1,720,993 research outputs found
Front Propagation in Stirred Media
No full textThe problem of asymptotic features of front propagation in stirred media is addressed for laminar and turbulent velocity fields. In particular we consider the problem in two dimensional steady and unsteady cellular flows in the limit of very fast reaction and sharp front, i.e., in the geometrical optics limit. In the steady case we provide an analytical approximation for the front speed, v f, as a function of the stirring intensity, U, in good agreement with the numerical results. In the unsteady (time-periodic) case, albeit the Lagrangian dynamics is chaotic, chaos in the front dynamics is relevant only for a transient. Asymptotically the front evolves periodically and chaos manifests only in the spatially wrinkled structure of the front. In addition we study front propagation of reactive fields in systems whose diffusive behavior is anomalous. The features of the front propagation depend, not only on the scaling exponent ν, which characterizes the diffusion properties, (〈x(t) - x(0)) 2〉 ~ t 2ν, but also on the detailed shape of the probability distribution of the diffusive process. © 2011 Springer Basel AG
Statistical analysis of fixed income market
No full textWe present cross and time series analysis of price fluctuations in the US Treasury fixed income market. Bonds have been classified according to a suitable metric based on the correlation among them. The classification shows how the correlation among fixed income securities depends strongly on their maturity. We study also the structure of price fluctuations for single time series
Should government minimize debt service cost and risk? : a closer look at the debt strategy simulation approach
No full textSimulation-based cost-risk analysis of the interest expenditure is increasingly used for policy evaluation of public debt strategies by governments around the world. This paper is a first attempt to empirically evaluate this approach by comparing its implications for the maturity structure of public debt with those derived from the optimal taxation theory of debt management. To this end, we simulate the time path of the distribution of the interest expenditure for stylized portfolios of different maturities using simple stochastic models of the evolution of the term structure of interest rates, and examine the performance of such portfolios with standard cost-risk indicators. We find that: i) the ranking of debt portfolios by expenditure risk may depend on the length of the simulation period; to obtain the same policy conclusions as the optimal taxation theory, the time horizon must extend up to the redemption date of the longest maturity bond issued over the simulation period; ii) in sharp contrast with optimal taxation theory, a cost-risk trade off naturally emerges when a risk premium on long term bonds is considered, but this may not be sufficient to identify the optimal maturity structure. Our analysis points to the danger of assuming the cost-risk minimization of the interest expenditure as the main objective of debt management. A policy that either aims to minimize the interest expenditure over a too short horizon or does not consider that risk premiums may reflect a fair price for insurance may lead to sub-optimal debt strategie
Superfast front propagation in reactive systems with non-Gaussian diffusion
No full textWe study a reactive field transported by a non-Gaussian process
instead of a standard diffusion. If the process increments follow
a probability distribution with exponential tails, the usual
qualitative behaviour of the standard reaction diffusion system,
i.e., exponential tails for the reacting field and a
constant front speed, are recovered. But, if the process has
power law tails and the reaction is pulled, the reacting field
shows power law tails and the front speed increases exponentially
with time. The comparison with other transport processes which
exhibit anomalous diffusion shows that not only the presence of
anomalous diffusion, but also its detailed mechanism, is relevant
for the front propagation in reactive systems
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Discreteness effects in a reacting system of particles with finite interaction radius
No full textAn autocatalytic reacting system with particles interacting at a finite distance is studied. We investigate the effects of the discrete-particle character of the model on properties like reaction rate, quenching phenomenon, and front propagation, focusing on differences with respect to the continuous case. We introduce a renormalized reaction rate depending both on the interaction radius and the particle density, and we relate it to macroscopic observables (e.g., front speed and front thickness) of the system
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