1,681 research outputs found
Superexpanders from group actions on compact manifolds
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
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
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
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
A new construction of CAT(0) cube complexes
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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