7,340 research outputs found
Delayed feedback as a means of control of noise-induced motion
Time--delayed feedback is exploited for controlling noise--induced motion in
coherence resonance oscillators. Namely, under the proper choice of time delay,
one can either increase or decrease the regularity of motion. It is shown that
in an excitable system, delayed feedback can stabilize the frequency of
oscillations against variation of noise strength. Also, for fixed noise
intensity, the phenomenon of entrainment of the basic oscillation period by the
delayed feedback occurs. This allows one to steer the timescales of
noise-induced motion by changing the time delay.Comment: 4 pages, 4 figures. In the replacement file Fig. 2 and Fig. 4(b),(d)
were amended. The reason is numerical error found, that affected the
quantitative estimates of correlation time, but did not affect the main
messag
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The Euro Crisis in the Mirror of the EMS: How Tying Odysseus to the Mast Avoided the Sirens but Led Him to Charybdi
Why was recovery from the euro area crisis delayed for a decade? The explanation lies in the absence of credible and timely policies to backstop financial intermediaries and sovereign debt markets. In this paper we add light and color to this analysis, contrasting recent experience with the 1992-3 crisis in the European Monetary System, when national central banks and treasuries more successfully provided this backstop. In the more recent episode, the incomplete development of the euro area constrained the ability of the ECB and other European institutions to do likewis
Recommended from our members
The Euro Crisis in the Mirror of the EMS: How Tying Odysseus to the Mast Avoided the Sirens but Led Him to Charybdis
Why was recovery from the euro area crisis delayed for a decade? The explanation lies in the absence of credible and timely policies to backstop financial intermediaries and sovereign debt markets. In this paper we add light and color to this analysis, contrasting recent experience with the 1992-3 crisis in the European Monetary System, when national central banks and treasuries more successfully provided this backstop. In the more recent episode, the incomplete development of the euro area constrained the ability of the ECB and other European institutions to do likewise.Keynes Fund at Cambridge University. The Making of the Euro-Area Crisis: Lessons from Theory and History (JHLP)
All-solid-state electrochromic reflectance device for emittance modulation in the far-infrared spectral region
All-solid-state electrochromic reflectance devices for thermal emittance modulation were designed for operation in the spectral region from mid- to far-infrared wavelengths (2–40 μm). All device constituent layers were grown by magnetron sputtering. The electrochromic (polycrystalline WO3), ion conductor (Ta2O5), and Li+ ion-storage layer (amorphous WO3), optimized for their infrared (IR) optical thicknesses, are sandwiched between a highly IR reflecting Al mirror, and a 90% IR transmissive Al grid top electrode, thereby meeting the requirements for a reversible Li+ ion insertion electrochromic device to operate within the 300 K blackbody emission range. Multicycle optical switching and emittance modulation is demonstrated. The measured change in emissivity of the device is to 20%
Enhancing the implementation of Occupational Health and Safety interventions through a design of the socio-technical interaction
Developing a Monitoring Framework to Estimate Wolf Distribution and Abundance in Southwest Alberta
Gray wolf (Canis lupus) populations are difficult to monitor because wolves can be elusive and occur in low densities. Traditional radiotelemetry-based monitoring methods have limited application when turnover is high within the wolf population and resources to maintain long-term collaring programs are limited. We worked collaboratively with Alberta Environmental Sustainable Resource Development between 2012 and 2014 to develop techniques for monitoring gray wolf populations in the absence of radiotelemetry in southwest Alberta. We surveyed potential rendezvous sites and collected DNA samples from wolf scats for genetic analysis and surveyed hunters for wolf sightings made during the hunting seasons. We fit false-positive occupancy models to annual detection data derived from genetic results and hunter surveys with Program PRESENCE. We found percent forest cover and human density positively influenced pack occupancy whereas detection probabilities varied by survey method, sampling effort, and sampling season. The model predicted wolf pack occupancy well and distribution and abundance estimates were consistent with agency predictions. While developing the monitoring framework, questions arose regarding pack turnover and population growth under widespread human harvest. Previous studies have focused on population recovery following wolf control actions but little emphasis is put on populations that exist under regular harvest. We will use genetic data to determine how immigration contributes to wolf population trends under a long-term harvest regime and tie this into pack occupancy through colonization and local extinction probabilities. This will expand the application of our occupancy model and will further clarify how wolf populations respond to long-term regulated harvest
