283 research outputs found
A Programming Approach for Complex Animations. Part II: Reconstruction of a Real Disaster
No full textThree years ago, during the excavation of a subway gallery near Neaples, a terrible gas explosion occurred with a terrain and building collapse. In this paper, we describe the geometric modeling and the visual simulation of some possible scenarios of the catastrophic event. The geometric models and the visual simulation, as well as the overall animation coordination, were developed using the functional design language PLaSM. Both animation and rendering were performed by an Open Inventor-based animation server, which plays motion data generated by the PLaSM interpreter. This paper will discuss both the design lines and some preliminary results of a very complex visual simulation project, accomplished by using a geometric programming approach. A methodology for symbolic representation of complex animations was already discussed in the companion paper [Bajaj C, Baldazzi C, Cutchin S, Paoluzzi A, Pascucci V, Vicentino M. A programming approach for complex animations. Part I. Methodology. Computer Aided Design 1999;31;695]
Probing the Debye spectrum in glasses using small system sizes
No full textWe investigate the low-frequency spectrum in a three-dimensional model of structural glass focusing on small system sizes, and using different observables, i.e., the density of states D(ω), the cumulative of the density of states F(ω), and the dynamical structure factor S(q,ω) in the harmonic approximation. When the glass is obtained by an instantaneous quench from high temperatures, we show that extended “phonon-like” modes always populate the low-energy spectrum. Looking at the properties of the dynamical structure factor S(q,ω), we observe that in agreement with early studies of Lennard-Jones glasses [V. Mazzacurati, G. Ruocco, and M. Sampoli, Europhys. Lett. 34, 681 (1996)10.1209/epl/i1996-00515-8], there are still extended modes below the lowest resonant peak. These modes give rise to a plateau in the S(q,ω) for ω→0. This result indicates that the low-energy spectrum of extended modes in glasses can be probed using small system sizes and performing instantaneous quench from high parental temperatures. As we recently observed [M. Paoluzzi, L. Angelani, G. Parisi, and G. Ruocco, Phys. Rev. Lett. 123, 155502 (2019)10.1103/PhysRevLett.123.155502], the situation changes when the glassy configuration is obtained by an instantaneous quench from lower temperatures. The former protocol suppresses extended modes below the lowest resonant peak emphasizing the localized modes with D(ω)∼ω^{4}
Fractal aggregation of active particles
No full textWe study active run-and-tumble particles in two dimensions with an additional two-state internal variable characterizing their motile or nonmotile state. Motile particles change irreversibly into nonmotile ones upon collision with a nonmotile particle. The system evolves towards an absorbing state where all particles are nonmotile. We initialize the system with one nonmotile particle in a bath of motile ones and study numerically the kinetics of relaxation to the absorbing state and its structure as a function of the density of the initial bath of motile particles and of their tumbling rate. We find a crossover from fractal aggregates at low density to homogeneous ones at high density. The persistence of single-particle dynamics as quantified by the tumbling rate pushes this crossover to a higher density and can be used to tune the porosity of the aggregate. At the lowest density the fractal dimension of the aggregate approaches that obtained in single-particle diffusion-limited aggregation. Our results could be exploited for the design of structures of desired porosity. The model is a first step towards the study of the collective dynamics of active particles that can exchange biological information
How non-equilibrium correlations in active matter reveal the topological crossover in glasses
No full textAs shown by early studies on mean-field models of the glass transition, the geometrical features of the energy landscape provide fundamental information on the crossover from high-temperature simple relaxational dynamics to low-temperature activated relaxation. In particular, the critical slowing down of dynamics typical of glass formers has been related to a crossover from a saddle-dominated energy landscape (at high temperatures) to a minima-dominated landscape (at low temperatures). We show that active particles can serve as a useful tool to gain insight into this topological crossover. Once configurations equilibrated down in the glassy phase are provided, we show how features of the landscape are revealed by switching on some activity in particle dynamics. In particular we explain here the mechanism, taking as a reference point the pure p-spin model, by which the presence of self-propulsion is expected to induce critical stationary non-equilibrium correlations in correspondence to the minima-to saddles crossover
PLASM Functional Approach to Design: Representation of Geometry
No full textPLASM (the Programming Language for Solid Modelling) is a solid-modelling-oriented design language strongly inspired by the functional language FL. In a PLASM environment, every geometrical object is generated by evaluating a suitable language expression which produces a polyhedral solid model. The language adopts a dimension-independent approach to geometry representation and algorithms. The generated objects are always geometrically consistent since the validity of geometry is guaranteed at a syntactical level. In fact (a) each well-formed expression is obtained by proper composition of well-formed subexpressions, (b) the evaluation of a well-formed (and polyhedrally typed) expression produces a valid solid model. In this paper, the representation scheme used in the language is given and some language scripts are shown and discussed
Transient flow force estimation on the pilot stage of a hydraulic valve.
No full textThe effect of flow forces on the spool equilibrium of hydraulic components is well known, and a number of methods have been developed in order to estimate their effect. They span from analytical expression, to experimental evaluation, to CFD analysis. This last approach is usually considered too demanding to the purpose of hydraulic component design, however a careful approach to the problem statement can lead to the collection of a complete set of data, starting from a limited number of numerical runs. A further extension to transient flow is made possible by the acceptance of further approximations on the effect of fluid compressibility, leading to a computational technique able to extend the amount of information extracted from a single model
Geometric programming: a programming approach to geometric design
No full textThis article presents a functional programming approach to geometric design with embedded polyhedral complexes. Its main goals are to show the expressive power of the language as well as its usefulness for geometric design. The language, named PLASM (the Programming LAnguage for Solid Modelling), introduces a very high level approach to “constructive” or “generative” modelling. Geometrical objects are generated by evaluating some suitable language expressions. Because generating expressions can be easily combined, the language also extends the standard variational geometry approach by supporting classes of geometric objects with varying topology and shape. The design language PLASM can be roughly considered as a geometry-oriented extension of a subset of the functional language FL. The language takes a dimension-independent approach to geometry representation and algorithms. In particular it implements an algebraic calculus over embedded polyhedra of any dimension. The generated objects are always geometrically consistent because the validity of geometry is guaranteed at a syntactical level. Such an approach allows one to use a representation scheme which is weaker than those usually adopted in solid modelers, thus encompassing a broader geometric domain, which contains solids, surfaces, and wire-frames, as well as higher-dimensional objects
Thermodynamic first order transition and inverse freezing in a 3D spin glass
No full textWe present a numerical study of the random Blume-Capel model in three dimensions. The phase diagram is characterized by spin-glass-paramagnet phase transitions of both first and second order in the thermodynamic sense. Numerical simulations are performed using the exchange Monte Carlo algorithm, providing clear evidence for inverse freezing. The main features at criticality and in the phase coexistence region are investigated. We are not privy to other 3D short-range systems with quenched disorder undergoing inverse freezing. © 2010 The American Physical Society
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