APPLICAZIONE DEGLI ULTRASUONI AL TRATTAMENTO DELLE LEGHE ALLO STATO LIQUIDO

Nella produzione industriale di leghe metalliche da fonderia l’ottenimento di una struttura a grano fine edomogeneo, povera in porosità ed irregolarità, è traducibile in un incremento delle proprietà meccaniche. Adoggi queste caratteristiche sono ricavate tramite l’utilizzo di ben consolidati processi produttivi e tramitel’aggiunta di elementi affinanti e modificanti, i quali comportano tuttavia onerose spese aggiuntive, gravantiin modo cospicuo sul costo dei pezzi prodotti.Nuove tecnologie stanno inoltre nascendo, al fine di migliorare o sostituire quelle già esistenti: ne è un esempiola produzione di leghe aventi caratteristiche tixotropiche, ove l’ottenimento di una lega allo stato semi-solidopermette di riempire lo stampo con moto laminare e non turbolento, garantendo compattezza ed uniformità delfronte di avanzamento con conseguente riduzione della quantità di gas intrappolato (da cui hanno origine leporosità, una delle problematiche principali in fonderia) [1].L’applicazione di onde ultrasonore direttamente al bagno liquido (trattamento US), potrebbe rappresentareuna svolta nella produzione di leghe metalliche, portando all’ottenimento di pezzi ad elevate caratteristichemeccaniche senza l’utilizzo di costosi elementi migliorativi. Alcuni studi condotti presso centri universitariesteri, ma non ancora applicati industrialmente, mostrano infatti come questo tipo di onde inducano fenomenidi tipo cavitativo all’interno del metallo liquido, favorendo un affinamento del grano ed una riduzione delleporosità [2-3]. Scopo del presente studio è stato quello di analizzare ed ottimizzare questa nuova tecnologia,applicando onde ultrasonore opportunamente generate a leghe metalliche fuse, onde studiarne l’effetto sullamicrostruttura e sulle proprietà meccaniche.Obiettivo finale della ricerca è stato l’ottenimento di una lega con microstruttura globulare, utilizzabile perapplicazioni in semisolido [4]

Propagator of a Charged Particle with a Spin in Uniform Magnetic and Perpendicular Electric Fields

We construct an explicit solution of the Cauchy initial value problem for the time-dependent Schroedinger equation for a charged particle with a spin moving in a uniform magnetic field and a perpendicular electric field varying with time. The corresponding Green function (propagator) is given in terms of elementary functions and certain integrals of the fields with a characteristic function, which should be found as an analytic or numerical solution of the equation of motion for the classical oscillator with a time-dependent frequency. We discuss a particular solution of a related nonlinear Schroedinger equation and some special and limiting cases are outlined.Comment: 17 pages, no figure

Effect of a sweeping conductive wire on electrons stored in the Penning trap between the KATRIN spectrometers

The KATRIN experiment is going to search for the mass of the electron antineutrino down to 0.2 eV/c^2. In order to reach this sensitivity the background rate has to be understood and minimised to 0.01 counts per second. One of the background sources is the unavoidable Penning trap for electrons due to the combination of the electric and magnetic fields between the pre- and the main spectrometer at KATRIN. In this article we will show that by sweeping a conducting wire periodically through such a particle trap stored particles can be removed, an ongoing discharge in the trap can be stopped, and the count rate measured with a detector looking at the trap is reduced.Comment: Final version published in EPJ A, 14 pages, 19 figures (21 files

Oral ondansetron versus domperidone for symptomatic treatment of vomiting during acute gastroenteritis in children: multicentre randomized controlled trial

