102,685 research outputs found
Unraveling the solidification path of a pahoehoe "cicirara" lava from Mount Etna volcano
No full textThe solidified surface of a lava flow reflects the viscosity of its molten fraction and the crystal content during flow; crystal-poor basaltic lavas produce pahoehoe fields, whereas crystal-rich ones solidify with aa carapaces. At Mount Etna volcano aa morphologies are very common, in turn, pahoehoe lavas are rare. The latter are locally named “cicirara” due to the presence of cm-sized plagioclase phenocrysts much more abundant than in aa lavas. The phenocryst content of “cicirara” lavas contrasts with the low viscosity generally associated with pahoehoe morphology. Therefore, to reconcile the discrepancy between textural and volcanic observations, we have studied the most primitive pahoehoe “cicirara” lava sampled until now. Two samples at 0.5 and 1 m from the bottom of the two-meter thick lava flow were investigated on the basis of their mineral compositional variations and textural features, i.e. size frequency and crystal size distribution (CSD). Results coupled with rheological models indicate that only large phenocrysts of plagioclase (>1 mm) and clinopyroxene have grown before eruption. Thermobarometric models and petrological computations based on the composition of plagioclase and clinopyroxene phenocryst cores highlight that only a small amount (10-15 vol.%) of crystals equilibrated at 12 km of depth. Cumulative size frequency and CSD data also indicate that plagioclase and clinopyroxene phenocryst rims grew heterogeneously and coalesced around their cores at depths <1 km, before eruption. In this view, the “cicirara” lava was erupted with a low crystalline content that favoured the formation of its pahoehoe surface; however, crystals with a size <1 mm (~75 vol.%) solidified at post-eruptive conditions.
Our findings underline that the emplacement of high-viscosity aa or low-viscosity pahoehoe lavas is driven by the degree of undercooling imposed by the volatile exsolution rate in the shallowest portion of the Etnean plumbing system. A slow magma ascent rate promotes significant intratelluric degassing and widespread nucleation; consequently, the viscosity of the suspension significantly increases leading to an aa morphology. In contrast, pahoehoe “cicirara” lavas are associated with a rapid rise to the surface of poorly degassed, undercooled magmas
Low compressibility accretion disc formation in close binaries: the role of physical viscosity
No full textAims.Physical viscosity naturally hampers gas dynamics (rarefaction or compression). Such a role should
support accretion disc development inside the primary gravitation potential well in a close binary
system, even for low compressibility modelling. Therefore, from the astrophysical point of view, highly
viscous accretion discs could exist even in the low compressibility regime showing strong thermal
differences to high compressibility ones
Methods.We performed simulations of stationary Smooth Particle Hydrodynamics (SPH) low compressibility
accretion disc models for the same close binary system. Artificial viscosity operates in all models. The
absence of physical viscosity and a supersonic high mass transfer characterize the first model. Physical
viscosity and the same supersonic high mass transfer characterize the second model, whilst physical
viscosity and a subsonic low mass transfer characterize the third model. The same binary system
parameters, such as stellar masses and their separation, have been adopted, as well as the same
polytropic index . Thus we investigated the role of physical viscosity in mass and angular
momentum transport in the two viscid models and compare them to the inviscid model. An initial value of
the parameter has been considered for the physically viscous models, according to the
well-known Shakura and Sunjaev formulation, but simulations were carried out also for and
in the case of a supersonic mass transfer. Physical viscosity is represented by the
viscous force contribution expressed by the divergence of the symmetric viscous stress tensor in the
Navier-Stokes equation, while the viscous energy contribution is given by a symmetric combination of the
symmetric shear tensor times the particle velocity.
