A semantic deconstruction of session types

We investigate the semantic foundations of session types, by revisiting them in the abstract setting of labelled transition systems. The crucial insight is a simulation relation which generalises the usual syntax-directed notions of typing and subtyping, and encompasses both synchronous and asynchronous binary session types. This allows us to extend the session types theory to some common programming patterns which are not typically considered in the session types literature

A Calculus for Orchestration of Web Services

We introduce COWS (Calculus for Orchestration of Web Services), a new foundational language for SOC whose design has been influenced by WS-BPEL, the de facto standard language for orchestration of web services. COWS combines in an original way a number of ingredients borrowed from well-known process calculi, e.g. asynchronous communication, polyadic synchronization, pattern matching, protection, delimited receiving and killing activities, while resulting different from any of them. Several examples illustrates COWS peculiarities and show its expressiveness both for modelling imperative and orchestration constructs, e.g. web services, flow graphs, fault and compensation handlers, and for encoding other process and orchestration languages

Orchestrating Tuple-based Languages

The World Wide Web can be thought of as a global computing architecture supporting the deployment of distributed networked applications. Currently, such applications can be programmed by resorting mainly to two distinct paradigms: one devised for orchestrating distributed services, and the other designed for coordinating distributed (possibly mobile) agents. In this paper, the issue of designing a pro- gramming language aiming at reconciling orchestration and coordination is investigated. Taking as starting point the orchestration calculus Orc and the tuple-based coordination language Klaim, a new formalism is introduced combining concepts and primitives of the original calculi. To demonstrate feasibility and effectiveness of the proposed approach, a prototype implementation of the new formalism is described and it is then used to tackle a case study dealing with a simplified but realistic electronic marketplace, where a number of on-line stores allow client applications to access information about their goods and to place orders

Radio AGN in spiral galaxies

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society. © 2015 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.Radio AGN in the nearby Universe are more likely to be found in galaxies with early-type morphology, the detection rate in spiral or late-type galaxies (LTGs) being around an order of magnitude lower. We combine the mJy Imaging VLBA Exploration at 20cm (mJIVE-20) survey with the Sloan Digital Sky Survey (SDSS), to study the relatively rare population of AGN in LTGs that have nuclear radio luminosities similar to that in their early-type counterparts. The LTG AGN population is preferentially hosted by galaxies that have high stellar masses (M* > 10^10.8 MSun), red colours and low star-formation rates, with little dependence on the detailed morphology or local environment of the host LTG. The merger fraction in the LTG AGN is around 4 times higher than that in the general LTG population, indicating that merging is an important trigger for radio AGN in these systems. The red colours of our systems extend recent work which indicates that merger-triggered AGN in the nearby Universe appear after the peak of the associated starburst, implying that they do not strongly regulate star formation. Finally, we find that in systems where parsec-scale jets are clearly observed in our VLBI images, the jets are perpendicular to the major axis of the galaxy, indicating alignment between the accretion disc and the host galaxy stellar disc.Peer reviewe

Diffusion in liquid mixtures

The understanding of transport and mixing in fluids in the presence and in the absence of external fields and reactions represents a challenging topic of strategic relevance for space exploration. Indeed, mixing and transport of components in a fluid are especially important during long-term space missions where fuels, food and other materials, needed for the sustainability of long space travels, must be processed under microgravity conditions. So far, the processes of transport and mixing have been investigated mainly at the macroscopic and microscopic scale. Their investigation at the mesoscopic scale is becoming increasingly important for the understanding of mass transfer in confined systems, such as porous media, biological systems and microfluidic systems. Microgravity conditions will provide the opportunity to analyze the effect of external fields and reactions on optimizing mixing and transport in the absence of the convective flows induced by buoyancy on Earth. This would be of great practical applicative relevance to handle complex fluids under microgravity conditions for the processing of materials in space

Newborn spheroids at high redshift: when and how did the dominant, old stars in today's massive galaxies form?

