Identifying all abelian periods of a string in quadratic time and relevant problems

Abelian periodicity of strings has been studied extensively over the last years. In 2006 Constantinescu and Ilie defined the abelian period of a string and several algorithms for the computation of all abelian periods of a string were given. In contrast to the classical period of a word, its abelian version is more flexible, factors of the word are considered the same under any internal permutation of their letters. We show two O(|y|^2) algorithms for the computation of all abelian periods of a string y. The first one maps each letter to a suitable number such that each factor of the string can be identified by the unique sum of the numbers corresponding to its letters and hence abelian periods can be identified easily. The other one maps each letter to a prime number such that each factor of the string can be identified by the unique product of the numbers corresponding to its letters and so abelian periods can be identified easily. We also define weak abelian periods on strings and give an O(|y|log(|y|)) algorithm for their computation, together with some other algorithms for more basic problems.Comment: Accepted in the "International Journal of foundations of Computer Science

Resonant Tunneling in Truly Axial Symmetry Mn12 Single-Molecule Magnets: Sharp Crossover between Thermally Assisted and Pure Quantum Tunneling

Magnetization measurements of a truly axial symmetry Mn12-tBuAc molecular nanomagnet with a spin ground state of S = 10 show resonance tunneling. This compound has the same magnetic anisotropy as Mn12-Ac but the molecules are better isolated and the crystals have less disorder and a higher symmetry. Hysteresis loop measurements at several temperatures reveal a well-resolved step fine-structure which is due to level crossings of excited states. All step positions can be modeled by a simple spin Hamiltonian. The crossover between thermally assisted and pure quantum tunneling can be investigated with unprecedented detail.Comment: 5 pages, 6 figure

Prognostic indication of power cable degradation

The reliability and the health performance of network assets are of a great interest due to power network operators. This project investigates methods of developing a prognostic capability for evaluating the health and long term performance of ageing distribution cable circuits. From the instant of installation and operation, the insulating materials of a cable will begin to age as a result of a combination of mechanical, thermal and electrical factors. Development of simulation models can significantly improve the accuracy of prognostics, allowing the targeting of maintenance and reduction of in service failures [1]. Real-time measurements taken close to underground cables can update the simulation models giving a more accurate prognostic model.Currently the project investigates a thermal prognostic simulation model which will predict the likely temperature impact on a cable at burial depth according to weather conditions and known loading. Anomalies of temperature measurements along the cable compared to predicted temperatures will indicate a possible degradation activity in a cable. An experimental surface trough has been set up where operation of power cables is simulated with a control system which is able to model any cable loading. The surface temperature of the cable is continuously monitored as well as the weather conditions such as solar radiation, soil moisture content, wind speed, humidity, rainfall and air-temperature<br/

Implementation of a novel online condition monitoring thermal prognostic indicator system

This research aims to develop a reliable and robust online condition monitoring thermal prognostic indicator system which will reduce the risk of failures in a Power System Network. Real-time measurements (weather conditions, temperature of the cable joints or terminations, loading demand) taken close to underground cable will update the prognostic simulation model. Anomalies of the measurements along the cable will be compared with the predicted ones hence indicating a possible degradation activity in the cable. The use of such systems within a power networks will provide a smarter way of prognostic condition monitoring in which you measure less and model more. The use of suggested thermal models will enable the power network operators to maximize asset utilization and minimize constraint costs in the system

Condition monitoring and prognostic indicators for network reliability

Large-scale investment in transmission and distribution networks are planned over the next 10-15 years to meet future demand and changes in power generation. However, it is important that existing assets continue to operate reliably and their health maintained. A research project is considering the increased use of simulation models that could provide accurate prognostics, targeting maintenance and reduce in service failures. Such models could be further refined with parameters obtained from on-line measurements at the asset. It is also important to consider the future development of the research agenda for condition monitoring of power networks and with colleagues from National Grid, PPA Energy and the Universities of Manchester and Strathclyde, the research team are preparing a Position Paper on this subject

'Diverse mobilities': second-generation Greek-Germans engage with the homeland as children and as adults

This paper is about the children of Greek labour migrants in Germany. We focus on two life-stages of ‘return’ for this second generation: as young children brought to Greece on holidays or sent back for longer periods, and as young adults exercising an independent ‘return’ migration. We draw both on literature and on our own field interviews with 50 first- and second-generation Greek-Germans. We find the practise of sending young children back to Greece to have been surprisingly widespread yet little documented. Adult relocation to the parental homeland takes place for five reasons: (i) a ‘search for self’; (ii) attraction of the Greek way of life; (iii) the actualisation of the ‘family narrative of return’ by the second, rather than the first, generation; (iv) life-stage events such as going to university or marrying a Greek; (v) escape from a traumatic event or oppressive family situation. Yet the return often brings difficulties, disillusionment, identity reappraisal, and a re-evaluation of the German context