Postcritical Behavior of Cables Undergoing Two Simultaneous Galloping Modes

A nonlinear two degree-of-freedom model, describing a flexible elastic suspended cable undergoing galloping oscillations, is analyzed. By using a perturbative approach, the critical conditions occuring for different values of the aerodynamic coefficients are described. Two different type of critical conditions, corresponding to simple or double Hopf bifurcations are found. The nonlinear postcritical behavior of single taut strings in 1:1 primary internal resonance is studied through the multiple scale perturbation method. In the double Hopf bifurcation case the influence of the detuning between the critical eigenvalues on the postcritical behavior is illustrated. It is found that quasi-periodic motions, which are likely to occur in the linear field when the two critical frequencies are incommensurable, are really unstable in the nonlinear range. Therefore, the postcritical behavior of the string consists of stable periodic motions for any detuning values

Effect of cathode contacting on anode supported cell performances and degradation

The contact geometry effect on anode-supported cells (ASC) has been evaluated comparing the use of platinum meshes and Crofer 22 APU bipolar plates as current collectors. Additionally, the application of a La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) paste between the electrode and the current collector allowed estimating the beneficial effect of the contacting layer enhancing the current distribution at the cathode side. Cells have been electrically loaded for 100 hours to investigate the polarization effects on their performances by means of current-voltage curves and electrochemical impedance spectroscopy. Post-experiment analyses have been carried out to support the electrochemical observation

VIV regimes and simplified solutions by the spectral model description

The present paper discusses technical aspects of the vortex-induced vibrations (VIVs) of structures excited by the wind in the framework of the spectral model, which is applied by many codes and guidelines for civil engineering verifications. Quantitative thresholds related to Scruton number domains, where the structural response can be considered in \u201cforced vibration\u201d or \u201clock-in\u201d regime, are proposed. In this way, the type of VIV response and its evaluation can be assessed with simple calculations that use the parameters already present in codes and guidelines. An analytical solution of the original model allows straightforward evaluations inclusive of operative criteria to properly consider structural and flow conditions concerning the coefficients governing the VIV response in the spectral description, leaving out some assumptions that are commonly adopted. Extensive numerical applications, limited here to circular cylinders and including a real full-scale chimney, allow to identify the most significant parameters of the model and the criticalities connected with their choice

Constant-frequency time cells in the vortex-shedding from a square cylinder in accelerating flows

An extensive experimental campaign has been carried out in a multiple-fan wind tunnel to study the effects of flow acceleration on a sectional model of a sharp-edged square cylinder. Different levels of positive and negative acceleration are reproduced, which are compatible with those induced by full-scale thunderstorm outflows. Various initial and final conditions are also explored and, in all conditions, multiple test repeats are carried out in order to obtain satisfactory ensemble averages. Particular attention is devoted to the acquisition of signals associated with vortex-shedding, for which tailored time-frequency analyses, based on the continuous wavelet and Hilbert transforms, are introduced. Sensitivity analyses are carried out on a selection of the relevant pa-rameters that better allow the tracing of the temporal variation of the shedding frequency. Time intervals in which the shedding frequency is constant, separated by discontinuities, are found during the transients. The number and extent of such constant-frequency time cells and discontinuities seem to be connected with the flow acceleration, but are not strictly repetitive. For higher levels of acceleration the ensemble mean of the Strouhal number is found to be comparable with or moderately lower than the steady-flow value corresponding to the instantaneous velocity

A 400 Ma-long Nd-Hf isotopic evolution of melt-modified garnet-pyroxenites in an ancient subcontinental lithosphere (Lanzo North ophiolite, Western Alps)

