Epigenetic modifications of the viral and host cell genomes regularly occur in EBV-associated lymphomas and carcinomas. The cell type-dependent usage of latent EBV promoters is determined by the cellular epigenetic machinery. Viral oncoproteins interact with the very same epigenetic regulators and alter the cellular epigenotype and gene-expression pattern: there are common gene sets hypermethylated in both EBV-positive and EBV-negative neoplasms of different histological types. A group of hypermethylated promoters may represent, however, a unique EBV-associated epigenetic signature in EBV-positive gastric carcinomas. By contrast, EBV-immortalized B-lymphoblastoid cell lines are characterized by genome-wide demethylation and loss and rearrangement of heterochromatic histone marks. Early steps of EBV infection may also contribute to reprogramming of the cellular epigenome.

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High power ultrafast lasers are nowadays able to provide high ablation rates and meet the technical requirements and performances needed for many industrial applications. However depositing more energy into the target may induce heat accumulation, and consequently enhances the ablation efficiency as well as introduces some detrimental effect on the processing quality. So, the key issue is to improve throughput while maintaining the processing quality and preventing from any deformation of the work piece. In this paper we present some comparative results on surface ablation of Aluminum, Copper, Molybdenum and stainless steel in both picosecond and femtosecond regimes. Trials have been performed using two high power Yb-doped fibre ultrafast lasers which are tunable in pulse duration (350 fs to 10 ps, up to 20 W). Samples have been characterized with confocal microscopy and scanning electron microscopy. We discuss the effect of pulse duration, repetition rate, fluence and energy dose per mm on ablation efficiency, processing quality and ripples formation.

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