O(N)-symmetric vector models for N large

So far, universal properties of O(N) symmetric critical systems have been derived within the framework of the formal ϵ = 4−d expansion. Therefore, it is reassuring to verify that the results obtained in this way remain valid, at least in some limiting case, even when ϵ is not infinitesimal. Here it is shown in the example of the O(N) symmetric (ϕ2)2 field theory, the same universal properties can also be derived at fixed dimension in the large N limit and, more generally, order by order in an 1/N expansion. Moreover, large N techniques are also useful, because they provide an insight into other non-perturbative questions, including issues relevant to four-dimensional physics like renormalons and triviality. Using a large N expansion, we exhibit a remarkable relation between the (ϕ2)2 field theory and the non-linear σ-model, valid to all orders.

Quantum spin chains and classical integrable systems

This chapter is a review of the recently established quantum-classical correspondence for integrable systems based on the construction of the master T-operator. For integrable inhomogeneous quantum spin chains with gl(N)-invariant R-matrices in finite-dimensional representations, the master T-operator is a sort of generating function for the family of commuting quantum transfer matrices depending on an infinite number of parameters. Any eigenvalue of the master T-operator is the tau-function of the classical modified KP hierarchy. It is a polynomial in the spectral parameter which is identified with the 0th time of the hierarchy. This implies a remarkable relation between the quantum spin chains and classical many-body integrable systems of particles of the Ruijsenaars-Schneider type. As an outcome, a system of algebraic equations can be obtained for the spectrum of the spin chain Hamiltonians.

Classical extension of quantum-correlated separable states

Li and Luo [Phys. Rev. A 78 (2008) 024303] discovered a remarkable relation between discord and entanglement. It establishes that all separable states can be obtained via reduction of a classically-correlated state "living" in a space of larger dimension. Starting from this result, we discuss here an optimal classical extension of separable states and explore this notion for low-dimensional systems. We find that the larger the dimension of the classical extension, the larger the discord in the original separable state. Further, we analyze separable states of maximum discord in ℂ2 ⊗ ℂ2 and their associated classical extensions showing that, from the reduction of a classical state in (ℂ2 ⊗ ℂ3) ⊗ ℂ2, one can obtain a separable state of maximum discord in ℂ2 ⊗ ℂ2.

Precursory seismicity pattern before strong earthquakes in Greece

The temporal variation of seismicity, based on the retrospective analyses of three seismic parameters <em>i.e.</em>, number of earthquakes, bvalue and energy released, have shown significant changes. Their remarkable relation with strong earthquakes occurrence was formulated as a qualitative character precursory seismicity pattern, which were interpreted in terms of a strong earthquakes occurrence preparation phases. The main characteristic of this pattern is that permits the identification of two period of low and high probability for an earthquake occurrence, suggesting its utility in the current seismic hazard assessment, by the continuous monitoring of the temporal variation of the seismic parameters in a given area. This paper investigates the qualitative and quantitative characteristics of the proposed precursory seismicity pattern, before al strong earthquakes occurrence in Greece the time period 2000-2008.

Study of Relations between Computer Experience and Readiness to Access Internet Resources

The paper presents results of studies among computer users, demonstrating a remarkable relation between history of computer use (computer experience) and readiness to access Internet resources (Internet access). The observed relation, referred to as ‘Internet entry delay syndrome’, may be described as follows: the greater the user’s computer experience, the longer it takes him/her to decide on accessing Internet and using it on a regular basis. The delay is markedly shorter for inexperienced computer users. The results of the study can be invaluable for Internet Service Providers (ISPs), allowing for more precise design of network infrastructure, as well as for local administration authorities striving to implement the policy of information society through development of information structures and services and improving Internet access on local and regional scale.

Automated Classification of Variable Stars for ASAS Data

With the advent of surveys generating multi-epoch photometry and their discoveries of large numbers of variable stars, the classification of the obtained time series has to be automated. We have developed a classification algorithm for the periodic variable stars using a Bayesian classifier on a Fourier decomposition of the light curve. This algorithm is applied to ASAS (AII Sky Automated Survey, Pojmanski, 2000). In ASAS 85% of the variables are red giants. A remarkable relation between their period and amplitude is found for a large fraction of those stars.