35 research outputs found
Growth instability due to lattice-induced topological currents in limited mobility epitaxial growth models
The energetically driven Ehrlich-Schwoebel (ES) barrier had been generally
accepted as the primary cause of the growth instability in the form of
quasi-regular mound-like structures observed on the surface of thin film grown
via molecular beam epitaxy (MBE) technique. Recently the second mechanism of
mound formation was proposed in terms of a topologically induced flux of
particles originating from the line tension of the step edges which form the
contour lines around a mound. Through large-scale simulations of MBE growth on
a variety of crystalline lattice planes using limited mobility, solid-on-solid
models introduced by Wolf-Villain and Das Sarma-Tamborenea in 2+1 dimensions,
we propose yet another type of topological uphill particle current which is
unique to some lattice, and has hitherto been overlooked in the literature.
Without ES barrier, our simulations produce spectacular mounds very similar, in
some cases, to what have been observed in many recent MBE experiments. On a
lattice where these currents cease to exist, the surface appears to be
scale-invariant, statistically rough as predicted by the conventional continuum
growth equation.Comment: 10 pages, 12 figure
Automated reliability assessment for spectroscopic redshift measurements
We present a new approach to automate the spectroscopic redshift reliability
assessment based on machine learning (ML) and characteristics of the redshift
probability density function (PDF).
We propose to rephrase the spectroscopic redshift estimation into a Bayesian
framework, in order to incorporate all sources of information and uncertainties
related to the redshift estimation process, and produce a redshift posterior
PDF that will be the starting-point for ML algorithms to provide an automated
assessment of a redshift reliability.
As a use case, public data from the VIMOS VLT Deep Survey is exploited to
present and test this new methodology. We first tried to reproduce the existing
reliability flags using supervised classification to describe different types
of redshift PDFs, but due to the subjective definition of these flags, soon
opted for a new homogeneous partitioning of the data into distinct clusters via
unsupervised classification. After assessing the accuracy of the new clusters
via resubstitution and test predictions, unlabelled data from preliminary mock
simulations for the Euclid space mission are projected into this mapping to
predict their redshift reliability labels.Comment: Submitted on 02 June 2017 (v1). Revised on 08 September 2017 (v2).
Latest version 28 September 2017 (this version v3
Game theoretic path selection to support security in device-to-device communications
Device-to-Device (D2D) communication is expected to be a key feature sup- ported by 5G networks, especially due to the proliferation of Mobile Edge Computing (MEC), which has a prominent role in reducing network stress by shifting computational tasks from the Internet to the mobile edge. Apart from being part of MEC, D2D can extend cellular coverage allowing users to communicate directly when telecommunication infrastructure is highly congested or absent. This significant departure from the typical cellular paradigm imposes the need for de- centralised network routing protocols. Moreover, enhanced capabilities of mobile devices and D2D networking will likely result in proliferation of new malware types and epidemics. Although the literature is rich in terms of D2D routing protocols that enhance quality-of-service and energy consumption, they provide only basic security support, e.g., in the form of encryption. Routing decisions can, however, contribute to collaborative detection of mobile malware by leveraging different kinds of anti-malware software installed on mobile devices. Benefiting from the cooperative nature of D2D communications, devices can rely on each other’s contributions to detect malware. The impact of our work is geared to- wards having more malware-free D2D networks. To achieve this, we designed and implemented a novel routing protocol for D2D communications that optimises routing decisions for explicitly improving malware detection. The protocol identifies optimal network paths, in terms of malware mitigation and energy spent for malware detection, based on a game theoretic model. Diverse capabilities of network devices running different types of anti-malware software and their potential for inspecting messages relayed towards an intended destination device are leveraged using game theoretic tools. An optimality analysis of both Nash and Stackelberg security games is undertaken, including both zero and non-zero sum variants, and the Defender’s equilibrium strategies. By undertaking network simulations, theoretical results obtained are illustrated through randomly generated network scenarios showing how our protocol outperforms conventional routing protocols, in terms of expected payoff, which consists of: security damage inflicted by malware and malware detection cost