6,235 research outputs found
Stochastic resonance with weak monochromatic driving: gains above unity induced by high-frequency signals
We study the effects of a high-frequency (HF) signal on the response of a
noisy bistable system to a low-frequency subthreshold sinusoidal signal. We
show that, by conveniently choosing the ratio of the amplitude of the HF signal
to its frequency, stochastic resonance gains greater than unity can be measured
at the low-frequency value. Thus, the addition of the HF signal can entail an
improvement in the detection of weak monochromatic signals. The results are
explained in terms of an effective model and illustrated by means of numerical
simulations.Comment: 5 pages, 2 figure
A generalized Chudley-Elliott vibration-jump model in activated atom surface diffusion
Here the authors provide a generalized Chudley-Elliott expression for
activated atom surface diffusion which takes into account the coupling between
both low-frequency vibrational motion (namely, the frustrated translational
modes) and diffusion. This expression is derived within the Gaussian
approximation framework for the intermediate scattering function at low
coverage. Moreover, inelastic contributions (arising from creation and
annihilation processes) to the full width at half maximum of the quasi-elastic
peak are also obtained.Comment: (5 pages, 2 figures; revised version
Dataplane Specialization for High-performance OpenFlow Software Switching
OpenFlow is an amazingly expressive dataplane program-
ming language, but this expressiveness comes at a severe
performance price as switches must do excessive packet clas-
sification in the fast path. The prevalent OpenFlow software
switch architecture is therefore built on flow caching, but
this imposes intricate limitations on the workloads that can
be supported efficiently and may even open the door to mali-
cious cache overflow attacks. In this paper we argue that in-
stead of enforcing the same universal flow cache semantics
to all OpenFlow applications and optimize for the common
case, a switch should rather automatically specialize its dat-
aplane piecemeal with respect to the configured workload.
We introduce ES WITCH , a novel switch architecture that
uses on-the-fly template-based code generation to compile
any OpenFlow pipeline into efficient machine code, which
can then be readily used as fast path. We present a proof-
of-concept prototype and we demonstrate on illustrative use
cases that ES WITCH yields a simpler architecture, superior
packet processing speed, improved latency and CPU scala-
bility, and predictable performance. Our prototype can eas-
ily scale beyond 100 Gbps on a single Intel blade even with
complex OpenFlow pipelines
Long-term impact of sewage sludge application on soil microbial biomass: An evaluation using meta-analysis
The Long-Term Sludge Experiments (LTSE) began in 1994 as part of continuing research into the effects of sludge-borne heavy metals on soil fertility. The long-term effects of Zn, Cu, and Cd on soil microbial biomass carbon (Cmic) were monitored for 8 years (1997-2005) in sludge amended soils at nine UK field sites. To assess the statutory limits set by the UK Sludge (Use in Agriculture) Regulations the experimental data has been reviewed using the statistical methods of meta-analysis. Previous LTSE studies have focused predominantly on statistical significance rather than effect size, whereas meta-analysis focuses on the magnitude and direction of an effect, i.e. the practical significance, rather than its statistical significance. The results presented here show that significant decreases in Cmic have occurred in soils where the total concentrations of Zn and Cu fall below the current UK statutory limits. For soils receiving sewage sludge predominantly contaminated with Zn, decreases of approximately 7–11% were observed at concentrations below the UK statutory limit. The effect of Zn appeared to increase over time, with increasingly greater decreases in Cmic observed over a period of 8 years. This may be due to an interactive effect between Zn and confounding Cu contamination which has augmented the bioavailability of these metals over time. Similar decreases (7–12%) in Cmic were observed in soils receiving sewage sludge predominantly contaminated with Cu; however, Cmic appeared to show of recovery after a period of 6 years. Application of sewage sludge predominantly contaminated with Cd appeared to have no effect on Cmic at concentrations below the current UK statutory limit
Double Entropic Stochastic Resonance
We demonstrate the appearance of a purely entropic stochastic resonance (ESR)
occurring in a geometrically confined system, where the irregular boundaries
cause entropic barriers. The interplay between a periodic input signal, a
constant bias and intrinsic thermal noise leads to a resonant ESR-phenomenon in
which feeble signals become amplified. This new phenomenon is characterized by
the presence of two peaks in the spectral amplification at corresponding
optimal values of the noise strength. The main peak is associated with the
manifest stochastic resonance synchronization mechanism involving the
inter-well noise-activated dynamics while a second peak relates to a regime of
optimal sensitivity for intra-well dynamics. The nature of ESR, occurring when
the origin of the barrier is entropic rather than energetic, offers new
perspectives for novel investigations and potential applications. ESR by itself
presents yet another case where one constructively can harvest noise in driven
nonequilibrium systems.Comment: 6 pages, 7 figures ; Europhys. Lett., in press (2009
ContribuciĂłn al estudio faunĂstico del bentos fluvial del rĂo Lozoya (Sierra de Guadarrama, España)
OrganizaciĂłn funcional de las comunidades de macroinvertebrados acuáticos de un sistema fluvial de montaña (Sistema Central, rĂo Manzanares, España)
Linking tourism, retirement migration and social capital
A general trend in the study of international retirement migration has been the increased attention paid to the social contacts and network connections of the migrants in both the destination and the origin areas. These studies have examined the extent to which migrants build social relationships with their neighbours and the host society while also maintaining social links with their countries of origin, addressing the central role that leisure travel plays in sustaining increasingly dispersed social networks and maintaining the social capital of these networks and of the individuals involved in them. Using a case study approach to examine British retirement migration to Spain, we explore the relevance of transnational social networks in the context of international retirement migration, particularly the intensity of bidirectional visiting friends and relatives (VFR) tourism flows and the migrants' social contacts with friends and/or family back in their home country. Building on the concept of social capital and Putnam's distinction between bonding and bridging social capital, we propose a framework for the analysis of the migrants' international social networks. The results of a study conducted based on a sample of 365 British retirees living in the coast of Alicante (Spain) show both the strength of the retirees' international bonding social capital and the role of 'VFR's travel and communication technologies in sustaining the migrants' transnational social practices and, ultimately, their international bonding social capital. It also provides evidence for the reinforcing links between tourism-related mobility and amenity-seeking migration in later life. © 2013 © 2013 Taylor & Francis
- …