Algorithms For Extracting Timeliness Graphs

We consider asynchronous message-passing systems in which some links are timely and processes may crash. Each run defines a timeliness graph among correct processes: (p; q) is an edge of the timeliness graph if the link from p to q is timely (that is, there is bound on communication delays from p to q). The main goal of this paper is to approximate this timeliness graph by graphs having some properties (such as being trees, rings, ...). Given a family S of graphs, for runs such that the timeliness graph contains at least one graph in S then using an extraction algorithm, each correct process has to converge to the same graph in S that is, in a precise sense, an approximation of the timeliness graph of the run. For example, if the timeliness graph contains a ring, then using an extraction algorithm, all correct processes eventually converge to the same ring and in this ring all nodes will be correct processes and all links will be timely. We first present a general extraction algorithm and then a more specific extraction algorithm that is communication efficient (i.e., eventually all the messages of the extraction algorithm use only links of the extracted graph)

Unified Software for Multi-Functional G-Code: A Method for Implementing Multi-Technology Additive Manufacturing

Additive manufacturing (AM) began a manufacturing revolution moving industrial production into consumer homes. With interest shifting toward multi-functional parts fabricated through AM technologies, multi-functional fabrication systems are now being developed. Merging different manufacturing technologies into a single machine is a challenge, but ongoing research in the development of multi-technology systems has shown promise. The software and automation aspects of multi-technology systems are being developed in unison. This paper explores the challenges and approaches to developing software that interfaces with multifunctional CADs and creates files for direct use in multi-technology AM machines.Mechanical Engineerin

A synthetic population of Wolf-Rayet stars in the LMC based on detailed single and binary star evolution models

Without doubt, mass transfer in close binary systems contributes to the populations of Wolf-Rayet (WR) stars in the Milky Way and the Magellanic Clouds. However, the binary formation channel is so far not well explored. We want to remedy this by exploring large grids of detailed binary and single star evolution models computed with the publicly available MESA code, for a metallicity appropriate for the Large Magellanic Cloud (LMC). The binary models are calculated through Roche-lobe overflow and mass transfer, until the initially more massive star exhausts helium in its core. We distinguish models of WR and helium stars based on the estimated stellar wind optical depth. We use these models to build a synthetic WR population, assuming constant star formation. Our models can reproduce the WR population of the LMC to significant detail, including the number and luminosity functions of the main WR subtypes. We find that for binary fractions of 100% (50%), all LMC WR stars below $10^6\,L_{\odot}$ ($10^{5.7}\,L_{\odot}$) are stripped binary mass donors. We also identify several insightful mismatches. With a single star fraction of 50\%, our models produce too many yellow supergiants, calling either for a larger initial binary fraction, or for enhanced mass-loss near the Humphreys-Davidson limit. Our models predict more long-period WR binaries than observed, arguably due to an observational bias towards short periods. Our models also underpredict the shortest-period WR binaries, which may have implications for understanding the progenitors of double black hole mergers. The fraction of binary produced WR stars may be larger than often assumed, and outline the risk to mis-calibrate stellar physics when only single star models are used to reproduce the observed WR stars.Comment: 15 pages + 13 pages appendix, 14 figures, 2 table

Orbital contribution to the magnetic properties of nanowires: Is the orbital polarization ansatz justified?

We show that considerable orbital magnetic moments and magneto-crystalline anisotropy energies are obtained for a Fe monatomic wire described in a tight-binding method with intra-atomic electronic interactions treated in a full Hartree Fock (HF) decoupling scheme. Even-though the use of the orbital polarization ansatz with simplified Hamiltonians leads to fairly good results when the spin magnetization is saturated this is not the case of unsaturated systems. We conclude that the full HF scheme is necessary to investigate low dimensional systems

Matching theory as enabler of efficient spectrum management in 5G networks

This is the peer reviewed version of the following article: Tsirakis, C, Lopez‐Aguilera, E, Agapiou, G, Varoutas, D. Matching theory as enabler of efficient spectrum management in 5G networks. Trans Emerging Tel Tech. 2020; 31:e3769., which has been published in final form at https://doi.org/10.1002/ett.3769. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions.This paper analyzes the spectrum trading problem in virtualized fifth generation (5G) networks in order to enhance the network performance with respect to the spectrum utilization. The problem is modeled as a Many-to-Many Matching (M2MM) game with utility-based preferences and determines the matching between mobile network operators and mobile virtual network operators. The two proposed versions of utility functions for each set aim at maximizing the satisfaction of both sets with conflicting interests and improving the overall spectrum efficiency. In the simulation evaluation, the proposed scheme is compared with three different schemes in terms of the system utility, individual and pair matching satisfaction. We also investigate the scalability aspects, the strategy plan impact on the matching performance of our proposed scheme, and, at the same time, we attempt to make appropriate assumptions closer to reality. Our proposed scheme shows much better performance than the other schemes achieving a quite high level of satisfaction for the matching result on both sets.Postprint (author's final draft

