36,101 research outputs found
Electrodeposition of copper from mixed sulphateâchloride acidic electrolytes at rotating disc electrode
The effect of chloride ion on the deposition of copper from low metal concentrations in aqueous, acid sulphate solutions was investigated. The electrolytes contained 0·05 mol dm?3 CuSO4 and 0·5 mol dm?3 Na2SO4 at pH 2 and 296 K. The chloride ion concentration was varied in a wide range from 0·03 to 2·0 mol dm?3. Linear sweep voltammetry was carried out under well defined flow conditions at a smooth platinum rotating disc electrode. The progressive transition from a single, two-electron reaction for the reduction of Cu(II)?Cu(0) to two, single-electron reactions for the reduction sequence: Cu(II)?Cu(I)?Cu(0) was clearly evident as the chloride ion concentration increased. The charge transfer and mass transport characteristics of these reactions were evaluated. The formal potential for the Cu II) reduction to Cu(I), the shift in the potential region for complete mass transport controlled reduction of Cu(I) to Cu(0) and the potential for hydrogen evolution at the deposited copper were also studied. A semi-logarithmic relationship between exchange current density and half-wave potential for Cu(II)?Cu(I) with chloride ion was achieved when the Cl?/Cu(II) ratio in the electrolytes exceeded 2, due to the presence of the Cu(I) dichlorocuprous anion, CuCl2?
Deep-inelastic Electron-Photon Scattering at High Q^2 : Neutral and Charged Current Reactions
We present the results of a calculation of deep inelastic electron-photon
scattering at a linear collider for very high virtuality of the intermediate
gauge boson up to NLO in perturbative QCD. The real photon is produced
unpolarized via the Compton back scattering of laser light of the incoming
beam. For values close to the masses squared of the Z and W gauge bosons,
the deep inelastic electron-photon scattering process receives important
contributions not only from virtual photon exchange but also from the exchange
of a Z-boson and a W-boson. We find that the total cross section for center of
mass energies above is at least of and has an
important charged current contribution.Comment: Talk given at the International Conference on the Structure and
Interactions of the Photon, PHOTON 99, Freiburg im Breisgau, Germany, May
23-27, 1999. To be published in the Proceedings. 6 pages, 6 postscript
figures. The complete paper, including figures, is also available via
anonymous ftp at ftp://ttpux2.physik.uni-karlsruhe.de/ttp99/ttp99-30/ or via
www at http://www-ttp.physik.uni-karlsruhe.de/Preprints
The infrared environments of masers associated with star formation
The near infrared (1-2um) and the thermal infrared (3-25um) trace many of the
environments in which masers are thought to reside, including shocks, outflows,
accretion disks, and the dense medium near protostars. After a number of recent
surveys it has been found that there is a higher detection rate of mid-IR
emission towards masers than cm radio continuum emission from UC HII regions,
and that the mid-IR emission is actually more closely cospatial to the maser
locations. A high percentage of water and methanol masers that are not
coincident with the UC HII regions in massive star forming regions are likely
to be tracing outflows and extremely young high mass stars before the onset of
the UC HII region phase. After a decade of groundwork supporting the hypothesis
that linarly distributed class II methanol masers may generally trace accretion
disks around young massive stars, compelling evidence is mounting that these
masers may generally be associated with outflows instead. Substantiation of
this claim comes from recent outflow surveys and high angular resolution mid-IR
imaging of the maser environments.Comment: 8 pages, 2 figures, to appear in the proceedings of IAUS 242
"Astrophysical Masers and Their Environments", eds. J. Chapman & W. Baan. A
version with higher resolution is available at
http://www.ctio.noao.edu/~debuize
Oxidation of the borohydride Ion at silver nanoparticles on a glassy carbon electrode (GCE) using pulsed potential techniques
Direct oxidation borohydride fuel cells are very attractive energy conversion devices. Silver has been reported as one of the few materials which can catalyze an 8-electron oxidation. Potential step amperometric pulse techniques to synthesize nanostructured silver material on flat glassy carbon electrodes is reported and significant differences with bulk silver deposit have been observed. The oxidation of borohydride ion on the silver particles occurs at -0.025 V vs. SCE and the potential decreases towards negative values at longer cycle times. The oxidation current also decreases with the number of cycles, suggesting that the silver active sites become partially blocked by oxidation products of borohydride. The electroactive area per unit electrode area of silver was relatively low for particles deposited using potential step amperometric techniques on glassy carbon (0.002 cm2 per cm-2) compared with the area found at a polycrystalline silver electrode (0.103 cm2 per cm-2
Embedded Stellar Populations towards Young Massive Star Formation Regions I. G305.2+0.2
We present deep, wide-field J, H and Ks images taken with IRIS2 on the Anglo
Australian Telescope, towards the massive star formation region G305.2+0.2.
