Magnetic pattern at supergranulation scale: the Void Size Distribution

The large-scale magnetic pattern of the quiet sun is dominated by the magnetic network. This network, created by photospheric magnetic fields swept into convective downflows, delineates the boundaries of large scale cells of overturning plasma and exhibits voids in magnetic organization. Such voids include internetwork fields, a mixed-polarity sparse field that populate the inner part of network cells. To single out voids and to quantify their intrinsic pattern a fast circle packing based algorithm is applied to 511 SOHO/MDI high resolution magnetograms acquired during the outstanding solar activity minimum between 23 and 24 cycles. The computed Void Distribution Function shows a quasi-exponential decay behavior in the range 10-60 Mm. The lack of distinct flow scales in such a range corroborates the hypothesis of multi-scale motion flows at the solar surface. In addition to the quasi-exponential decay we have found that the voids reveal departure from a simple exponential decay around 35 Mm.Comment: 6 pages, 8 figures, to appear in Astronomy and Astrophysic

Black Holes, Gravitational Waves and Space Time Singularities

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Regulatory role of Pax6 on cell division cycle associated 7 and cortical progenitor cell proliferation

Forebrain development is controlled by a set of transcription factors which are expressed in dynamic spatiotemporal patterns in the embryonic forebrain and are known to regulate complex gene networks. Pax6 is a transcription factor that regulates corticogenesis and mutations affecting Pax6 protein levels cause neurodevelopmental defects in the eyes and forebrain in both humans and mice. In previous studies, it was shown that the graded expression pattern of Pax6 protein, which is high rostro-laterally to low caudo-medially in the cerebral cortex, is critical for its control of cell cycle progression and proliferation of cortical progenitors. However the underlying mechanisms are still unclear. Based on a microarray analysis carried out in our laboratory, a number of cell cycle-related candidate genes that may be affected by Pax6 have been identified. One such gene, Cell division cycle associated 7 (Cdca7) is expressed in a counter-gradient against that of Pax6. In my current study, I found that Cdca7 mRNA expression in the telencephalon is upregulated in Pax6 null (Small eye) mutants and downregulated in mice that overexpress PAX6 (PAX77) across developing time points from E12.5 to E15.5. There are several potential Pax6 binding motifs located in the genomic locus upstream of Cdca7. However, by chromatin immunoprecipitation, it is showed that none of the predicted binding sites are physically bound by Pax6. Promoter luciferase assays using fragments combining five suspected binding motifs show that Pax6 is functionally critical. Cdca7 is also identified as a Myc and E2F1 direct target and is upregulated in some tumours but its biological role is not fully understood. Current work using in utero electroporation to overexpress Cdca7 around the lateral telencephalon, where Cdca7 expression levels are normally low, tested the effects on the proliferation and differentiation of cortical progenitor cells in this region. In E12.5 mice embryos, overexpression of Cdca7 protein causes fewer intermediate progenitor cells and post-mitotic neurons to be produced but these effects were not found in E14.5 embryos. This result implies that Cdca7 may affect cell fate decision during cortical development

Stellar Turbulent Convection: The Multiscale Nature of the Solar Magnetic Signature

The multiscale dynamics associated with turbulent convection present in physical systems governed by very high Rayleigh numbers still remains a vividly disputed topic in the community of astrophysicists, and in general, among physicists dealing with heat transport by convection. The Sun is a very close star for which detailed observations and estimations of physical properties on the surface, connected to the processes of the underlying convection zone, are possible. This makes the Sun a unique natural laboratory in which to investigate turbulent convection in the hard turbulence regime, a regime typical of systems characterized by high values of the Rayleigh number. In particular, it is possible to study the geometry of convection using the photospheric magnetic voids (or simply voids), the quasi-polygonal quiet regions nearly devoid of magnetic elements, which cover the whole solar surface and which form the solar magnetic network. This work presents the most extensive statistics, both in the spatial scales studied (1–80 Mm) and in the temporal duration (SC 23 and SC 24), to investigate the multiscale nature of solar magnetic patterns associated with the turbulent convection of our star. We show that the size distribution of the voids, in the 1–80 Mm range, for the 317,870 voids found in the 692 analyzed magnetograms, is basically described by an exponential function

Impaired spatio-temporal coordination of subventricular neurogenesis is restored by physical exercise

