115 research outputs found
Node Labels in Local Decision
The role of unique node identifiers in network computing is well understood
as far as symmetry breaking is concerned. However, the unique identifiers also
leak information about the computing environment - in particular, they provide
some nodes with information related to the size of the network. It was recently
proved that in the context of local decision, there are some decision problems
such that (1) they cannot be solved without unique identifiers, and (2) unique
node identifiers leak a sufficient amount of information such that the problem
becomes solvable (PODC 2013).
In this work we give study what is the minimal amount of information that we
need to leak from the environment to the nodes in order to solve local decision
problems. Our key results are related to scalar oracles that, for any given
, provide a multiset of labels; then the adversary assigns the
labels to the nodes in the network. This is a direct generalisation of the
usual assumption of unique node identifiers. We give a complete
characterisation of the weakest oracle that leaks at least as much information
as the unique identifiers.
Our main result is the following dichotomy: we classify scalar oracles as
large and small, depending on their asymptotic behaviour, and show that (1) any
large oracle is at least as powerful as the unique identifiers in the context
of local decision problems, while (2) for any small oracle there are local
decision problems that still benefit from unique identifiers.Comment: Conference version to appear in the proceedings of SIROCCO 201
Size-dependent infrared properties of MgO nanoparticles with evidence of screening effect
We have investigated the infrared (IR) absorption properties of MgO nanoparticles (NPs) with the means of molecular dynamics simulations. Several size effects have been observed. We show in particular that the absorption of IR radiation does not occur predominantly through the polariton mode but preferentially through surface modes. This enhanced surface absorption is found to result from the absence of dielectric screening of the first atomic layer of the NPs. We demonstrate concomitantly that a macroscopic description of electrodynamics is inadequate to capture these unusual IR properties
A general lower bound for collaborative tree exploration
We consider collaborative graph exploration with a set of agents. All
agents start at a common vertex of an initially unknown graph and need to
collectively visit all other vertices. We assume agents are deterministic,
vertices are distinguishable, moves are simultaneous, and we allow agents to
communicate globally. For this setting, we give the first non-trivial lower
bounds that bridge the gap between small () and large () teams of agents. Remarkably, our bounds tightly connect to existing results
in both domains.
First, we significantly extend a lower bound of
by Dynia et al. on the competitive ratio of a collaborative tree exploration
strategy to the range for any . Second,
we provide a tight lower bound on the number of agents needed for any
competitive exploration algorithm. In particular, we show that any
collaborative tree exploration algorithm with agents has a
competitive ratio of , while Dereniowski et al. gave an algorithm
with agents and competitive ratio , for any
and with denoting the diameter of the graph. Lastly, we
show that, for any exploration algorithm using agents, there exist
trees of arbitrarily large height that require rounds, and we
provide a simple algorithm that matches this bound for all trees
Deterministic meeting of sniffing agents in the plane
Two mobile agents, starting at arbitrary, possibly different times from
arbitrary locations in the plane, have to meet. Agents are modeled as discs of
diameter 1, and meeting occurs when these discs touch. Agents have different
labels which are integers from the set of 0 to L-1. Each agent knows L and
knows its own label, but not the label of the other agent. Agents are equipped
with compasses and have synchronized clocks. They make a series of moves. Each
move specifies the direction and the duration of moving. This includes a null
move which consists in staying inert for some time, or forever. In a non-null
move agents travel at the same constant speed, normalized to 1. We assume that
agents have sensors enabling them to estimate the distance from the other agent
(defined as the distance between centers of discs), but not the direction
towards it. We consider two models of estimation. In both models an agent reads
its sensor at the moment of its appearance in the plane and then at the end of
each move. This reading (together with the previous ones) determines the
decision concerning the next move. In both models the reading of the sensor
tells the agent if the other agent is already present. Moreover, in the
monotone model, each agent can find out, for any two readings in moments t1 and
t2, whether the distance from the other agent at time t1 was smaller, equal or
larger than at time t2. In the weaker binary model, each agent can find out, at
any reading, whether it is at distance less than \r{ho} or at distance at least
\r{ho} from the other agent, for some real \r{ho} > 1 unknown to them. Such
distance estimation mechanism can be implemented, e.g., using chemical sensors.
