112 research outputs found
A mathematical model for the atomic clock error in case of jumps
We extend the mathematical model based on stochastic differential equations
describing the error gained by an atomic clock to the cases of anomalous
behavior including jumps and an increase of instability. We prove an exact
iterative solution that can be useful for clock simulation, prediction, and
interpretation, as well as for the understanding of the impact of clock error
in the overall system in which clocks may be inserted as, for example, the
Global Satellite Navigation Systems
First passage times of two-correlated processes: analytical results for the Wiener process and a numerical method for diffusion processes
Given a two-dimensional correlated diffusion process, we determine the joint
density of the first passage times of the process to some constant boundaries.
This quantity depends on the joint density of the first passage time of the
first crossing component and of the position of the second crossing component
before its crossing time. First we show that these densities are solutions of a
system of Volterra-Fredholm first kind integral equations. Then we propose a
numerical algorithm to solve it and we describe how to use the algorithm to
approximate the joint density of the first passage times. The convergence of
the method is theoretically proved for bivariate diffusion processes. We derive
explicit expressions for these and other quantities of interest in the case of
a bivariate Wiener process, correcting previous misprints appearing in the
literature. Finally we illustrate the application of the method through a set
of examples.Comment: 18 pages, 3 figure
Joint densities of first hitting times of a diffusion process through two time dependent boundaries
Consider a one dimensional diffusion process on the diffusion interval
originated in . Let and be two continuous functions of
, with bounded derivatives and with and , . We study the joint distribution of the two random
variables and , first hitting times of the diffusion process through
the two boundaries and , respectively. We express the joint
distribution of in terms of and
and we determine a system of integral equations verified by
these last probabilities. We propose a numerical algorithm to solve this system
and we prove its convergence properties. Examples and modeling motivation for
this study are also discussed
Some exact results on Lindley process with Laplace jumps
We consider a Lindley process with Laplace distributed space increments. We
obtain closed form recursive expressions for the density function of the
position of the process and for its first exit time distribution from the
domain . We illustrate the results in terms of the parameters of the
process. The work is completed by an open source version of the software
Absence of polyphenol oxidase in cynomorium coccineum, a widespread holoparasitic plant
Polyphenol oxidase (PPO, E.C. 1.14.18.1) is a nearly ubiquitous enzyme that is widely distributed among organisms. Despite its widespread distribution, the role of PPO in plants has not been thoroughly elucidated. In this study, we report for the absence of PPO in Cynomorium coccineum, a holoparasitic plant adapted to withstand unfavorable climatic conditions, growing in Mediterranean countries and amply used in traditional medicine. The lack of PPO has been demonstrated by the absence of enzymatic activity with various substrates, by the lack of immunohistochemical detection of the enzyme, and by the absence of the PPO gene and, consequently, its expression. The results obtained in our work allow us to exclude the presence of the PPO activity (both latent and mature forms of the enzyme), as well as of one or more genes coding for PPO in C. coccineum. Finally, we discuss the possible significance of PPO deficiency in parasitic plants adapted to abiotic stress
Discovery and Characterization of a Distinct Cyclic Nucleotide Binding Pocket in HCN Channels
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