar-turbulent transitional regime. The impacting event for a given system is described in terms of the Reynolds number and the particle Stokes number. Experimental results for the impact are compared with the trajectories predicted by theoretical particle tracing models for a range of configurations to determine the role of the viscous boundary layer in retarding the particles and reducing the rate of collision with the substrate. In particular a 2D model based on a stagnation point flow is used together with 3D numerical simulations. We show how the simple 2D model provides a tractable way of understanding the general collision behaviour, while more advanced 3D simulation can be helpful in understanding the details of the flow

    Alberto Zamboni (1941-2010)

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    Microfluidics approach to investigate foam hysteretic behaviour

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    A new construction of CAT(0) cube complexes

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    We introduce the notion of cube complex with coupled link (CLCC) as a mean of constructing interesting CAT(0) cubulated groups. CLCCs are defined locally, making them a useful tool to use when precise control over the links is required. In this paper we study some general properties of CLCCs, such as their (co)homological dimension and criteria for hyperbolicity. Some examples of fundamental groups of CLCCs are RAAGs, RACGs, surface groups and some manifold groups. As immediate applications of our criteria, we reprove the fact that RACGs are hyperbolic if and only if their defining graph is 5-large and we also provide a number of explicit examples of 3-dimensional cubulated hyperbolic groups.Comment: 5 figure
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