A major aim of neural stem cells field is to harness endogenous neurogenesis to replace neurons damaged as a consequence of brain damage and neurodegeneration. Olfactory interneurons arise throughout life from neural stem cells residing in the subventricular zone (SVZ) of the lateral ventricle. Post mitotic neuroblast then migrate along the rostral migratory stream (RMS) to the olfactory bulb where undergone to fully maturation and functional integration in the olfactory circuitry. To ensure a continuous source of newly-generated adult interneurons, stem and progenitor cell proliferation, neuroblast migration, and terminal differentiation must be tightly coordinated. In this study we analyzed the effect of physical exercise in orchestrating the different steps of subventricular neurogenesis in a mouse lacking the antiproliferative gene Btg1 which displays an impaired subventricular neurogenesis. As previously demonstrated Btg1 loss-of-function mice exhibit a strong reduction of proliferation associated with a premature exit from the cell cycle and an anticipated migration toward the olfactory bulb where the neuroblast fail to fully differentiate and consequently to be specifically recruited in olfactory-dependent memory circuitry. In the study we demonstrate that running fully reverses the profound reduction of proliferation within the SVZ of the lateral ventricle in the Btg1-deficient mice, mainly through a recruitment and expansion of the quiescent neural stem cells (NSCs) . Moreover, cell cycle analysis reveals that 12 days of running induces a shortening of the S-phase and consequently of the whole cell cycle length in both neural stem (GFAP+, type C) and progenitor (DCX+, type A) cells of Btg1 knockout mice, allowing the restoring of a proper coordination between the cell cycle exit and the initial phase of post-mitotic neuroblasts migration. These events result in a increased rate of terminal maturation and integration in the olfactory- dependent memory circuits. Finally, as previously stated by others, we does not detect any beneficial effect of running in the subventricular zone wild type mice . All together these in vivo data suggest that a) the quiescent state of neural stem cells lacking the cell cycle inhibitory control can be reactivated by running; b) the cell cycle kinetics in the adult SVZ plays a pivotal role not only for proliferation but also for the tight coordination of cell cycle exit, migration and terminal differentiation. In vitro analysis demonstrates that running induces a great expansion of primary neurospheres isolated by Btg1 ko subvrenticular zone, supporting the in vivo observation about the increase of neural stem pool in this neurogenic niche. However the running-dependent hyperproliferation of the neural stem cells leads to a rapid depletion of the stem cell pool and /or to its ability to further expand in vitro. This fact suggest that the effect of running on the Btg1 knock out neural stem cell proliferation is not cell-autonomous but strictly dependent on niche environment. We can hypothesized that the presence of still unknown factors triggered by physical activity in the subventricular niche promotes and maintains in vivo the hyperproliferative state of neural stem cells in the Btg1 knockout mice

TGF beta/BMP activate the smooth muscle/bone differentiation programs in mesoangioblasts

Mesoangioblasts are vessel-derived stem cells that can be induced to differentiate into different cell types of the mesoderm such as muscle and bone. The gene expression profile of four clonal derived lines of mesoangioblasts was determined by DNA micro-array analysis: it was similar in the four lines but different from 10T1/2 embryonic fibroblasts, used as comparison. Many known genes expressed by mesoangioblasts belong to response pathways to developmental signalling molecules, such as Writ or TGFbeta/BMP Interestingly, mesoangioblasts express receptors of the TGFbeta/BMP family and several Smads and, accordingly, differentiate very efficiently into smooth muscle cells in response to TGFbeta and into osteoblasts in response to BMP In addition, insulin signalling promotes adipogenic differentiation, possibly through the activation of IGF-R. Several Writs and Frizzled, Dishevelled and Tcfs are expressed, suggesting the existence of an autocrine loop for proliferation and indeed, forced expression of Frzb-1 inhibits cell division. Mesoangioblasts also express many neuro-ectodermal genes and yet undergo only abortive neurogenesis, evens after forced expression of neurogenin 1 or 2, MASH or NeuroD. Finally, mesoangioblasts express several pro-inflammatory genes, cytokines and cytokine receptors, which may explain their ability to be recruited by tissue inflammation. Our data define a unique phenotype for mesoangioblasts, explain several of their biological features and set the basis for future functional studies on the role of these cells in tissue histogenesis and repair

Solar particle event detected by ALTEA on board the International Space Station

Context. Solar activity poses substantial risk for astronauts of the International Space Station (ISS) both on board and during extravehicular activity. An accurate assessment of the charged radiation flux in space habitats is necessary to determine the risk and the specific type of radiation exposure of ISS crew members, and to develop ways to protect future crews for planetary missions, even in case of high solar activity. Aims. To reduce the present-day uncertainties about the nature and magnitude of the particle fluxes in space habitats during a solar event, it is fundamental to measure those fluxes in situ. Methods. The ALTEA (Anomalous Long Term Effects on Astronauts) experiment on board the ISS is an active detector composed of six silicon telescopes and is able to follow the dynamics of the radiation flux. During its operation in 2012 a number of flux peaks were detected in correspondence with solar events. Results. We present in this work an analysis of the ALTEA data measured during the March 7th, 2012 solar event, produced by NOAA AR11429. Conclusions. During this event, the flux was enhanced tenfold with respect to ‘‘quiet Sun’’ conditions, producing strong dose increases at high geomagnetic latitudes