Pyroxenite veining is widely preserved in peridotite massifs, and used to derive information on the origin and evolution of upper mantle domains. These lithospheric mantle sections can be isolated from the convecting mantle for >1 Ga or more, suffering a long history of melting and/or melt-rock reaction processes, which modify their original chemical and isotopic compositions. Here, we show the effect of ancient process of melt-rock reaction in the chemistry of garnet pyroxenites from Lanzo North Massif, an iconic lithospheric mantle section exhumed during the opening of the Jurassic Alpine Tethys. Selected pyroxenites are more than 10 cm thick, and embedded within peridotites that have textures and chemical compositions indicative of a complex history of interaction with migrating melts. Whole rock and clinopyroxene Nd-Hf isotopes of the pyroxenites consistently indicate that the first melt-rock reaction event occurred at ~400 Ma, likely in combination with exhumation from the garnet to the spinel-facies mantle conditions. Two samples still retain textural relicts and chemical evidence of precursor garnet and have high εNd (~12) for comparatively low εHf (~10), when recalculated at 400 Ma, which suggest that they were less affected by this ancient percolation process. The chemical evidence of such a long history of melt-rock reactions was preserved from 400 Ma until present. Finally, two pyroxenites located within plagioclase peridotites show evidence for an event of re-equilibration at plagioclase-facies conditions, likely triggered by infiltration of melt in the host rock. These samples reveal the coexistence of two internal Sm-Nd isochrones at 152 ± 30 Ma and 149 ± 13 Ma, thereby providing temporal constraints to the event of melt impregnation of the host peridotites as consequence of the opening of the Ligurian Tethys ocean

The ultrasound risk stratification systems for thyroid nodule have been evaluated against papillary carcinoma. A meta-analysis

Thyroid imaging reporting and data systems (TIRADS) are used to stratify the malignancy risk of thyroid nodule by ultrasound (US) examination. We conducted a meta-analysis to evaluate the pooled cancer prevalence and the relative prevalence of papillary, medullary, follicular thyroid cancer (PTC, MTC, and FTC) and other malignancies among nodules included in studies evaluating their performance. Four databases were searched until February 2020. Original articles with at least 1000 nodules, evaluating the performance of at least one TIRADS among AACE/ACE/AME, ACR-TIRADS, ATA, EU-TIRADS, or K-TIRADS, and reporting data on the histological diagnosis of malignant lesions were included. The number of malignant nodules, PTC, FTC, MTC and other malignancies in each study was extracted. For statistical pooling of data, a random-effects model was used. Nine studies were included, evaluating 19,494 thyroid nodules. The overall prevalence of malignancy was 34% (95%CI 21 to 49). Among 6162 histologically proven malignancies, the prevalence of PTC, FTC, MTC and other malignancies was 95%, 2%, 1%, and 1%, respectively. A high heterogeneity was found for all the outcomes. A limited number of studies generally conducted using a retrospective design was found, with possible selection bias. Acknowledging this limitation, TIRADSs should be regarded as accurate tools to diagnose PTC only. Proposed patterns and/or cut-offs should be revised and other strategies considered to improve their performance in the assessment of FTC, MTC and other malignancies

Petrology, Mineral and Isotope Geochemistry of the External Liguride Peridotites (Northern Apennines, Italy)

Mantle peridotites of the External Liguride (EL) units (Northern Apennines) represent slices of subcontinental lithospheric mantle emplaced at the surface during early stages of rifting of the Jurassic Ligurian Piemontese basin. Petrological, ion probe and isotopic investigations have been used to unravel the nature of their mantle protolith and to constrain the timing and mechanisms of their evolution. EL peridotites are dominantly fertile spinel Iherzolites partly recrystallizfd in the plagiodase Iherzplite stability field Clinopyroxenes stable in the spinel-facies assemblage have nearly fiat REE patterns (CeN/SmN=0·6-0·8) at (10-16)×C1 and high Na, Sr, Ti and Zr contents. Kaersutitic-Ti-pargasitic amphiboles also occur in the spinel-facies assemblage. Their LREE-depleted REE spectra and very low Sr, Zr and Ba contents indicate that they crystallized from hydrous fluids with low concentrations of incompatible elements. Thermometric estimates on the spinelfacies parageneses yield lithospheric equilibrium temperatures in the range 1000-1100°C, in agreement with the stability of amphibole, which implies T<1100°C. Sr and Nd isotopic compositions, determined on carefully handpicked clinopyroxene separates, plot within the depleted end of the MORB field (87Sr/86Sr=0·70222-0·70263; 143Nd/144Nd=0·513047-0·513205) similar to many subcontinental orogenic spinel Iherzolites from the western Mediterranean area (e.g. Ivrea Zpne and Lanzfl N). The interpretation of the EL Iherzolites as subcontinental lithospheric mantle is reinforced by the occurrence of one extremely depleted isotopic composition (87Sr/86Sr=0·701736; 143Nd/144Nd=0·513543). Sr and Nd model ages, calculated assuming both CHUR and DM mantle sources, range between 2·4 Ga and 780 Ma. In particular, the 1·2-Ga Sr age and the 780-Ma Nd age can be regarded as minimum ages of differentiation. The transition from spinel-to plagioclase-facies assemblage, accompanied by progressive deformation (from granular to tectonite-mylonite textures), indicate that the EL Iherzolites experienced a later, subsolidus decompressional evolution, starting from subcontinental lithospheric levels. Sm/Nd isochrons on plagioclase-clinopyroxene pairs furnish ages of ∽165 Ma. This early Jurassic subsolidus decompressional history is consistent with uplift by means of denudation in response to passive and asymmetric lithospheric extension. This is considered to be the most suitable geodynamic mechanism to account for the exposure of huge bodies of subcontinental lithospheric mantle during early stages of opening of an oceanic basi

