The onset of thermal convection in an infinite Prandtl number, variable viscosity, compressible Earth's mantle by the mean-field approximation

The values of the Rayleigh number critical for the onset of Thermal instability in an infinite Prandtl number, compressible Earth’s mantle are determined against the aspect ratio (the ratio between the width and the depth of the cell) for constant and for pressure- and temperature-dependent viscosity. The procedure adopted follows the experimental approach which determines the critical Rayleigh number as the value at which the heat flux across the fluid exceeds the conductive one. We solve the single-mode mean-field equations for the conservation of mass, momentum and energy and evaluate the Nusselt number, i.e. the ratio between the actual heat transfer and the heat which would be transported only by conduction. The value of the Rayleigh number for which the Nusselt number exceeds unity can be identified as the critical value. Between incompressible and compressible fluids with constant viscosity the critical Rayleigh numbers differ at most by 10–20% for cells aspect ratios between 0.1 to about 30, while at larger aspect ratios compressibility yields critical Rayleigh numbers one or more orders of magnitude larger. For variable viscosity, since a more viscous interior prevents motion, a much higher Rayleigh number is required for the onset of convection. It is also shown how viscous dissipation of heat increases the critical Rayleigh number, while compressibility favours the onset of convection

MODELING OF THE THERMAL STATE OF MT. VESUVIUS FROM 1631 AD

The last eruptive event at Mt. Vesuvius occurred in 1944 AD, ending a cycle of continuous eruptive activity started with the sub-plinian event of 1631 AD. The aim of this research is i) to model the thermal evolution of the volcanic system from 1631 AD up to the present and ii) to investigate the possible process leading the volcano to the current state of quiescence. A finiteelement software is employed to solve the time-dependent energy equation and obtain the thermal field in the volcanic edifice and the surrounding medium. Volcanological, petrological and geophysical constraints are used to define the crustal structure beneath the volcanic edifice, the magma supply system active since 1631 AD, and the physico-chemical conditions of magma. Thermodynamic properties of magma and wall rocks have been evaluated from well-established thermo-chemical compilations and data from the literature. It is shown that heat transfer due to magma degassing is required in addition to the heat conduction in order to obtain transient depthtemperature fields consistent with geochemical observations, high crustal magnetization, and rigid behavior of the shallow crust as indicated by geophysical data. Surface data of carbon dioxide soil flux coming out from the Mt. Vesuvius crater are taken to constrain such an additional heat flux. The agreement between modeled and measured temperatures at the crater since 1944 AD proves the consistency of the model. It is concluded that the present state of quiescence of Mt. Vesuvius is mostly a consequence of the absence of magma supply from the deep reservoir into the shallower system. This allows the cooling of residual magma left within the volcanic conduit and the transition from continuous eruptive activity to the condition of conduit obstruction. In this scenario, the hydrothermal system may have developed subsequent to the cooling of the magma within the conduit. Our findings are a direct consequence of the high concentration of CO2 in the most mafic Vesuvian magmas: the low solubility of CO2, with respect to H2O, enables a high mass flux of carbon dioxide through the volcanic edifice. The results of this study are relevant for hazard assessment at Vesuvius and indicate directions for further investigation, such as the role of the hydrothermal system on the thermal energy budget of the volcanic system and its relationships with fluids released by crustal structures likely to host the magmatic reservoir. In general, the role of the high concentration of carbon dioxide in magmas should be more questioned and investigated when studying the behavior of volcanic systems, particularly in South Italy volcanoes