Evidence for a direct band gap in the topological insulator Bi2Se3 from theory and experiment

Using angle-resolved photoelectron spectroscopy and ab-initio GW calculations, we unambiguously show that the widely investigated three-dimensional topological insulator Bi2Se3 has a direct band gap at the Gamma point. Experimentally, this is shown by a three-dimensional band mapping in large fractions of the Brillouin zone. Theoretically, we demonstrate that the valence band maximum is located at the Brillouin center only if many-body effects are included in the calculation. Otherwise, it is found in a high-symmetry mirror plane away from the zone center.Comment: 8 pages, 4 figure

Spectrum trading in virtualized multi-tenant 5G networks

© 2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.In this research work, we analyze the problem of spectrum trading in virtualized multi-tenant 5G networks using principles from matching theory. More specifically, we deal with the matching problem among the Mobile Network Operators (MNOs) and the Mobile Virtual Network Operators (MVNOs) and we propose a matching scheme that takes into account the preferences of each entity in terms of different utility variables. Our proposal includes a many-to-many matching scheme, that is an extension of the deferred acceptance algorithm, where each MNO and MVNO can cooperate with one or more MVNOs and MNOs, respectively. The performance of our proposed scheme is finally investigated by comparing it with various schemes and some useful conclusions are drawn.Postprint (author's final draft

Kink far below the Fermi level reveals new electron-magnon scattering channel in Fe

Many properties of real materials can be modeled using ab initio methods within a single-particle picture. However, for an accurate theoretical treatment of excited states, it is necessary to describe electron-electron correlations including interactions with bosons: phonons, plasmons, or magnons. In this work, by comparing spin- and momentum-resolved photoemission spectroscopy measurements to many-body calculations carried out with a newly developed first-principles method, we show that a kink in the electronic band dispersion of a ferromagnetic material can occur at much deeper binding energies than expected (E_b=1.5 eV). We demonstrate that the observed spectral signature reflects the formation of a many-body state that includes a photohole bound to a coherent superposition of renormalized spin-flip excitations. The existence of such a many-body state sheds new light on the physics of the electron-magnon interaction which is essential in fields such as spintronics and Fe-based superconductivity.Comment: 6 pages, 2 figure

A basis for variational calculations in d dimensions

In this paper we derive expressions for matrix elements (\phi_i,H\phi_j) for the Hamiltonian H=-\Delta+\sum_q a(q)r^q in d > 1 dimensions. The basis functions in each angular momentum subspace are of the form phi_i(r)=r^{i+1+(t-d)/2}e^{-r^p/2}, i >= 0, p > 0, t > 0. The matrix elements are given in terms of the Gamma function for all d. The significance of the parameters t and p and scale s are discussed. Applications to a variety of potentials are presented, including potentials with singular repulsive terms of the form b/r^a, a,b > 0, perturbed Coulomb potentials -D/r + B r + Ar^2, and potentials with weak repulsive terms, such as -g r^2 + r^4, g > 0.Comment: 22 page

The determinants of hotels' marketing managers' green marketing behaviour

Little is known about the factors underlying the pro-environmental behaviour of marketing managers. This paper explores the determinants of green marketing practices in the Red Sea hotel sector in Egypt. The research model assesses green marketing practices against the personal and organisational values of the marketing managers, together with a range of organisational and demographic variables expected to influence hotels' environmental behaviour. From a valid sample of 89 marketing managers responsible for 194 hotels, it was found that organisational contextual variables, and in particular targeting Western tourists, being affiliated to an international hotel chain and the marketers' own demographics, including age, academic subject studied and gender, were the best predictors of more proactive green marketing. Personal environmental values did not explain the pro-environmental behaviour of marketers, and the organisational environmental values that had explained part of their ethical behaviour had resulted from voluntarism rather than utilitarian or conformance-based values. Government policies also appeared to be ineffective determinants. The implications for green marketing practices are also discussed. © 2010 Taylor & Francis