50 research outputs found
Special issue on DISC 2010
This special issue of Distributed Computing is based on papers that originally appeared as extended abstracts in the Proceedings of the 24th International Symposium on Distributed Computing (DISC2010), held in Cambridge, Massachusetts on August 13–15, 2010. The papers for the Special Issue were chosen by the Program Committee from the 32 regular papers presented at the Symposium, based on their quality and representation of the spectrum of topics encompassed by the Symposium. In addition to being reviewed, in preliminary form, by the Program Committee, the full papers submitted for the Special Issue were refereed according to the standard practices of Distributed Computing (due to time constrains, some papers could not appear in this volume). We thank the Members of the Editorial Board for their work in editing this issue, and the referees and the authors of these papers for their respective contributions
Black holes as antimatter factories
We consider accretion of matter onto a low mass black hole surrounded by
ionized medium. We show that, because of higher mobility of protons than
electrons, the black hole would acquire positive electric charge. If the black
hole's mass is about or below g, the electric field at the horizon
can reach the critical value which leads to vacuum instability and
electron--positron pair production by the Schwinger mechanism. Since the
positrons are ejected by the emergent electric field, while electrons are
back--captured, the black hole operates as an antimatter factory which
effectively converts protons into positrons.Comment: 5 pages, no figure. v2: with discussion section not included in the
refereed versio
Informatikai algoritmusok 2.
A könyv a Magyar Tudományos Akadémia támogatásával készül
Canalization of Gene Expression and Domain Shifts in the Drosophila Blastoderm by Dynamical Attractors
The variation in the expression patterns of the gap genes in the blastoderm of
the fruit fly Drosophila melanogaster reduces over time as a
result of cross regulation between these genes, a fact that we have demonstrated
in an accompanying article in PLoS Biology (see Manu et al.,
doi:10.1371/journal.pbio.1000049). This biologically essential process is an
example of the phenomenon known as canalization. It has been suggested that the
developmental trajectory of a wild-type organism is inherently stable, and that
canalization is a manifestation of this property. Although the role of gap genes
in the canalization process was established by correctly predicting the response
of the system to particular perturbations, the stability of the developmental
trajectory remains to be investigated. For many years, it has been speculated
that stability against perturbations during development can be described by
dynamical systems having attracting sets that drive reductions of volume in
phase space. In this paper, we show that both the reduction in variability of
gap gene expression as well as shifts in the position of posterior gap gene
domains are the result of the actions of attractors in the gap gene dynamical
system. Two biologically distinct dynamical regions exist in the early embryo,
separated by a bifurcation at 53% egg length. In the anterior region,
reduction in variation occurs because of stability induced by point attractors,
while in the posterior, the stability of the developmental trajectory arises
from a one-dimensional attracting manifold. This manifold also controls a
previously characterized anterior shift of posterior region gap domains. Our
analysis shows that the complex phenomena of canalization and pattern formation
in the Drosophila blastoderm can be understood in terms of the
qualitative features of the dynamical system. The result confirms the idea that
attractors are important for developmental stability and shows a richer variety
of dynamical attractors in developmental systems than has been previously
recognized
Developing a Consistent Domain-Oriented Distributed Object Service
This paper presents a new algorithm for a reconfigurable distributed domain-oriented atomic object
service, called DO-RAMBO, which stands for Domain-Oriented Reconfigurable Atomic Memory for
Basic Objects. This service is suitable for inclusion as a middleware system service for distributed
applications requiring atomic read/write data. The implementation substantially extends and refines the
abstract RAMBO algorithm of Lynch and Shvartsman that supports individual atomic objects. In this
paper domains are introduced to allow the users to group related atomic objects. The new implementation
manages configurations on the basis of domains, significantly improving the utility and the performance
of the resulting service. DO-RAMBO guarantees consistency under asynchrony, message loss, node
crashes, new node arrivals, and node departures. We present the formal algorithm development for
DO-RAMBO and give analytical and empirical results that illustrate the benefit of the new approach.This work is supported in part by the NSF Grants 9988304, 9984778, 0121277, and 0311368