Gli "ASTRI" di Horn: l'astronomo che ha progettato il futuro

Guido Horn d’Arturo (Trieste 1879-Bologna 1967), ebreo triestino, fu direttore dell’Osservatorio universitario di Bologna per un trentennio, interrotto solo dalle leggi razziali. Questa mostra, nata nel 2017 in occasione del cinquantesimo anniversario della sua morte, lo ricorda come scienziato geniale, pioniere della divulgazione scientifica, personaggio eclettico, patriota e viene oggi riproposta, riveduta e ampliata, in occasione della dedica a Guido Horn d’Arturo del telescopio ASTRI (Astrofisica con Specchi a Tecnologia Replicante), operativo a Serra La Nave e parte di un più grande progetto, Cherenkov Telescope Array, CTA, che, tra l’altro, ha i propri uffici a Bologna. Anche ASTRI, infatti, come i moderni grandi telescopi, tra i quali l’European Extremely Large Telescope dell’ESO -39 m con 798 tasselli- che sarà operativo in Cile nel 2024, e nello spazio il James Webb Space Telescope della Nasa -6,5 m con 18 tasselli- il cui lancio è previsto nel 2021, è l’erede di una metodologia del tutto nuova di costruzione e aggiustamento degli specchi dei telescopi: “lo specchio a tasselli” di Guido Horn d’Arturo. Ideato negli anni Trenta e costruito effettivamente solo negli anni Cinquanta, il prototipo, di 1,8 m di diametro complessivi e composto di 61 tasselli esagonali, rivoluzionò radicalmente lo sviluppo della moderna astronomia osservativa. La collocazione di ASTRI nel territorio di Catania, motivo di grande soddisfazione per l’intera città, è stata di incentivo a celebrare questa illustre figura anche attraverso la riedizione della mostra bolognese all’interno del Monastero dei Benedettini, antica sede dell’Osservatorio di Catania, luogo in cui avvennero gli esordi della carriera scientifica di Horn D’Arturo e in cui lo scienziato avrebbe tanto desiderato ritornare

Measurements of charmed-meson production in interactions between 350 GeV/c π−\pi^- particles and nuclei

Charmed-meson production by $350$~GeV/$c$ {$\pi^-$} particles incident on copper and tungsten targets has been studied in the WA$92$ experiment, performed at the CERN $\Omega^\prime$ spectrometer. Results obtained are reported and discussed. Reconstruction of decays from the set ${\rm D}^0 \rightarrow {\rm K}^- \pi^+$, ${\rm D}^0 \rightarrow {\rm K}^- \pi^- \pi^+ \pi^+$, ${\rm D}^+ \rightarrow {\rm K}^- \pi^+ \pi^+$, ${{\rm D}_{\rm s}}^+ \rightarrow \phi \pi^+$ and charge conjugates has yielded a sample of $7280 \pm 108$ charmed mesons, produced with \xf > 0, \langle \xf \rangle = 0.18 and \langle {\pt}^2 \rangle = 1.86~{\rm (GeV/}c{\rm )}^2. Assuming a relationship $\sigma = \sigma_0 A^\alpha$ between the cross-section, $\sigma$, per nucleus of mass $A$ and the nucleonic cross-section, $\sigma_0$, the $\alpha$ value found for the detected charmed particles is $0.95 \pm 0.06 \pm 0.03$. Taking $\alpha = 1$, the measured cross-sections per nucleon for \xf > 0 production are $7.78 \pm 0.14 \pm 0.52$~$\mu$barn for ${\rm D}^0$/$\bar{\rm D}^0$, $3.28 \pm 0.08 \pm 0.29$~$\mu$barn for ${\rm D}^+$/${\rm D}^-$ and $1.29 \pm 0.16 \pm 0.33$~$\mu$barn for ${{\rm D}_{\rm s}}^+$/${{\rm D}_{\rm s}}^-$. Differential cross-sections with respect to \xf and {\pt}^2 have been determined for the various types of charmed meson, and particle-antiparticle asymmetries have been analysed

Measurement of the beauty production cross-section in 350 GeV/c π−\pi^- -Cu interactions

Using a sample of $10^8$ triggered events, produced in $\pi^-$--$\,$Cu interactions at 350~GeV$/c$, we have identified 26 beauty events. The estimated background in this sample is $0.6 \pm 0.6$ events. From these data, assuming a linear A-dependence, we measure a beauty production cross-section integrated over all $x_F$ of $5.7 {+1.3 \atop -1.1}~{\mathrm {(stat.)}} {+0.6 \atop -0.5}~{\mathrm {(syst.)}}~$nb/N

WA92: a fixed target experiment to trigger on and identify beauty particle decays

We describe the detectors and trigger system used in the CERN WA92 experiment. The experiment was designed to study the production and decay of beauty particles from 350 GeV/$c\,$ $\,\pi^-$ interactions in copper and tungsten targets. Charged particle tracking is performed using the Omega spectrometer. Silicon microstrip detectors are used to provide precise tracking information in the region of the production and the decay of heavy-flavoured particles and to trigger on the resulting high impact parameter tracks. The precision of vertex reconstruction corresponds to $\pm 3.7\%$ of the mean B-decay proper lifetime. Lepton and high transverse momentum hadron signals are also used in the trigger, which accepts 29\% of B-decays and rejects 98\% of non-beauty interactions