Domino effect for world market fluctuations

In order to emphasize cross-correlations for fluctuations in major market places, series of up and down spins are built from financial data. Patterns frequencies are measured, and statistical tests performed. Strong cross-correlations are emphasized, proving that market moves are collective behaviors.Comment: 8 pages, 5 figures, submitted to EPJ

Effect of friction in a toy model of granular compaction

We proposed a toy model of granular compaction which includes some resistance due to granular arches. In this model, the solid/solid friction of contacting grains is a key parameter and a slipping threshold Wc is defined. Realistic compaction behaviors have been obtained. Two regimes separated by a critical point Wc* of the slipping threshold have been emphasized : (i) a slow compaction with lots of paralyzed regions, and (ii) an inverse logarithmic dynamics with a power law scaling of grain mobility. Below the critical point Wc*, the physical properties of this frozen system become independent of Wc. Above the critical point Wc*, i.e. for low friction values, the packing properties behave as described by the classical Janssen theory for silos

Networks of equities in financial markets

We review the recent approach of correlation based networks of financial equities. We investigate portfolio of stocks at different time horizons, financial indices and volatility time series and we show that meaningful economic information can be extracted from noise dressed correlation matrices. We show that the method can be used to falsify widespread market models by directly comparing the topological properties of networks of real and artificial markets.Comment: 9 pages, 8 figures. Accepted for publication in EPJ

Flow of magnetic repelling grains in a two-dimensional silo

During a typical silo discharge, the material flow rate is determined by the contact forces between the grains. Here, we report an original study concerning the discharge of a two-dimensional silo filled with repelling magnetic grains. This non-contact interaction leads to a different dynamics from the one observed with conventional granular materials. We found that, although the flow rate dependence on the aperture size follows roughly the power-law with an exponent $3/2$ found in non-repulsive systems, the density and velocity profiles during the discharge are totally different. New phenomena must be taken into account. Despite the absence of contacts, clogging and intermittence were also observed for apertures smaller than a critical size determined by the effective radius of the repulsive grains.Comment: 6 pages, 8 figure

Relationships between inner ear and sagitta growth during ontogenesis of three <i>Carapini</i> species, and consequences of life-history events on the otolith microstructure

Three species of Carapidae have in common a tenuis larval stage, during which they settle in the lagoon and take refuge in the same species of holothuroid. From the juvenile stage, Carapus homei and C. boraborensis are commensal, whereas Encheliophis gracilis is parasitic. The aims of this study were to analyse to what extent the ontogenetic changes of the otic capsule affected the shape of the inner ear and how environmental cues, due to the above-mentioned life history and the style, could influence the structure of the sagitta. Sagittal sections revealed a three-dimensional asymmetry with a nucleus close to the proximal surface. Observations of the growth axis of the sagitta suggest it has a morphogenetic impact on the otic cavity. Each sagitta contains three main zones related to the life stages of the fish. Bands and checks were observed in the third zone in C. homei and C. boraborensis, but this pattern was less discernible in E. gracilis. These structural differences in zone 3 could be related to the commensal and parasitic life styles of these fishes. Further studies dealing with otosac features and otolith functions are suggested

Ontogenic and ecological control of metamorphosis onset in a carapid fish, <i>Carapus homei</i>: experimental evidence from vertebra and otolith comparisons

In Carapus homei, reef colonisation is associated with a penetration inside a sea cucumber followed by heavy transformations during which the length of the fish is reduced by 60%. By comparing vertebral axis to otolith ontogenetic changes, this study aimed (i) to specify the events linked to metamorphosis, and (ii) to establish to what extent these fish have the ability to delay it. Different larvae of C. homei were caught when settling on the reef and kept in different experimental conditions for at least 7 days and up to 21 days: darkness or natural light conditions, presence of sea cucumber or not, and food deprivation or not. Whatever the nutritional condition, a period of darkness seems sufficient to initiate metamorphosis. Twenty-one days in natural light conditions delayed metamorphosis, whereas the whole metamorphosis process is the fastest (15 days) for larvae living in sea cucumbers. Whether the metamorphosis was initiated or not, otoliths were modified with the formation of a transition zone, whose structure varied depending on the experimental conditions. At day 21, larvae maintained in darkness had an otolith transition zone with more increments (around 80), albeit wider than those (more or less 21) of individuals kept under natural lighting. These differences in otolith growth could indicate an increased incorporation rate of released metabolites by metamorphosing larvae. However, the presence of a transition zone in delayed-metamorphosis larvae suggests that these otolith changes record the endogenously-induced onset of metamorphosis, whereas body transformations seem to be modulated by the environmental conditions of settlement

Expression of myofibrillar proteins and parvalbumin isoforms in white muscle of the developing turbot <i>Scophthalmus maximus</i> (Pisces, Pleuronectiformes)

Expression of polymorphic myofibrillar and sarcoplasmic proteins was investigated in the fish Scophthalmus maximus (L.) undergoing metamorphosis. A range of electrophoretic techniques was used to monitor sequential synthesis of isoforms from hatching to the adult stage. Two isoforms (larval and adult) of myosin light chain LC2 and troponin-I were successively detected during turbot growth, in addition to variations in the peptide composition of myosin heavy chains. Two isoforms of troponin-T also appeared sequentially, but the first to make its appearance was not detected until the juvenile stage. The composition of alkali light chains, actin, tropomyosin, and troponin-C did not seem to change as the fish progressed through the different stages. Parvalbumin isoforms were isolated and their physico-chemical parameters defined. As in the other fish examined so far, there appeared a succession of larval (PA IIa and PA IIb) and adult (PA V) parvalbumin isoforms through the life of the fish. All these biochemical changes occurred gradually in the course of turbot development, and did not appear particularly related to metamorphosis but rather to physiological needs of the different growth stages

Effect of an electric field on an intermittent granular flow

Granular gravity driven flows of glass beads have been observed in a silo with a flat bottom. A DC high electric field has been applied perpendicularly to the silo to tune the cohesion. The outlet mass flow has been measured. An image subtraction technique has been applied to visualize the flow geometry and a spatiotemporal analysis of the flow dynamics has been performed. The outlet mass flow is independent of voltage, but a transition from funnel flow to rathole flow is observed. This transition is of probabilistic nature and an intermediate situation exists between the funnel and the rathole situations. At a given voltage, two kinds of flow dynamics can occur : a continuous flow or an intermittent flow. The electric field increases the probability to observe an intermittent flow.Comment: Accepted for publication in PRE on Apr 9, 201

Scaling in the Bombay Stock Exchange Index

In this paper we study BSE Index financial time series for fractal and multifractal behaviour. We show that Bombay stock Exchange (BSE)Index time series is mono-fractal and can be represented by a fractional Brownian motion.Comment: 11 pages,3 figure