Effect of in-mould inoculant composition on microstructure and fatigue behaviour of heavy section ductile iron castings

In this paper, the influence of the in-mould inoculant composition on microstructure and fatigue behaviour of heavy section ductile iron (EN GJS 700-2) castings has been investigated. Axial fatigue tests under nominal load ratio R=0 have been performed on specimens taken from the core of large casting components. Metallographic analyses have been carried out by means of optical microscopy and important microstructural parameters that affect the mechanical properties of the alloy, such as nodule count, nodularity and graphite shape, were measured. Furthermore, Scanning Electron Microscopy was used to investigate the fracture surfaces of the samples in order to identify crack initiation and propagation zones. Cracks initiation sites have been found to be microshrinkages close to specimens\u2019 surface in most cases. It was found that in-mould inoculant composition strongly influences the alloy microstructure, such as nodule count and shrinkage porosities size, as well as the fatigue resistance of heavy section ductile iron castings

Review of recent advances in local approaches applied to pre-stressed components under fatigue loading

Fatigue strength of mechanical components in the high cycle regime depends on both the applied loading and the intensity of any residual stress field induced by either non-homogeneous plastic deformation or the solidification of a local portion of material due to welding operations. In presence of geometric variations that are amenable to being modelled as a sharp V-notch, the residual stress distribution near the notch tip is singular and follows the same form as the solution obtained by Williams in 1952 where the intensity of the asymptotic stress field is quantified by the notch stress intensity factor (NSIF). However, the residual stress varies during fatigue loading and a stable value may be reached. Numerical models have been developed for the calculation of the residual NSIFs and their variation under fatigue loading. Taking advantage of these models, new local approaches have also been recently developed which are able to predict the fatigue strength of pre-stressed notched components. The present paper provides a brief review of such recent advances

Thermal load-induced notch stress intensity factors derived from averaged strain energy density

Under the hypothesis of steady-state heat transfer and plane-strain conditions, the intensity of the stress distributions ahead of sharp V-notch tips can be expressed in terms of thermal notch stress intensity factors (thermal NSIFs) which can be used for fatigue strength assessments of notched components. The calculation of thermal NSIFs requires both an uncoupled thermal-mechanical numerical analysis and a very refined mesh. For these reasons, the numerical simulation becomes considerably expensive and time-consuming above all if large 2D or 3D models have to be solved. Refined meshes are not necessary when the aim of the finite element analysis is to determine the mean value of the local strain energy density on a control volume surrounding the points of stress singularity. On the other hand, the NSIFs value can be directly determined by the strain energy density. In this work, the method for rapid calculations of NSIFs based on averaged strain energy density, recently published in literature, is extended to thermal problem

Validation of TESS exoplanet candidates orbiting solar analogues in the all-sky PLATO input catalogue

Funding: G.M. acknowledges the support of the Erasmus+ Programme of the European Union and of the doctoral grant funded by the University of Padova and by the Italian Ministry of Education, University and Research (MIUR). G.M. is also grateful to the Centre for Exoplanet Science, University of St Andrews (StA-CES) for hospitality and computing resources. GPi, LBo, VNa, and FZM acknowledge the funding support from Italian Space Agency (ASI) regulated by ‘Accordo ASI-INAF n. 2013-016-R.0 del 9 luglio 2013 e integrazione del 9 luglio 2015 CHEOPS Fasi A/B/C’. We acknowledge the support of PLATO ASI-INAF agreements n.2015-019-R0-2015 and n. 2015-019-R.1-2018. T.G.W. and A.C.C. acknowledge support from STFC consolidated grant number ST/V000861/1, and UKSA grant ST/R003203/1.The Transiting Exoplanet Survey Satellite (TESS) is focusing on relatively bright stars and has found thousands of planet candidates. However, mainly because of the low spatial resolution of its cameras (≈ 21 arcsec/pixel), TESS is expected to detect several false positives (FPs); hence, vetting needs to be done. Here, we present a follow-up program of TESS candidates orbiting solar-analogue stars that are in the all-sky PLATO input catalogue. Using Gaia photometry and astrometry we built an absolute colour-magnitude diagram and isolated solar-analogue candidates’ hosts. We performed a probabilistic validation of each candidate using the vespa software and produced a prioritized list of objects that have the highest probability of being genuine transiting planets. Following this procedure, we eliminated the majority of FPs and statistically vetted 23 candidates. For this remaining set, we performed a stellar neighbourhood analysis using Gaia Early Data Release 3 and centroid motion tests, greatly enhancing the on-target probability of 12 of them. We then used publicly available high-resolution imaging data to confirm their transit source and found five new, fully validated planets. For the remaining candidates, we propose on-off photometry to further refine the list of genuine candidates and prepare for the subsequent radial velocity follow-up.Publisher PDFPeer reviewe

The complete worldsheet S matrix of superstrings on AdS3×S3×T4 with mixed three-form flux

We determine the off-shell symmetry algebra and representations of Type IIB superstring theory on AdS3×S3×T4 with mixed R-R and NS-NS three-form flux. We use these to derive the non-perturbative worldsheet S matrix of fundamental excitations of the superstring theory. Our analysis includes both massive and massless modes and shows how turning on mixed three-form flux results in an integrable deformation of the S matrix of the pure R-R theory