Exponential decay for the damped wave equation in unbounded domains
We study the decay of the semigroup generated by the damped wave equation in
an unbounded domain. We first prove under the natural geometric control
condition the exponential decay of the semigroup. Then we prove under a weaker
condition the logarithmic decay of the solutions (assuming that the initial
data are smoother). As corollaries, we obtain several extensions of previous
results of stabilisation and control
Twisted and Nontwisted Bifurcations Induced by Diffusion
We discuss a diffusively perturbed predator-prey system. Freedman and
Wolkowicz showed that the corresponding ODE can have a periodic solution that
bifurcates from a homoclinic loop. When the diffusion coefficients are large,
this solution represents a stable, spatially homogeneous time-periodic solution
of the PDE. We show that when the diffusion coefficients become small, the
spatially homogeneous periodic solution becomes unstable and bifurcates into
spatially nonhomogeneous periodic solutions.
The nature of the bifurcation is determined by the twistedness of an
equilibrium/homoclinic bifurcation that occurs as the diffusion coefficients
decrease. In the nontwisted case two spatially nonhomogeneous simple periodic
solutions of equal period are generated, while in the twisted case a unique
spatially nonhomogeneous double periodic solution is generated through
period-doubling.
Key Words: Reaction-diffusion equations; predator-prey systems; homoclinic
bifurcations; periodic solutions.Comment: 42 pages in a tar.gz file. Use ``latex2e twisted.tex'' on the tex
files. Hard copy of figures available on request from
[email protected]
On the Mechanism of Time--Delayed Feedback Control
The Pyragas method for controlling chaos is investigated in detail from the
experimental as well as theoretical point of view. We show by an analytical
stability analysis that the revolution around an unstable periodic orbit
governs the success of the control scheme. Our predictions concerning the
transient behaviour of the control signal are confirmed by numerical
simulations and an electronic circuit experiment.Comment: 4 pages, REVTeX, 4 eps-figures included Phys. Rev. Lett., in press
also available at
http://athene.fkp.physik.th-darmstadt.de/public/wolfram.htm
A transient homotypic interaction model for the influenza A virus NS1 protein effector domain
Influenza A virus NS1 protein is a multifunctional virulence factor consisting of an RNA binding domain (RBD), a short linker, an effector domain (ED), and a C-terminal 'tail'. Although poorly understood, NS1 multimerization may autoregulate its actions. While RBD dimerization seems functionally conserved, two possible apo ED dimers have been proposed (helix-helix and strand-strand). Here, we analyze all available RBD, ED, and full-length NS1 structures, including four novel crystal structures obtained using EDs from divergent human and avian viruses, as well as two forms of a monomeric ED mutant. The data reveal the helix-helix interface as the only strictly conserved ED homodimeric contact. Furthermore, a mutant NS1 unable to form the helix-helix dimer is compromised in its ability to bind dsRNA efficiently, implying that ED multimerization influences RBD activity. Our bioinformatical work also suggests that the helix-helix interface is variable and transient, thereby allowing two ED monomers to twist relative to one another and possibly separate. In this regard, we found a mAb that recognizes NS1 via a residue completely buried within the ED helix-helix interface, and which may help highlight potential different conformational populations of NS1 (putatively termed 'helix-closed' and 'helix-open') in virus-infected cells. 'Helix-closed' conformations appear to enhance dsRNA binding, and 'helix-open' conformations allow otherwise inaccessible interactions with host factors. Our data support a new model of NS1 regulation in which the RBD remains dimeric throughout infection, while the ED switches between several quaternary states in order to expand its functional space. Such a concept may be applicable to other small multifunctional proteins
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