66,517 research outputs found
Small-world behavior in a system of mobile elements
We analyze the propagation of activity in a system of mobile automata. A
number r L^d of elements move as random walkers on a lattice of dimension d,
while with a small probability p they can jump to any empty site in the system.
We show that this system behaves as a Dynamic Small-World (DSW) and present
analytic and numerical results for several quantities. Our analysis shows that
the persistence time T* (equivalent to the persistence size L* of small-world
networks) scales as T* ~ (r p)^(-t), with t = 1/(d+1).Comment: To appear in Europhysics Letter
B_{s,d} -> l^+ l^- and K_L -> l^+ l^- in SUSY models with non-minimal sources of flavour mixing
We present a general analysis of B_{s,d}-> l^+ l^- and K_L -> l^+ l^- decays
in supersymmetric models with non-minimal sources of flavour mixing. In spite
of the existing constraints on off-diagonal squark mass terms, these modes
could still receive sizeable corrections, mainly because of Higgs-mediated
FCNCs arising at large tan(beta). The severe limits on scenarios with large
tan(beta) and non-negligible {tilde d}^i_{R(L)}-{d-tilde}^j_{R(L)} mixing
imposed by the present experimental bounds on these modes and Delta B=2
observables are discussed in detail. In particular, we show that scalar-current
contributions to K_L -> l^+ l^- and B-{bar B} mixing set non-trivial
constraints on the possibility that B_s -> l^+ l^- and B_d -> l^+ l^- receive
large corrections.Comment: 18 pages, 4 figures (v2: minor changes, published version
The sharp threshold for bootstrap percolation in all dimensions
In r-neighbour bootstrap percolation on a graph G, a (typically random) set A
of initially 'infected' vertices spreads by infecting (at each time step)
vertices with at least r already-infected neighbours. This process may be
viewed as a monotone version of the Glauber dynamics of the Ising model, and
has been extensively studied on the d-dimensional grid . The elements of
the set A are usually chosen independently, with some density p, and the main
question is to determine , the density at which percolation
(infection of the entire vertex set) becomes likely.
In this paper we prove, for every pair , that there is a
constant L(d,r) such that as , where denotes an r-times iterated
logarithm. We thus prove the existence of a sharp threshold for percolation in
any (fixed) number of dimensions. Moreover, we determine L(d,r) for every pair
(d,r).Comment: 37 pages, sketch of the proof added, to appear in Trans. of the AM
Ligand-controlled divergent formation of alkenyl- or allylboronates catalyzed by Pd, and synthetic applications
The use of different ligands allows the preparation of either allyl- or alkenylboronates by Pd-catalyzed borylation of allylic carbonates containing alkyne groups. Unprecedented borylative cyclisation to alkenylboronates takes place with PCy3. The difficult dissociation of NHC ligands allows borylation of carbonates in the presence of alkynes. Oxidation, regioselective Suzuki coupling, as well as Au-catalyzed cycloisomerisation of boronates illustrate the potential synthetic applications of these reactionsThis work was supported by the MICINN (CTQ2010-15927) and the CAM (Project AVANCAT). We thank the UAM for a fellowship to R. L.-D., and the CCC-UAM for computation tim
The Fontao’s mine
[Abstract] The Fontao Mine (Vila de Cruces) was exploited from 1934 to 1973, having a little period without activity (1963-1968) in wich underground mining was changed to open pit.
L a t e r , the mine has remained closed. In 2001, the Vila de Cruces council, worried by the
conservation of Fontao mining heritage financed a prefeasibility study about the mine
recovery in order to transform it into the Galicia Mining Park. During the carrying out
of the project, many technical documents related to the mines and the ore body were
handled, so a whole idea about the main geological and mining features was possible to
obtain. This work seeks to show these ones and recover the name and memory of Fontao
Mine, which was so important to Spanish economy, specially in that hard post II Wo r l d
War da
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Normal stress differences in non-Brownian fiber suspensions
International audienceIn this paper, we present an experimental study of the normal stress differences that arise in non-Brownian rigid fiber suspensions subject to a shear flow. While early measurements of the normal stress in fiber suspensions in Newtonian fluids measured only N 1 − N 2 , the recent work of Snook et al. J. Fluid Mech. 758 486 (2014) and the present paper provide the first measurements of N 1 and N 2 separately. Snook et al perform such measurements with a gap that is very wide compared with the fiber length, whereas the present paper explores the effects of confinement when the gap is 4-10 times the fiber length. The first and the second normal stress differences are measured using a single experiment which consists of determining the radial profile of the second normal stress, along the velocity gradient direction, Σ 22 , in a torsional flow between two parallel discs. Suspensions are made of monodisperse fibers immersed in a neutrally buoyant Newtonian fluid. Two fiber lengths and three aspect ratios a r = L/d, and a wide range of concentrations have been tested. N 1 is found to be positive while N 2 is negative and the magnitude of both normal stress differences increases when nL 2 d increases, n being the number fraction of fibers. The magnitude of N 2 is found to be much smaller than N 1 only for high aspect ratios and low fiber concentrations
High purity nanoparticles exceed stoichiometry limits in rebox chemistry: the nano way to cleaner water
A potentially cheaper and more effective way of cleaning wastewater has been discovered by scientists
at Nazarbayev University and the University of Brighton researching nanotechnology [1]. It is well
established that when particles are reduced to the nanoscale unexpected effects occur. Silver, for example,
interacts with mercury ions in a fixed ratio of atoms (stoichiometry), typically 2:1, which presents a limit
that has never been exceeded. In this project we used an alternative chemical procedure based on modified
quartz sand to immobilise silver nanoparticles (NPs) with control over their size. We found that when the
size of the silver NPs decreased below 35 nm the amount of mercury ions reacting with silver increased
beyond the long-held limit and rose to a maximum of 1:1.2 for 10 nm sized silver
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