MAGNETIC OXIDE NANOPARTICLES WITH ANISOTROPIC SHAPE OR HETEROGENEOUS STRUCTURE

To briefly summarize the work reported in this PhD thesis, we can say that the study of the solvothermal synthesis of MnO NPs led to procedures to obtain anisotropic MnO NPs starting from manganese(II) oleate and stearate. A detailed investigation on the influence of the reaction conditions on the size, shape, crystal structure and magnetic properties of the obtained nanoparticles was carried out, including a detailed comparison between the two precursors (manganese oleate and manganese stearate) and surfactants (oleic acid and stearic acid) and a thorough investigation of the influence of the precursor : surfactant molar ratio. Having used MnO as antiferromagnetic material for the core-shell structure, we were prompted to further consider the use of MnS, an antiferromagnetic sulfide with the N\ue9el temperature \uf040 160 K (higher than the MnO TN = 116 K). The higher N\ue9el temperature makes MnS a good candidate for the building of an exchange-bias coupling. MnS, unlike MnO, presents three different polymorphs: cubic \u3b1-MnS (rock-salt), cubic \u3b2-MnS (zinc-blende), and hexagonal \u3b3-MnS (wurtzite). Thus, synthetic investigation about MnS NPs was mainly focused on the control of the nanoparticle crystal phase that, in our case, could be achieve through the use of different surfactants. Polymorphism control is a crucial point because different polymorphs exhibit different physical properties, among which, the magnetic behavior. Next, we focused on the synthetic strategy to coat anisotropic MnO NPs with a FeOx coating (FeOx stands for Fe3-xO4-x, 0 64 x 64 1). We conceived to approach this problem by a two step strategy. First, we set out to develop a procedure to grow a FeOx shell (several nanometers thick) onto large (20-30 nm) isotropic MnO cores; once obtained such procedure, we will optimize it to uniformly coat anisotropic NPs. Using isotropic MnO NPs as cores, many synthetic strategies were devised and assessed with respect to the achievement of growing a significantly thick and uniform iron oxide shell simultaneously preventing the formation of undesired homogeneous iron oxide nanoparticles. We finally developed a procedure able to grow a FeOx shell of up to 6 nm on the MnO core. We are at present working on the development of a multi-step procedure to achieve a thicker and more compact FeOx shell. The synthesis of core-shell MnO@FeOx NPs and their characterization by electron microscopy (C-TEM, electron diffraction, HRTEM, Analytical TEM) are described in detail in the Thesis, while the magnetic characterization are in progress in these days. Besides the main aim of my Thesis research, we decided to explore the feasibility to use MnO nanoparticles having different crystallographic faces as a catalysts in the water splitting reaction. We just started a collaboration with Dott. A. Minguzzi, O. Lugaresi and A. Visibile at the University of Milan to carry out an electrochemical study to investigate whether nanoparticle with different shape, the surface of which are different crystal faces, have unequal catalytic activity in the water splitting reaction. Since the work is at an early stage, here we reported only samples treatment and characterization before the electrochemical tests that are currently in progress. Finally, a complete magnetic characterization of thin-film assemblies of Ni@NiO core-shell nanoparticles, was performed and here reported thanks to a research project carried out in collaboration with the group of Professor S. D\u2019Addato, Dr. P. Luches, and Prof. S. Valeri at CNR NANO S3 and University of Modena and Reggio Emilia. Nanoparticles were synthesized by metal vapor deposition in Modena and their magnetic behavior was investigated in our laboratory by SQUID magnetometry. The Ni@NiO core-shell assemblies prepared by a three-layer procedure (NiO layer \u2013 Ni NPs \u2013 NiO layer) turned out to display a large exchange bias that could be accurately tuned by varying the thickness of the top NiO layer

