UNIVERSITY OF PATRAS Design of a MATLAB toolbox for term-document matrix generation

Data clustering and many other fundamental operations in data mining and information retrieval are built using computational kernels from numerical linear algebra and operate on very large, sparse term-document matrices. To facilitate these tasks, we have built TMG, a toolbox for the generation and incremental modification of term-document matrices from text collections. The toolbox is written entirely in MATLAB, a powerful and popular problem solving environment for linear algebra. It can be used in research and education contexts to streamline document preprocessing and prototyping of algorithms for information retrieval. We outline the design and use of TMG and present results, from standard and readily available datasets of moderate size, concerning the effect of stemming and term weighting on clustering algorithms based on the vector space model

Linear electron beam assisted roll-to-roll in-vacuum flexographic patterning for flexible thermoelectric generators

In this work, we investigated the use of in-line linear electron beam irradiation (LEB) surface treatment integrated into a commercially compatible roll-to-roll (R2R) processing line, as a single fluorocarbon cleaning step, following flexography oil masking used to pattern layers for devices. Thermoelectric generators (TEGs) were selected as the flexible electronic device demonstrator; a green renewable energy harvester ideal for powering wearable technologies. BiTe/BiSbTe-based flexible TEGs (f-TEGs) were fabricated using in-line oil patterned aluminium electrodes, followed by a 600 W LEB cleaning step, in which the duration was optimised. A BiTe/BiSbTe f-TEG using an oil-patterned electrode and a 15 min LEB clean (to remove oil prior to BiTe/BiSbTe deposition) showed similar Seebeck and output power (S ~ 0.19 mV K−1 and p = 0.02 nW at ΔT = 20 K) compared to that of an oil-free reference f-TEG, demonstrating the success of using the LEB as a cleaning step to prevent any remaining oil interfering with the subsequent active material deposition. Device lifetimes were investigated, with electrode/thermoelectric interface degradation attributed to an aluminium/fluorine reaction, originating from the fluorine-rich masking oil. A BiTe/GeTe f-TEG using an oil-patterned/LEB clean, exceeded the lifetime of the comparable BiTe/BiSbTe f-TEG, highlighting the importance of deposited material reactivities with the additives from the masking oil, in this case fluorine. This work therefore demonstrates (i) full device architectures within a R2R system using vacuum flexography oil patterned electrodes; (ii) an enabling Electron beam cleansing step for removal of oil remnants; and (iii) that careful selection of masking oils is needed for the materials used when flexographic patterning during R2R