898 research outputs found

    Quark-antiquark potential in defect conformal field theory

    Get PDF
    We consider antiparallel Wilson lines in N = 4 super Yang-Mills in the presence of a codimension-1 defect. We compute the Wilson lines’ expectation value both at weak coupling, in the gauge theory, and at strong coupling, by finding the string configurations which are dual to this operator. These configurations display a Gross-Ooguri transition between a connected, U-shaped string phase and a phase in which the string breaks into two disconnected surfaces. We analyze in detail the critical configurations separating the two phases and compare the string result with the gauge theory one in a certain double scaling limit

    The effects of a revised 7^7Be e−^--capture rate on solar neutrino fluxes

    Get PDF
    The electron-capture rate on 7^7Be is the main production channel for 7^7Li in several astrophysical environments. Theoretical evaluations have to account for not only the nuclear interaction, but also the processes in the plasma where 7^7Be ions and electrons interact. In the past decades several estimates were presented, pointing out that the theoretical uncertainty in the rate is in general of few percents. In the framework of fundamental solar physics, we consider here a recent evaluation for the 7^7Be+e−^- rate, not used up to now in the estimate of neutrino fluxes. We analysed the effects of the new assumptions on Standard Solar Models (SSMs) and compared the results obtained by adopting the revised 7^7Be+e−^- rate to those obtained by the one reported in a widely used compilation of reaction rates (ADE11). We found that new SSMs yield a maximum difference in the efficiency of the 7^7Be channel of about -4\% with respect to what is obtained with the previously adopted rate. This fact affects the production of neutrinos from 8^8B, increasing the relative flux up to a maximum of 2.7\%. Negligible variations are found for the physical and chemical properties of the computed solar models. The agreement with the SNO measurements of the neutral current component of the 8^8B neutrino flux is improved.Comment: 7 pages, 3 figures, 4 tables. Accepted for the publication on A&

    Harmonisation Initiatives of Copernicus Data Quality Control

    Get PDF
    The Copernicus Space Component Data Access system (CSCDA) incorporates data contributions from a wide range of satellite missions. Through EO data handling and distribution, CSCDA serves a set of Copernicus Services related to Land, Marine and Atmosphere Monitoring, Emergency Management and Security and Climate Change. The quality of the delivered EO products is the responsibility of each contributing mission, and the Copernicus data Quality Control (CQC) service supports and complements such data quality control activities. The mission of the CQC is to provide a service of quality assessment on the provided imagery, to support the investigation related to product quality anomalies, and to guarantee harmonisation and traceability of the quality information. In terms of product quality control, the CQC carries out analysis of representative sample products for each contributing mission as well as coordinating data quality investigation related to issues found or raised by Copernicus users. Results from the product analysis are systematically collected and the derived quality reports stored in a searchable database. The CQC service can be seen as a privileged focal point with unique comparison capacities over the data providers. The comparison among products from different missions suggests the need for a strong, common effort of harmonisation. Technical terms, definitions, metadata, file formats, processing levels, algorithms, cal/val procedures etc. are far from being homogeneous, and this may generate inconsistencies and confusion among users of EO data. The CSCDA CQC team plays a significant role in promoting harmonisation initiatives across the numerous contributing missions, so that a common effort can achieve optimal complementarity and compatibility among the EO data from multiple data providers. This effort is done in coordination with important initiatives already working towards these goals (e.g. INSPIRE directive, CEOS initiatives, OGC standards, QA4EO etc.). This paper describes the main actions being undertaken by CQC to encourage harmonisation among space-based EO systems currently in service

    On the Origin of the Early Solar System Radioactivities. Problems with the AGB and Massive Star Scenarios

    Get PDF
    Recent improvements in stellar models for intermediate-mass and massive stars are recalled, together with their expectations for the synthesis of radioactive nuclei of lifetime τ≲25\tau \lesssim 25 Myr, in order to re-examine the origins of now extinct radioactivities, which were alive in the solar nebula. The Galactic inheritance broadly explains most of them, especially if rr-process nuclei are produced by neutron star merging according to recent models. Instead, 26^{26}Al, 41^{41}Ca, 135^{135}Cs and possibly 60^{60}Fe require nucleosynthesis events close to the solar formation. We outline the persisting difficulties to account for these nuclei by Intermediate Mass Stars (2 ≲\lesssim M/M⊙≲7−8_\odot \lesssim 7 - 8). Models of their final stages now predict the ubiquitous formation of a 13^{13}C reservoir as a neutron capture source; hence, even in presence of 26^{26}Al production from Deep Mixing or Hot Bottom Burning, the ratio 26^{26}Al/107^{107}Pd remains incompatible with measured data, with a large excess in 107^{107}Pd. This is shown for two recent approaches to Deep Mixing. Even a late contamination by a Massive Star meets problems. In fact, inhomogeneous addition of Supernova debris predicts non-measured excesses on stable isotopes. Revisions invoking specific low-mass supernovae and/or the sequential contamination of the pre-solar molecular cloud might be affected by similar problems, although our conclusions here are weakened by our schematic approach to the addition of SN ejecta. The limited parameter space remaining to be explored for solving this puzzle is discussed.Comment: Accepted for publication on Ap

    Magnetic-buoyancy-induced mixing in AGB stars: Fluorine nucleosynthesis at different metallicities

