18 research outputs found
Effect of Reducing Atmosphere on the Magnetism of Zn1-xCoxO Nanoparticles
We report the crystal structure and magnetic properties of Zn1-xCoxO
nanoparticles synthesized by heating metal acetates in organic solvent. The
nanoparticles were crystallized in wurtzite ZnO structure after annealing in
air and in a forming gas (Ar95%+H5%). The X-ray diffraction and X-ray
photoemission spectroscopy (XPS) data for different Co content show clear
evidence for the Co+2 ions in tetrahedral symmetry, indicating the substitution
of Co+2 in ZnO lattice. However samples with x=0.08 and higher cobalt content
also indicate the presence of Co metal clusters. Only those samples annealed in
the reducing atmosphere of the forming gas, and that showed the presence of
oxygen vacancies, exhibited ferromagnetism at room temperature. The air
annealed samples remained non-magnetic down to 77K. The essential ingredient in
achieving room temperature ferromagnetism in these Zn1-xCoxO nanoparticles was
found to be the presence of additional carriers generated by the presence of
the oxygen vacancies.Comment: 11 pages, 6 figures, submitted to Nanotechnology IO
Construction, assembly and tests of the ATLAS electromagnetic end-cap calorimeters
The construction and the assembly of the two end-caps of the ATLAS liquid argon electromagnetic calorimeter as well as their test and qualification programs are described. The work described here started at the beginning of 2001 and lasted for approximately three years. The results of the qualification tests performed before installation in the LHC ATLAS pit are given. The detectors are now installed in the ATLAS cavern, full of liquid argon and being commissioned. The complete detectors coverage is powered with high voltage and readout
Study of in the vicinity of
Using 2917 of data accumulated at 3.773~,
44.5~ of data accumulated at 3.65~ and data accumulated
during a line-shape scan with the BESIII detector, the reaction
is studied considering a possible interference
between resonant and continuum amplitudes. The cross section of
,
, is found to have two
solutions, determined to be () pb with the phase angle
(0.11 pb at the 90% confidence level),
or ) pb with both of which
agree with a destructive interference. Using the obtained cross section of
, the cross section of , which is useful information for the future PANDA experiment, is
estimated to be either () nb ( nb at 90% C.L.) or
nb
Pb<sup>2+</sup>âCalcite Interactions under Far-from-Equilibrium Conditions: Formation of Micropyramids and Pseudomorphic Growth of Cerussite
The
presence of impurity ions is known to significantly influence
mineral surface morphology during crystal growth from aqueous solution,
but knowledge on impurity ionâmineral interactions during dissolution
under far-from-equilibrium conditions remains limited. Here we show
that calcite (CaCO<sub>3</sub>) exhibits a rich array of dissolution
features in acidic Pb-bearing solutions. During the initial stage,
calcite exhibits nonclassical surface features characterized as micropyramids
that developed spontaneously. Subsequent pseudomorphic growth of cerussite
(PbCO<sub>3</sub>) was observed, where nucleation occurred entirely
within a pore space created by dissolution at the calcite/substrate
interface. Uneven growth rates yielded a cerussite shell made of lath-
or dendritic-shaped crystals. The cerussite phase was separated from
the calcite by pores of less than 200 nm under transmission X-ray
microscopy, consistent with the interface-coupled dissolutionâprecipitation
mechanism. These results show that impurity metal ions exert significant
control over the microscale dissolution features found on mineral
surfaces and provide new insights into interpreting and designing
microstructures observed in natural and synthetic carbonate minerals
by dissolution. In addition, heterogeneous microenvironments created
in transport limited reactions in pore spaces may lead to unusual
growth forms during crystal nucleation and precipitation
Lipid production in batch and fed-batch cultures of <it>Rhodosporidium toruloides</it> from 5 and 6 carbon carbohydrates
<p>Abstract</p> <p>Background</p> <p>Microbial lipids are a potential source of bio- or renewable diesel and the red yeast <it>Rhodosporidium toruloides</it> is interesting not only because it can accumulate over 50% of its dry biomass as lipid, but also because it utilises both five and six carbon carbohydrates, which are present in plant biomass hydrolysates.</p> <p>Methods</p> <p><it>R. toruloides</it> was grown in batch and fed-batch cultures in 0.5 L bioreactors at pH 4 in chemically defined, nitrogen restricted (C/N 40 to 100) media containing glucose, xylose, arabinose, or all three carbohydrates as carbon source. Lipid was extracted from the biomass using chloroform-methanol, measured gravimetrically and analysed by GC.