Modification of aluminium-silicon alloys by rare-earth additions

Cast aluminium-silicon (Al-Si) alloys are used extensively in various industries due to their advantageous properties such as high strength-to-weight ratio, good corrosion resistance and high fluidity which allows for defect-free complex castings. Under normal casting conditions the microstructure is composed of silicon needles in an aluminium matrix. These provide propagation planes for defects and therefore deteriorate the mechanical properties. By adding certain elements, usually strontium (Sr), the Si needles change to fibres, however this is also known to increase porosity in castings. The mechanism that causes the change from needles to fibres has been extensively debated and a number of theories can be found in the literature, revolving around both the nucleation and growth stages of eutectic Si. In this thesis high purity materials were used to prepare hypoeutectic unmodified and Sr-modified Al-Si alloys to which cerium (Ce) or yttrium (Y) were added and differences between these alloys in the solidification progression and microstructure were investigated. The addition of 1% Ce or Y to unmodified Al-Si produced a partially modified eutectic Si, whilst full modification was retained when these were added to Sr-modified Al-Si. These additions also resulted in a significant decrease in the eutectic growth temperatures and in the formation of Al2Si2Ce or Al2Si2Y intermetallic phases. It is suggested that similar to the Al2Si2Sr in Sr-modified Al-Si these intermetallic phases nucleate on aluminium phosphide (AlP) and thus do not allow for the nucleation of eutectic silicon on this phase. Three dimensional atom probe tomography (3D APT) of Y-partially-modified Al-Si showed a preferential segregation of yttrium within the eutectic Si. By means of optical microscopy and high resolution x-ray computed tomography (XCT), it was also demonstrated that the Sr modification significantly increases the porosity in cast Al-Si alloys which is reduced following the rare-earth additions

Providing End-to-End Connectivity to SIP User Agents Behind NATs

The widespread diffusion of private networks in SOHO scenarios is fostering an increased deployment of Network Address Translators (NATs). The presence of NATs seriously limits end-to-end connectivity and prevents protocols like the Session Initiation Protocol (SIP) from working properly. This document shows how the Address List Extension (ALEX), which was originally developed to provide dual-stack and multi-homing support to SIP, can be used, with minor modifications, to ensure end-to-end connectivity for both media and signaling flows, without relying on intermediate relay nodes whenever it is possibl

Community core detection in transportation networks

This work analyses methods for the identification and the stability under perturbation of a territorial community structure with specific reference to transportation networks. We considered networks of commuters for a city and an insular region. In both cases, we have studied the distribution of commuters' trips (i.e., home-to-work trips and viceversa). The identification and stability of the communities' cores are linked to the land-use distribution within the zone system, and therefore their proper definition may be useful to transport planners.Comment: 8 pages, 13 figure

Stone Observatory at Bric Pinarella (Finale Ligure, Italy)

This paper reports the latest findings on the stone observatory of Bric Pinarella (Finale Ligure, Savona, northern Italy), first described in 2006 at the conference of the Italian Society of Archaeoastronomy (SIA). The settlement is located near the upland plain of the Manie, which is an area known for the archaeological remains and the natural attractions. The settlement is constituted of three archaeological evidences: a small building, two short standing stones 44 centimetres apart, and a standing stone vertically fitted in the ground with a natural hole in its free end. Archeoastronomical investigations demonstrated that the hole in the standing stone allows positioning of the sunrise at the equinoxes over the Manie skyline, whereas the two standing stones allow tracing of the local meridian with azimuth 360-180. Other possible astronomical functions such as the identification of the elongation of the Sun from the east cardinal point and the study of the Sun and Moon's upper meridian transit (in this respect the site could be described as a rudimentary meridian circle) are discussed in the paper. Despite the fact that, to date, its construction time is still unknown, the most recent findings show that the whole site could be an old astronomical observatory

Modification of Al-Si alloys by Ce or Ce with Sr

Al-Si alloys were modified by addition of cerium (Ce) or Ce plus strontium (Sr) to study the effect on the eutectic silicon (Si) morphology. The modified alloys were characterized using scanning electron microscopy (SEM), x-ray diffraction (XRD) analysis, and thermal analysis to understand the effect of Ce and Sr on their microstructure. The results showed that addition of 1% Ce resulted in only partial modification of the Si phase, whereas addition of Ce with 0.04% Sr resulted in complete modification of the alloy. Addition of 1% Ce decreased the eutectic arrest temperature by about 10°C, compared with a 5°C drop with Sr addition only. SEM energy-dispersive spectroscopy (EDS) and XRD results revealed formation of Al2Si2Ce intermetallic in the Ce-modified Al-Si alloys. Differential scanning calorimetry (DSC) showed that the intermetallic formed just before the eutectic phase

A behavioral model of evolutionary dynamics and optimal regulation of tax evasion

The paper studies the dynamics of compliance in a population of agents that decide whether to engage in tax evasion depending on an evolutionary adaptation process, when payoffs are assumed to have the realistic features of Prospect Theory utilities. The paper also considers the optimal control problem of a tax authority that targets the maximization of the expected stream of tax revenues choosing auditing effort. The analysis produces novel and rich results, including conditions for the convergence to an asymptotically stable interior equilibrium, the existence of multiple equilibria and discontinuities in the optimal control.Web of Science50897

On hypercyclic fully zero-simple semihypergroups

Let I be the class of fully zero-simple semihypergroups generated by a hyperproduct. In this paper we study some properties of residual semihypergroup (H_+; star) of a semihypergroup (H; \u25e6)in I. Moreover, we find sufficient conditions for (H; \u25e6) and (H_+; star) to be cyclic

On Further Properties of Fully Zero-Simple Semihypergroups

Let $mfF_0$ the class of fully zero-simple semihypergroups. In this paper we study the main properties of residual semihypergroup $(H_+, star)$ of a semihypergroup $(H, circ)$ in $mfF_0$. We prove that the quotient semigroup $H_+/eta^*_{H_+}$ is a completely simple and periodic semigroup. Moreover, we find the necessary and sufficient conditions for $(H_+, star)$ to be a torsion group and, in particular, an Abelian $2$-group

3D atom probe tomography study on segregation of yttrium in modified Al-Si alloys

Yttrium segregation behavior in Al-Si alloys has been studied using the three-dimensional atom probe tomography technique. Al-Si alloys were prepared by casting method, and yttrium was added to modify the eutectic silicon morphology in these alloys. The results indicated that yttrium is preferentially located within the Si phase, with the highest concentration at the interface between eutectic Al and eutectic Si

Source and dynamics of a volcanic caldera unrest : Campi Flegrei, 1983–84

Acknowledgements We thank Tiziana Vanorio, Antonella Amoruso, Luca Crescentini, Nicholas Rawlinson, Yasuko Takei, and David Cornwell for the valuable suggestions regarding the methodology and interpretation. Reviews from Tim Greenfield and two anonymous reviewers helped improving both clarity of the manuscript and interpretation. The Royal Society of Edinburgh - Accademia dei Lincei Bilateral Agreement, the Santander Mobility Award of the College of Physical Sciences, University of Aberdeen, and the TIDES EU COST action granted L.D.S. travel grants for the realisation of this study. E.D.P. has been supported by the EPHESTO and KNOWAVES projects, funded by the Spanish Ministry of Education and Science.Peer reviewedPublisher PD