1,058 research outputs found

    The resolution of whole Earth seismic tomographic models

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    We evaluate the resolution of whole Earth structure achieved by compressional wave traveltime data from the International Seismological Centre (ISC); the measure of resolution we employ, provided by the direct calculation of the model resolution matrix, is more rigorous than the traditional (and computationally cheaper) one obtained through synthetic/checkerboard tests. Our work completes the introductive study of Boschi (2003), where only mantle models derived with a very simple regularization scheme were considered. Here, we expand Boschi's database with measurements of compressional waves reflected by, or refracted through, the Earth's core-mantle boundary (CMB) and core. In analogy with the work of Soldati et al. (2003), we treat CMB topography and heterogeneous outer core structure as free parameters of our inversions; analysing model resolution matrices, we attempt to explain the known discrepancy between deep Earth structure mapped by seismic waves reflected and refracted by the cor

    Outer core density heterogeneity and the discrepancy between PKP and PcP travel time observations

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    We derive 3-D maps of the Earth’s mantle, CMB and outer core by means of least squares tomographic inversions. The data set includes compressional wave travel time measurements associated with the phases P, PcP, PKPbc, PKPdf, all based on the bulletins of the International Seismological Centre (1964-1995), after source relocation by Antolik et al. [2001]. Maps of the CMB derived independently from only core-reflected (PcP) or only core-refracted (PKP) phases are not well correlated. We study the radial coherence of whole-Earth tomographic images, to investigate potential trade-offs between CMB undulations and velocity anomalies in the mantle and/or outer core. We find that imaged lateral heterogeneities in the outer core are correlated with the topography of the CMB. This, together with the studies of Wahr and De Vries [1989] and Piersanti et al. [2001], suggests that the core anomalies might not be entirely fictitious

    TENOGENIC DIFFERENTIATION PROTOCOL IN XENOGENIC-FREE MEDIA ENHANCES TENDON-RELATED MARKER EXPRESSION IN ADIPOSE-DERIVED STEM CELLS

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    Tendon injuries are common and current therapies often are unsuccessful. Cell-based therapy using mesenchymal stem cells (MSCs) seems to be the most promising approach to heal tendon. Moreover, providing safe and regulated cell therapy products to patients requires adherence to good manufacturing practices (GMP). Adipose-derived stem cells (n=4) were cultured in 6-well plates coated with type-I collagen in a chemically defined serum-free medium (SF) or a xenogenic-free human pooled platelet lysate medium (hPL). At passage 4, ASCs were induced to tendon lineage for 14 days using 100ng/ml CTGF, 10ng/ml TGFβ3, 50ng/ml BMP12 and 50µg/ml ascorbic acid in the SF (SF-TENO) or in the hPL (hPL-TENO) medium. Cells cultured without any supplements are used as control. Morphological appearance, cell viability and FACS were performed in undifferentiated cells to evaluate the xenogenic-free culture conditions; the gene and protein expression were performed by RT-PCR and immunofluorescence to evaluate to expression of stem cell- and tendon-related markers upon cell differentiation. SF-CTRL and hPL-CTRL showed similar viability and MSC's surface proteins and expressed the stemness markers NANOG, OCT4 and Ki67. Moreover, both SF-TENO and hPL-TENO expressed significant higher levels of SCX, COL1A1, COL3A1, COMP, MMP3 and MMP13 genes already at 3d (p<0.05) respect to CTRLs. Scleraxis and collagen were also detected in both SF-TENO and hPL-TENO at protein level in higher amount than CTRLs. In conclusion, ASCs exposed to CTGF, BMP12, TGFb3 and AA in both serum and xenogenic-free media possess similar tenogenic differentiation ability moving forward the GMP-compliant approaches for the clinical use of ASCs

    Global seismic tomography and modern parallel computers

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    A fast technological progress is providing seismic tomographers with computers of rapidly increasing speed and RAM, that are not always properly taken advantage of. Large computers with both shared-memory and distributedmemory architectures have made it possible to approach the tomographic inverse problem more accurately. For example, resolution can be quantified from the resolution matrix rather than checkerboard tests; the covariance matrix can be calculated to evaluate the propagation of errors from data to model parameters; the L-curve method can be applied to determine a range of acceptable regularization schemes. We show how these exercises can be implemented efficiently on different hardware architectures

    Fiber suspension investigation in a backward-facing step by PIV

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    A dilute suspension (volume fraction 0.05%) of rod-like particles in a turbulent backward-facing step flow at Reynolds number ReH=14900, is investigated by means of Particle Image Velocimetry. Two-way interactions between fluid and dispersed phase are analyzed by exploiting the high spatial resolution of the acquisitions. Mutual interactions between phases can be investigated by considering flow turbulence modulations and phenomena related to preferential concentration and orientation of fibers. Slight turbulence enhancement is reported in the laden flow and concentration data show a moderate tendency of fibers to accumulate at the channel centreline. Orientation data display a strong preferential orientation of fibers. Local fiber orientation is correlated to the direction of maximum shear showing a high level of correlation also in the flow regions featuring strong gradients

    Outer core density heterogeneity and the discrepancy between PKP and PcP travel time observations

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    We derive 3-D maps of the Earth’s mantle, CMB and outer core by means of least squares tomographic inversions. The data set includes compressional wave travel time measurements associated with the phases P, PcP, PKPbc, PKPdf, all based on the bulletins of the International Seismological Centre (1964-1995), after source relocation by Antolik et al. [2001]. Maps of the CMB derived independently from only core-reflected (PcP) or only core-refracted (PKP) phases are not well correlated. We study the radial coherence of whole-Earth tomographic images, to investigate potential trade-offs between CMB undulations and velocity anomalies in the mantle and/or outer core. We find that imaged lateral heterogeneities in the outer core are correlated with the topography of the CMB. This, together with the studies of Wahr and De Vries [1989] and Piersanti et al. [2001], suggests that the core anomalies might not be entirely fictitious

    On the mystery of the missing pie in graphene

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    We investigate in some detail the structure of the electromagnetic current density for the pseudo-relativistic massless spinor effective model for graphene. It is shown that the pseudo-relativistic massless Dirac field theory in {\em 2+1} space-time dimensions and in the presence of a constant homogeneous electric field actually leads to the measured current density and to the minimum quantum conductivity.Comment: 10 pages, no figures, substantial changes and added reference

    The quantum Hall effect in graphene samples and the relativistic Dirac effective action

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    We study the Euclidean effective action per unit area and the charge density for a Dirac field in a two--dimensional spatial region, in the presence of a uniform magnetic field perpendicular to the 2D--plane, at finite temperature and density. In the limit of zero temperature we reproduce, after performing an adequate Lorentz boost, the Hall conductivity measured for different kinds of graphene samples, depending upon the phase choice in the fermionic determinant.Comment: Conclusions extended. References added. 9 pages. 1 figur

    Multi-channel communication vs. adaptive routing for reliable communication in WSNs

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    Interference and link dynamics constitute great concerns for stability and performance of protocols in WSNs. In this paper we evaluate the impact of channel hopping and adaptive routing on delay and reliability focusing on delay critical applications
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