34,059 research outputs found
Elasticity and Petri nets
Digital electronic systems typically use synchronous clocks and primarily assume fixed duration of their operations to simplify the design process. Time elastic systems can be constructed either by replacing the clock with communication handshakes (asynchronous version) or by augmenting the clock with a synchronous version of a handshake (synchronous version). Time elastic systems can tolerate static and dynamic changes in delays (asynchronous case) or latencies (synchronous case) of operations that can be used for modularity, ease of reuse and better power-delay trade-off. This paper describes methods for the modeling, performance analysis and optimization of elastic systems using Marked Graphs and their extensions capable of describing behavior with early evaluation. The paper uses synchronous elastic systems (aka latency-tolerant systems) for illustrating the use of Petri nets, however, most of the methods can be applied without changes (except changing the delay model associated with events of the system) to asynchronous elastic systems.Peer ReviewedPostprint (author's final draft
Test of general relativity: 1995-2002 measurement of frame-dragging
After an introduction on phenomena due to spin and mass-energy currents on
clocks and photons, we review the 1995-2001 measurements of the gravitomagnetic
field of Earth and Lense-Thirring effect obtained by analyzing the orbits of
the two laser-ranged satellites LAGEOS and LAGEOS II; this method has provided
a direct measurement of Earth's gravitomagnetism with accuracy of the order of
20 %. A future accurate measurement of the Lense-Thirring effect, at the level
of 1 % accuracy, may include the LARES experiment that will also provide other
basic tests of general relativity and gravitation. Finally, we report the
latest measurement of the Lense-Thirring effect, obtained in 2002 with the
LAGEOS satellites over nearly 8 years of data. This 2002 result fully confirms
and improves our previous measurements of the Earth frame-dragging: the
Lense-Thirring effect exists and its experimental value is within ~ 20 % of
what is predicted by Einstein's theory of general relativity.Comment: 12 pages, 2 figure
Quantile clocks
Quantile clocks are defined as convolutions of subordinators , with
quantile functions of positive random variables. We show that quantile clocks
can be chosen to be strictly increasing and continuous and discuss their
practical modeling advantages as business activity times in models for asset
prices. We show that the marginal distributions of a quantile clock, at each
fixed time, equate with the marginal distribution of a single subordinator.
Moreover, we show that there are many quantile clocks where one can specify
, such that their marginal distributions have a desired law in the class of
generalized -self decomposable distributions, and in particular the class of
self-decomposable distributions. The development of these results involves
elements of distribution theory for specific classes of infinitely divisible
random variables and also decompositions of a gamma subordinator, that is of
independent interest. As applications, we construct many price models that have
continuous trajectories, exhibit volatility clustering and have marginal
distributions that are equivalent to those of quite general exponential
L\'{e}vy price models. In particular, we provide explicit details for
continuous processes whose marginals equate with the popular VG, CGMY and NIG
price models. We also show how to perfectly sample the marginal distributions
of more general classes of convoluted subordinators when is in a sub-class
of generalized gamma convolutions, which is relevant for pricing of European
style options.Comment: Published in at http://dx.doi.org/10.1214/10-AAP752 the Annals of
Applied Probability (http://www.imstat.org/aap/) by the Institute of
Mathematical Statistics (http://www.imstat.org
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