    Get PDF
    DV and SC acknowledge S. Bagnulo for fruitful discussions. DV acknowledges financial support from the German-Israeli Foundation (GIF No. I-1500-303.7/2019). CA acknowledges financial support from the Agencia Estatal de Investigacion of the Spanish Ministerio de Ciencia e Innovacion through the FEDER founds projects PGC2018-095317-B-C2.Asymptotic giant branch (AGB) stars are considered to be among the most significant contributors to the fluorine budget in our Galaxy. While observations and theory agree at close-to-solar metallicity, stellar models at lower metallicities overestimate the fluorine production with respect to that of heavy elements. We present F-19 nucleosynthesis results for a set of AGB models with different masses and metallicities in which magnetic buoyancy acts as the driving process for the formation of the C-13 neutron source (the so-called C-13 pocket). We find that F-19 is mainly produced as a result of nucleosynthesis involving secondary N-14 during convective thermal pulses, with a negligible contribution from the N-14 present in the C-13 pocket region. A large F-19 production is thus prevented, resulting in lower fluorine surface abundances. As a consequence, AGB stellar models with mixing induced by magnetic buoyancy at the base of the convective envelope agree well with available fluorine spectroscopic measurements at low and close-to-solar metallicity.German-Israeli Foundation for Scientific Research and Development I-1500-303.7/2019Agencia Estatal de Investigacion of the Spanish Ministerio de Ciencia e Innovacion through the FEDER founds projects PGC2018-095317-B-C

    Photobiomodulation with a 645 nm Diode Laser of Saos-2 Cells and Platelet-Rich Plasma: The Potential for a New Mechanism of Action

    Get PDF
    Objective: The main focus of this in vitro study was to highlight possible differences between outcomes of photobiomodulation performed in the presence or absence of growth factors derived from platelet-rich plasma.Background: Photobiomodulation has garnered increasing attention, thanks to a large number of controlled clinical trials that have proven its efficacy in various oral pathologies. Nevertheless, the mechanism of action is still a matter of debate.Materials and methods: The cell model used was Saos-2ATTC HTB-85, a human osteosarcoma cell line that retains an osteogenic potential matching that of osteoblastic cells. Photobiomodulation was performed with a 645 nm diode laser; we investigated three different fluence values (2, 5, and 10 J/cm(2)) delivered with 3 different irradiation times (1, 2, and 4 min). The design of the study included a case-control structure. Cell viability was assessed by resazurin reduction assay before laser irradiation. We assessed cell differentiation by Alizarin-red Sigma Aldrich assay 48 h after the last laser irradiation.Results: Results show that the combination of photobiomodulation and platelet-rich plasma can lead to a statistically significant increase in both proliferation and differentiation rates.Conclusions: Only a defined amount of energy, that is, a fluence of 5 J/cm(2) delivered in 2 min and of 10 J/cm(2) in 4 min, was proven to be the most effective in the presence of platelet-rich plasma to induce cell proliferation and calcium deposition

    Nuclear astrophysics at the n TOF facility: Some key cases in low mass star evolution and Neutron Star Mergers

    Get PDF
    Nuclear astrophysics is an interdisciplinary field at the crossing of various branches, from experimental and theoretical studies of nuclear cross sections to stellar evolutionary models of high complexity. The physics of stellar interiors can be constrained only if the adopted inputs in stellar modelling are known with high accuracy. For the nucleosynthesis of heavy elements, neutron capture and neutron induced fission cross sections are among the major sources of uncertainty and, thus, any improvement in their estimates represents a progress toward a better comprehension of stellar processes. Here I will present an astrophysicist perspective on some measurements carried out at the n TOF facility at CERN. I will discuss some cases related to the slow neutron capture process (the s-process) and to the rapid neutron capture process (the r-process)

    NIKEL_AMC: Readout electronics for the NIKA2 experiment

    Full text link
    The New Iram Kid Arrays-2 (NIKA2) instrument has recently been installed at the IRAM 30 m telescope. NIKA2 is a state-of-art instrument dedicated to mm-wave astronomy using microwave kinetic inductance detectors (KID) as sensors. The three arrays installed in the camera, two at 1.25 mm and one at 2.05 mm, feature a total of 3300 KIDs. To instrument these large array of detectors, a specifically designed electronics, composed of 20 readout boards and hosted in three microTCA crates, has been developed. The implemented solution and the achieved performances are presented in this paper. We find that multiplexing factors of up to 400 detectors per board can be achieved with homogeneous performance across boards in real observing conditions, and a factor of more than 3 decrease in volume with respect to previous generations.Comment: 21 pages; 16 figure

    Theoretical estimate of the half-life for the radioactive 134^{134}Cs and 135^{135}Cs in astrophysical scenarios

    Get PDF
    We analyze the 55134^{134}_{55}Cs→56134\rightarrow^{134}_{56}Ba and 55135^{135}_{55}Cs→56135\rightarrow^{135}_{56}Ba β−\beta^- decays, which are crucial production channels for Ba isotopes in Asymptotic Giant Branch (AGB) stars. We reckon, from relativistic quantum mechanis, the effects of multichannel scattering onto weak decays, including nuclear and electronic excited states (ES) populated above ≃\simeq 10 keV, for both parent and daughter nuclei. We find increases in the half-lives for T>108T>10^8 K (by more than a factor 3 for 134^{134}Cs) as compared to previous works based on systematics. We also discuss our method in view of these previous calculations. An important impact on half-lives comes from nuclear ES decays, while including electronic temperatures yields further increases of about 20\% at energies 10-30 keV, typical of AGB stars of moderate mass (M≲8 M⊙M \lesssim 8~M_{\odot}). Despite properly considering these effects, the new rates remain sensitively lower than the TY values, implying longer half-lives at least above 8-9 keV. Our rate predictions are in substantial accord with recent results based on the shell model, and strongly modify branching ratios along the ss-process path previously adopted. With our new rate, nucleosynthesis models well account for the isotopic admixtures of Ba in presolar SiC grains and in the Sun.Comment: 15 pages, 3 figures, 5 tables. Accepted for publication in Ap
    • …