Grabber arm mechanism for the Italian Research Interim Stage (IRIS)

Two deployable arms, named grabbers, were designed and manufactured to provide lateral stability of the perigee spinning stage which will be deployed from the Space Shuttle cargo bay. The spinning stage is supported by a spin table on a cradle at its base. The Italian Research Interim Stage (IRIS) is designed to carry satellites of intermediate mass up to 900 kg. The requirements are defined and the mechanism is described. Functional test results are presented

Non-Equilibrium Phase Transition in an Atomistic Glassformer: the Connection to Thermodynamics

Tackling the low-temperature fate of supercooled liquids is challenging due to the immense timescales involved, which prevent equilibration and lead to the operational glass transition. Relating glassy behaviour to an underlying, thermodynamic phase transition is a long-standing open question in condensed matter physics. Like experiments, computer simulations are limited by the small time window over which a liquid can be equilibrated. Here we address the challenge of low temperature equilibration using trajectory sampling in a system undergoing a nonequilibrium phase transition. This transition occurs in trajectory space between the normal supercooled liquid and a glassy state rich in low-energy geometric motifs. Our results indicate that this transition might become accessible in equilibrium configurational space at a temperature close to the so-called Kauzmann temperature, and provide a possible route to unify dynamical and thermodynamical theories of the glass transition.Comment: accepted in Physical. Rev.

From glass formation to icosahedral ordering by curving three-dimensional space

Geometric frustration describes the inability of a local molecular arrangement, such as icosahedra found in metallic glasses and in model atomic glass-formers, to tile space. Local icosahedral order however is strongly frustrated in Euclidean space, which obscures any causal relationship with the observed dynamical slowdown. Here we relieve frustration in a model glass-forming liquid by curving 3-dimensional space onto the surface of a 4-dimensional hypersphere. For sufficient curvature, frustration vanishes and the liquid freezes in a fully icosahedral structure via a sharp `transition'. Frustration increases upon reducing the curvature, and the transition to the icosahedral state smoothens while glassy dynamics emerges. Decreasing the curvature leads to decoupling between dynamical and structural length scales and the decrease of kinetic fragility. This sheds light on the observed glass-forming behavior in the Euclidean space.Comment: 5 pages + supplementary materia

Dynamical heterogeneities in a two dimensional driven glassy model: current fluctuations and finite size effects

In this article, we demonstrate that in a transport model of particles with kinetic constraints, long-lived spatial structures are responsible for the blocking dynamics and the decrease of the current at strong driving field. Coexistence between mobile and blocked regions can be anticipated by a first-order transition in the large deviation function for the current. By a study of the system under confinement, we are able to study finite-size effects and extract a typical length between mobile regions

The literary text at the borders of linguistics and culture: A SF analysis of Les Murray’s ‘Migratory’

none1noThis article is concerned with the relations between literary text and context, and with the enabling role of lexicogrammatical and structural features in establishing connections between the former and the latter. It shows how foregrounding together with aspects of texture and of interpersonal and experiential meanings in "Migratory" by Les Murray function as a bridge to relate Murray's poem to its cultural contexts of creation and interpretation. What on a superficial reading appears to be a poem about bird migration is shown to be about human migration in a way that challenges hegemonic views of this phenomenon. This paper argues that foregrounding in the poem takes the form of grammatical and lexical parallelism and deviation. These parallelisms and deviations structure the poem textually and experientially into identifiable parts, dealing with the theme of migration from two different perspectives: one focused on an external landscape and bird habitat, the other on a perceptive/ affective abstract sphere suggestive of human consciousness. The poet's lexico-grammatical choices link the poem to a political theme contemporary with its context of creation: the reclaiming by native australians of lands taken from their ancestors by British colonizers. The poem is thus seen to propose an alternative representation of the Australian landscape and its original inhabitants to traditional ones of colonial myth.Si tratta di una pubblicazione di una casa editrice universitaria italiana, che include numerosi contributi internazionali scritti da studiosi che lavorano in università francesi, tedesche, spagnole, australiane, inglesi e slovene. L'articolo ha un impianto interdisciplinare che fa uso di una analisi stilistica per affrontare questioni ideologiche pertinenti alla recenti lotta degli aborigeni australiani per il riconoscimento dei loro territori.mixedM. TurciM. Turc

Solid phase properties and crystallization in simple model systems

We review theoretical and simulational approaches to the description of equilibrium bulk crystal and interface properties as well as to the nonequilibrium processes of homogeneous and heterogeneous crystal nucleation for the simple model systems of hard spheres and Lennard-Jones particles. For the equilibrium properties of bulk and interfaces, density functional theories employing fundamental measure functionals prove to be a precise and versatile tool, as exemplified with a closer analysis of the hard sphere crystalliquid interface. A detailed understanding of the dynamic process of nucleation in these model systems nevertheless still relies on simulational approaches. We review bulk nucleation and nucleation at structured walls and examine in closer detail the influence of walls with variable strength on nucleation in the Lennard-Jones fluid. We find that a planar crystalline substrate induces the growth of a crystalline film for a large range of lattice spacings and interaction potentials. Only a strongly incommensurate substrate and a very weakly attractive substrate potential lead to crystal growth with a non-zero contact angle

Morphometric approach to many-body correlations in hard spheres

We model the thermodynamics of local structures within the hard sphere liquid at arbitrary volume fractions through the \textit{morphometric} calculation of $n$-body correlations. We calculate absolute free energies of local geometric motifs in excellent quantitative agreement with molecular dynamics simulations across the liquid and supercooled liquid regimes. We find a bimodality in the density library of states where five-fold symmetric structures appear lower in free energy than four-fold symmetric structures, and from a single reaction path predict a relaxation barrier which scales linearly in the compressibility factor. The method provides a new route to assess changes in the free energy landscape at volume fractions dynamically inaccessible to conventional techniques.Comment: 6+17 pages, 3 figure

Devitrification of the Kob-Andersen glass former: Competition with the locally favored structure

Supercooled liquids are kinetically trapped materials in which the transition to a thermodynamically more stable state with long-range order is strongly suppressed. To assess the glass-forming abilities of a liquid empirical rules exist, but a comprehensive microscopic picture of devitrification is still missing. Here we study the crystallization of a popular model glass former, the binary Kob-Andersen mixture, in small systems. We perform trajectory sampling employing the population of the locally favored structure as order parameter. While for large population a dynamical phase transition has been reported, here we show that biasing towards a small population of locally favored structures induces crystallization, and we estimate the free energy difference. This result sheds new light on the competition between local and global structure in glass-forming liquids and its implications for crystallization