18,559 research outputs found
Two snap-stabilizing point-to-point communication protocols in message-switched networks
A snap-stabilizing protocol, starting from any configuration, always behaves
according to its specification. In this paper, we present a snap-stabilizing
protocol to solve the message forwarding problem in a message-switched network.
In this problem, we must manage resources of the system to deliver messages to
any processor of the network. In this purpose, we use information given by a
routing algorithm. By the context of stabilization (in particular, the system
starts in an arbitrary configuration), this information can be corrupted. So,
the existence of a snap-stabilizing protocol for the message forwarding problem
implies that we can ask the system to begin forwarding messages even if routing
information are initially corrupted. In this paper, we propose two
snap-stabilizing algorithms (in the state model) for the following
specification of the problem: - Any message can be generated in a finite time.
- Any emitted message is delivered to its destination once and only once in a
finite time. This implies that our protocol can deliver any emitted message
regardless of the state of routing tables in the initial configuration. These
two algorithms are based on the previous work of [MS78]. Each algorithm needs a
particular method to be transform into a snap-stabilizing one but both of them
do not introduce a significant overcost in memory or in time with respect to
algorithms of [MS78]
Fast and Compact Distributed Verification and Self-Stabilization of a DFS Tree
We present algorithms for distributed verification and silent-stabilization
of a DFS(Depth First Search) spanning tree of a connected network. Computing
and maintaining such a DFS tree is an important task, e.g., for constructing
efficient routing schemes. Our algorithm improves upon previous work in various
ways. Comparable previous work has space and time complexities of bits per node and respectively, where is the highest
degree of a node, is the number of nodes and is the diameter of the
network. In contrast, our algorithm has a space complexity of bits
per node, which is optimal for silent-stabilizing spanning trees and runs in
time. In addition, our solution is modular since it utilizes the
distributed verification algorithm as an independent subtask of the overall
solution. It is possible to use the verification algorithm as a stand alone
task or as a subtask in another algorithm. To demonstrate the simplicity of
constructing efficient DFS algorithms using the modular approach, We also
present a (non-sielnt) self-stabilizing DFS token circulation algorithm for
general networks based on our silent-stabilizing DFS tree. The complexities of
this token circulation algorithm are comparable to the known ones
Stabilizing data-link over non-FIFO channels with optimal fault-resilience
Self-stabilizing systems have the ability to converge to a correct behavior
when started in any configuration. Most of the work done so far in the
self-stabilization area assumed either communication via shared memory or via
FIFO channels. This paper is the first to lay the bases for the design of
self-stabilizing message passing algorithms over unreliable non-FIFO channels.
We propose a fault-send-deliver optimal stabilizing data-link layer that
emulates a reliable FIFO communication channel over unreliable capacity bounded
non-FIFO channels
Interfacial tension in water at solid surfaces
A model for the formation of cavitation nuclei in liquids has recently been
presented with basis in interfacial liquid tension at non-planar solid surfaces
of concave form. In the present paper investigations of water-solid interfaces
by atomic force microscopy are reported to illuminate experimentally effects of
interfacial liquid tension. The results support that such tension occurs and
that voids develop at solid-liquid interfaces.Comment: RevTeX, 5 pages including 8 figure
Silent MST approximation for tiny memory
In network distributed computing, minimum spanning tree (MST) is one of the
key problems, and silent self-stabilization one of the most demanding
fault-tolerance properties. For this problem and this model, a polynomial-time
algorithm with memory is known for the state model. This is
memory optimal for weights in the classic range (where
is the size of the network). In this paper, we go below this
memory, using approximation and parametrized complexity.
More specifically, our contributions are two-fold. We introduce a second
parameter~, which is the space needed to encode a weight, and we design a
silent polynomial-time self-stabilizing algorithm, with space . In turn, this allows us to get an approximation algorithm for the problem,
with a trade-off between the approximation ratio of the solution and the space
used. For polynomial weights, this trade-off goes smoothly from memory for an -approximation, to memory for exact solutions,
with for example memory for a 2-approximation
CENP-A Is Dispensable for Mitotic Centromere Function after Initial Centromere/Kinetochore Assembly
Human centromeres are defined by chromatin containing the histone H3 variant CENP-A assembled onto repetitive alphoid DNA sequences. By inducing rapid, complete degradation of endogenous CENP-A, we now demonstrate that once the first steps of centromere assembly have been completed in G1/S, continued CENP-A binding is not required for maintaining kinetochore attachment to centromeres or for centromere function in the next mitosis. Degradation of CENP-A prior to kinetochore assembly is found to block deposition of CENP-C and CENP-N, but not CENP-T, thereby producing defective kinetochores and failure of chromosome segregation. Without the continuing presence of CENP-A, CENP-B binding to alphoid DNA sequences becomes essential to preserve anchoring of CENP-C and the kinetochore to each centromere. Thus, there is a reciprocal interdependency of CENP-A chromatin and the underlying repetitive centromere DNA sequences bound by CENP-B in the maintenance of human chromosome segregation
Dynamical stabilization of matter-wave solitons revisited
We consider dynamical stabilization of Bose-Einstein condensates (BEC) by
time-dependent modulation of the scattering length. The problem has been
studied before by several methods: Gaussian variational approximation, the
method of moments, method of modulated Townes soliton, and the direct averaging
of the Gross-Pitaevskii (GP) equation. We summarize these methods and find that
the numerically obtained stabilized solution has different configuration than
that assumed by the theoretical methods (in particular a phase of the
wavefunction is not quadratic with ). We show that there is presently no
clear evidence for stabilization in a strict sense, because in the numerical
experiments only metastable (slowly decaying) solutions have been obtained. In
other words, neither numerical nor mathematical evidence for a new kind of
soliton solutions have been revealed so far. The existence of the metastable
solutions is nevertheless an interesting and complicated phenomenon on its own.
We try some non-Gaussian variational trial functions to obtain better
predictions for the critical nonlinearity for metastabilization but
other dynamical properties of the solutions remain difficult to predict
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