<p>Abstract</p> <p>Background</p> <p>Vomiting in children with acute gastroenteritis (AG) is not only a direct cause of fluid loss but it is also a major factor of failure of oral rehydration therapy (ORT). Physicians who provide care to paediatric patients in the emergency department (ED) usually prescribe intravenous fluid therapy (IVT) for mild or moderate dehydration when vomiting is the major symptom. Thus, effective symptomatic treatment of vomiting would lead to an important reduction in the use of IVT and, consequently, of the duration of hospital stay and of frequency of hospital admission. Available evidence on symptomatic treatment of vomiting shows the efficacy of the most recently registered molecule (ondansetron) but a proper evaluation of antiemetics drugs largely used in clinical practice, such as domperidone, is lacking.</p> <p>Objectives</p> <p>To compare the efficacy of ondansetron and domperidone for the symptomatic treatment of vomiting in children with AG who have failed ORT.</p> <p>Methods/Design</p> <p>Multicentre, double-blind randomized controlled trial conducted in paediatric EDs. Children aged from 1 to 6 years who vomiting, with a presumptive clinical diagnosis of AG, and without severe dehydration will be included. After the failure of a initial ORS administration in ED, eligible children will be randomized to receive: 1) ondansetron syrup (0,15 mg/Kg of body weight); 2) domperidone syrup (0,5 mg/Kg of body weight); 3) placebo. The main study outcome will be the percentage of patients needing nasogastric or IVT after symptomatic oral treatment failure, defined as vomiting or fluid refusal after a second attempt of ORT. Data relative to study outcomes will be collected at 30 minute intervals for a minimum of 6 hours. A telephone follow up call will be made 48 hours after discharge. A total number of 540 children (i.e. 180 patients in each arm) will be enrolled.</p> <p>Discussion</p> <p>The trial results would provide evidence on the efficacy of domperidone, which is largely used in clinical practice despite the lack of proper evaluation and a controversial safety profile, as compared to ondansetron, which is not yet authorized in Italy despite evidence supporting its efficacy in treating vomiting. The trial results would contribute to a reduction in the use of IVT and, consequently, in hospital admissions in children with AG. The design of this RCT, which closely reflect current clinical practice in EDs, will allow immediate transferability of results.</p> <p>Trial Registration</p> <p>ClinicalTrials.gov: <a href="http://www.clinicaltrials.gov/ct2/show/NCT01257672">NCT01257672</a></p

Ultrasounds: a New Technology for Alloys Degassing, Grain Refinement and Obtainment of a Thixotropic Structure

The aim of the present research is to investigate the improvements induced by the use of power ultrasound to foundry alloys, instead of wrought ones, so as to promote its application in the production of castings. It is a fact that grain refinement and degassing by themselves do not guarantee high performance of cast components. In fact, apart from those defects given by dissolved hydrogen or coarse microstructure, a further problem for casting quality is the po-rosity produced by turbulent flows during die filling, mainly in the case of die-casting. Differ-ent approaches have been studied in order to avoid porosity caused by turbulent filling, as injecting into the die cavity an alloy in semi-solid state, i.e. characterized by a thixotropic microstructure consisting of primary phase globules suspended in a liquid matrix. Power ultrasounds applied to the metal, at a temperature between the liquidus and the soli-dus, enables the fragmentation of the dendrites under development, as well as an increase of the number of active nuclei, resulting in a globular microstructure appropriate for semi-solid applications. Therefore, a further aim of this research was to study the suitability of the US technique for producing semi-solid feedstock directly from molten metal, as an energy effi-cient and easy alternative to the traditional routes

Effetto del trattamento ad ultrasuoni di leghe allo stato liquido sulla resistenza a corrosione

