On Redundancy Elimination Tolerant Scheduling Rules

In (Ferrucci, Pacini and Sessa, 1995) an extended form of resolution, called Reduced SLD resolution (RSLD), is introduced. In essence, an RSLD derivation is an SLD derivation such that redundancy elimination from resolvents is performed after each rewriting step. It is intuitive that redundancy elimination may have positive effects on derivation process. However, undesiderable effects are also possible. In particular, as shown in this paper, program termination as well as completeness of loop checking mechanisms via a given selection rule may be lost. The study of such effects has led us to an analysis of selection rule basic concepts, so that we have found convenient to move the attention from rules of atom selection to rules of atom scheduling. A priority mechanism for atom scheduling is built, where a priority is assigned to each atom in a resolvent, and primary importance is given to the event of arrival of new atoms from the body of the applied clause at rewriting time. This new computational model proves able to address the study of redundancy elimination effects, giving at the same time interesting insights into general properties of selection rules. As a matter of fact, a class of scheduling rules, namely the specialisation independent ones, is defined in the paper by using not trivial semantic arguments. As a quite surprising result, specialisation independent scheduling rules turn out to coincide with a class of rules which have an immediate structural characterisation (named stack-queue rules). Then we prove that such scheduling rules are tolerant to redundancy elimination, in the sense that neither program termination nor completeness of equality loop check is lost passing from SLD to RSLD.Comment: 53 pages, to appear on TPL

Palmitoylethanolamide is a disease-modifying agent in peripheral neuropathy : pain relief and neuroprotection share a PPAR-alpha-mediated mechanism

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Transcriptome regulation during the X chromosome inactivation process

In mammals, female cells achieve dosage compensation between the sexes randomly chosing and transcriptionally silencing one of the two X chromosomes through a process known as X-chromosome inactivation (XCI). This process is initiated during early development through up-regulation of the long non-coding RNA Xist, which mediates chromosome-wide gene silencing of the future inactive chromosome (Xi) in cis. Upon completion of the XCI process Xi will maintain its silenced state in all daughter cells, which results in the genetic mosaicism of female organisms. Cell differentiation, Xist up-regulation and gene silencing are thought to be coupled at multiple levels to ensure inactivation of exactly one out of two X chromosomes.In this thesis I performed an integrated analysis of all three processes through the analysis of allele-specific single-cell RNA-sequencing data. Specifically, I investigated the endogenous random XCI process in hybrid mouse embryonic stem cells at different time points throughout cellular differentiation developing dedicated analysis approaches that rely on the high number of polymorphisms between the two parental strains.Putative Xist regulators were identified exploiting the inter-cellular heterogeneity of XCI onset. A large fraction of cells transiently expressed Xist on both X chromosomes which resulted in biallelic gene silencing right before being resolved to a monoallelic state, confirming a prediction of the stochastic model of XCI. The two X chromosomes showed different gene silencing dynamics, and a number of strain-specific escapees (namely, genes that escape transcriptional silencing) were identified and experimentally validated. These results suggest that genetic variation modulates the XCI process at multiple levels, providing a potential explanation for the long-known X-controlling element (Xce) effect, which leads to preferential inactivation of a specific X chromosome in inter-strain crosses.Overall, this work provides a detailed picture of the different levels of regulation that govern both Xist up-regulation and the initiation of XCI

Optical polarisation of the Crab pulsar: precision measurements and comparison to the radio emission

The linear polarisation of the Crab pulsar and its close environment was derived from observations with the high-speed photo-polarimeter OPTIMA at the 2.56-m Nordic Optical Telescope in the optical spectral range (400 - 750 nm). Time resolution as short as 11 microseconds, which corresponds to a phase interval of 1/3000 of the pulsar rotation, and high statistics allow the derivation of polarisation details never achieved before. The degree of optical polarisation and the position angle correlate in surprising details with the light curves at optical wavelengths and at radio frequencies of 610 and 1400 MHz. Our observations show that there exists a subtle connection between presumed non-coherent (optical) and coherent (radio) emissions. This finding supports previously detected correlations between the optical intensity of the Crab and the occurrence of giant radio pulses. Interpretation of our observations require more elaborate theoretical models than those currently available in the literature.Comment: 21 pages, 13 figures, uses AMS.sty, mn2e.cls, mn2e.bst and natbib.sty, submitted to MNRA

A Tale of Two Current Sheets

I outline a new model of particle acceleration in the current sheet separating the closed from the open field lines in the force-free model of pulsar magnetospheres, based on reconnection at the light cylinder and "auroral" acceleration occurring in the return current channel that connects the light cylinder to the neutron star surface. I discuss recent studies of Pulsar Wind Nebulae, which find that pair outflow rates in excess of those predicted by existing theories of pair creation occur, and use those results to point out that dissipation of the magnetic field in a pulsar's wind upstream of the termination shock is restored to life as a viable model for the solution of the "$\sigma$" problem as a consequence of the lower wind 4-velocity implied by the larger mass loading.Comment: 17 pages, 6 figures, Invited Review, Proceedings of the "ICREA Workshop on The High-Energy Emission from Pulsars and their Systems", Sant Cugat, Spain, April 12-16, 201