Microwave-Assisted Preparation of High Entropy Alloys

Microwaves at the ISM (Industrial, Scientific and Medical, reserved internationally) frequency of 2450 or 5800 MHz have been used to prepare FeCoNiCuAl, FeCrNiTiAl and FeCoCrNiAl2.5 high entropy alloys by direct heating of pressed mixtures of metal powders. The aim of this work is to explore a new microwave-assisted near-net-shape technology, using a powder metallurgy approach for the preparation of high entropy alloys, able to overcome the limits of current melting technologies (defects formation) or solid state ones (time demanding). High entropy alloy compositions have been selected so as to comprise at least one ferromagnetic element and one highly reactive couple, like Ni-Al, Ti-Al, Co-Al or Fe-Al. Results show that direct microwave heating of the powder precursors occurs, and further heating generation is favored by the ignition of exothermal reactions in the load. Microwaves have been applied both for the ignition and sustaining of such reactions, showing that by the proposed technique, it is possible to control the cooling rate of the newly-synthesized high entropy alloys. Results showed also that microwave heating in predominant magnetic field regions of the microwave applicator is more effective at controlling the cooling rate. The herein proposed microwave-assisted powder metallurgy approach is suitable to retain the shape of the load imparted during forming by uniaxial pressing. The homogeneity of the prepared high entropy alloys in all cases was good, without the dendritic segregation typical of arc melting, even if some partially-unreacted powders were detected in the samples

Ai limiti della funzione rappresentativa: divieto di mandato imperativo e voto sulle questioni di coscienza

La prima parte del saggio, dedicata alla “libertà di coscienza” del parlamentare, propone riflessioni sulla natura della rappresentanza politica (nazionale) e sulla definizione di "funzione rappresentativa". Essa si concentra inoltre sul concetto di libero mandato parlamentare (e sulle trasformazioni che quest'ultimo ha subito); sul significato del voto segreto nelle deliberazioni relative ai diritti fondamentali (artt. 49 R.C. e 113 R.S.); sul rapporto tra legge e giurisdizione nelle decisioni politiche in materia di bioetica. Nella seconda parte, lo scritto mette in evidenza il particolare rapporto che s'instaura tra rappresentanti e rappresentati nei casi in cui siano in gioco deliberazioni sulle "questioni di coscienza". Si sottolineano così quali spazi di manovra siano riconosciuti agli eletti in queste materie ma anche i limiti costituzionalmente rilevanti che la loro azione incontra. Particolare rilievo viene riservato al tema del fine-vita, benché non si manchi di analizzare anche altri casi "difficili" (ad esempio, aborto e procreazione assistita). Nell'ultima parte del lavoro si elencano gli strumenti che la Costituzione predispone proprio per reagire alle ipotesi in cui parlamentari non rispettino la libertà di coscienza degli elettori

From Field to Shelf: How Microwave-Assisted Extraction Techniques Foster an Integrated Green Approach

Microwave-assisted extraction of organic compounds from vegetal matrixes is a relatively young field of research. The exceptional results achievable at the laboratory scale by microwave-assisted extraction, like shorter extraction times, lower average temperatures, reduction of organic solvents use, higher yields and selectivity, as well as energy and cost saving, are not always accompanied by a successful scale up. Nevertheless, microwave-assisted techniques of extraction have been multiplying during last decades. In this framework, a deeper knowledge of microwave applicator design criteria is mandatory. This chapter starts from the basis of microwave heating and the relevant material properties involved in a successful microwave-assisted extraction application, to continue with a short overview on how such properties can be measured and used to optimize the experimental setup or a possible scale up of the process under investigation. A comprehensive review of recent applications of microwave-assisted extraction, applied to vegetal matrixes, is presented next. The chapter ends reviewing duplex treatments of vegetal matrixes for extraction purposes, where microwave heating is coupled to other techniques, like ultrasounds, and indicating new paths, where the recent advent of new microwave solid-state generators has led to better process control and higher yields and energy efficiency

Studio e realizzazione di un sistema di gestione fault tolerance applicato ad una piattaforma di calcolo distribuito a livello geografico

The last decade has seen an unprecedented growth in grid infrastructures. Grid characteristics, such as high heterogeneity, complexity and distribution create many new technical challenges, which need to be addressed. Among these technical challenges, failure management is a key area, important for both the applications and for the grid operation activities. In this thesis work i have undertaken a comprehensive analysis and assessment of several services of the gLite middleware currently in use in the EGEE Grid, the largest grid infrastructure in the world. Sites in the EGEE production grid infrastructure are required to provide their services on a continuous basis. The same is true for central grid infrastructure services. Therefore, it is important not only to know the current status of the various sites and central services but also to obtain information about this status in the long run. Service level agreement (SLA) negotiation plays a very important role in manufacturing grid. I extended the Nagios monitoring framework with high availability features in order to implementan efficient grid monitoring system. The main goal of this system is to achieve better availability of grid hosts and services, by precise problem detection and instant notification. This would also enable utilizing system's mechanisms for automatic recovery of services in order to improve the present rates, and so improve the availability and reliability of the EGEE grid production infrastructure. The aim of such an initiative is to provide a sustainable infrastructure based on National Grid Initiatives (NGIs), with the final result of delivering a large-scale production Grid infrastructure able to provide reliable and predictable services

breast conservation and sentinel lymph node biopsy after neoadjuvant systemic therapy

