2021, Articolo in rivista, ENG
Lorenzini R.; Gobbin M.; RFX-mod team
The comparison between deuterium and hydrogen plasmas at high current in the RFX-mod experiment proves that the reversed field pinch configuration experiences the isotope effect in a way analogous to tokamak experiments. Both energy and particle confinement exhibit a favourable scaling with the isotope mass Mi, respectively, as M0.3i and as M0.45i. This effect is mainly due to the mitigation of transport at the edge, which is driven by electrostatic fluctuations, although a mitigation of the stochastic transport in the plasma core is also observed. As in tokamaks, the MHD properties are modified when the gas mass is changed. The most evident modification regards the spectrum of tearing modes that are more stable in deuterium, so that the duration and the purity of quasi single helicity (QSH) phases are enhanced. The thermal structures that develop during the QSH phases enclose a plasma volume that is wider in deuterium discharges than in hydrogen ones.
2019, Articolo in rivista, ENG
Barbara Ballarin, Maria Cristina Cassani , Daniele Nanni, Chiara Parise, Davide Barreca , Giorgio Carraro , Alberto Riminucci, Ilaria Bergenti, Vittorio Morandi, Andrea Migliori, Elisa Boanini
Magnetic Fe 3 O 4 (magnetite) nanoparticles are synthesized via a chemical precipitation route in different alkaline environments (NH 3 or NaOH) and subsequently functionalized with a (propynylcarbamate)triethoxysilane moiety, with the aim of promoting the nucleation and subsequent stabilization of gold nanoparticles. The propynylcarbamate group is able to capture the gold precursor (HAuCl 4 ), spontaneously reduce it, and stabilize the resulting Au nanoaggregates. The obtained results show that though the dimensions of the starting magnetite substrate depend on the base used in the preparation, they remain unaltered upon the subsequent modification. Conversely, the average Au nanoparticle dimensions can be conveniently tailored as a function of the base used in Fe 3 O 4 preparation and the presence/absence of the organic functionalization. The smallest dimensions (15 nm) are obtained for AuNP supported on propynylcarbamate-functionalized Fe 3 O 4 prepared in the presence of ammonia. Magnetization measurements highlight that all the Au/Fe 3 O 4 nanocomposites display a superparamagnetic behavior and those obtained using ammonia showed consistently smaller Hc and Mr values (av. values of 7.4 Oe and 0.8 emu/g) than those prepared with sodium hydroxide (av. values of 28 Oe and 2.8 emu/ g).
2018, Articolo in rivista, ENG
M. Cernea (1); B. S. Vasile (2); V. A. Surdu (2); R. Trusca (2); C. Bartha (1); F. Craciun (3); C. Galassi (4)
One of the most promising ways for the realization of multi-functional materials is the integration of oxides with different properties in artificial heterostructures. In this paper, a novel piezoelectric-ferromagnetic heterostructure consisting of 0.92Na(0.5)Bi(0.5)TiO(3)-0.08BaTiO(3) (abbreviated as BNT-BT0.08) and CoFe2O4 layers is fabricated on Si-Pt substrate, by sol-gel method coupled with spin-coating technique. The composite thin film shows only perovskite Bi0.5Na0.5TiO3-like rhombohedral phase and CoFe2O4 cubic phase. The thickness of CoFe2O4 and BNT-BT0.08 layers is similar to 280 and similar to 400 nm, respectively. BNT-BT0.08/CoFe2O4 heterostructure thin film shows a saturation magnetization of 0.11 emu/g at 5 K and 0.07 emu/g at 295 K, dielectric constant of 235 at 1 kHz and tunability of 70% at 1 kHz and an electric field E = 110 kV/cm. The results reveal that the investigated hybrid piezoelectric/ferromagnetic structure shows piezoelectric behavior, good ferroelectric and ferromagnetic properties. This bilayer composite can be used in miniature low-frequency magnetic sensor and piezoelectric sensor for biomedical domain.
2017, Rapporto tecnico, ENG
Edoardo Spirandelli
This Technical Report describes the choice of new batteries for M.A.R.C. vehicle.