We study ~330 massive (M* > 10^9.5 MSun), newborn spheroidal galaxies (SGs) around the epoch of peak star formation (1<z<3), to explore the high-redshift origin of SGs and gain insight into when and how the old stellar populations that dominate today's Universe formed. The sample is drawn from the HST/WFC3 Early-Release Science programme, which provides deep 10-filter (0.2 - 1.7 micron) HST imaging over a third of the GOODS-South field. We find that the star formation episodes that built the SGs likely peaked in the redshift range 2<z<5 (with a median of z~3) and have decay timescales shorter than ~1.5 Gyr. Starburst timescales and ages show no trend with stellar mass in the range 10^9.5 < M* < 10^10.5 MSun. However, the timescales show increased scatter towards lower values ( 10^10.5 MSun, and an age trend becomes evident in this mass regime: SGs with M* > 10^11.5 MSun are ~2 Gyrs older than their counterparts with M* < 10^10.5 MSun. Nevertheless, a smooth downsizing trend with galaxy mass is not observed, and the large scatter in starburst ages indicate that SGs are not a particularly coeval population. Around half of the blue SGs appear not to drive their star formation via major mergers, and those that have experienced a recent major merger, show only modest enhancements (~40%) in their specific star formation rates. Our empirical study indicates that processes other than major mergers (e.g. violent disk instability driven by cold streams and/or minor mergers) likely play a dominant role in building SGs, and creating a significant fraction of the old stellar populations that dominate today's Universe.Comment: MNRAS in pres

Simulation study of Non-ergodicity Transitions: Gelation in Colloidal Systems with Short Range Attractions

Computer simulations were used to study the gel transition occurring in colloidal systems with short range attractions. A colloid-polymer mixture was modelled and the results were compared with mode coupling theory expectations and with the results for other systems (hard spheres and Lennard Jones). The self-intermediate scattering function and the mean squared displacement were used as the main dynamical quantities. Two different colloid packing fractions have been studied. For the lower packing fraction, $\alpha$-scaling holds and the wave-vector analysis of the correlation function shows that gelation is a regular non-ergodicity transition within MCT. The leading mechanism for this novel non-ergodicity transition is identified as bond formation caused by the short range attraction. The time scale and diffusion coefficient also show qualitatively the expected behaviour, although different exponents are found for the power-law divergences of these two quantities. The non-Gaussian parameter was also studied and very large correction to Gaussian behaviour found. The system with higher colloid packing fraction shows indications of a nearby high-order singularity, causing $\alpha$-scaling to fail, but the general expectations for non-ergodicity transitions still hold.Comment: 13 pages, 15 figure

An infrared study of local galaxy mergers

A. Carpineti, et al., “An infrared study of local galaxy mergers”, Astronomy & Astrophysics, Vol. 577, May 2015. This version of record is available online at: https://doi.org/10.1051/0004-6361/201425276 Reproduced with Permission from Astronomy and Astrophysics, © ESO 2016.We combine a large, homogeneous sample of $\sim$3000 local mergers with the Imperial IRAS Faint Source Redshift Catalogue (IIFSCz), to perform a blind far-infrared (FIR) study of the local merger population. The IRAS-detected mergers are mostly ($98\%$) spiral-spiral systems, residing in low density environments, a median FIR luminosity of $10^{11} L_\odot$ (which translates to a median star formation rate of around 15$M_\odot yr^{-1}$). The FIR luminosity -- and therefore the star formation rate -- shows little correlation with group richness and scales with the total stellar mass of the system, with little or no dependence on the merger mass ratio. In particular, minor mergers (mass ratios $Peer reviewedFinal Published versio

The limited role of galaxy mergers in driving stellar mass growth over cosmic time

© The Author(s) 2017. This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited. Published by Oxford University Press on behalf of the Royal Astronomical Society.A key unresolved question is the role that galaxy mergers play in driving stellar mass growth over cosmic time. Recent observational work hints at the possibility that the overall contribution of `major' mergers (mass ratios $\gtrsim$1:4) to cosmic stellar mass growth may be small, because they enhance star formation rates by relatively small amounts at high redshift, when much of today's stellar mass was assembled. However, the heterogeneity and relatively small size of today's datasets, coupled with the difficulty in identifying genuine mergers, makes it challenging to $\textit{empirically}$ quantify the merger contribution to stellar mass growth. Here, we use Horizon-AGN, a cosmological hydrodynamical simulation, to comprehensively quantify the contribution of mergers to the star formation budget over the lifetime of the Universe. We show that: (1) both major and minor mergers enhance star formation to similar amounts, (2) the fraction of star formation directly attributable to merging is small at all redshifts (e.g. $\sim$35 and $\sim$20 per cent at z$\sim$3 and z$\sim$1 respectively) and (3) only $\sim$25 per cent of today's stellar mass is directly attributable to galaxy mergers over cosmic time. Our results suggest that smooth accretion, not merging, is the dominant driver of stellar mass growth over the lifetime of the Universe.Peer reviewedFinal Published versio