Noise Induced Complexity: From Subthreshold Oscillations to Spiking in Coupled Excitable Systems

We study stochastic dynamics of an ensemble of N globally coupled excitable elements. Each element is modeled by a FitzHugh-Nagumo oscillator and is disturbed by independent Gaussian noise. In simulations of the Langevin dynamics we characterize the collective behavior of the ensemble in terms of its mean field and show that with the increase of noise the mean field displays a transition from a steady equilibrium to global oscillations and then, for sufficiently large noise, back to another equilibrium. Diverse regimes of collective dynamics ranging from periodic subthreshold oscillations to large-amplitude oscillations and chaos are observed in the course of this transition. In order to understand details and mechanisms of noise-induced dynamics we consider a thermodynamic limit $N\to\infty$ of the ensemble, and derive the cumulant expansion describing temporal evolution of the mean field fluctuations. In the Gaussian approximation this allows us to perform the bifurcation analysis; its results are in good agreement with dynamical scenarios observed in the stochastic simulations of large ensembles

Impact of system parameter selection on radar sensor performance in automotive applications

The paper deals with the investigation of relevant boundary conditions to be considered in order to operate 77/79 GHz narrow and ultra wide band automotive radar sensors in the automotive platform and the automotive environment

Cost-effectiveness of CTA, MRA and DSA in patients with non-traumatic subarachnoid haemorrhage

OBJECTIVES: Intra-arterial digital subtraction angiography (DSA), magnetic resonance angiography (MRA) and computed tomographic angiography (CTA) are imaging modalities used for diagnostic work-up of non-traumatic subarachnoid haemorrhage. The aim of our study was to compare the cost-effectiveness of MRA, DSA and CTA in the first year after the bleed. METHODS: A decision model was used to calculate costs and benefits (in quality-adjusted life-years [QALYs]) that accrued to cohorts of 1,000 patients. Costs and characteristics of diagnostic tests, therapy, patients’ quality of life and associated costs were respected. The diagnostic strategy with highest QALYs and lowest costs was considered most cost-effective. RESULTS: DSA was the most effective diagnostic option, yielding on average 0.6039 QALYs (95 % CI, 0.5761–0.6327) per patient, followed by CTA 0.5983 QALYs (95 % CI, 0.5704–0.6278) and MRA 0.5947 QALYs (95 % CI, 0.5674–0.6237). Cost was lowest for DSA (39,808 €; 95 % CI, 37,182–42,663), followed by CTA (40,748 €; 95 % CI, 37,937–43,831) and MRA (41,814 €; 95 % CI, 38,730–45,146). A strategy of CTA followed by DSA if CTA was negative or coiling deemed not feasible, was as effective as DSA alone at average costs of 39,767€ (95 % CI, 36,903–42,402). CONCLUSION: A combined strategy of CTA and DSA was found to be the most cost-effective diagnostic approach. MAIN MESSAGES: • We defined a standard model for cost-effectiveness analysis in diagnostic imaging. • Comparing total 1-year health costs and benefits, CTA is superior to MRA. • A strategy of combining CTA and DSA was found to be the most cost-effective diagnostic approach

Tracking serendipitous interactions: How individual cultures shape the office

In many work environments, serendipitous interactions between members of different groups may lead to enhanced productivity, collaboration and knowledge dissemination. Two factors that may have an influence on such interactions are cultural differences between individuals in highly multicultural workplaces, and the layout and physical spaces of the workplace itself. In this work, we investigate how these two factors may facilitate or hinder inter-group interactions in the workplace. We analyze traces collected using wearable electronic badges to capture face-to-face interactions and mobility patterns of employees in a research laboratory in the UK. We observe that those who interact with people of different roles tend to come from collectivist cultures that value relationships and where people tend to be comfortable with social hierarchies, and that some locations in particular are more likely to host serendipitous interactions, knowledge that could be used by organizations to enhance communication and productivity.This work was supported by the Google Europe Fellowship in Mobile Computing.This is the author accepted manuscript. The final version is published in the Proceedings of the ACM Conference on Computer Supported Cooperative Work and Social Computing and can be found in the ACM digital library here: http://dl.acm.org/citation.cfm?doid=2531602.2531641

Collapse of Flux Tubes

The dynamics of an idealized, infinite, MIT-type flux tube is followed in time as the interior evolves from a pure gluon field to a $\overline q \ q$ plasma. We work in color U(1). $\overline q\ q$ pair formation is evaluated according to the Schwinger mechanism using the results of Brink and Pavel. The motion of the quarks toward the tube endcaps is calculated by a Boltzmann equation including collisions. The tube undergoes damped radial oscillations until the electric field settles down to zero. The electric field stabilizes the tube against pinch instabilities; when the field vanishes, the tube disintegrates into mesons. There is only one free parameter in the problem, namely the initial flux tube radius, to which the results are very sensitive. Among various quantities calculated is the mean energy of the emitted pions.Comment: 16 pages plus 12 figures. RevTex3. DOE/ER/40427-160N9