Accretion and nuclear activity in Virgo early-type galaxies

We use Chandra observations to estimate the accretion rate of hot gas onto the central supermassive black hole in four giant (of stellar mass 10E11 - 10E12 solar masses) early-type galaxies located in the Virgo cluster. They are characterized by an extremely low radio luminosity, in the range L < 3E25 - 10E27 erg/s/Hz. We find that, accordingly, accretion in these objects occurs at an extremely low rate, 0.2 - 3.7 10E-3 solar masses per year, and that they smoothly extend the relation accretion - jet power found for more powerful radio-galaxies. This confirms the dominant role of hot gas and of the galactic coronae in powering radio-loud active galactic nuclei across ~ 4 orders of magnitude in luminosity. A suggestive trend between jet power and location within the cluster also emerges.Comment: Accepted for publication in A&

The MURALES survey II. Presentation of MUSE observations of 20 3C low-z radio galaxies and first results

We present observations of a complete sub-sample of 20 radio galaxies from the Third Cambridge Catalog (3C) with redshift <0.3 obtained from VLT/MUSE optical integral field spectrograph. These data have been obtained as part of the survey MURALES (a MUse RAdio Loud Emission line Snapshot survey) with the main goal of exploring the Active Galactic Nuclei (AGN) feedback process in a sizeable sample of the most powerful radio sources at low redshift. We present the data analysis and, for each source, the resulting emission line images and the 2D gas velocity field. Thanks to their unprecedented depth (the median 3 sigma surface brightness limit in the emission line maps is 6X10^-18 erg s-1 cm-2 arcsec-2, these observations reveal emission line structures extending to several tens of kiloparsec in most objects. In nine sources the gas velocity shows ordered rotation, but in the other cases it is highly complex. 3C sources show a connection between radio morphology and emission line properties. Whereas, in three of the four Fanaroff and Riley Class I radio galaxies (FRIs), the line emission regions are compact, ~1 kpc in size; in all but one of the Class II radiogalaxies FRIIs, we detected large scale structures of ionized gas with a median extent of 17 kpc. Among the FRIIs, those of high and low excitation show extended gas structures with similar morphological properties, suggesting that they both inhabit regions characterized by a rich gaseous environment on kpc scale.Comment: Accepted for publication in A&

Extended X-ray emission in radio galaxies: the peculiar case of 3C 305

Extended X-ray structures are common in Active Galactic Nuclei (AGNs). Here we present the first case of a Compact Steep Spectrum (CSS) radio galaxy, 3C 305, in which the X-ray radiation appears to be associated with the optical emission line region, dominated by the [O III]5007. On the basis of a morphological study, performed using the comparison between the X-rays, the optical and the radio band, we argue that the high energy emission has a thermal nature and it is not directly linked to the radio jet and hotspots of this source. Finally, we discuss the origin of the extended X-ray structure connected with the optical emission line region following two different interpretations: as due to the interaction between matter outflows and shock-heated environment gas, or as due to gas photoionized by nuclear emission.Comment: 5 pages, 2 figures, Accepted for publication in The ApJL Comments: references and affilitations correcte

Transitive X-ray spectrum and PeV gamma-ray cutoff in the M87 jet: Electron "Pevatron"

We propose a modified version of the X-ray spectral index and an intrinsic cutoff frequency of inverse Compton radiation from the brightest knot of the M87 jet, in conjunction with an application of the new conceptions of injection and diffusive shock acceleration (DSA) of electrons in magnetized filamentary plasma to the specified source. The drop of the X-ray flux density in a transitive frequency region is associated with the interplay of ordinary synchrotron cooling and weaker magnetic fields concomitant with the smaller scale filaments that allow the electron injection, while the radio-optical synchrotron continuum is dominantly established by the major electrons that are quasi-secularly bound to larger filaments. With reference to, particularly, the updated external Compton model, we demonstrate that in the Klein-Nishina regime fading inverse Comptonization, the injected electrons can be stochastically energized up to a Lorentz factor as high as $5\times 10^{10}$ in the temporal competition with diffuse synchrotron cooling; this value is larger than that attainable for a simple DSA scenario based on the resonant scattering diffusion of the gyrating electrons bound to a supposed magnetic field homogeneously pervading the entire knot. The upper limits of the photon frequency boosted via conceivable inverse Compton processes are predicted to be of the common order of $\sim 10^{30}$ Hz. The variability of the broadband spectrum is also discussed in comparison to the features of a blazar light curve. The present scenario of a peta-eV (PeV; $10^{15}$ eV) electron accelerator, the "Pevatron," might provide some guidance for exploring untrod hard X-ray and gamma-ray bands in forthcoming observations.Comment: 34 pages, 6 figures, matches version published in Ap

