20,950 research outputs found
Diverse perceptions of smart spaces
This is the era of smart technology and of ‘smart’ as a meme, so we have run three workshops to examine the ‘smart’ meme and the exploitation of smart environments. The literature relating to smart spaces focuses primarily on technologies and their capabilities. Our three workshops demonstrated that we require a stronger user focus if we are advantageously to exploit spaces ascribed as smart: we examined the concept of smartness from a variety of perspectives, in collaboration with a broad range of contributors. We have prepared this monograph mainly to report on the third workshop, held at Bournemouth University in April 2012, but do also consider the lessons learned from all three. We conclude with a roadmap for a fourth (and final) workshop, which is intended to emphasise the overarching importance of the humans using the spac
Exact results for the Kardar--Parisi--Zhang equation with spatially correlated noise
We investigate the Kardar--Parisi--Zhang (KPZ) equation in spatial
dimensions with Gaussian spatially long--range correlated noise ---
characterized by its second moment --- by means of dynamic field theory and the
renormalization group. Using a stochastic Cole--Hopf transformation we derive
{\em exact} exponents and scaling functions for the roughening transition and
the smooth phase above the lower critical dimension . Below
the lower critical dimension, there is a line marking the stability
boundary between the short-range and long-range noise fixed points. For , the general structure of the renormalization-group equations
fixes the values of the dynamic and roughness exponents exactly, whereas above
, one has to rely on some perturbational techniques. We discuss the
location of this stability boundary in light of the exact results
derived in this paper, and from results known in the literature. In particular,
we conjecture that there might be two qualitatively different strong-coupling
phases above and below the lower critical dimension, respectively.Comment: 21 pages, 15 figure
Limiting stable currents in bounded electron and ion streams
The classical static analysis of the infinite planar diode has been extended to include the effects of finite transverse beam size. Simple expressions have been found for the increase in maximum stable current density over that of an infinite stream for finite cylindrical and strip streams flowing between plates of infinite diodes. The results are also given in terms of stream perveance. The effect of a nonuniform distribution of current across the stream is shown to be relatively small. Experimental values of maximum stable current agree with those obtained from the analysis. A further extension of the static analysis has been made to include the effects of additional conducting plane boundaries parallel to the stream motion. For length-to-width ratios L/D less than 0.25 the tube is adequately described by the results for the infinite planar diode and for L/D greater than 4, the infinitely-long drift tube theory suffices. At intermediate values of L/D, the maximum amount of current that can be stably passed through the tube is greater than that predicted by either asymptotic theory
Universal fluctuations in growth dynamics of economic systems
The growth of business firms is an example of a system of complex interacting
units that resembles complex interacting systems in nature such as earthquakes.
Remarkably, work in econophysics has provided evidence that the statistical
properties of the growth of business firms follow the same sorts of power laws
that characterize physical systems near their critical points. Given how
economies change over time, whether these statistical properties are
persistent, robust, and universal like those of physical systems remains an
open question. Here, we show that the scaling properties of firm growth
previously demonstrated for publicly-traded U.S. manufacturing firms from 1974
to 1993 apply to the same sorts of firms from 1993 to 2015, to firms in other
broad sectors (such as materials), and to firms in new sectors (such as
Internet services). We measure virtually the same scaling exponent for
manufacturing for the 1993 to 2015 period as for the 1974 to 1993 period and
virtually the same scaling exponent for other sectors as for manufacturing.
Furthermore, we show that fluctuations of the growth rate for new industries
self-organize into a power law over relatively short time scales.Comment: 15 pages, 7 figure
Propagation and Relaxation of Tension in Stiff Polymers
We present a unified theory for the longitudinal dynamic response of a stiff
polymer in solution to various external perturbations (mechanical excitations,
hydrodynamic flows, electrical fields, temperature quenches ...) that can be
represented as sudden changes of ambient/boundary conditions. The theory relies
on a comprehensive analysis of the non--equilibrium propagation and relaxation
of backbone stresses in a wormlike chain. We recover and substantially extend
previous results based on heuristic arguments. Intriguing new experimental
implications are pointed out.Comment: 4 pages, 3 figure
Determining species tree topologies from clade probabilities under the coalescent
One approach to estimating a species tree from a collection of gene trees is
to first estimate probabilities of clades from the gene trees, and then to
construct the species tree from the estimated clade probabilities. While a
greedy consensus algorithm, which consecutively accepts the most probable
clades compatible with previously accepted clades, can be used for this second
stage, this method is known to be statistically inconsistent under the
multispecies coalescent model. This raises the question of whether it is
theoretically possible to reconstruct the species tree from known probabilities
of clades on gene trees. We investigate clade probabilities arising from the
multispecies coalescent model, with an eye toward identifying features of the
species tree. Clades on gene trees with probability greater than 1/3 are shown
to reflect clades on the species tree, while those with smaller probabilities
may not. Linear invariants of clade probabilities are studied both
computationally and theoretically, with certain linear invariants giving
insight into the clade structure of the species tree. For species trees with
generic edge lengths, these invariants can be used to identify the species tree
topology. These theoretical results both confirm that clade probabilities
contain full information on the species tree topology and suggest future
directions of study for developing statistically consistent inference methods
from clade frequencies on gene trees.Comment: 25 pages, 2 figure
Floppy modes and non-affine deformations in random fiber networks
We study the elasticity of random fiber networks. Starting from a microscopic
picture of the non-affine deformation fields we calculate the macroscopic
elastic moduli both in a scaling theory and a self-consistent effective medium
theory. By relating non-affinity to the low-energy excitations of the network
(``floppy-modes'') we achieve a detailed characterization of the non-affine
deformations present in fibrous networks.Comment: 4 pages, 2 figures, new figure
Studying top quark decay into the polarized W-boson in the TC2 model
We study the decay mode of top quark decaying into Wb in the TC2 model where
the top quark is distinguished from other fermions by participating in a strong
interaction. We find that the TC2 correction to the decay width is generally several percent and maximum value can reach 8% for the
currently allowed parameters. The magnitude of such correction is comparable
with QCD correction and larger than that of minimal supersymmetric model. Such
correction might be observable in the future colliders. We also study the TC2
correction to the branching ratio of top quark decay into the polarized W
bosons and find the correction is below . After considering the TC2
correction, we find that our theoretical predictions about the decay branching
ratio are also consistent with the experimental data.Comment: 8 pages, 4 figure
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