arXiv subjects

T. Aste

Publications and source records attributed to T. Aste.

30 records · Page 2Linked to original sources

arXiv2004

Surface instabilities in granular matter and ion-sputtered surfaces

We apply a theoretical approach, originally introduced to describe aeolian ripples formation in sandy deserts, to the study of surface instability in ion sputtered surfaces. The two phenomena are distinct by several orders of magnitudes and by several physical mechanisms, but they obey to similar geometrical constraints and therefore they can be described by means of the same approach. This opens a novel conceptual framework for the study of the dynamical surface roughening and ripple formation on crystal and amorphous surfaces during ion sputtering.

cond-mat.dis-nn↗

arXiv2004

Innovation flow through social networks: Productivity distribution

A detailed empirical analysis of the productivity of non financial firms across several countries and years shows that productivity follows a non-Gaussian distribution with power law tails. We demonstrate that these empirical findings can be interpreted as consequence of a mechanism of exchanges in a social network where firms improve their productivity by direct innovation or/and by imitation of other firm's technological and organizational solutions. The type of network-connectivity determines how fast and how efficiently information can diffuse and how quickly innovation will permeate or behaviors will be imitated. From a model for innovation flow through a complex network we obtain that the expectation values of the productivity level are proportional to the connectivity of the network of links between firms. The comparison with the empirical distributions reveals that such a network must be of a scale-free type with a power-law degree distribution in the large connectivity range.

physics.soc-ph↗

arXiv2004

Long term memories of developed and emerging markets: using the scaling analysis to characterize their stage of development

The scaling properties encompass in a simple analysis many of the volatility characteristics of financial markets. That is why we use them to probe the different degree of markets development. We empirically study the scaling properties of daily Foreign Exchange rates, Stock Market indices and fixed income instruments by using the generalized Hurst approach. We show that the scaling exponents are associated with characteristics of the specific markets and can be used to differentiate markets in their stage of development. The robustness of the results is tested by both Monte-Carlo studies and a computation of the scaling in the frequency-domain.

cond-mat.stat-mech↗

arXiv2004

Investigating the Geometrical Structure of Disordered Sphere Packings

Bead packs of up to 150,000 mono-sized spheres with packing densities ranging from 0.58 to 0.64 have been studied by means of X-ray Computed Tomography. These studies represent the largest and the most accurate description of the structure of disordered packings at the grain-scale ever attempted. We investigate the geometrical structure of such packings looking for signatures of disorder. We discuss ways to characterize and classify these systems and the implications that local geometry can have on densification dynamics.

cond-mat.dis-nn↗

arXiv2004

An interest rates cluster analysis

An empirical analysis of interest rates in money and capital markets is performed. We investigate a set of 34 different weekly interest rate time series during a time period of 16 years between 1982 and 1997. Our study is focused on the collective behavior of the stochastic fluctuations of these time-series which is investigated by using a clustering linkage procedure. Without any a priori assumption, we individuate a meaningful separation in 6 main clusters organized in a hierarchical structure.

cond-mat.stat-mech↗

arXiv2003

Exchanges in complex networks: income and wealth distributions

We investigate the wealth evolution in a system of agents that exchange wealth through a disordered network in presence of an additive stochastic Gaussian noise. We show that the resulting wealth distribution is shaped by the degree distribution of the underlying network and in particular we verify that scale free networks generate distributions with power-law tails in the high-income region. Numerical simulations of wealth exchanges performed on two different kind of networks show the inner relation between the wealth distribution and the network properties and confirm the agreement with a self-consistent solution. We show that empirical data for the income distribution in Australia are qualitatively well described by our theoretical predictions.

cond-mat.stat-mech↗

arXiv2003

Ripples and Ripples: from Sandy Deserts to Ion-Sputtered Surfaces

We study the morphological evolution of surfaces during ion sputtering and we compare their dynamical roughening with aeolian ripple formation in sandy deserts. We show that the two phenomena can be described within the same theoretical framework. This approach explains the different dynamical behaviors experimentally observed in metals or in semiconductors and amorphous systems. In the case of ion erosion, we find exponential growth at constant wavelength up to a critical roughness $W_c$. Whereas, in metals, by introducing the contribution of the Erlich-Schwoebel barrier, we find a transition from an exponential growth to a power law evolution.

cond-mat.mtrl-sci↗

arXiv2003

Using the Scaling Analysis to Characterize Financial Markets

We empirically analyze the scaling properties of daily Foreign Exchange rates, Stock Market indices and Bond futures across different financial markets. We study the scaling behaviour of the time series by using a generalized Hurst exponent approach. We verify the robustness of this approach and we compare the results with the scaling properties in the frequency-domain. We find evidence of deviations from the pure Brownian motion behavior. We show that these deviations are associated with characteristics of the specific markets and they can be, therefore, used to distinguish the different degrees of development of the markets.

cond-mat.stat-mech↗

arXiv2002

Stratifications of cellular patterns

Geometrically, foams or covalent graphs can be decomposed into successive layers or strata. Disorder of the underlying structure imposes a characteristic roughening of the layers. Our main results are hysteresis and convergence in the layer sequences. 1) If the direction of construction is reversed, the layers are different in the up and down sequences (irreversibility); nevertheless, under suitable but non-restrictive conditions, the layers come back, exactly, to the initial profile, a hysteresis phenomenon. 2) Layer sequences based on different initial conditions (e.g. different starting cells) converge, at least in the cylindrical geometry. Jogs in layers may be represented as pairs of opposite dislocations, moving erratically due to the disorder of the underlying structure and ending up annihilating when colliding.

cond-mat.dis-nn↗

arXiv1997

The topological structure of 2D disordered cellular systems

We analyze the structure of two dimensional disordered cellular systems generated by extensive computer simulations. These cellular structures are studied as topological trees rooted on a central cell or as closed shells arranged concentrically around a germ cell. We single out the most significant parameters that characterize statistically the organization of these patterns. Universality and specificity in disordered cellular structures are discussed.

cond-mat.dis-nn↗

arXiv1997

Topological correlations in soap froths

Correlation in two-dimensional soap froth is analysed with an effective potential for the first time. Cells with equal number of sides repel (with linear correlation) while cells with different number of sides attract (with NON-bilinear) for nearest neighbours, which cannot be explained by the maximum entropy argument. Also, the analysis indicates that froth is correlated up to the third shell neighbours at least, contradicting the conventional ideas that froth is not strongly correlated.

cond-mat.dis-nn↗

arXiv1996

Statistical properties and shell analysis in random cellular structures

We investigate the statistical properties of two dimensional random cellular systems (froths) in term of their shell structure. The froth is analyzed as a system of concentric layers of cells around a given central cell. We derive exact analytical relations for the topological properties of the sets of cells belonging to these layers. Experimental observations of the shell structure of two-dimensional soap froth are made and compared with the results on two kinds of Voronoi constructions. It is found that there are specific differences between soap froths and purely geometrical constructions. In particular these systems differ in the topological charge of clusters as a function of shell number, in the asymptotic values of defect concentrations, and in the number of cells in a given layer. We derive approximate expressions with no free parameters which correctly explain these different behaviors.

cond-mat.dis-nn↗