2017, Articolo in rivista, ENG
Alonge, Francesco (1), Cirrincione, Maurizio (2), Pucci, Marcello (3), Sferlazza, Antonino (1)
This paper proposes a nonlinear observer for induction machine drives based on space-vector dynamic model of induction machine, expressed in state form, which presents the peculiarity of taking into consideration the magnetic saturation of the iron core. This observer is particularly suitable in order to obtain high accuracy in rotor flux estimation, in both amplitude and phase position, during working conditions characterized by varying flux, among which the most important are those during electrical losses minimization. A Lyapunov-based convergence analysis is proposed in order to suitably compute the numerical observer gain guaranteeing the convergence of the estimation error. The proposed nonlinear observer has been tested by means of simulations and experiments carried out on a suitably developed test setup. Its behavior has been compared with that obtained with a standard full-order Luenberger observer that assumes the linearity of the magnetization characteristic. The paper shows the capability of the proposed nonlinear observer to correctly estimate amplitude and phase of the rotor flux under flux varying conditions. Moreover, the proposed observer exhibits a higher accuracy than that obtained with the standard observer, which does not consider the estimated magnetization characteristic.
2017, Contributo in atti di convegno, ENG
Zin V.; Agresti F.; Barison S.; Fedele L.; Litti L.; Meneghetti M.; Fabrizio M.
Nanofluids containing lyotropic mineral particles responsive to external magnetic fields are rising large interest, since they combine the fluidity and anisotropy of liquid crystals with the specific magnetic and transport properties of dispersed mineral compounds. Goethite (?-FeOOH) based colloids are mineral liquid crystals exhibiting a peculiar magnetic behaviour, which allows tuning their properties by the application of an external magnetic field. In this work, suspensions in polyalphaolefin of goethite nanorods with different morphology and size have been prepared for anti-friction and anti-wear purposes. The tribological performance of ?-FeOOH has been rarely reported in literature. As goethite is a chemically reactive material, it represents a suitable functional additive in lubricants to promote the formation of a protective tribofilm during the rubbing process, because of tribo-chemical reactions, especially under severe working conditions, such as mixed and boundary lubrication. Nanofluids have been characterized regarding both the viscosity and the stability over time. A ball-on-flat test configuration has been used, in presence of variably oriented magnetic field. The orientation of the external magnetic field and the resulting orientation of nanorods within the lubricant influenced the friction coefficient in the steady state. The anti-wear mechanisms were analysed by comprehensive characterization of tribofilm using Raman spectroscopy, SEM, X-EDS and nanoindentation techniques. This work demonstrates the outstanding anti-wear properties of goethite-based nanofluids, since a decrease of one order of magnitude has been measured for worn volume. The slight decrease of the friction coefficient suggests that nano-additives primarily accomplish an effective anti-wear function rather than simply acting as friction modifiers.
2017, Articolo in rivista, ENG
Pugliese, Marco; Ferrara, Francesco; Bramanti, Alessandro Paolo; Gigli, Giuseppe; Gigli, Giuseppe; Maiorano, Vincenzo
We present a new in-plane magnetically actuated microfluidic valve. Its simple design includes a circular area joining two channels lying on the same plane. The area is parted by a septum lying on and adhering to a magneto-active polymeric 'floor' membrane, keeping the channels normally separated (valve closed). Under the action of a magnetic field, the membrane collapses, letting the liquid flow below the septum (valve open). The valve was extensively characterized experimentally, and modeled and optimized theoretically. The growing interest in lab on chips, especially for diagnostics and precision medicine, is driving researchers towards smart, efficient and low cost solutions to the management of biological samples. In this context, the valve developed in this work represents a useful building-block for microfluidic applications requiring precise flow control, its main features being easy and rapid manufacturing, biocompatibility and low cost.
2016, Articolo in rivista, ENG
Bucci F.; Sanna A.; Continenza A.; Katrych S.; Karpinski J.; Gross E.K.U.; Profeta G.
