Probabilistic Reliable Multicast in Ad Hoc Networks

When striving for reliability, multicast protocols are most commonly designed as deterministic solutions. Such an approach seems to make the reasoning about reliability guarantees (traditionally binary "all-or-nothing"- like) in the face of packet losses and/or node crashes. It is however precisely this determinism that tends to become a limiting factor when aiming at both reliability and scalability, particularly in highly dynamic networks, e.g., ad hoc networks. Gossip-based multicast protocols appear to be a viable path towards providing multicast reliability guarantees. Such protocols embrace the non-deterministic nature of ad hoc networks, providing analytically predictable probabilistic reliability guarantees at a reasonable overhead. This paper presents the Route Driven Gossip (RDG) protocol, a gossip-based multicast protocol designed precisely to meet a more practical specification of probabilistic reliability in ad hoc networks. Our RDG protoool can be deployed on any basic on-demand routing protocol, achieving a high level of reliability without relying on any inherent multicast primitive. We illustrate our RDG protocol by layering it on top of the ¡°bare¡± DSR protocol, and convey our claims of reliability and scalability through both analysis and simulation

Corrigendum to "A thermodynamic model of mixed organic–inorganic aerosols to predict activity coefficients" published in Atmos. Chem. Phys., 8, 4559–4593, 2008

No abstract available

Ion-beam-induced bending of freestanding amorphous nanowires: The importance of the substrate material and charging

Ion-beam irradiation offers great flexibility and controllability in the construction of freestanding nanostructures with multiple advanced functionalities. Here, we present and discuss the bending of free-standing nanowires, against, towards, and ultimately parallel to a flux of directional ion irradiation. Bending components both along and perpendicular to the incident ion beam were observed, and the bending behavior was found to depend both on the ion beam scanning strategy and on the conductivity of the supporting substrate. This behavior is explained by an ion-irradiation-related electrostatic interaction. Our findings suggest the prospect of exploiting this technique to engineer 3D nanostructures for advanced applications

CoNi/Pt interface roughness probed by nonlinear magneto-optics, x-ray scattering and atomic force microscopy

The crystallographic contribution of the nonlinear magneto-optical response from CoNi/Pt interfaces appears to scale linearly with increasing interface roughness as determined by small angle x-ray scattering and atomic force microscopy. From the magnetic contribution it follows that the increased interface roughness causes the interface moment to turn out of plane while the bulk of the film has an in-plane magnetization

Tetragonal to Orthorhombic Transition of GdFeAsO Studied by Single-Crystal Synchrotron X-Ray Diffraction

A study of the tetragonal to orthorhombic phase transition of GdFeAsO is presented. Planes of the reciprocal space were reconstructed form single-crystal synchrotron X-ray diffraction data. By cooling below the structural transition temperature splitting of the Bragg reflections was observed corresponding to four different twin domain orientations. A model was developed to quantify the distortion of the lattice from the position of the splitted reflections relative to each other. Constrained 2D-Cauchy fits of several splitted reflections provided positions of the reflections. The influence of the structural distortion was detectable already above the structural transition temperature hinting at fluctuations in the tetragonal phase.Comment: 6 pages, 6 figure

Route Driven Gossip: Probabilistic Reliable Multicast in Ad Hoc Networks

Traditionally, reliable multicast protocols are deterministic in nature. It is precisely this determinism that tends to become their limiting factor when aiming at reliability and scalability, particularly in highly dynamic networks, e.g., ad hoc networks. As probabilistic protocols, gossip-based multicast protocols, recently (re-)discovered in wired networks, appear to be a viable means to "fight fire with fire'' by exploiting the non-deterministic nature of ad hoc networks. This paper presents a protocol that is designed to meet a more practical specification of probabilistic reliability; this gossip-based multicast protocol, called Route Driven Gossip (RDG), can be deployed on any basic on-demand routing protocol. RDG is custom-tailored to ad hoc networks, achieving a high level of reliability without relying on any inherent multicast primitive. We illustrate our RDG protocol by layering it on top of the "bare'' DSR protocol. We prove the reliability and scalability of RDG through both analysis and simulation

PILOT: ProbabilistIc Lightweight grOup communication sysTem for Mobile Ad Hoc Networks

Providing reliable group communication is an ever recurring issue in distributed settings. In mobile ad hoc networks, this issue becomes more significant since all nodes act as peers, while the issue gets even more challenging due to highly dynamic and unpredictable topology changes. In order to overcome these difficulties, we deviate from the conventional point of view, i.e., we "fight fire with fire", by exploiting the nondeterministic nature of ad hoc networks. Inspired by the principles of gossip mechanisms and probabilistic quorum systems, we present in this paper a ProbabilistIc Lightweight grOup communication sysTem (PILOT) for ad hoc networks, a two layer system consisting of a set of protocols for reliable multicasting and data sharing in mobile ad hoc networks. The system performance, in terms of both reliability (fault tolerance) and efficiency (overhead), is predictable and controllable. We present an analysis of PILOT performance, which is used to fine tune protocol parameters to obtain the desired tradeoff between reliability and efficiency. We confirm the predictability and tunability of PILOT through simulations with ns-2

Spin relaxation: From 2D to 1D

In inversion asymmetric semiconductors, spin-orbit interactions give rise to very effective relaxation mechanisms of the electron spin. Recent work, based on the dimensionally constrained D'yakonov Perel' mechanism, describes increasing electron-spin relaxation times for two-dimensional conducting layers with decreasing channel width. The slow-down of the spin relaxation can be understood as a precursor of the one-dimensional limit

Recent development and perspectives of machines for lattice QCD

I highlight recent progress in cluster computer technology and assess status and prospects of cluster computers for lattice QCD with respect to the development of QCDOC and apeNEXT. Taking the LatFor test case, I specify a 512-processor QCD-cluster better than 1$/Mflops.Comment: 14 pages, 17 figures, Lattice2003(plenary

Ordering of dipolar Ising crystals

We study Ising systems of spins with dipolar interactions. We find a simple approximate relation for the interaction energy between pairs of parallel lattice columns of spins running along the Ising spin direction. This relation provides insight into the relation between lattice geometry and the nature of the ordered state. It can be used to calculate ground state energies. We have also obtained ground state energies and ordering temperatures T_0 from Monte Carlo simulations. Simple empirical relations, that give T_0 for simple and body centered tetragonal lattices in terms of lattice parameters are also established. Finally, the nature of the ordered state and T_0 are determined for Fe_8 clusters, which crystallize on a triclinic lattice.Comment: 13 pages, 4 eps figures, to be published in PRB. For related work, see http://pipe.unizar.es/~jf