</p> <p>Results</p> <p>Lipid production was most efficient with glucose (up to 25 g lipid L<sup>â1</sup>, 48 to 75% lipid in the biomass, at up to 0.21 g lipid L<sup>â1</sup> h<sup>â1</sup>) as the sole carbon source, but high lipid concentrations were also produced from xylose (36 to 45% lipid in biomass). Lipid production was low (15â19% lipid in biomass) with arabinose as sole carbon source and was lower than expected (30% lipid in biomass) when glucose, xylose and arabinose were provided simultaneously. The presence of arabinose and/or xylose in the medium increased the proportion of palmitic and linoleic acid and reduced the proportion of oleic acid in the fatty acids, compared to glucose-grown cells.</p> <p>High cell densities were obtained in both batch (37 gâL<sup>â1</sup>, with 49% lipid in the biomass) and fed-batch (35 to 47 gâL<sup>â1</sup>, with 50 to 75% lipid in the biomass) cultures. The highest proportion of lipid in the biomass was observed in cultures given nitrogen during the batch phase but none with the feed. However, carbohydrate consumption was incomplete when the feed did not contain nitrogen and the highest total lipid and best substrate consumption were observed in cultures which received a constant low nitrogen supply.</p> <p>Conclusions</p> <p>Lipid production in <it>R. toruloides</it> was lower from arabinose and mixed carbohydrates than from glucose or xylose. Although high biomass and lipid production were achieved in both batch and fed-batch cultures with glucose as carbon source, for lipid production from mixtures of carbohydrates fed-batch cultivation was preferable. Constant feeding was better than intermittent feeding. The feeding strategy did not affect the relative proportion of different fatty acids in the lipid, but the presence of C5 sugars did.</p
Search for emission of gamma-ray bursts with the ARGO-YBJ detector
The ARGO-YBJ experiment has been designed to decrease the energy threshold of tipical Extensive Air Shower arrays by exploiting the high altitude location (Tibet P.R. China, 4300 m a.s..l.) and the full coverage. The lower energy limit of the detector (a few GeV) is reached with the single particle technique, recording the counting rate at fixed time intervals. We present the first results concerning the search for emission from Gamma-Ray Bursts in coincidence with satellite detections
First results on the angular resolution of the ARGO-YBJ detector
We present the first results on the angular resolution of the ARGO-YBJ detector
in data taking at the Yangbajing Laboratory (Tibet, P.R. China, 4300 m a.s.l.)
Status of the ARGO-YBJ experiment
The ARGO-YBJ experiment, under construction at the Yangbaijing Laboratory (P.R.
China, 4300 m a.s.l.), is a full coverage detector of dimension 74ÂŁ78 m2 made by a single layer
of Resistive Plate Counters. About 10% of the final active area (» 700 m2) is in stable operation
to check the detector performance and the reconstruction algorithms. In this paper the status of the
experiment and the analysis of the first data are presented
Very High Energy Gamma Ray Astronomy and Cosmic Ray Physics with the ARGO-YBJ experiment
Gamma ray astronomy at energies 1011 1013 eV, which are strictly related to the identication and study of the cosmic ray acceleration sites, is the main scientic goal of the ARGO-YBJ experiment. The detector, which is now being assembled in Tibet (China) at 4300 m a.s.l., is a full coverage Extensive Air Shower array consisting of a carpet of Resistive Plate Chambers covering a surface of about 7000 m2. The high altitude ( atmospheric depth 600 g/cm2 ) and the full coverage ensure a very low primary photon energy threshold at few hundreds GeV (close to the limits of the satellite technology), while the detector time resolution st 1ns gives a good pointing accuracy, thus allowing a high sensitivity to g -ray sources. Moreover the large eld of view and the high duty-cycle ensure the continuous monitoring of the sky in the declination band 20 d 80 . The detector layout, performance and location, offer a unique possibility to make also a deep study of several characteristics of the hadronic component of the cosmic ray ux up to energies of hundreds of TeV. In particular, the structure of the shower core, the lateral distribution, the energy spectra and the angular (e.g. anisotropies) and time (e.g. solar ares) ux modulations can be measured with high sensitivity. Moreover, the use of a full coverage detector with a high space granularity gives detailed images of the shower front, that can be used to test different hypotheses on the cosmic ray interactions, the shower development in the atmosphere and particle physics at very high energies. In this work the general layout of the detector and its performance will be described, together with some of the rst results coming from the data analysis of a relevant fraction of the apparatus that is already operating