As a follow-up to the discovery of a new family of Fe-based superconductors, namely, the RE4Fe2As2Te1-xO4 (42214) (RE = Pr, Sm, and Gd), we present a detailed ab initio study of these compounds highlighting the role of rare-earth (RE) atoms, external pressure, and Te content on their physical properties. Modifications of the structural, magnetic, and electronic properties of the pure (e.g., x=0.0) 42214 compounds and their possible correlations with the observed superconducting properties are calculated and discussed. The careful analysis of the results obtained shows that (i) changing the RE atoms allows one to tune the internal pressure acting on the As height with respect to the Fe planes; (ii) similarly to other Fe pnictides, the 42214 pure compounds show an antiferromagnetic-stripe magnetic ground state phase joined by an orthorhombic distortion (not experimentally found yet); (iii) smaller RE atoms increase the magnetic instability of the compounds possibly favoring the onset of the superconducting state; (iv) external pressure induces the vanishing of the magnetic order with a transition to the tetragonal phase and can be a possible experimental route towards higher superconducting critical temperature (Tc); and (v) Te vacancies act on the structural parameters, changing the As height and affecting the stability of the magnetic phase.
2015, Articolo in rivista, ENG
Samal, Sangram K.; Goranov, Vitaly; Dash, Mamoni; Russo, Alessandro; Shelyakova, Tatiana; Graziosi, Patrizio; Lungaro, Lisa; Riminucci, Alberto; Uhlarz, Marc; Banobre-Lopez, Manuel; Rivas, Jose; Herrmannsdoerfer, Thomas; Rajadas, Jayakumar; De Smedt, Stefaan; Braeckmans, Kevin; Kaplan, David L.; Dediu, V. Alek
A versatile approach for the design and fabrication of multilayer magnetic scaffolds with tunable magnetic gradients is described. Multilayer magnetic gelatin membrane scaffolds with intrinsic magnetic gradients were designed to encapsulate magnetized bioagents under an externally applied magnetic field for use in magnetic-field-assisted tissue engineering. The temperature of the individual membranes increased up to 43.7 degrees C under an applied oscillating magnetic field for 70 s by magnetic hyperthermia, enabling the possibility of inducing a thermal gradient inside the final 3D multilayer magnetic scaffolds. On the basis of finite element method simulations, magnetic gelatin membranes with different concentrations of magnetic nanoparticles were assembled into 3D multilayered scaffolds. A magnetic-gradient-controlled distribution of magnetically labeled stem cells was demonstrated in vitro. This magnetic biomaterial-magnetic cell strategy can be expanded to a number of different magnetic biomaterials for various tissue engineering applications.
2015, Abstract in atti di convegno, ENG
Tiberto, P.; Celegato, F.; Barrera, G.; Barrera, G.; Conta, G.; Conta, G.; Coisson, M.; Manzin, A.; Aprile, G.; Aprile, G.; Boarino, L.; Seguini, G.; Lupi, F. Ferrarese; Giammaria, T.; Perego, M.
Synthesis of nanopatterned magnetic materials offers advanced capabilities in tailoring material structures and opens up new opportunities for engineering innovative devices (i.e. electronic and biomedical). In the frame of magnetic materials, the most demanding application consists in fabricating high-density arrays for use in data storage and magnetic sensors for spintronics [1]. In the last decade, many routes for the reliable fabrication of magnetic nanostructures have been extensively investigated, including top-down lithography and bottom-up self-assembly processes. Conventional electron beam lithography (EBL) soon turned out to be limited by low-speed and high costs while self-assembling emerged as a viable and handy alternative technique for designing nanostructures over a wide area on magnetic thin films.
2013, Articolo in rivista
Viscuso S.; Pittaccio S.