The introduction of ultrasonic waves in the liquid bath, that induce cavitation effects, allows to refine and degas the alloy in a single step without the addition of nucleants agents, with a subsequent reduction of the production costs and the obtainment of an easier process. Moreover, this technology can be applied for the obtainment of semi-solid alloys, characterized by globules of primary phase surrounded by the eutectic, as confirmed by recent studies. The aim of this work is to evaluate the effect of ultrasound treatment (UST) on the corrosion resistance of Aluminium and Zinc foundry alloys. The different alloys have been treated at the liquid state and then cast in a small laboratory die. The corrosion resistance of the treated samples was evaluate by means of potentiodynamic tests in NaCl 0,5M solution and acetic salt spray tests. The results were compared with those obtained from not ultrasound treated samples. Further samples analyses were carried out by means of optical microscope (OM) and scanning electron microscope (SEM), in order to better understand the corrosion phenomena occurred on the samples surfaces during salt spray test. For the Aluminium alloy AISi5 it was observed that: - UST induces a refinement and a homogenization of the microstructure, with the formation of globular grains; - porosity strongly decreases; - intermetallics particles have same chemical composition but smaller size in the treated samples respect to the not treated ones; - higher micro-hardness values are observed in the treated samples. Concerning the corrosion tests: - US treated alloys show a better corrosion behaviour and a higher corrosion potential, probably related to a more uniform distribution of the solute; - in both samples, corrosion begins and propagates through the eutectic, favoured from silicon and intermetallics particles; - the higher porosity of not treated samples makes worse the corrosion resistance. For the Zinc alloy ZA27 it was observed that: - UST does not produce a substantial microstructure variation, even if dendrites appear slightly rounded; - microhardness tests show a light improvement of mechanical properties of the US treated alloy, characterized by a more homogeneous structure; - as for AISi5, the corrosion rate of the treated samples appears lower than that of not treated ones, even if not treated samples have a more noble potential; - for both samples, the corrosion propagation is through the transformed eutectic, rich in copper, extending inside the grains, where the Al composition is higher; - the depth of corrosion attack is higher in the case of not treated samples

Effect of ultrasound treatment of AlSi5 liquid alloy on corrosion resistance

The application of power ultrasound to liquid alloys can be a simple and cost effective method to induce both degassing and grain refinement in a single step, without the need of inert gas or inoculants additions. In this paper the treatment of liquid hypoeutectic AlSi5 alloy by ultrasound waves and its effects on microstructure were investigated. The corrosion behaviour of ultrasound treated samples were compared to that of non treated ones by means of immersion and electrochemical tests. It was observed that the ultrasound treated alloy offers better quality, higher mechanical properties and improved corrosion resistance, as a consequence of a more uniform distribution of the solute

Effetto del trattamento ad ultrasuoni di leghe allo stato liquido sulla resistenza a corrosione

The introduction of ultrasonic waves in the liquid bath, that induce cavitation effects, allows to refine and degas the alloy in a single step without the addition of nucleants agents, with a subsequent reduction of the production costs and the obtainment of an easier process. Moreover, this technology can be applied for the obtainment of semi-solid alloys, characterized by globules of primary phase surrounded by the eutectic, as confirmed by recent studies. The aim of this work is to evaluate the effect of ultrasound treatment (UST) on the corrosion resistance of Aluminium and Zinc foundry alloys. The different alloys have been treated at the liquid state and then cast in a small laboratory die. The corrosion resistance of the treated samples was evaluate by means of potentiodynamic tests in NaCl 0,5M solution and acetic salt spray tests. The results were compared with those obtained from not ultrasound treated samples. Further samples analyses were carried out by means of optical microscope (OM) and scanning electron microscope (SEM), in order to better understand the corrosion phenomena occurred on the samples surfaces during salt spray test. For the Aluminium alloy AISi5 it was observed that: - UST induces a refinement and a homogenization of the microstructure, with the formation of globular grains; - porosity strongly decreases; - intermetallics particles have same chemical composition but smaller size in the treated samples respect to the not treated ones; - higher micro-hardness values are observed in the treated samples. Concerning the corrosion tests: - US treated alloys show a better corrosion behaviour and a higher corrosion potential, probably related to a more uniform distribution of the solute; - in both samples, corrosion begins and propagates through the eutectic, favoured from silicon and intermetallics particles; - the higher porosity of not treated samples makes worse the corrosion resistance. For the Zinc alloy ZA27 it was observed that: - UST does not produce a substantial microstructure variation, even if dendrites appear slightly rounded; - microhardness tests show a light improvement of mechanical properties of the US treated alloy, characterized by a more homogeneous structure; - as for AISi5, the corrosion rate of the treated samples appears lower than that of not treated ones, even if not treated samples have a more noble potential; - for both samples, the corrosion propagation is through the transformed eutectic, rich in copper, extending inside the grains, where the Al composition is higher; - the depth of corrosion attack is higher in the case of not treated samples