Airborne observations of the Eyjafjalla volcano ash cloud over Europe during air space closure in April and May 2010

© Author(s) 2011. This work is distributed under the Creative Commons Attribution 3.0 LicenseAirborne lidar and in-situ measurements of aerosols and trace gases were performed in volcanic ash plumes over Europe between Southern Germany and Iceland with the Falcon aircraft during the eruption period of the Eyjafjalla1 volcano between 19 April and 18 May 2010. Flight planning and measurement analyses were supported by a refined Meteosat ash product and trajectory model analysis. The volcanic ash plume was observed with lidar directly over the volcano and up to a distance of 2700 km downwind, and up to 120 h plume ages. Aged ash layers were between a few 100 m to 3 km deep, occurred between 1 and 7 km altitude, and were typically 100 to 300 km wide. Particles collected by impactors had diameters up to 20 μm diameter, with size and age dependent composition. Ash mass concentrations were derived from optical particle spectrometers for a particle density of 2.6 g cm-3 and various values of the refractive index (RI, real part: 1.59; 3 values for the imaginary part: 0, 0.004 and 0.008). The mass concentrations, effective diameters and related optical properties were compared with ground-based lidar observations. Theoretical considerations of particle sedimentation constrain the particle diameters to those obtained for the lower RI values. The ash mass concentration results have an uncertainty of a factor of two. The maximum ash mass concentration encountered during the 17 flights with 34 ash plume penetrations was below 1 mg m-3. The Falcon flew in ash clouds up to about 0.8 mg m-3 for a few minutes and in an ash cloud with approximately 0.2 mg -3 mean-concentration for about one hour without engine damage. The ash plumes were rather dry and correlated with considerable CO and SO2 increases and O3 decreases. To first order, ash concentration and SO2 mixing ratio in the plumes decreased by a factor of two within less than a day. In fresh plumes, the SO2 and CO concentration increases were correlated with the ash mass concentration. The ash plumes were often visible slantwise as faint dark layers, even for concentrations below 0.1 mg m-3. The large abundance of volatile Aitken mode particles suggests previous nucleation of sulfuric acid droplets. The effective diameters range between 0.2 and 3 μm with considerable surface and volume contributions from the Aitken and coarse mode aerosol, respectively. The distal ash mass flux on 2 May was of the order of 500 (240-1600) kgs -1. The volcano induced about 10 (2.5-50) Tg of distal ash mass and about 3 (0.6-23) Tg of SO2 during the whole eruption period. The results of the Falcon flights were used to support the responsible agencies in their decisions concerning air traffic in the presence of volcanic ash.Peer reviewe

Off-diagonal Gluon Mass Generation and Infrared Abelian Dominance in the Maximally Abelian Gauge in Lattice QCD

We study effective mass generation of off-diagonal gluons and infrared abelian dominance in the maximally abelian (MA) gauge. Using the SU(2) lattice QCD, we investigate the propagator and the effective mass of the gluon field in the MA gauge with the U(1)$_3$ Landau gauge fixing. The Monte Carlo simulation is performed on the $12^3 \times 24$ lattice with $2.2 \le \beta \le 2.4$, and also on the $16^4$ and $20^4$ lattices with $2.3 \le \beta \le 2.4$. In the MA gauge, the diagonal gluon component $A_\mu^3$ shows long-range propagation, and infrared abelian dominance is found for the gluon propagator. In the MA gauge, the off-diagonal gluon component $A_\mu^\pm$ behaves as a massive vector boson with the effective mass $M_{\rm off} \simeq 1.2$ GeV in the region of r \gsim 0.2 fm, and its propagation is limited within short range. We conjecture that infrared abelian dominance can be interpreted as infrared inactivity of the off-diagonal gluon due to its large mass generation induced by the MA gauge fixing.Comment: 31 pages, 7 figures and 2 tables included, changed title, corrected typos and updated reference, accepted for publication in Physical Review

Periodic ground state for the charged massive Schwinger model

It is shown that the charged massive Schwinger model supports a periodic vacuum structure for arbitrary charge density, similar to the common crystalline layout known in solid state physics. The dynamical origin of the inhomogeneity is identified in the framework of the bozonized model and in terms of the original fermionic variables.Comment: 19 pages, 10 figures, revised version, accepted in Phys. Rev.