Energy diffusion in hard-point systems

We investigate the diffusive properties of energy fluctuations in a one-dimensional diatomic chain of hard-point particles interacting through a square--well potential. The evolution of initially localized infinitesimal and finite perturbations is numerically investigated for different density values. All cases belong to the same universality class which can be also interpreted as a Levy walk of the energy with scaling exponent 3/5. The zero-pressure limit is nevertheless exceptional in that normal diffusion is found in tangent space and yet anomalous diffusion with a different rate for perturbations of finite amplitude. The different behaviour of the two classes of perturbations is traced back to the "stable chaos" type of dynamics exhibited by this model. Finally, the effect of an additional internal degree of freedom is investigated, finding that it does not modify the overall scenarioComment: 16 pages, 15 figure

One-dimensional asymmetrically coupled maps with defects

In this letter we study chaotic dynamical properties of an asymmetrically coupled one-dimensional chain of maps. We discuss the existence of coherent regions in terms of the presence of defects along the chain. We find out that temporal chaos is instantaneously localized around one single defect and that the tangent vector jumps from one defect to another in an apparently random way. We quantitatively measure the localization properties by defining an entropy-like function in the space of tangent vectors.Comment: 9 pages + 4 figures TeX dialect: Plain TeX + IOP macros (included

New Universality of Lyapunov Spectra in Hamiltonian Systems

A new universality of Lyapunov spectra {\lambda_i} is shown for Hamiltonian systems. The universality appears in middle energy regime and is different from another universality which can be reproduced by random matrices in the following two points. One is that the new universality appears in a limited range of large i/N rather than the whole range, where N is degrees of freedom. The other is Lyapunov spectra do not behave linearly while random matrices give linear behavior even on 3D lattice. Quadratic terms with smaller nonlinear terms of potential functions play an intrinsic role in the new universality.Comment: 19 pages, 16 Encapsulated Postscript figures, LaTeX (100 kb

Length-weight relationships of three reef-associated fishes Lutjanus gibbus, Pinjalo lewisi and Pristipomoides filamentosus off Kochi, southwest coast of India

Length-weight relationships (LWRs) of three reef-associated fishes belonging to the family Lutjanidae viz ., Lutjanus gibbus (Forsskal, 1775), Pinjalo lewisi Randall, Allen & Anderson, 1987 and Pristipomoides filamentosus (Valenciennes, 1830), were estimated based on 548 samples collected from trawl net and hook and line fishery off Kochi, southwest coast of India. Sampling was done at Kochi (Lat. 09°56′327′′N, Long. 76°15′764′′E) and Munambam (Lat. 10°10′965′′N, Long. 76°10′258′′E) landing centers from May 2017 to November 2019. The estimated coefficient (b value) ranged from 2.597 ( P. lewisi , N = 89) to 2.902 (P. filamentosus , N = 240). Coefficient of determination (r2) ranged from 0.906 ( L. gibbus ) to 0.952 ( P. filamentosus), indicating a strong functional LWRs that were highly significant (p <0.001). The study reports the new maximum total length (TLmax) for P. lewisi and also records first estimates of length-weight relationships for three major species of snappers from the region. The generated LWR parameters will be of great importance in evaluating the biological changes in fish stocks and for developing sustainable management measures for snappers in the southeastern Arabian Sea

Stochastic dynamics of model proteins on a directed graph

A method for reconstructing the energy landscape of simple polypeptidic chains is described. We show that we can construct an equivalent representation of the energy landscape by a suitable directed graph. Its topological and dynamical features are shown to yield an effective estimate of the time scales associated with the folding and with the equilibration processes. This conclusion is drawn by comparing molecular dynamics simulations at constant temperature with the dynamics on the graph, defined by a temperature dependent Markov process. The main advantage of the graph representation is that its dynamics can be naturally renormalized by collecting nodes into "hubs", while redefining their connectivity. We show that both topological and dynamical properties are preserved by the renormalization procedure. Moreover, we obtain clear indications that the heteropolymers exhibit common topological properties, at variance with the homopolymer, whose peculiar graph structure stems from its spatial homogeneity. In order to obtain a clear distinction between a "fast folder" and a "slow folder" in the heteropolymers one has to look at kinetic features of the directed graph. We find that the average time needed to the fast folder for reaching its native configuration is two orders of magnitude smaller than its equilibration time, while for the bad folder these time scales are comparable. Accordingly, we can conclude that the strategy described in this paper can be successfully applied also to more realistic models, by studying their renormalized dynamics on the directed graph, rather than performing lengthy molecular dynamics simulations.Comment: 15 pages, 12 figure

