8,310 research outputs found
Synthesis and properties of Co-doped titanate nanotubes and their optical sensitization with methylene blue
Here we report on a novel chemical route to synthesize homogenous cobalt
doped titanate nanotubes (CoTNT), using an amorphous Co-doped precursor. The
influence of the synthesis temperature, autoclave dwell time and metal doping
on the structural and microstructural as well as on the optical properties of
the synthesized titanate nanotubes is studied and discussed. The optical band
gaps of the CoTNT samples are red shifted in comparison with the values
determined for the undoped samples, such red shifts bringing the absorption
edge of the CoTNT samples into the visible region. CoTNT materials also
demonstrate particular high adsorption ability for methylene blue, the amount
of the adsorbed dye being higher than the one predictable for a monolayer
formation. This suggests the possibility of intercalation of the dye molecule
between the TiO6 layers of the TNT structure. It is also shown that the
methylene blue sensitized Co-doped nanostructures are highly stable under UV
radiation and present a strong and broad absorption in the visible region.Comment: 31 pages, 3 tables, 7 figure
Primary and secondary scintillation measurements in a xenon Gas Proportional Scintillation Counter
NEXT is a new experiment to search for neutrinoless double beta decay using a
100 kg radio-pure high-pressure gaseous xenon TPC. The detector requires
excellent energy resolution, which can be achieved in a Xe TPC with
electroluminescence readout. Hamamatsu R8520-06SEL photomultipliers are good
candidates for the scintillation readout. The performance of this
photomultiplier, used as VUV photosensor in a gas proportional scintillation
counter, was investigated. Initial results for the detection of primary and
secondary scintillation produced as a result of the interaction of 5.9 keV
X-rays in gaseous xenon, at room temperature and at pressures up to 3 bar, are
presented. An energy resolution of 8.0% was obtained for secondary
scintillation produced by 5.9 keV X-rays. No significant variation of the
primary scintillation was observed for different pressures (1, 2 and 3 bar) and
for electric fields up to 0.8 V cm-1 torr-1 in the drift region, demonstrating
negligible recombination luminescence. A primary scintillation yield of 81 \pm
7 photons was obtained for 5.9 keV X-rays, corresponding to a mean energy of 72
\pm 6 eV to produce a primary scintillation photon in xenon.Comment: 16 pages, 10 figures, accepted for publication in JINS
Synthesis of sub-5 nm Co-doped SnO nanoparticles and their structural, microstructural, optical and photocatalytic properties
A swift chemical route to synthesize Co-doped SnO nanopowders is
described. Pure and highly stable SnCoO (0 x
0.15) crystalline nanoparticles were synthesized, with mean grain sizes <
5 nm and the dopant element homogeneously distributed in substitutional sites
of the SnO matrix. The UV-visible diffuse reflectance spectra of the
SnCoO samples reveal red shifts, the optical bandgap
energies decreasing with increasing Co concentration. The Urbach energies of
the samples were calculated and correlated with their bandgap energies. The
photocatalytic activity of the SnCoO samples was
investigated for the 4-hydroxylbenzoic acid (4-HBA) degradation process. A
complete photodegradation of a 10 ppm 4-HBA solution was achieved using 0.02%
(w/w) of SnCoO nanoparticles in 60 min of
irradiation.Comment: 29 pages, 2 tables, 10 figure
Dynamical instability in kicked Bose-Einstein condensates: Bogoliubov resonances
Bose-Einstein condensates subject to short pulses (`kicks') from standing
waves of light represent a nonlinear analogue of the well-known chaos paradigm,
the quantum kicked rotor. Previous studies of the onset of dynamical
instability (ie exponential proliferation of non-condensate particles)
suggested that the transition to instability might be associated with a
transition to chaos. Here we conclude instead that instability is due to
resonant driving of Bogoliubov modes. We investigate the excitation of
Bogoliubov modes for both the quantum kicked rotor (QKR) and a variant, the
double kicked rotor (QKR-2). We present an analytical model, valid in the limit
of weak impulses which correctly gives the scaling properties of the resonances
and yields good agreement with mean-field numerics.Comment: 8 page
An experimental study of gill net and trammel net 'ghost fishing' off the Algarve (southern Portugal)
Four 100 m lengths of both monofilament gill nets and trammel nets were deployed at depths between 15 and 18 m off the coast of the Algarve (south of Portugal) between April 1995 and June 1996. The nets were set on a natural rocky bottom with one end cut loose to simulate lost nets. Changes in net structure (net height, effective fishing area, movement, colonisation, wear and tear) and their catches (species, sizes, numbers, and biomass) were monitored by divers. Similar patterns were observed in all the nets, with a sharp decrease in net height and effective fishing area, and an increase in visibility within the first few weeks. Net movement was negligible except in the case of interference from other fishing gears. Catch rates were initially comparable to normally fished gill nets and trammel nets in this area, but decreased steadily over time. No sea birds, reptiles or mammals were caught in any of the 8 nets. Catches were dominated by fish (89 % by number, at least 27 species), in particular by sea breams (Sparidae) and wrasses (Labridae). Under the conditions experienced throughout the study the fishing Lifetime of a 'lost' net is between 15 and 20 wk. Based on an exponential model, we estimated that 100 m lengths of gill net and trammel net will catch 314 and 221 fish respectively over a 17 wk period. However, we consider this to be an underestimate due to high rates of predation and scavenging by octopuses, cuttlefish, moray eels, conger eels, and other fish such as the wrasse Coris julis. When the nets were surveyed in the following spring, 8 to 11 mo after being deployed, they were found to be completely destroyed or heavily colonised by algae and had become incorporated into the reef
Construction of coherent states for physical algebraic systems
We construct a general state which is an eigenvector of the annihilation
operator of the Generalized Heisenberg Algebra. We show for several systems,
which are characterized by different energy spectra, that this general state
satisfies the minimal set of conditions required to obtain Klauder's minimal
coherent states.Comment: 15 pages, 3 figure
- …