Seismic hazard assessment in the Northern Aegean Sea (Greece) through discrete Semi-Markov modeling.

Οι ημι-Μαρκοβιανές αλυσίδες χρησιμοποιούνται για τη μελέτη της σεισμικότητας στο Βόρειο  Αιγαίο.  Η  βασική  τους  διαφορά  από  τις  Μαρκοβιανές  αλυσίδες  είναι  ότι επιτρέπουν  μια  οποιαδήποτε  αυθαίρετη  κατανομή  για  τους  χρόνους  παραμονής (χρόνοι μεταξύ διαδοχικών σεισμών). Υποθέτουμε ότι η χρονοσειρά των σεισμών που έχουν  γίνει  στο  Βόρειο  Αιγαίο  αποτελεί  μια  διακριτή  ημι-Μαρκοβιανή  αλυσίδα. Θεωρείται ότι οι χρόνοι παραμονής ακολουθούν γεωμετρικές ή διακριτές κατανομές Weibull. Πρώτα ταξινομήθηκαν τα δεδομένα σε δυο κατηγορίες, όπου κατάσταση 1: Μέγεθος 6.5 -7 και κατάσταση 2 Μέγεθος>7, και στη συνέχεια σε τρεις κατηγορίες, όπου   κατάσταση 1: μέγεθος 6.5 -6.7,   κατάσταση 2 :   Μέγεθος 6.8 -7.1   και κατάσταση 3 : Μέγεθος 7.2 -7.4 . Εκτιμήθηκαν οι παράμετροι των συναρτήσεων πιθανότητας των χρόνων  παραμονής  και  υπολογίστηκαν  οι  πίνακες  πυρήνες  της  ημι-Μαρκοβιανής αλυσίδας για όλες τις παραπάνω περιπτώσεις. Έγινε σύγκριση των πινάκων πυρήνων και   προέκυψαν συμπεράσματα για  τη μελλοντική σεισμική επικινδυνότητα στην υπό μελέτη περιοχή.Semi-Markov  chains  are  used  for  studying  the  evolution  of  seismicity  in  the Northern Aegean Sea (Greece). Their main difference from the Markov chains is that   they  allow the sojourn times (i.e. the time between successive earthquakes), to follow any arbitrary distribution. It is assumed that the time series of earthquakes that  occurred  in  Northern  Aegean  Sea  form  a  discrete  semi-Markov  chain. The probability law of the sojourn times, is considered to be the geometric distribution or   the   discrete  Weibull  distribution. Firstly,  the  data  are  classified  into  two categories that is, state 1: Magnitude 6.5  -7 and state 2 Magnitude>7, and secondly into three categories , that is    state 1: Magnitude 6.5-6.7, state 2: Magnitude 6.8-7.1 and state 3: Magnitude 7.2-7.4 . This methodology is followed in order to obtain more accurate results and find out whether there exists an impact of the different classification on the results. The parameters of the probability laws of the sojourn times are estimated and the semi-Markov kernels are  evaluated for all the above cases  .  The  semi-Markov  kernels  are  compared and  the   conclusions  are  drawn relatively to future seismic hazard in the area under study

A Note on Scalar Field Theory in AdS_3/CFT_2

We consider a scalar field theory in AdS_{d+1}, and introduce a formalism on surfaces at equal values of the radial coordinate. In particular, we define the corresponding conjugate momentum. We compute the Noether currents for isometries in the bulk, and perform the asymptotic limit on the corresponding charges. We then introduce Poisson brackets at the border, and show that the asymptotic values of the bulk scalar field and the conjugate momentum transform as conformal fields of scaling dimensions \Delta_{-} and \Delta_{+}, respectively, where \Delta_{\pm} are the standard parameters giving the asymptotic behavior of the scalar field in AdS. Then we consider the case d=2, where we obtain two copies of the Virasoro algebra, with vanishing central charge at the classical level. An AdS_3/CFT_2 prescription, giving the commutators of the boundary CFT in terms of the Poisson brackets at the border, arises in a natural way. We find that the boundary CFT is similar to a generalized ghost system. We introduce two different ground states, and then compute the normal ordering constants and quantum central charges, which depend on the mass of the scalar field and the AdS radius. We discuss certain implications of the results.Comment: 24 pages. v2: added minor clarification. v3: added several comments and discussions, abstract sligthly changed. Version to be publishe

University Staff Teaching Allocation: Formulating and Optimising a Many-Objective Problem

This is the author accepted manuscript. The final version is available from ACM via the DOI in this record.The codebase for this paper is available at https://github.com/fieldsend/gecco_2017_staff_teaching_allocationThe allocation of university staff to teaching exhibits a range of often competing objectives. We illustrate the use of an augmented version of NSGA-III to undertake the seven-objective optimisation of this problem, to fi nd a trade-off front for a university department using real world data. We highlight its use in decision-making, and compare solutions identi fied to an actual allocation made prior to the availability of the optimisation tool. The criteria we consider include minimising the imbalance in workload distribution among staff; minimising the average load; minimising the maximum peak load; minimising the staff per module; minimising staff dissatisfaction with teaching allocations; and minimising the variation from the previous year’s allocation (allocation churn). We derive mathematical forms for these various criteria, and show we can determine the maximum possible values for all criteria and the minimum values for most exactly (with lower bounds on the remaining criteria). For many of the objectives, when considered in isolation, an optimal solution may be obtained rapidly. We demonstrate the advantage of utilising such extreme solutions to drastically improve the optimisation effi ciency in this many-objective optimisation problem. We also identify issues that NSGA-III can experience due to selection between generations

Optimal competitiveness for the Rectilinear Steiner Arborescence problem

We present optimal online algorithms for two related known problems involving Steiner Arborescence, improving both the lower and the upper bounds. One of them is the well studied continuous problem of the {\em Rectilinear Steiner Arborescence} ($RSA$). We improve the lower bound and the upper bound on the competitive ratio for $RSA$ from $O(\log N)$ and $\Omega(\sqrt{\log N})$ to $\Theta(\frac{\log N}{\log \log N})$, where $N$ is the number of Steiner points. This separates the competitive ratios of $RSA$ and the Symetric-$RSA$, two problems for which the bounds of Berman and Coulston is STOC 1997 were identical. The second problem is one of the Multimedia Content Distribution problems presented by Papadimitriou et al. in several papers and Charikar et al. SODA 1998. It can be viewed as the discrete counterparts (or a network counterpart) of $RSA$. For this second problem we present tight bounds also in terms of the network size, in addition to presenting tight bounds in terms of the number of Steiner points (the latter are similar to those we derived for $RSA$)

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Janus within Janus

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B-Meson Gateways to Missing Charmonium Levels

We outline a coherent strategy for exploring the four remaining narrow charmonium states [\eta_{c}^{\prime}(2\slj{1}{1}{0}), h_{c}(1\slj{1}{2}{1}), \eta_{c2}(1\slj{1}{3}{2}), and \psi_{2}(1\slj{3}{3}{2})] expected to lie below charm threshold. Produced in $B$-meson decays, these levels should be identifiable \textit{now} via striking radiative transitions among charmonium levels and in exclusive final states of kaons and pions. Their production and decay rates will provide much needed new tests for theoretical descriptions of heavy quarkonia.Comment: 5 pages, uses ReVTeX and BibTe