Words with the Maximum Number of Abelian Squares

An abelian square is the concatenation of two words that are anagrams of one another. A word of length $n$ can contain $\Theta(n^2)$ distinct factors that are abelian squares. We study infinite words such that the number of abelian square factors of length $n$ grows quadratically with $n$.Comment: To appear in the proceedings of WORDS 201

Learning about sustainability through experiencing complex, adverse conditions typical of the South : reflections from the African Catchment Games played in Finland 2008

The African Catchment Game is an innovative role playing game which was played twice in Finland in 2008 as part of the CIMO funded collaboration between Finland Futures Research Centre and Rhodes University. It simulates a "real imaginary country" and enables participants to explore and experience how southern countries may or may not develop scenarios of sustainable resource extraction and consumption. New processes modelling climatic variability, water management and consumption were introduced for these two game runs. This imaginary country has roles for an urban/industrial sector, the informal sector, trading intermediaries, overseas trade, a government comprised of a president and two ministers, peasant and commercial farmers. Chapman's original game, Green Revolution Game/Exaction, is based on systems and complexity theories from the 1970s and 1980s. Our modifications to Chapman’s game are underpinned by theories of Complex Adaptive Systems and educational approaches based on constructivist, active/experiential learning models. The paper presents an analysis of the two Finnish games from the perspectives of the participants and the game managers. Participants’ information came from pre and post game questionnaires and the focus group discussions that were part of the debriefing pro-cess. These two methods enabled us to examine the local and network processes which de-veloped during the games. Global scale processes of production, consumption, resource utilization, trading and water provision was collected by the game managers as part of their management processes throughout each game run. Our analysis shows that the par-ticipants’ understanding altered and deepened as a result of playing the game. The nature of the game, as a Complex Adaptive System, and the constructivist learning approach through which the game is experienced means that lessons of a more universal nature cannot be extrapolated

Learning About Water Management through the African Catchment Game

The African Catchment Game (ACG) is an innovative role-playing game for Geography educators that simulates a “real imaginary country”. It enables the participants to explore how rural and urban stakeholders in southern African countries may, or may not, develop scenarios of sustainable wateruse. The ACG has been developed from Graham Chapman’s the Green Revolution Game/Exaction of the 1970s and 1980s. Our modifications to Chapman’s game are under-pinned by theories of Complex Adaptive Systems and educational approaches based on constructivist, active/experiential learningmodels. This paper examines the impact of two game runs through examining the experiences of the participants and managers of the game and analyzing empirical data collected during each game run. The African Catchment Game was played twice in Finland in 2008 as part of a collaboration intended to explore the possibilities of simulations being used as tools for predicting African futures.Our analysis shows that the participants’ understanding altered and deepened as a result of playing the game. The nature of the game, as a Complex Adaptive System, and the use of a constructivist learning approach, means that the particular learning that took place cannot be extrapolated to more universalcontexts, but the value of the learning process can be more generally applied

Exploring risk related to future climates through role-playing games: the African catchment game

Risk is the result of two interacting components: hazard and vulnerability. Climatic hazards are related to extrinsic factors such as drought or severe storms. Vul- nerability is the result of intrinsic factors that often arise from the socio-political- economic context. The interplay of risk and vulnerability is difficult to predict. Although computer models have been widely used to forecast climate related risk, albeit with con- siderable uncertainty, they can never capture sufficiently the vulnerability of human sys- tems to these hazards. Role-playing games can be used more realistically to simulate pos- sible outcomes of different climate change scenarios, and allow players to reflect on their significance. The authors have developed the African Catchment Game to simulate a wa- ter scarce African country. Risk can be modelled mechanistically by changing the nature of the annual rainfall input. Vulnerability can in part be modelled by changing the start- ing parameters (such as access to land and resources) and, secondly, through the unpredictable response of players to game dynamics. Players’ reflections demonstrate that through the game they become more aware of the concept of risk and the complex response of individuals and societies that determine their vulnerability to climatic hazards. This paper reflects on the potential for developing the game further as a tool for participatory learning around climate change, based on the authors’ experience of playing the game with participants from South Africa

Development of a triple GEM UV-photon detector operated in pure CF4 for the PHENIX experiment

Results obtained with a triple GEM detector operated in pure CF4 with and without a reflective CsI photocathode are presented. The detector operates in a stable mode at gains up to 10^4. A deviation from exponential growth starts to develop when the total charge exceeds ~ 4 10^6 e leading to gain saturation when the total charge is ~ 2 10^7 e and making the structure relatively robust against discharges. No aging effects are observed in the GEM foils after a total accumulated charge of ~ 10 mC/cm^2 at the anode. The ion back-flow current to the reflective photocathode is comparable to the electron current to the anode. However, no significant degradation of the CsI photocathode is observed for a total ion back-flow charge of ~ 7 mC/cm^2.Comment: 14 pages, 11 figures, Submitted to NIM

Palindromic complexity of trees

We consider finite trees with edges labeled by letters on a finite alphabet $\varSigma$. Each pair of nodes defines a unique labeled path whose trace is a word of the free monoid $\varSigma^*$. The set of all such words defines the language of the tree. In this paper, we investigate the palindromic complexity of trees and provide hints for an upper bound on the number of distinct palindromes in the language of a tree.Comment: Submitted to the conference DLT201

A d-Step Approach for Distinct Squares in Strings

We present an approach to the problem of maximum number of distinct squares in a string which underlines the importance of considering as key variables both the length n and n − d where d is the size of the alphabet. We conjecture that a string of length n and containing d distinct symbols has no more than n − d distinct squares, show the critical role played by strings satisfying n = 2d, and present some properties satisfied by strings of length bounded by a constant times the size of the alphabet

A Hadron Blind Detector for the PHENIX Experiment

A novel Hadron Blind Detector (HBD) has been developed for an upgrade of the PHENIX experiment at RHIC. The HBD will allow a precise measurement of electron-positron pairs from the decay of the light vector mesons and the low-mass pair continuum in heavy-ion collisions. The detector consists of a 50 cm long radiator filled with pure CF4 and directly coupled in a windowless configuration to a triple Gas Electron Multiplier (GEM) detector with a CsI photocathode evaporated on the top face of the first GEM foil.Comment: 4 pages, 3 figures, Quark Matter 2005 conference proceeding