Combined with 3.6, 4.5, 5.8 and 8.0 micron data from the GLIMPSE survey on the
Spitzer Space Telescope, we investigate the properties of the embedded stellar
populations. After removing contamination from foreground stars we separate the
sources based on their IR colour. Strong extended emission in the GLIMPSE
images hampers investigation of the most embedded sources towards the known
sites of massive star formation. However, we find a sizeable population of IR
excess sources in the surrounding region free from these completeness effects.
Investigation reveals the recent star formation activity in the region is more
widespread than previously known.
Stellar density plots show the embedded cluster in the region, G305.24+0.204,
is offset from the dust emission. We discuss the effect of this cluster on the
surrounding area and argue it may have played a role in triggering sites of
star formation within the region. Finally, we investigate the distribution of
IR excess sources towards the cluster, in particular their apparent lack
towards the centre compared with its immediate environs.Comment: 16 pages, 16 figures (significantly size reduced), 2 tables, accepted
MNRA
Radio Observations of New Galactic Bulge Planetary Nebulae
We observed 64 newly identified galactic bulge planetary nebulae in the radio
continuum at 3 and 6 cm with the Australia Telescope Compact Array. We present
their radio images, positions, flux densities, and angular sizes. The survey
appears to have detected a larger ratio of more extended planetary nebulae with
low surface brightness than in previous surveys. We calculated their distances
according to Van de Steene & Zijlstra (1995). We find that most of the new
sample is located on the near side around the galactic center and closer in
than the previously known bulge PNe. Based on H-alpha images and spectroscopic
data, we calculated the total H-alpha flux. We compare this flux value with the
radio flux density and derive the extinction. We confirm that the distribution
of the extinction values around the galactic center rises toward the center, as
expected.Comment: accepted for publication in A&
MRK 1216 & NGC 1277 - An orbit-based dynamical analysis of compact, high velocity dispersion galaxies
We present a dynamical analysis to infer the structural parameters and
properties of the two nearby, compact, high velocity dispersion galaxies
MRK1216 & NGC1277. Combining deep HST imaging, wide-field IFU stellar
kinematics, and complementary long-slit spectroscopic data out to 3 R_e, we
construct orbit-based models to constrain their black hole masses, dark matter
content and stellar mass-to-light ratios. We obtain a black hole mass of
log(Mbh/Msun) = 10.1(+0.1/-0.2) for NGC1277 and an upper limit of log(Mbh/Msun)
= 10.0 for MRK1216, within 99.7 per cent confidence. The stellar mass-to-light
ratios span a range of Upsilon_V = 6.5(+1.5/-1.5) in NGC1277 and Upsilon_H =
1.8(+0.5/-0.8) in MRK1216 and are in good agreement with SSP models of a single
power-law Salpeter IMF. Even though our models do not place strong constraints
on the dark halo parameters, they suggest that dark matter is a necessary
ingredient in MRK1216, with a dark matter contribution of 22(+30/-20) per cent
to the total mass budget within 1 R_e. NGC1277, on the other hand, can be
reproduced without the need for a dark halo, and a maximal dark matter fraction
of 13 per cent within the same radial extent. In addition, we investigate the
orbital structures of both galaxies, which are rotationally supported and
consistent with photometric multi-S\'ersic decompositions, indicating that
these compact objects do not host classical, non-rotating bulges formed during
recent (z <= 2) dissipative events or through violent relaxation. Finally, both
MRK 1216 and NGC 1277 are anisotropic, with a global anisotropy parameter delta
of 0.33 and 0.58, respectively. While MRK 1216 follows the trend of
fast-rotating, oblate galaxies with a flattened velocity dispersion tensor in
the meridional plane of the order of beta_z = delta, NGC 1277 is highly
tangentially anisotropic and seems to belong kinematically to a distinct class
of objects.Comment: 27 pages, 15 figures and 4 tables. Accepted for publication in MNRA
A Farm-Level Evaluation of Conditions Under Which Farmers Will Supply Biomass Feedstocks for Energy Production
This study evaluated the risk management potential of including biomass crops as a diversification strategy for a grain farm in northwest Tennessee. Results indicate that adding biomass crops to the farm enterprise mix could improve mean net revenues and reduced net revenue variability.Resource /Energy Economics and Policy,
The 3D printing of a polymeric electrochemical cell body and its characterisation
An undivided flow cell was designed and constructed using additive manufacturing technology and its mass transport characteristics were evaluated using the reduction of ferricyanide, hexacyanoferrate (III) ions at a nickel surface. The dimensionless mass transfer correlation Sh = aRebScdLee was obtained using the convective-diffusion limiting current observed in linear sweep voltammetry; this correlation compared closely with that reported in the literature from traditionally machined plane parallel rectangular flow channel reactors. The ability of 3D printer technology, aided by computational graphics, to rapidly and conveniently design, manufacture and re-design the geometrical characteristics of the flow cell ishighlighted
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