L’energia di attivazione nel processo di ricristallizzazione del bronzo: influenza del tenore di stagno

Nell’attuale produzione di leghe Cu-Sn semilavorate l’attività industriale è orientata essenzialmente su composizioni inferiori o uguali all’ 8 wt.%. Tra le problematiche connesse al ciclo di produzione sono particolarmente importanti quelle legate al processo di ricristallizzazione che, nonostante l’utilizzo di queste leghe fin dall’antichità, non è stato ancora sistematicamente studiato in modo approfondito. L’analisi calorimetrica ha permesso di seguire il processo di ricristallizzazione in tutte le sue fasi e, in particolare: - di misurare la temperatura di onset, di picco e di fine processo, per la ricristallizzazione primaria; - di ottenere i valori delle temperature di picco in funzione delle velocità di riscaldamento; dati necessari per calcolare l’energia di attivazione tramite il metodo di Kissinger modificato. Le composizioni prese in esame, in questa prima fase della ricerca, sono leghe al: 0.165 - 0.25 – 0.50 – 0.75 – 0.84 – 1 – 2 – 3 – 4 – 5 – 6 – 7 – 8 (Sn wt.%) e per tutte le leghe sono stati considerati due diversi gradi di incrudimento: riduzione di spessore del 50 e del 75%

Studio di saldabilità (LBW,FSW, EBW) di leghe da pressocolata a base alluminio

Le leghe da pressocolata sono generalmente difficilmente saldabili con i processi ad arco tradizionali acausa dei cicli termici di saldatura blandi che possono provocare la precipitazione di fasi fragili in ZTA e altempo stesso la complicata geometria dei pezzi può di fatto rendere inapplicabili certe tecnologie(saldature in interstizi non raggiungibili con torce di saldatura tradizionali). Di qui l’esigenza di uno studiodi saldabilità con processi alternativi come quelli ad energia concentrata (fascio laser e fascio elettronico) oil caratteristico processo Friction Stir che permette di saldare facilmente materiali basso fondenti come leleghe di alluminio senza portarle a fusione (fattore che in questo caso può rivelarsi molto positivo). Lo studio inquestione ha previsto l’utilizzo delle tre tecnologie di saldatura sopracitate tramite la tecnica conosciuta come“beads on plate” che consiste nella realizzazione di cordoni di saldatura direttamente su materiale base senzaunire fisicamente due pezzi ma che di fatto permette ugualmente di stabilire l’applicabilità o meno di undeterminato processo. Come materiali per la sperimentazione è stato previsto l’utilizzo di lastrinepressofuse da 2 e 4 mm di spessore, di due differenti leghe Al/Si modificate allo Stronzio riconducibili ai gruppiAlSi9Mn ed AlSi9MgMn. La prima caratterizzata dall’assenza di Magnesio, la seconda con tenori dello stessocompresi fra lo 0.1 e lo 0.5% (quindi inquadrabile come lega indurente per precipitazione)