252 research outputs found
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 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 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; 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 & 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
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