Results.The results show that physical viscosity supports
and favours accretion disc formation despite the very low compressibility assumed. On the contrary,
in the inviscid case no evident disc structure appears. In all models neither shock fronts nor
extended clear spirals in the radial flow develop
Fosfomycin tromethamine in uncomplicated urinary tract infections: a clinical study
No full textThe aim of our study was to verify if the empiric therapy with a single dose of 3 g fosfomycin tromethamine in patients with uncomplicated urinary tract infections (UTIs) was able to clinically resolveand to microbiologically eradicate the infection. A total of 387 out of the 400 patients (274 cases with acute and 113 cases with recurrent uncomplicated UTIs) were enrolled in the clinical study. Clinical and microbiological assessments were performed before and at 8-10 days after the administration. At follow-up high clinical recovery (88.9%) and bacteriological (94.9%) eradication rates were achieved. Gastrointestinal side effects were found in only 4.3% of patients. In conclusion, a single-dose administration regimen of fosfomycin tromethamine should be encouraged as a first choice of drug therapy for uncomplicated UTIs
Dike emplacement and related hazard in volcanoes with sector collapse: the 2007 Stromboli (Italy) eruption
No full textUnderstanding dike propagation is fundamental for hazard mitigation. In February 2007, two effusive vents opened (at 650 and 400 m a.s.l.) along the inner flank of Sciara del Fuoco (SdF) sector collapse at Stromboli. The summit craters collapsed, obstructing the central conduit, choking the vents and increasing the deformation within SdF. Here a new vent opened (500 m a.s.l.), releasing the deformation. The eruption continued from the 400 m vent, after a summit explosion, until early April. The vents were fed by laterally propagating feeder dikes, following the maximum gravitational stresses within a cone with sector collapse. Vent location is similar to that of the 2002-2003 eruption, fed by dikes triggering landslides and tsunami. Such a dike propagation represents a constant feature of the recent Stromboli eruptions. However, this eruption did not develop catastrophic landslides, suggesting that their triggering also depends on other factors, such as the magmatic pressure
Refertazione istopatologica e fattori prognostici del carcinoma mammario: requisiti minimi
No full textAnti-leukotrienes in the treatment of allergic conjunctivities and comorbidities in children: an update
No full textThe term “Allergy” actually includes a variety of different diseases (rhinitis, conjunctivitis, asthma, urticaria, and dermatitis) with a common pathological basis linked to the release of chemical mediators such as histamine, platelet-activating factor, arachidonic acid metabolites, and chemotactic factors secreted by mastocytes, basophils, and eosinophils. The key-role of leukotrienes (LTs) as mediators in allergic and inflammatory response justifies possible therapeutic use of leukotriene antago-nists in other allergic diseases beyond asthma. LTs modifiers reduce asthma symptoms, short-acting beta2-antagonist (SABA) use, and asthma exacerbations, and improve all indexes of pulmonary function, as measured by the increases in forced expiratory flow at one second (FEV1), peak expiratory flow (PEF), quality of life, and indices of bronchial inflammation (blood eosino-phils, inflammatory cells in the bronchial mucosa, exhaled nitric oxide, substance P, neurokinin A, eosinophil cationic protein, and serum myeloperoxidase). Anti-LTs have also been successfully used by some authors to control allergic diseases such as rhinitis, atopic dermatitis, chronic urticaria and allergic conjuncitivitis. Moreover, recently, new reports have been published concerning other conditions (migraine prophylaxis, sleep disorders, inflammatory bowel disease, and nasal polyposis) that broaden the future range of clinical applications. Topical ocular montelukast can be a potential therapeutic drug with a new route of administration that can be used for treatment of allergic conjunctivitis
PERIPHERAL BLOCKS WITH ENS : ELECTROPHYSIOLOGY, MATERIALS AND CLINICAL APPLICATIONS
No full textIl lavoro riporta un’analisi critica delle teorie sui presupposti elettrofisiologici che supportano la neurostimolazione, rivisitate alla luce di analisi e considerazioni originali.
Mediante un excursus storico, vengono sottolineati i progressi raggiunti e le notevoli prospettive nell’esecuzione di anestesie periferiche, grazie alla continua evoluzione degli strumentari ed alla fervente ricerca di sempre più numerosi autori italiani e stranieri.
Viene, inoltre, sistematizzata l’applicazione clinica della “teoria delle componenti” per l’anestesia distrettuale dell’arto superiore ed inferiore e la procedura per la corretta esecuzione di blocchi anestetici con ENS.
This paper gives a critical analysis of the theories and supposition regarding electrophysiology that support neurostimulation, viewed under the light of original analysis and consideration.
An historical survey reveals the progress attained in the execution of local anaesthetics and its prospects for the future, thanks to the continuous evolution of the equipment and fervent research of an ever growing number of Italian and foreign authors. The clinical application of the “component theory” in local anaesthesia of the upper and lower limbs and the procedure for the correct execution of anaesthetic blocks with ENS are also systematise
Il varicocele essenziale: risultati preliminari della nostra esperienza e proposta di un nuovo criterio classificativo.
No full textDeep sea explosive eruptions may be not so different from subaerial eruptions
Get PDFThe dynamics of deep sea explosive eruptions, the dispersion of the pyroclasts, and how submarine eruptions differ from the subaerial ones are still poorly known due to the limited access to sea environments. Here, we analyze two ash layers representative of the proximal and distal deposits of two submarine eruptions from a 500 to 800 m deep cones of the Marsili Seamount (Italy). Fall deposits occur at a distance of more than 1.5 km from the vent, while volcanoclastic flows are close to the flanks of the cone. Ash shows textures indicative of poor magma-water interaction and a gas-rich environment. X-ray microtomography data on ash morphology and bubbles, along with gas solubility and ash dispersion models suggest 200–400 m high eruptive columns and a sea current velocity <5 cm/s. In deep sea environments, Strombolian-like eruptions are similar to the subaerial ones provided that a gas cloud occurs around the vent
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