Adulteration of essential oils: A multitask issue for quality control. three case studies: Lavandula angustifolia mill., Citrus limon (l.) Osbeck and Melaleuca alternifolia (Maiden &amp; Betche) Cheel

The quality control of essential oils (EO) principally aims at revealing the presence of adulterations and at quantifying compounds that are limited by law by evaluating EO chemical compositions, usually in terms of the normalised relative abundance of selected markers, for comparison to reference values reported in pharmacopoeias and/or international norms. Common adulterations of EO consist of the addition of cheaper EO or synthetic materials. This adulteration can be detected by calculating the percent normalised areas of selected markers or the enantiomeric composition of chiral components. The dilution of the EO with vegetable oils is another type of adulteration. This adulteration is quite devious, as it modifies neither the qualitative composition of the resulting EO nor the marker’s normalised percentage abundance, which is no longer diagnostic, and an absolute quantitative analysis is required. This study aims at verifying the application of the two above approaches (i.e., normalised relative abundance and absolute quantitation) to detect EO adulterations, with examples involving selected commercial EO (lavender, bergamot and tea tree) adulterated with synthetic components, EO of different origin and lower economical values and heavy vegetable oils. The results show that absolute quantitation is necessary to highlight adulteration with heavy vegetable oils, providing that a reference quantitative profile is available

What do HST and Chandra tell us about the jet and the nuclear region of the radio galaxy 3C270?

The HST/STIS ultraviolet image of the FR I radio galaxy 3C270 shows the presence of a jet-like structure emerging from the position of the nucleus. This feature, which represents the first jet-like component ever detected in the UV in a radio galaxy with jets lying almost on the plane of the sky, has the same position angle as the jet in the radio and X-ray images. We propose two different scenarios for the origin of the emission: i) non-thermal synchrotron from a mildly relativistic component of the jet; ii) scattered light from the nucleus, where a BL Lac source may be hosted. Either of these pictures would have important consequences for the AGN unification schemes and for our knowledge of the jet structure. In the Chandra image a faint counter-jet is also present. From a comparative analysis of the HST images and Chandra X-ray spectrum, we find that the nucleus is only moderately obscured. The obscuring structure might well reside in the geometrically thin dark disk observed on large scales. This fits the scenario in which a standard geometrically and optically thick torus is not present in FR I radio galaxies.Comment: 13 pages, 5 figures, in press on ApJ. Revised version, the discussion has been improved according to the requests of the refere

The Jet of 3C 17 and the Use of Jet Curvature as a Diagnostic of the X-ray Emission Process

We report on the X-ray emission from the radio jet of 3C 17 from Chandra observations and compare the X-ray emission with radio maps from the VLA archive and with the optical-IR archival images from the Hubble Space Telescope. X-ray detections of two knots in the 3C 17 jet are found and both of these features have optical counterparts. We derive the spectral energy distribution for the knots in the jet and give source parameters required for the various X-ray emission models, finding that both IC/CMB and synchrotron are viable to explain the high energy emission. A curious optical feature (with no radio or X-ray counterparts) possibly associated with the 3C 17 jet is described. We also discuss the use of curved jets for the problem of identifying inverse Compton X-ray emission via scattering on CMB photons.Comment: 6 pages, 6 figure (3 in color), 4 tables, ApJ accepte