Statistical-mechanical formulation of Lyapunov exponents

We show how the Lyapunov exponents of a dynamic system can in general be expressed in terms of the free energy of a (non-Hermitian) quantum many-body problem. This puts their study as a problem of statistical mechanics, whose intuitive concepts and techniques of approximation can hence be borrowed.Comment: 10 pages, 3 figures, RevTex

Giant sized rays landed at Cochin Fisheries Harbour

On 4th March 2017, three huge rays - two Mobula tarpacana and one Manta birostris were landed at Cochin Fisheries Harbour. They were caught in long lines, which were operated for skipjack tuna. These rays caught off Ratnagiri coast at a depth of 500m weighed around 400 kg each. Of these, Mobula tarpacana locally called 'Kakkathirandi' measured 2.4 m in disc width (DW)

Evaluation of the Quality of Commercial Fish Feeds in India with Respect to Microbiological Parameters

This paper describes the first comprehensive study of the quality of commercial fish feeds in India with regard to microbiological indices. Quality of feed is an important parameter that has a direct impact on the outcome of any aquaculture system. Microbiological parameters such as total plate count (TPC), Escherichia coli (CFUg-1), coliformes (CFUg-1), Enterobacteriaceae (CFUg-1) and yeast and mould (CFUg-1) counts were analysed using 3M™ Petrifilm™ as per guidelines. The TPC ranged from 2.0 × 102 to3.13 × 104 CFUg-1 in different feeds. Presence of E. coli was detected in one of the feeds with 1.15×102 CFUg-1. Coliform bacteria were not detected in any of the feeds. Enterobacteriaceae was present in three feeds in the range of 5.45 × 102 to 1.58×103 CFUg-1. Yeast and mould count ranged from <10 to 1.68 × 104 CFUg-1 in the feeds analyzed. The results obtained from the present study indicate that the feeds were contaminated with micro-organisms. As far as Indian scenario is concerned, there exist several feed companies which do not comply with the quality regulations and specifications as laid down by the Bureau of Indian Standards (BIS). In addition, specifications are not available for aqua feeds regarding the acceptable levels of microbiological parameters. Hence the present study calls for a standardized code of quality to be observed by feed manufacturing companies for quality products

Acoustic breathers in two-dimensional lattices

The existence of breathers (time-periodic and spatially localized lattice vibrations) is well established for i) systems without acoustic phonon branches and ii) systems with acoustic phonons, but also with additional symmetries preventing the occurence of strains (dc terms) in the breather solution. The case of coexistence of strains and acoustic phonon branches is solved (for simple models) only for one-dimensional lattices. We calculate breather solutions for a two-dimensional lattice with one acoustic phonon branch. We start from the easy-to-handle case of a system with homogeneous (anharmonic) interaction potentials. We then easily continue the zero-strain breather solution into the model sector with additional quadratic and cubic potential terms with the help of a generalized Newton method. The lattice size is $70\times 70$. The breather continues to exist, but is dressed with a strain field. In contrast to the ac breather components, which decay exponentially in space, the strain field (which has dipole symmetry) should decay like $1/r^a, a=2$. On our rather small lattice we find an exponent $a\approx 1.85$

Localized behavior in the Lyapunov vectors for quasi-one-dimensional many-hard-disk systems

We introduce a definition of a "localization width" whose logarithm is given by the entropy of the distribution of particle component amplitudes in the Lyapunov vector. Different types of localization widths are observed, for example, a minimum localization width where the components of only two particles are dominant. We can distinguish a delocalization associated with a random distribution of particle contributions, a delocalization associated with a uniform distribution and a delocalization associated with a wave-like structure in the Lyapunov vector. Using the localization width we show that in quasi-one-dimensional systems of many hard disks there are two kinds of dependence of the localization width on the Lyapunov exponent index for the larger exponents: one is exponential, and the other is linear. Differences, due to these kinds of localizations also appear in the shapes of the localized peaks of the Lyapunov vectors, the Lyapunov spectra and the angle between the spatial and momentum parts of the Lyapunov vectors. We show that the Krylov relation for the largest Lyapunov exponent $\lambda\sim-\rho\ln\rho$ as a function of the density $\rho$ is satisfied (apart from a factor) in the same density region as the linear dependence of the localization widths is observed. It is also shown that there are asymmetries in the spatial and momentum parts of the Lyapunov vectors, as well as in their $x$ and $y$-components.Comment: 41 pages, 21 figures, Manuscript including the figures of better quality is available from http://www.phys.unsw.edu.au/~gary/Research.htm