Each agent emits some chemical substance (scent), and the sensor of the other
agent detects it, i.e., sniffs. The intensity of the scent decreases with the
distance.Comment: A preliminary version of this paper appeared in the Proc. 23rd
International Colloquium on Structural Information and Communication
Complexity (SIROCCO 2016), LNCS 998
Fundamental issues in nanoscale heat transfer: From Coherenc to interfacial resistance in heat conduction
Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.When system sizes shrink to nanoscales as in the case of electronic and optical devices, heat transfer laws are altered due to the modification of the basic physical mechanisms at play, especially in the fields of conduction. We expose recent advances in the understanding of heat conduction in semi-conductor superlattices. The effect of (i) coherence and (ii) interfaces becoming predominant, we use a direct simulation technique -i.e. Molecular Dynamics- to estimate the thermal resistance generated by those effects.dc201
Byzantine Gathering in Networks
This paper investigates an open problem introduced in [14]. Two or more
mobile agents start from different nodes of a network and have to accomplish
the task of gathering which consists in getting all together at the same node
at the same time. An adversary chooses the initial nodes of the agents and
assigns a different positive integer (called label) to each of them. Initially,
each agent knows its label but does not know the labels of the other agents or
their positions relative to its own. Agents move in synchronous rounds and can
communicate with each other only when located at the same node. Up to f of the
agents are Byzantine. A Byzantine agent can choose an arbitrary port when it
moves, can convey arbitrary information to other agents and can change its
label in every round, in particular by forging the label of another agent or by
creating a completely new one.
What is the minimum number M of good agents that guarantees deterministic
gathering of all of them, with termination?
We provide exact answers to this open problem by considering the case when
the agents initially know the size of the network and the case when they do
not. In the former case, we prove M=f+1 while in the latter, we prove M=f+2.
More precisely, for networks of known size, we design a deterministic algorithm
gathering all good agents in any network provided that the number of good
agents is at least f+1. For networks of unknown size, we also design a
deterministic algorithm ensuring the gathering of all good agents in any
network but provided that the number of good agents is at least f+2. Both of
our algorithms are optimal in terms of required number of good agents, as each
of them perfectly matches the respective lower bound on M shown in [14], which
is of f+1 when the size of the network is known and of f+2 when it is unknown
Le référentiel taxonomique Florical et les caractéristiques de la flore vasculaire indigène de la Nouvelle-Calédonie
The taxonomic reference base Florical and characteristics of the native vascular flora of New Caledonia. The floristic inventory presented here comprises the evolving computerised database Florical (http://www.botanique.nc/herbier/florical). As of the date of publication, it lists all native vascular plant species (as well as infraspecific taxa) present in the territory of New Caledonia, whether validly published or in press, along with their basionym, organised according to the most recent classifications systems (APG III 2009 for the angiosperms, Smith et at [2006] for the ferns and lycophytes, and Mabberley [2009] for the gymnosperms), accompanied by their status (native or endemic) and the various vegetation types in which they occur. After a brief historical review of our knowledge of New Caledonian botany, the characteristics (richness, composition and endemism) of the different taxonomic groups (ferns and lycophytes, gymnosperms and then angiosperms -mono- and dicotyledons) are analyzed, followed by an assessment of the distribution of these groups among the vegetation types. The vascular flora of New Caledonia is characterised by its high level of richness (3371 species, including 3099 for the flowering plants alone), despite the absence or under-representation of some taxa that are abundantly represented elsewhere in the tropics, and especially by its remarkable distinctiveness (with endemism at the species level reaching 74,7%, and 77.8% for the flowering plants). The flora stands out by the presence of several relictual taxa and a high level of speciation among certain groups, despite the fact that the island was re-colonised relatively recently following the total submersion of its much older basement during the Paleocene and the Oligocene. Details of the measures taken to conserve this extraordinary natural heritage show that only 3.4% of the territory's total surface area is effectively protected. Despite the undeniable progress made in recent years by the authorities concerned, significant work remains to be done, especially in the northern Province
Asynchronous rendezvous with different maps
© Springer Nature Switzerland AG 2019. This paper provides a study on the rendezvous problem in which two anonymous mobile entities referred to as robots rA and rB are asked to meet at an arbitrary node of a graph G = (V,E). As opposed to more standard assumptions robots may not be able to visit the entire graph G. Namely, each robot has its own map which is a connected subgraph of G. Such mobility restrictions may be dictated by the topological properties combined with the intrinsic characteristics of robots preventing them from visiting certain edges in E. We consider four different variants of the rendezvous problem introduced in [Farrugia et al. SOFSEM’15] which reflect on restricted maneuverability and navigation ability of rA and rB in G. In the latter, the focus is on models in which robots’ actions are synchronised. The authors prove that one of the maps must be a subgraph of the other. I.e., without this assumption (or some extra knowledge) the rendezvous problem does not have a feasible solution. In this paper, while we keep the containment assumption, we focus on asynchronous robots and the relevant bounds in the four considered variants. We provide some impossibility results and almost tight lower and upper bounds when the solutions are possible
Quantum coherent control of highly multipartite continuous-variable entangled states by tailoring parametric interactions
The generation of continuous-variable multipartite entangled states is
important for several protocols of quantum information processing and
communication, such as one-way quantum computation or controlled dense coding.
In this article we theoretically show that multimode optical parametric
oscillators can produce a great variety of such states by an appropriate
control of the parametric interaction, what we accomplish by tailoring either
the spatio-temporal shape of the pump, or the geometry of the nonlinear medium.
Specific examples involving currently available optical parametric oscillators
are given, hence showing that our ideas are within reach of present technology.Comment: 14 pages, 5 figure
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