Actuators based on standard technologies often do not comply with environmental constraints on electromagnetic noise. Even though shape memory actuators are not ferromagnetic, activation by Joule's effect poses a question about magnetic compatibility. This article presents a new concept design of a rotary actuator based on a double coil of NiTi wire, which permits to abate dramatically the electromagnetic fields generated. A particular implementation of the idea was devised as a case study to investigate feasibility. The desired torque and stroke were 83 N cm and 40 degrees, respectively, and mechanical tests confirmed that a maximal stroke of 38 degrees can be achieved for resisting torques ranging from 33 to 122 N cm. The built prototype proved appropriate to respond to the needs of a neuroscience study requiring mobilization of the ankle. So, this device was tested during measurement of brain activity in healthy subjects with both magnetoencephalography and functional magnetic resonance imaging, that is, diagnostic equipment with very demanding constraints on electromagnetic noise. Neither magnetoencephalography signals nor the functional magnetic resonance imaging images were affected by any electromagnetic noise or artifacts, allowing for further analysis and extraction of neurological features. Besides the discussed uses, this type of actuator could find an application in several fields, such as biomedical, robotic, aerospace, or automotive.
2009, Articolo in rivista, ENG
Piro S.; Gabrielli R.
Non-destructive geophysical prospecting methods are increasingly used for the investigation of archaeological sites, especially where a detailed physical and geometrical reconstruction of structures is required prior to any excavationwork.Often, due to the limited size and depth of an archaeological structure, it may be rather difficult to single out its position and extent because of the generally low signal-to-noise (S/N) ratio. This can be overcome by improving data acquisition and processing techniques and integrating different geophysical methods. In this work the results of a multimethodological surveys, used with the aim of detecting sharp discontinuities (boundary of cavities and fractures in the host medium) at the Archaeological Test Site of Sabine Necropolis at Research Area of National Research Council of Rome (Montelibretti, Italy) are shown. For the survey a combination of passive and active methods (magnetic, ground-penetrating radar (GPR), and dipole-dipole geoelectric (DDG)), topographical and three-dimensional laser scanner surveys and archaeological excavations were used to study the state of conservation of underground tombs. With all geophysical methods a high-resolution data acquisition was adopted with the aim of reconstructing a global vision of the study area. Signal processing and amplitude time-slice representation techniques were used for the analysis of GPR data. The bi-dimensional cross-correlation technique was applied to enhance the S/N ratio of the magnetic data. An example of the integration (both qualitative and quantitative) of these results is presented for a portion of the investigated area in the Sabine Necropolis at Colle del Forno (Rome, Italy). Archaeological excavations were then conducted systematically after completing the geophysical surveys and interpretations (from 2000 to 2006), which confirmed the location and shape of the individual chamber tombs with associated corridors.
2009, Articolo in rivista, ENG
Campana S. (1); Dabas M. (2); Marasco L. (1); Piro S. (3); Zamuner D. (3)
The area described in this article was 'detected' by the Laboratory for Landscape Archeology and Remote Sensing, Universityof Siena research team during aerial prospection in spring 2005. Analysis of the aerial photographs allowed interpretation of the site as a triple-ditched enclosure. During subsequent field-walking survey a number of archaeological artefacts were collected and mapped. Differential global positioning system (DGPS) survey confirmed the morphological pattern of the site, which seems to represent a survival of the Early Medieval Age settlement pattern on the coastal plain. The field-walking and DGPS surveys were followed by a programme of geophysical survey combining three different methods: differential magnetics (Overhauser probe), ground-penetrating radar (GPR) and Automatic Resistivity Profiler (ARP#, Geocarta). Finally, three sample areas were excavated, mainly to test the evidence collected previously. The excavation data 'ditches, post-holes, domestic pottery, animal bones, and wall remains' support the interpretation of the site as the first earth-and-timber castle mound, or motte, to be identified in Tuscany.
2008, Articolo in rivista, ENG
Cardarelli E. (1); Fischanger F. (2); Piro S. (3)
In the last few years, the location and characterization of buried historical objects is a task that generally lends itself to geophysics, thanks to the improvement of automatically measuring geophysical systems and the development of specific software for inversion problems. Furthermore, the integration of different methods permits an interpretation in which potential misunderstandings and the uncertainty of results can be reduced. The aim of the present work was to detect buried structures in an unexplored area of a Sabine Necropolis (700-300 B.C.) located in the area of the National Research Council (at Montelibretti, Rome). During the survey, three different geophysical techniques have been employed; fluxgate gradiometry, Electrical Resistivity Tomography and Ground-Penetrating Radar. The results are compared, integrated and interpreted indicating location of unknown buried tombs. An additional objective of this study consisted of testing new finite element modelling routines that have been integrated into the inversion algorithm developed by the authors in the past years, and, to compare the 2D inversion results with the ones achieved with the 3D Finite element inversion software ERTLab. Finally, the interpreted geophysical results have been verified through archaeological direct excavation in 2005, which have confirmed the location, dimensions and shape of the buried structure (tomb).
