44,670 research outputs found
A model for dynamic communicators
We develop and test an intuitively simple dynamic network model to describe the type of time-varying connectivity structure present in many technological settings. The model assumes that nodes have an inherent hierarchy governing the emergence of new connections. This idea draws on newly established concepts in online human behaviour concerning the existence of discussion catalysts, who initiate long threads, and online leaders, who trigger feedback. We show that the model captures an important property found in e-mail and voice call data – ‘dynamic communicators’ with sufficient foresight or impact to generate effective links and having an influence that is grossly underestimated by static measures based on snaphots or aggregated data
Strong correlations generically protect d-wave superconductivity against disorder
We address the question of why strongly correlated d-wave superconductors,
such as the cuprates, prove to be surprisingly robust against the introduction
of non-magnetic impurities. We show that, very generally, both the
pair-breaking and the normal state transport scattering rates are significantly
suppressed by strong correlations effects arising in the proximity to a Mott
insulating state. We also show that the correlation-renormalized scattering
amplitude is generically enhanced in the forward direction, an effect which was
previously often ascribed to the specific scattering by charged impurities
outside the copper-oxide planes.Comment: 4+e page
Exploiting Temporal Complex Network Metrics in Mobile Malware Containment
Malicious mobile phone worms spread between devices via short-range Bluetooth
contacts, similar to the propagation of human and other biological viruses.
Recent work has employed models from epidemiology and complex networks to
analyse the spread of malware and the effect of patching specific nodes. These
approaches have adopted a static view of the mobile networks, i.e., by
aggregating all the edges that appear over time, which leads to an approximate
representation of the real interactions: instead, these networks are inherently
dynamic and the edge appearance and disappearance is highly influenced by the
ordering of the human contacts, something which is not captured at all by
existing complex network measures. In this paper we first study how the
blocking of malware propagation through immunisation of key nodes (even if
carefully chosen through static or temporal betweenness centrality metrics) is
ineffective: this is due to the richness of alternative paths in these
networks. Then we introduce a time-aware containment strategy that spreads a
patch message starting from nodes with high temporal closeness centrality and
show its effectiveness using three real-world datasets. Temporal closeness
allows the identification of nodes able to reach most nodes quickly: we show
that this scheme can reduce the cellular network resource consumption and
associated costs, achieving, at the same time, a complete containment of the
malware in a limited amount of time.Comment: 9 Pages, 13 Figures, In Proceedings of IEEE 12th International
Symposium on a World of Wireless, Mobile and Multimedia Networks (WOWMOM '11
Magnetotransport in a double quantum wire: Modeling using a scattering formalism built on the Lippmann-Schwinger equation
We model electronic transport through a double quantum wire in an external
homogeneous perpendicular magnetic field using a scattering formalism built on
the Lippmann-Schwinger equation. In the scattering region a window is opened
between the parallel wires allowing for inter- and intra-wire scattering
processes. Due to the parity breaking of the magnetic field the ensuing subband
energy spectrum of the double wire system with its regimes of hole- and
electron-like propagating modes leads to a more structure rich conductance as a
function of the energy of the incoming waves than is seen in a single
parabolically confined quantum wire. The more complex structure of the
evanescent modes of the system also leaves its marks on the conductance.Comment: RevTeX, 8 pages with 10 included postscript figures, high resolution
version available at http://hartree.raunvis.hi.is/~vidar/Rann/DW_VGCST_06.pd
Fin loads and control-surface hinge moments measured in full-scale wind-tunnel tests on the X-24A flight vehicle
Fin loads and control surface hinge moments measured in full scale wind tunnel tests on X-24A flight vehicl
Non-adiabatic Current Excitation in Quantum Rings
We investigate the difference in the response of a one-dimensional
semiconductor quantum ring and a finite-width ring to a strong and short-lived
time-dependent perturbation in the THz regime. In both cases the persistent
current is modified through a nonadiabatic change of the many-electron states
of the system, but by different mechanisms in each case.Comment: LaTeX, 5 pages with 6 embedded postscript figures, submitted to 20th
Nordic Semiconductor Meeting, Tampere (2003
Phase-locking in Multi-Frequency Brillouin Oscillator via Four Wave Mixing
Stimulated Brillouin scattering (SBS) and Kerr-nonlinear four wave-mixing
(FWM) are among the most important and widely studied nonlinear effects in
optical fibres. At high powers SBS can be cascaded producing multiple Stokes
waves spaced by the Brillouin frequency shift. Here, we investigate the complex
nonlinear interaction of the cascade of Stokes waves, generated in a
Fabry-Perot chalcogenide fibre resonator through the combined action of SBS and
FWM. We demonstrate the existence of parameter regimes, in which pump and
Stokes waves attain a phase-locked steady state. Real-time measurements of 40ps
pulses with 8GHz repetition rate are presented, confirming short-and long-term
stability. Numerical simulations qualitatively agree with experiments and show
the significance of FWM in phase-locking of pump and Stokes waves. Our findings
can be applied for the design of novel picosecond pulse sources with GHz
repetition rate for optical communication systems
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