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<i>Trifolium nigrescens</i> Viv. subsp. <i>nigrescens</i>, leguminosa foraggera utilizzabile nel miglioramento dei pascoli in Sardegna: 1. Prime acquisizioni, su popolazioni naturali sarde

On the basis of a botanical survey of naturally established pastures in Sardinia (Italy), ball clover (Trifolium nigrescens p.p.) appeared to be one of the most widespread annual forage legumes. Thirteen natural populations collected in Sardinia in late spring 1987 were evaluated in 1987-88 at Sassari for chromosome number, fertility indexes, 1,000 seed weight, plant diameter 90 day after sowing (sowing date Oct. 30, 1987), flowering time, average stem length, number of stems and dry matter yield per plant at harvest (harvesting date May 19, 1988). All the populations were diploid (2n = 2x = 16), allogamous, self-incompatible and belonged to T. nigrescens Viv. subsp. nigrescens. The wide variability of the agronomic traits under study permits to obtain positive results with breeding programs aimed at developing ball clover varieties for pasture improvement in Sardinia. In particular, at population level 1,000 seed weight ranged from 0.163 g to 0.307 g, flowering time from Mar 13 to Apr 4 and dry matter yield per plant from 7.9 g to 17.9 g. In conclusion, the multiple regression analysis and the path coefficients analysis showed that average stem lenght could be used to assess the dry matter potentialities of the plants in the evaluation of large germplasm collections of ball clover. Allo scopo di iniziare la valutazione del germoplasma sardo di Trifolium nigrescens p.p., una delle leguminose foraggere annuali più diffuse nei pascoli naturali dell'isola, nella tarda primavera 1987 tredici popolazioni naturali sono state raccolte in differenti aree della Sardegna. Le popolazioni sono state valutate, a Sassari, nel corso del 1987-88 per numero cromosomico, indici di fertilità per autofecondazione e libera impollinazione, peso di 1.000 semi, diametro della pianta a 90 giorni dalla semina, epoca di fioritura, lunghezza degli steli, numero di steli e peso secco della pianta alla raccolta. Tutte le popolazioni sono risultate diploidi (2n = 2x = 16), allogarne, autoincompatibili, ad impollinazione entomofila e appartenenti alla specie T. nigrescens Viv. subsp. nigrescens. La variabilità osservata per i caratteri agronomici in esame suggerisce la possibilità di ottenere risultati positivi con programmi di miglioramento genetico volti allo sviluppo di varietà di T. nigrescens da utilizzare nel miglioramento dei pascoli in aree marginali della Sardegna. Di notevole interesse è la variabilità tra le medie delle popolazioni messa in luce per il peso di 1.000 semi (tra 0,163 g e 0,307 g), l'epoca di fioritura (tra il 13 marzo e il 4 aprile) e la produzione di sostanza secca per pianta (tra 7,9 g e 17,9 g). L'analisi della regressione multipla e l'analisi dei "path coefficients" hanno evidenziato che la produzione di sostanza secca per pianta è fortemente influenzata dalla lunghezza media degli steli. Poiché la determinazione di questo secondo carattere è più rapida di quella relativa alla produzione di sostanza secca, almeno nelle prime fasi di valutazione del germoplasma di T. nigrescens sarebbe possibile aumentare il numero di accessioni studiate utilizzando la lunghezza media degli steli per valutare indirettamente le potenzialità produttive delle piante

Microwave processing of high entropy alloys: A powder metallurgy approach

Microwaves at the ISM frequency of 2450 and 5800 MHz have been exploited to prepare FeCoNiCrAl-family high entropy alloys by direct heating of pressed mixtures of metal powders. The aim of this work is to explore a new microwave assisted near-net-shape technology, using powder metallurgy approach for the preparation of high entropy alloys, able to overcome the limits of current melting technologies (defects formation) or solid state ones (time demanding). Results show that direct microwave heating of the powder precursors occurs, and further heating generation is favored by the ignition of exothermal reactions in the compound. Microwave processing, exploited both for the ignition and sustaining of such reactions, has been compared to reactive sintering in laboratory furnace and mechanical alloying in a planetary ball milling. Results demonstrate that microwave required the shortest time and lowest energy consumption, thus it is promising time- and cost-saving synthetic route

Al, cu and zr addition to high entropy alloys: The effect on recrystallization temperature

The equimolar Cr, Mn, Fe, Co and Ni alloy, first produced in 2004, was unexpectedly found to be single-phase. Consequently, a new concept of materials was developed: high entropy alloys (HEA) forming a single solid-solution with a near equiatomic composition of the constituting elements. In this study, an equimolar CoCrFeMnNi HEA was modified by the addition of 5 at% of either Al, Cu or Zr. The cold-rolled alloys were annealed for 30 minutes at high temperature to investigate the recrystallization kinetics. The evolution of the grain boundary and the grain size were investigated, from the as-cast to the recrystallized state. Results show that the recrystallized single phase FCC structures exhibits different twin grains density, grain size and recrystallization temperatures as a function of the at.% of modifier alloying elements added. In comparison to the equimolar CoCrFeMnNi, the addition of modifier elements increases significantly the recrystallization temperature after cold deformation. The sluggish diffusion (typical of HEA alloys), the presence of a solute in solid solution as well as the low twin boundary energy are responsible for the lower driving force for recrystallization