3,346 research outputs found
Technetium nitrido-peroxo complexes: An unexplored class of coordination compounds
The purpose of this work was to further expand the chemistry of mixed technetium nitrido-peroxo complexes, a still poorly explored class of compounds containing the Tc(VII) moiety, [99gTc][Tc(N)(O2)2]. A number of novel complexes of the formula [99gTc][Tc(N)(O2)2(L)] with bidentate ligands (L) (where L = deprotonated alanine, glycine, proline) were prepared by reacting a solution of nitrido-technetic(VI) acid with L in the presence of a source of H2O2. Alternatively, the complex [99gTc][Tc(N)(O2)2X]- (X = Cl, Br) was used as a precursor for substitution reactions where the halogenide ion was replaced by the bidentate ligand. The new complexes were characterized by elemental analysis and mass spectroscopy. The preparation of the analogous [99mTc][Tc(N)(O2)2] moiety, radiolabeled with the metastable isomer Tc-99m, was also studied at a no-carrier-added level, using S-methyl-N-methyl-dithiocarbazate as the donor of the nitrido nitrogen atoms
Deep near-infrared imaging of W3 Main: constraints on stellar cluster formation
Embedded clusters like W3 Main are complex and dynamically evolving systems
that represent an important phase of the star formation process. We aim at the
characterization of the entire stellar content of W3 Main in a statistical
sense to identify possible differences in evolutionary phase of the stellar
populations and find clues about the formation mechanism of this massive
embedded cluster. Methods. Deep JHKs imaging is used to derive the disk
fraction, Ks-band luminosity functions and mass functions for several
subregions in W3 Main. A two dimensional completeness analysis using artificial
star experiments is applied as a crucial ingredient to assess realistic
completeness limits for our photometry. We find an overall disk fraction of 7.7
2.3%, radially varying from 9.4 3.0 % in the central 1 pc to 5.6
2.2 % in the outer parts of W3 Main. The mass functions derived for three
subregions are consistent with a Kroupa and Chabrier mass function. The mass
function of IRSN3 is complete down to 0.14 Msun and shows a break at M
0.5 Msun. We interpret the higher disk fraction in the center as evidence for a
younger age of the cluster center. We find that the evolutionary sequence
observed in the low-mass stellar population is consistent with the observed age
spread among the massive stars. An analysis of the mass function variations
does not show evidence for mass segregation. W3 Main is currently still
actively forming stars, showing that the ionizing feedback of OB stars is
confined to small areas ( 0.5 pc). The FUV feedback might be influencing
large regions of the cluster as suggested by the low overall disk fraction.Comment: 15 pages, 13 figures, accepted by A&
Reanalysis of the FEROS observations of HIP 11952
Aims. We reanalyze FEROS observations of the star HIP 11952 to reassess the
existence of the proposed planetary system. Methods. The radial velocity of the
spectra were measured by cross-correlating the observed spectrum with a
synthetic template. We also analyzed a large dataset of FEROS and HARPS
archival data of the calibrator HD 10700 spanning over more than five years. We
compared the barycentric velocities computed by the FEROS and HARPS pipelines.
Results. The barycentric correction of the FEROS-DRS pipeline was found to be
inaccurate and to introduce an artificial one-year period with a semi-amplitude
of 62 m/s. Thus the reanalysis of the FEROS data does not support the existence
of planets around HIP 11952.Comment: 7 pages, 8 figures, 1 tabl
Innovative nanomaterials for fuel cells fed with biogas
Challenges on sustainability promote research policy focused on renewable-energy technology development in order to enhance global energy security, local energy independence, environmental protection and economic growth. Biomass resources offer renewable energies that can play a key role in the current global strategies for reducing greenhouse gas emissions by partially replacing fossil fuels. The conversion of biomass chemical energy into electrical energy and cogenerated heat can be obtained by fuel cells. In particular, molten carbonate fuel cell (MCFC)
is the most suitable device for bioenergy production because it can be fed directly with biogas, whose primary constituents all improve the performance of the cell.
However hydrogen sulfide, which is the main biogas impurity, poisons the traditional nickel based anode, affecting the power and the endurance of the cell. In order to overcome this problem, an innovative anode material that resists against the sulfide corrosions has been developed. This material, made of a nanostructured and porous nickel support covered with a thin layer of ceria, exhibits high sulfur tolerance and recovering capability
Stars in the Hubble Ultra Deep Field
We identified 46 unresolved source candidates in the Hubble Ultra Deep Field,
down to i775 = 29.5. Unresolved objects were identified using a parameter S,
which measures the deviation from the curve-of-growth of a point source.
Extensive testing of this parameter was carried out, including the effects of
decreasing signal-to-noise and of the apparent motions of stars, which
demonstrated that stars brighter than i775 = 27.0 could be robustly identified.
