Comparative mapping and targeted-capture sequencing of the gametocidal loci in Aegilops sharonensis

Gametocidal (Gc) chromosomes or elements in species such as Aegilops sharonensis are preferentially transmitted to the next generation through both the male and female gametes when introduced into wheat. Furthermore, any genes, e.g. genes that control agronomically important traits, showing complete linkage with gametocidal elements, are also transmitted preferentially to the next generation without the need for selection. The mechanism for the preferential transmission of the gametocidal elements appears to occur by the induction of extensive chromosome damage in any gametes that lack the gametocidal chromosome in question. Previous studies on the mechanism of the gametocidal action in Ae. sharonensis indicates that at least two-linked elements are involved. The first, the ‘breaker’ element, induces chromosome breakage in gametes, which have lost the gametocidal elements while the second, the ‘inhibitor’ element, prevents the chromosome breakage action of the ‘breaker’ element in gametes, which carry the Gc elements. In this study, we have used comparative genomic studies to map 54 single nucleotide polymorphism (SNP) markers in an Ae. sharonensis 4SshL introgression segment in wheat and have also identified 18 candidate genes in Ae. sharonensis for the ‘breaker’ element through targeted sequencing of this 4SshL introgression segment. This valuable genomic resource will aide in further mapping the Gc locus that could be exploited in wheat breeding to produce new, superior varieties of wheat

Performance analysis of priority queueing systems in discrete time

The integration of different types of traffic in packet-based networks spawns the need for traffic differentiation. In this tutorial paper, we present some analytical techniques to tackle discrete-time queueing systems with priority scheduling. We investigate both preemptive (resume and repeat) and non-preemptive priority scheduling disciplines. Two classes of traffic are considered, high-priority and low-priority traffic, which both generate variable-length packets. A probability generating functions approach leads to performance measures such as moments of system contents and packet delays of both classes

Discrete time GI/Geom/1 queueing system with priority

We study a discrete time single server system with generic distribution of the number of arrivals in a time slot, geometric distribution of the service time and two classes of customers. The customers can be served only when each time slot begins. The customers of the second class can be served only if the customers of the first class are absent. The model is motivated by the description of the congestion in the information networks. We give a complete description of this systems: we are able to compute the expected waiting time of the customers of the two classes, and solving a boundary value problem we are able to write the probability distribution of the length of the queue. To obtain these results, we use judiciously the standard technique of the generating function of the probability distribution. Although the boundary value problem is relatively easy, it is has to be pointed out that the generating function is not simply the product of two independent generating functions for the two classes. (c) 2007 Published by Elsevier B.V

Queueing systems with pre-scheduled random arrivals

We consider a point process i + ξ i , where i Î \mathbbZiZ and the ξ i ’s are i.i.d. random variables with compact support and variance σ 2. This process, with a suitable rescaling of the distribution of ξ i ’s, is well known to converge weakly, for large σ, to the Poisson process. We then study a simple queueing system with this process as arrival process. If the variance σ 2 of the random translations ξ i is large but finite, the resulting queue is very different from the Poisson case. We provide the complete description of the system for traffic intensity ϱ = 1, where the average length of the queue is proved to be finite, and for ϱ < 1 we propose a very effective approximated description of the system as a superposition of a fast process and a slow, birth and death, one. We found interesting connections of this model with the statistical mechanics of Fermi particles. This model is motivated by air traffic systems

Asymptotics for the late arrivals problem

We study a discrete time queueing system where deterministic arrivals have i.i.d. exponential delays . We describe the model as a bivariate Markov chain, prove its ergodicity and study the joint equilibrium distribution. We write a functional equation for the bivariate generating function, finding the solution on a subset of its domain. This solution allows us to prove that the equilibrium distribution of the chain decays super-exponentially fast in the quarter plane. We exploit the latter result and discuss the numerical computation of the solution through a simple yet effective approximation scheme in a wide region of the parameters. Finally, we compare the features of this queueing model with the standard M/D/1 system, showing that the congestion turns out to be very different when the traffic intensity is close to 1

A-priori upper bounds for the set covering problem

In this paper we present a new bound obtained with the probabilistic method for the solution of the set covering problem with unit costs. The bound is valid for problems of fixed dimension, thus extending previous similar asymptotic results, and it depends only on the number of rows of the coefficient matrix and the row densities. We also consider the particular case of matrices that are almost block decomposable, and show how the bound may improve according to the particular decomposition adopted. Such final result may provide interesting indications for comparing different matrix decomposition strategies