251 research outputs found
Anisotropic critical currents in FeSe0.5Te0.5 films and the influence of neutron irradiation
We report on measurements of the superconducting properties of FeSe05Te05
thin films grown on lanthanum aluminate. The films have high transition
temperatures (above 19 K) and sharp resistive transitions in fields up to 15 T.
The temperature dependence of the upper critical field and the irreversibility
lines are steep and anisotropic, as recently reported for single crystals. The
critical current densities, assessed by magnetization measurements in a vector
VSM, were found to be well above 10^9 Am-2 at low temperatures. In all samples,
the critical current as a function of field orientation has a maximum, when the
field is oriented parallel to the film surface. The maximum indicates the
presence of correlated pinning centers. A minimum occurs in three films, when
the field is applied perpendicular to the film plane. In the forth film,
instead, a local maximum caused by c-axis correlated pinning centers was found
at this orientation. The irradiation of two films with fast neutrons did not
change the properties drastically, where a maximum enhancement of the critical
current by a factor of two was found
Microscopic analysis of the chemical reaction between Fe(Te,Se) thin films and underlying CaF
To understand the chemical reaction at the interface of materials, we
performed a transmission electron microscopy (TEM) observation in four types of
Fe(Te,Se) superconducting thin films prepared on different types of substrates:
CaF2 substrate, CaF2 substrate with a CaF2 buffer layer, CaF2 substrate with a
FeSe buffer layer, and a LaAlO3 substrate with a CaF2 buffer layer. Based on
the energy-dispersive X-ray spectrometer (EDX) analysis, we found possible
interdiffusion between fluorine and selenium that has a strong influence on the
superconductivity in Fe(Te,Se) films. The chemical interdiffusion also plays a
significant role in the variation of the lattice parameters. The lattice
parameters of the Fe(Te,Se) thin films are primarily determined by the chemical
substitution of anions, and the lattice mismatch only plays a secondary role.Comment: 30 pages, 9 figur
Impact of upstream landslide on perialpine lake ecosystem: An assessment using multi-temporal satellite data
Monitoring freshwater and wetland systems and their response to stressors of natural or anthropogenic origin is critical for ecosystem conservation. A multi-temporal set of 87 images, acquired by Sentinel-2 satellites over three years (2016–2018), provided quantitative information for assessing the temporal evolution of key ecosystem variables in the perialpine Lake Mezzola (northern Italy), which has suffered from the impacts of a massive landslide that took place upstream of the lake basin in summer 2017. Sentinel-2 derived products revealed an increase in lake turbidity triggered by the landslide that amounted to twice the average values scored in the years preceding and following the event. Hotspots of turbidity within the lake were in particular highlighted. Moreover, both submerged and riparian vegetation showed harmful impacts due to sediment deposition. A partial loss of submerged macrophyte cover was found, with delayed growth and a possible community shift in favor of species adapted to inorganic substrates. Satellite-derived seasonal dynamics showed that exceptional sediment load can overwrite climatic factors in controlling phenology of riparian reed beds, resulting in two consecutive years with shorter than normal growing season and roughly 20% drop in productivity, according to spectral proxies. Compared to 2016, senescence came earlier by around 20 days on average in 2017 season, and green-up was delayed by up to 50 days (20 days, on average) in 2018, following the landslide. The approach presented could be easily implemented for continuous monitoring of similar ecosystems subject to external pressures with periods of high sediment loads
Demography of the bottlenose dolphin Tursiops truncatus (Mammalia: Delphinidae) in the Eastern Ligurian Sea (NW Mediterranean): quantification of female reproductive parameters
AbstractThe reproductive histories of 41 adult bottlenose dolphin females were analysed using photo-identification data collected between 2006 and 2014 in four sub-areas of the eastern Ligurian Sea (northwest Mediterranean). The Rapallo sub-area revealed the highest (highly significant) frequency of encounters (per unit effort) of reproductive females in association with young individuals, therefore emerging as a candidate nursery area in the region. The estimated fertility rate of adult females ranged between 290 and 407 births per 1000 individuals per year, higher than that of other known bottlenose dolphin populations, with a calving interval between 2.45 and 3.5 years. These results will be useful for projecting future trends of this (sub)population
Epitaxial MgB2 thin films on ZrB2 buffer layers: structural characterization by synchrotron radiation
Structural and superconducting properties of magnesium diboride thin films
grown by pulsed laser deposition on zirconium diboride buffer layers were
studied. We demonstrate that the ZrB2 layer is compatible with the MgB2 two
step deposition process. Synchrotron radiation measurements, in particular
anomalous diffraction measurements, allowed to separate MgB2 peaks from ZrB2
ones and revealed that both layers have a single in plane orientation with a
sharp interface between them. Moreover, the buffer layer avoids oxygen
contamination from the sapphire substrate. The critical temperature of this
film is near 37.6 K and the upper critical field measured at Grenoble High
Magnetic Field Laboratory up to 20.3 T is comparable with the highest ones
reported in literature.Comment: 14 pages, 8 figures, submitted to Supercond. Sci. and Techno
Impact of polystyrene nanoparticles on marine diatom Skeletonema marinoi chain assemblages and consequences on their ecological role in marine ecosystems.