Low resolution grism spectra of the 28 objects brighter than i775 = 27.0
identify 18 M and later stellar type dwarfs, 2 candidate L-dwarfs, 2 QSOs, and
4 white dwarfs. Using the observed population of dwarfs with spectral type M4
or later, we derive a Galactic disk scale height of 400 \pm 100 pc for M and L
stars. The local white dwarf density is computed to be as high as (1.1 \pm 0.3)
x10^(-2) stars/pc^3. Based on observations taken 73 days apart, we determined
that no object in the field has a proper motion larger than 0.027"/year (3
sigma detection limit). No high velocity white dwarfs were identified in the
HUDF, and all four candidates appear more likely to be part of the Galactic
thick disk. The lack of detected halo white dwarfs implies that, if the dark
matter halo is 12 Gyr old, white dwarfs account for less than 10% of the dark
matter halo mass.Comment: 35 pages, 11 figures, accepted by Ap
Innovative nanomaterials for fuel cells fed with biogas
Challenges on sustainability promote research policy focused on renewable-energy technology development in order to enhance global energy security, local energy independence, environmental protection and economic growth. Biomass resources offer renewable energies that can play a key role in the current global strategies for reducing greenhouse gas emissions by partially replacing fossil fuels. The conversion of biomass chemical energy into electrical energy and cogenerated heat can be obtained by fuel cells. In particular, molten carbonate fuel cell (MCFC)
is the most suitable device for bioenergy production because it can be fed directly with biogas, whose primary constituents all improve the performance of the cell.
However hydrogen sulfide, which is the main biogas impurity, poisons the traditional nickel based anode, affecting the power and the endurance of the cell. In order to overcome this problem, an innovative anode material that resists against the sulfide corrosions has been developed. This material, made of a nanostructured and porous nickel support covered with a thin layer of ceria, exhibits high sulfur tolerance and recovering capability
Particle and light fragment emission in peripheral heavy ion collisions at Fermi energies
A systematic investigation of the average multiplicities of light charged
particles and intermediate mass fragments emitted in peripheral and
semiperipheral collisions is presented as a function of the beam energy,
violence of the collision and mass of the system.
The data have been collected with the "Fiasco" setup in the reactions
93Nb+93Nb at 17, 23, 30, 38AMeV and 116Sn+116Sn at 30, 38AMeV.
The midvelocity emission has been separated from the emission of the
projectile-like fragment. This last component appears to be compatible with an
evaporation from an equilibrated source at normal density, as described by the
statistical code Gemini at the appropriate excitation energy.
On the contrary, the midvelocity emission presents remarkable differences for
what concerns both the dependence of the multiplicities on the energy deposited
in the midvelocity region and the isotopic composition of the emitted light
charged particles.Comment: 18 pages, 17 figures, Revtex
Morphology and evolution of emission line galaxies in the Hubble Ultra Deep Field
We investigate the properties and evolution of a sample of galaxies selected
to have prominent emission lines in low-resolution grism spectra of the Hubble
Ultra Deep Field (HUDF). These objects, eGRAPES, are late type blue galaxies,
characterized by small proper sizes (R_50 < 2 kpc) in the 4350A rest-frame, low
masses (5x10^9 M_sun), and a wide range of luminosities and surface
brightnesses. The masses, sizes and volume densities of these objects appear to
change very little up to a redshift of z=1.5. On the other hand, their surface
brightness decreases significantly from z=1.5 to z=0 while their mass-to-light
ratio increases two-folds. This could be a sign that most of low redshift
eGRAPES have an older stellar population than high redshift eGRAPES and hence
that most eGRAPES formed at higher redshifts. The average volume density of
eGRAPES is (1.8 \pm 0.3)x10^{-3} Mpc^{-3} between 0.3 < z < 1.5. Many eGRAPES
would formally have been classified as Luminous Compact Blue Galaxies (LCBGs)
if these had been selected based on small physical size, blue intrinsic color,
and high surface brightness, while the remainder of the sample discussed in
this paper forms an extension of LCBGs towards fainter luminosities.Comment: Accepted, to appear in Ap
Internal Kinematics of Luminous Compact Blue Galaxies
We describe the dynamical properties which may be inferred from HST/STIS
spectroscopic observations of luminous compact blue galaxies (LCBGs) between
0.1<z<0.7. While the sample is homogeneous in blue rest-frame color, small size
and line-width, and high surface-brightness, their detailed morphology is
eclectic. Here we determine the amplitude of rotation versus random, or
disturbed motions of the ionized gas. This information affirms the accuracy of
dynamical mass and M/L estimates from Keck integrated line-widths, and hence
also the predictions of the photometric fading of these unusual galaxies. The
resolved kinematics indicates this small subset of LCBGs are dynamically hot,
and unlikely to be embedded in disk systems.Comment: To appear in "Starbursts: from 30 Doradus to Lyman Break Galaxies"
2005, eds. R. de Grijs and R. M. Gonzalez Delgado (Kluwer
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