AdS3/CFT2, finite-gap equations and massless modes

It is known that string theory on AdS 3 × M 7 backgrounds, where M 7 = S 3 × S 3 × S 1 or S 3 × T 4, is classically integrable. This integrability has been previously used to write down a set of integral equations, known as the finite-gap equations. These equations can be solved for the closed string spectrum of the theory. However, it has been known for some time that the finite-gap equations on these AdS 3 × M 7 backgrounds do not capture the dynamics of the massless modes of the closed string theory. In this paper we re-examine the derivation of the AdS 3 × M 7 finite-gap system. We find that the conditions that had previously been imposed on these integral equations in order to implement the Virasoro constraints are too strict, and are in fact not required. We identify the correct implementation of the Virasoro constraints on finite-gap equations and show that this new, less restrictive condition captures the complete closed string spectrum on AdS 3 × M 7

Observation of two new Ξb−\Xi_b^- baryon resonances

Two structures are observed close to the kinematic threshold in the $\Xi_b^0 \pi^-$ mass spectrum in a sample of proton-proton collision data, corresponding to an integrated luminosity of 3.0 fb$^{-1}$ recorded by the LHCb experiment. In the quark model, two baryonic resonances with quark content $bds$ are expected in this mass region: the spin-parity $J^P = \frac{1}{2}^+$ and $J^P=\frac{3}{2}^+$ states, denoted $\Xi_b^{\prime -}$ and $\Xi_b^{*-}$. Interpreting the structures as these resonances, we measure the mass differences and the width of the heavier state to be $m(\Xi_b^{\prime -}) - m(\Xi_b^0) - m(\pi^{-}) = 3.653 \pm 0.018 \pm 0.006$ MeV$/c^2$, $m(\Xi_b^{*-}) - m(\Xi_b^0) - m(\pi^{-}) = 23.96 \pm 0.12 \pm 0.06$ MeV$/c^2$, $\Gamma(\Xi_b^{*-}) = 1.65 \pm 0.31 \pm 0.10$ MeV, where the first and second uncertainties are statistical and systematic, respectively. The width of the lighter state is consistent with zero, and we place an upper limit of $\Gamma(\Xi_b^{\prime -}) < 0.08$ MeV at 95% confidence level. Relative production rates of these states are also reported.Comment: 17 pages, 2 figure

Observation of associated production of a ZZ boson with a DD meson in the~forward region

A search for associated production of a $Z$ boson with an open charm meson is presented using a data sample, corresponding to an integrated luminosity of $1.0\,\mathrm{fb}^{-`}$ of proton--proton collisions at a centre-of-mass energy of 7\,TeV, collected by the LHCb experiment. %% Seven candidate events for associated production of a $Z$ boson with a $D^0$ meson and four candidate events for a $Z$ boson with a $D^+$ meson are observed with a combined significance of 5.1standard deviations. The production cross-sections in the forward region are measured to be $$\sigma_{Z\rightarrow\mu^+\mu^-\!,D^0} = 2.50\pm1.12\pm0.22pb$$ $$\sigma_{Z\rightarrow\mu^+\mu^-\!,D^+} = 0.44\pm0.23\pm0.03pb,$$ where the first uncertainty is statistical and the second systematic.Comment: 18 pages, 2 figure

Measurement of the mass and lifetime of the Ωb−\Omega_b^- baryon

A proton-proton collision data sample, corresponding to an integrated luminosity of 3 fb$^{-1}$ collected by LHCb at $\sqrt{s}=7$ and 8 TeV, is used to reconstruct $63\pm9$ $\Omega_b^-\to\Omega_c^0\pi^-$, $\Omega_c^0\to pK^-K^-\pi^+$ decays. Using the $\Xi_b^-\to\Xi_c^0\pi^-$, $\Xi_c^0\to pK^-K^-\pi^+$ decay mode for calibration, the lifetime ratio and absolute lifetime of the $\Omega_b^-$ baryon are measured to be \begin{align*} \frac{\tau_{\Omega_b^-}}{\tau_{\Xi_b^-}} &= 1.11\pm0.16\pm0.03, \\ \tau_{\Omega_b^-} &= 1.78\pm0.26\pm0.05\pm0.06~{\rm ps}, \end{align*} where the uncertainties are statistical, systematic and from the calibration mode (for $\tau_{\Omega_b^-}$ only). A measurement is also made of the mass difference, $m_{\Omega_b^-}-m_{\Xi_b^-}$, and the corresponding $\Omega_b^-$ mass, which yields \begin{align*} m_{\Omega_b^-}-m_{\Xi_b^-} &= 247.4\pm3.2\pm0.5~{\rm MeV}/c^2, \\ m_{\Omega_b^-} &= 6045.1\pm3.2\pm 0.5\pm0.6~{\rm MeV}/c^2. \end{align*} These results are consistent with previous measurements.Comment: 11 pages, 5 figures, All figures and tables, along with any supplementary material and additional information, are available at https://lhcbproject.web.cern.ch/lhcbproject/Publications/LHCbProjectPublic/LHCb-PAPER-2016-008.htm