2,933 research outputs found
Melting of a nonequilibrium vortex crystal in a fluid film with polymers : elastic versus fluid turbulence
We perform a direct numerical simulation (DNS) of the forced, incompressible
two-dimensional Navier-Stokes equation coupled with the FENE-P equations for
the polymer-conformation tensor. The forcing is such that, without polymers and
at low Reynolds numbers \mbox{Re}, the film attains a steady state that is a
square lattice of vortices and anti-vortices. We find that, as we increase the
Weissenberg number \mbox{Wi}, a sequence of nonequilibrium phase transitions
transforms this lattice, first to spatially distorted, but temporally steady,
crystals and then to a sequence of crystals that oscillate in time,
periodically, at low \mbox{Wi}, and quasiperiodically, for slightly larger
\mbox{Wi}. Finally, the system becomes disordered and displays spatiotemporal
chaos and elastic turbulence. We then obtain the nonequilibrium phase diagram
for this system, in the \mbox{Wi} - \Omega plane, where \Omega \propto
{\mbox{Re}}, and show that (a) the boundary between the crystalline and
turbulent phases has a complicated, fractal-type character and (b) the
Okubo-Weiss parameter provides us with a natural measure for
characterizing the phases and transitions in this diagram.Comment: 16 pages, 17 figure
How should emerging economies manage their foreign exchange reserves?
Asia has emerged as the balancing wheel of global finance. The countries of Asia now account for 70 per cent of global foreign exchange reserves, compared to only 30 percent in 1990 and 21 per cent in the early 1970s. This paper explores theoretical interpretations for the relatively high demand for international reserves by developing countries especially in the Far East. This paper provides calculations of the minimal necessary level of international reserves based on benchmarks proposed by Wijnholds and Kapteyn, as well as a discussion of costs of reserves’ holding. It therefore provides empirical proof that exchange reserve levels for many of the developing countries have far exceeded the desirable levels. Paper then discusses the steps that central banks in these developing countries can take for an effective reserve management.Foreign exchange ; emerging economies; reserves; reserve level; east asia
A Novel Method to Calculate Click Through Rate for Sponsored Search
Sponsored search adopts generalized second price (GSP) auction mechanism
which works on the concept of pay per click which is most commonly used for the
allocation of slots in the searched page. Two main aspects associated with GSP
are the bidding amount and the click through rate (CTR). The CTR learning
algorithms currently being used works on the basic principle of (#clicks_i/
#impressions_i) under a fixed window of clicks or impressions or time. CTR are
prone to fraudulent clicks, resulting in sudden increase of CTR. The current
algorithms are unable to find the solutions to stop this, although with the use
of machine learning algorithms it can be detected that fraudulent clicks are
being generated. In our paper, we have used the concept of relative ranking
which works on the basic principle of (#clicks_i /#clicks_t). In this
algorithm, both the numerator and the denominator are linked. As #clicks_t is
higher than previous algorithms and is linked to the #clicks_i, the small
change in the clicks which occurs in the normal scenario have a very small
change in the result but in case of fraudulent clicks the number of clicks
increases or decreases rapidly which will add up with the normal clicks to
increase the denominator, thereby decreasing the CTR.Comment: 10 pages, 1 figur
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