2007, Articolo in rivista
Malavasi L., Mozzati M. C., Tealdi C., Azzoni C.B., Flor G.
2007, Articolo in rivista
Malavasi L., Ritter C., Mozzati M.C., Azzoni C.B., Flor G.
2007, Articolo in rivista
Azzoni C.B., Mozzati M.C., Massarotti V., Capsoni D., Bini M.
2007, Articolo in rivista
Mariani M., Aldrovandi S., Corti M., Lago J., Lascialfari A., Micotti E., Rettori A., Cinti F., Amato A., Baines C., Bogani L., Caneschi A., Cottrell S.P., Gatteschi D.
2006, Articolo in rivista, ENG
R. Buonsanti; V. Grillo; E. Carlino; C. Giannini; M. L. Curri; C. Innocenti; C. Sangregorio; K. Achterhold; F. G. Parak; A. Agostiano; P. D. Cozzoli
Asymmetric binary nanocrystals (BNCs), comprising one c-axis elongated anatase TiO2 section and one gamma-Fe2O3 spherical domain attached together, are synthesized by heterogeneous nucleation of iron oxide onto the longitudinal facets of TiO2 nanorods in a ternary surfactant mixture. The topologically controlled composition of the BNCs is ascertained by a combination of powder X-ray diffraction, Raman and Mössbauer spectroscopy, high-angle annular dark-field imaging, and high-resolution transmission electron microscopy lattice fringe mapping, while their size-dependent magnetic behavior is demonstrated by ac susceptibility measurements. The heteroepitaxial growth proceeds through a mechanism never observed before for colloidal nanoheterostructures: the two domains share a restricted and locally curved junction region, which accommodates efficiently the interfacial strain and retards the formation of misfit dislocations. It is believed that these BNCs, which combine the properties of two technologically relevant oxide materials, can pave the way to reinforced applications in several fields of nanoscience, such as in photocatalysis, in malignant cell treatments, and in nanocrystal assembly.
2004, Articolo in rivista, ENG
Buratti P.; Airoldi A.; Alladio F.; Annibaldi V.; Bruschi A.; Cirant S.; Coelho R.M.; Gandini F.; Giovannozzi E.; Lazzaro E.; Micozzi P.; Nowak S.; Porcelli F.; Ramponi G.; and Smeulders P.
The main magnetohydrodynamic (MHD) activities affecting the Frascati Tokamak Upgrade (FTU) high-field plasmas with limiter configuration are sawtooth relaxations and tearing modes. The period of sawtooth relaxations can be increased in FTU both by electron heating and by pellet particle deposition near the sawtooth inversion radius; both methods lead to full stabilization in proper conditions. The sawtooth period can be shortened as well by central heating. The influence of localized electron cyclotron resonance heating (ECRH) on the stability of m = 2 tearing modes has been studied in FTU by means of radial and power scans. Heating between the plasma center and the island location increases the island size, while heating at the island location produces mode stabilization if ECRH power exceeds a threshold value. These sawtooth and tearing mode studies show that some control of both phenomena can be achieved. Double-tearing modes in the form of regular, sawtooth-like relaxations have been observed in discharges with reversed magnetic shear. The development of these instabilities is particularly interesting in FTU as it happens in the absence of injected momentum. Long-lived m = 1 island structures are frequently observed following pellet deposition near the inversion radius; particle accumulation around the O-point enhances diagnostic sensitivity, thus allowing fine studies of island dynamics. MHD spectroscopy has revealed the existence of coherent waves at frequencies well above the drift-tearing range in thermal plasmas. In addition, broadband turbulence has been observed both in ohmic and in radio-frequency-heated plasmas. The amplitude of turbulent fluctuations increases with heating power and is anticorrelated with the neutron yield.