Marine diatoms have been identified among the most abundant taxa of microorganisms associated with plastic waste collected at sea. However, the impact of nano-sized plastic fragments (nanoplastics) at single cell and population level is almost unknown. We exposed the marine diatom Skeletonema marinoi to model polystyrene nanoparticles with carboxylic acid groups (PS-COOH NPs, 90 nm) for 15 days (1, 10, 50 mu g/mL). Growth, reactive oxygen species (ROS) production, and nano-bio-interactions were investigated. No effect on diatom growth was observed, however Dynamic light scattering (DLS) demonstrated the formation of large PS aggregates which were localized at the diatoms' fultoportula process (FPP), as shown by TEM images. Increase production of ROS and reduction in chain length were also observed upon PS NPs exposure (p < 0.005). The observed PS-diatom interaction could have serious consequences on diatoms ecological role on the biogeochemical cycle of carbon, by impairing the formation of fast-sinking aggregates responsible for atmospheric carbon fixation and sequestration in the ocean sea floor. S. marinoi exposure to PS NPs caused an increase of intracellular and extracellular oxidative stress, the reduction of diatom's chain length and the adhesion of PS NPs onto the algal surface
Growth methods of c-axis oriented MgB2 thin films by pulsed laser deposition
High quality MgB2 thin films have been obtained by pulsed laser deposition
both on MgO and on Al2O3 substrates using different methods. In the standard
two-step procedure, an amorphous precursor layer is deposited at room
temperature starting both from stoichiometric target and from boron target:
after this first step, it is annealed in magnesium atmosphere in order to
crystallize the superconducting phase. The so obtained films show a strong
c-axis orientation, evidenced by XRD analysis, a critical temperature up to 38
K and very high critical fields along the basal planes, up to 22T at 15K. Also
an in situ one step technique for the realization of superconducting MgB2 thin
films has been developed. In this case, the presence of an argon buffer gas
during deposition is crucial and we observe a strong dependence of the quality
of the deposited film on the background gas pressure. The influence of the Ar
atmosphere has been confirmed by time and space-resolved spectroscopy
measurements on the emission spectrum of the plume. The Ar pressure modifies
strongly the plasma kinetics by promoting excitation and ionization of the
plume species, especially of the most volatile Mg atoms, increasing their
internal energy.Comment: Paper presented at Boromag Workshop, Genoa 17-19 June 2002, in press
on SUS
In-situ Magnesium Diboride Superconducting Thin Films grown by Pulsed Laser Deposition
Superconducting thin films of MgB2 were deposited by Pulsed Laser Deposition
on magnesium oxide and sapphire substrates. Samples grown at 450C in an argon
buffer pressure of about 10-2 mbar by using a magnesium enriched target
resulted to be superconducting with a transition temperature of about 25 K.
Film deposited from a MgB2 sintered pellet target in ultra high vacuum
conditions showed poor metallic or weak semiconducting behavior and they became
superconducting only after an ex-situ annealing in Mg vapor atmosphere. Up to
now, no difference in the superconducting properties of the films obtained by
these two procedures has been evidenced.Comment: 10 pages, 4 figure
New Fe-based superconductors: properties relevant for applications
Less than two years after the discovery of high temperature superconductivity
in oxypnictide LaFeAs(O,F) several families of superconductors based on Fe
layers (1111, 122, 11, 111) are available. They share several characteristics
with cuprate superconductors that compromise easy applications, such as the
layered structure, the small coherence length, and unconventional pairing, On
the other hand the Fe-based superconductors have metallic parent compounds, and
their electronic anisotropy is generally smaller and does not strongly depend
on the level of doping, the supposed order parameter symmetry is s wave, thus
in principle not so detrimental to current transmission across grain
boundaries. From the application point of view, the main efforts are still
devoted to investigate the superconducting properties, to distinguish intrinsic
from extrinsic behaviours and to compare the different families in order to
identify which one is the fittest for the quest for better and more practical
superconductors. The 1111 family shows the highest Tc, huge but also the most
anisotropic upper critical field and in-field, fan-shaped resistive transitions
reminiscent of those of cuprates, while the 122 family is much less anisotropic
with sharper resistive transitions as in low temperature superconductors, but
with about half the Tc of the 1111 compounds. An overview of the main
superconducting properties relevant to applications will be presented. Upper
critical field, electronic anisotropy parameter, intragranular and
intergranular critical current density will be discussed and compared, where
possible, across the Fe-based superconductor families
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