Search results for "C lo"
showing 10 items of 794 documents
Improve the dielectric properties of PrSrNi0.8Mn0.2O4 compounds by longer mechanical milling
2018
Abstract Structural and dielectric properties of PrSrNi 0.8 Mn 0.2 O 4 ceramics elaborated by a rapid method combining mechanical milling and heat treatment were studied for the first time. The raw materials are milled at different times ( t mil = 0, 5, 10, 20 and 30 h) and annealed at 1300 °C for 8 h to produce a revealed PrSrNi 0.8 Mn 0.2 O 4 single phase, exhibiting tetragonal structure with space group I 4/ mmm . This result was confirmed by using the TEM/ED pattern for sample milled at 30 h using the [001] orientation. The corresponding lattice images show a well-ordered compound, indicating the absence of stacking faults and the growth of the crystallites. Giant dielectric response …
Enhancement of the dielectric response through Al-substitution in La1.6Sr0.4NiO4 nickelates
2016
The structures and dielectric properties of La1.6Sr0.4Ni1−xAlxO4 (x = 0, 0.2 and 0.4) ceramics elaborated using the Pechini method were studied for the first time. The same unique tetragonal phase was found in all compounds. The lattice parameters were found using Rietveld refinement. The surface morphology characterization and elemental analysis of these samples were respectively carried out using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). A giant dielectric response was observed in these ceramics, and one dielectric relaxation was found. The substitution of nickel with aluminum results in a colossal dielectric constant value (>106). The dielectric l…
Microwave properties and structure of La–Ti–Si–B–O glass-ceramics for applications in GHz electronics
2017
Abstract A dielectric bulk glass-ceramic of the La 2 O 3 –TiO 2 –SiO 2 –B 2 O 3 system is developed which is able to fulfill the requirements for dielectric loading-based mobile communication technologies. It is shown that the given dielectric requirements can be fulfilled by glass-ceramic materials without being dependent on ceramic processing techniques. The material exhibited permittivity values of 20 ɛ r Qf τ f τ f material with a Qf value of 9500 GHz and ɛ r = 21.4 could be achieved at a ceramming temperature T cer = 870 °C. The material is aimed to provide an alternative to existing, commercially used sintered ceramic materials. Further focus is laid on the investigation of the dom…
Domain Walls Motions in Barium Titanate Ceramics
1996
The shear modulus and mechanical loss at low frequencies (0.01, 0.3, 1 Hz) are measured by an inverted pendulum for BaTiO 3 ceramic with large grain sizes. The permittivity and dielectric losses are also investigated for the same material at higher frequencies between 1 and 100 kHz as function of temperature. Those results show several relaxation peaks in the ferroelectric phases. The activation energy of each peak is obtained to be 0.29, 0.45, 0.68, 0.92 eV. The influences of strain amplitude and thermal treatments are studied specially for the mechanical relaxation peak located in the tetragonal phase. All the relaxation peaks could be associated to the interaction of oxygen vacancies in …
Switching by Domain-Wall Automotion in Asymmetric Ferromagnetic Rings
2017
A ring-shaped magnetic logic device offers two vortex states (clockwise and counterclockwise) to encode bits, with relative stability against external magnetic fields. The dynamics of magnetization switching in such structures, though, still need unraveling. The authors present direct experimental visualization of reproducible, robust switching in magnetic rings via domain-wall automotion, which does not require an applied field. Simulations reveal that annihilation of domain walls through automotion always occurs, with the detailed topology of the walls only influencing the dynamics locally, in line with the experimental results.
Pharmaceuticals and other urban contaminants threaten Amazonian freshwater ecosystems
2021
Abstract Urban areas in the Brazilian Amazon have grown at an unprecedented rate during the last years. About 90% of the wastewater produced by these urban areas are discharged untreated into Amazonian freshwater ecosystems, constituting a potential environmental pathway for pharmaceuticals and other chemicals consumed by modern societies (e.g. psychostimulants, personal-care products, hormones). The distribution of these chemicals into the Amazon River and their potential risks for freshwater biodiversity have not been evaluated so far. Here, we show the results of the largest chemical monitoring campaign conducted in the Amazon region. We assessed exposure patterns for 43 pharmaceuticals …
Modelling Regional Air Quality in the Canadian Arctic: Simulation of an Arctic Summer Field Campaign
2017
Model simulations of an Arctic summer field campaign were carried out. The model results were compared with observational data from both ground-based monitoring and in situ measurements on-board multiple mobile platforms. The model was able to well capture regional sources and transport affecting the Arctic air quality. It is shown that the study area was impacted by North American (NA) regional biomass burning emissions. The model-observation comparison also corroborates previous findings on possible roles of marine-biogenic sources in aerosol production in the Arctic MBL during summertime.
Ocean Acidification and the End-Permian Mass Extinction: To What Extent does Evidence Support Hypothesis?
2012
International audience; Ocean acidification in modern oceans is linked to rapid increase in atmospheric CO 2 , raising concern about marine diversity, food security and ecosystem services. Proxy evidence for acidification during past crises may help predict future change, but three issues limit confidence of comparisons between modern and ancient ocean acidification, illustrated from the end-Permian extinction, 252 million years ago: (1) problems with evidence for ocean acidification preserved in sedimentary rocks, where proposed marine dissolution surfaces may be subaerial. Sedimentary evidence that the extinction was partly due to ocean acidification is therefore inconclusive; (2) Fossils…
Numerical evidence for thermohaline circulation reversals during the Maastrichtian
2005
[1] The sensitivity of the Maastrichtian thermohaline circulation to the opening/closing of marine communications between the Arctic and North Pacific oceans is investigated through a set of numerical experiments using the model CLIMBER-2 (Earth Model of Intermediate Complexity). We show here that the opening or closing of an Arctic-Pacific marine gateway induces transitions between different equilibrium states of the thermohaline circulation. Sensitivity tests of the inferred modes of thermohaline circulation to atmospheric CO2 level changes have also been explored. An abrupt switch in deep convection from high northern to high southern latitudes, a change consistent with isotopic evidence…
Transient metazoan reefs in the aftermath of the end-Permian mass extinction
2011
5 pages; International audience; Recovery from the devastating Permian-Triassic mass extinction about 252 million years ago is usually assumed to have spanned the entire 5 million years of the Early Triassic epoch1,2. The post-crisis interval was characterized by large-scale fluctuations of the global carbon cycle and harsh marine conditions, including a combination of ocean acidification, euxinia, and fluctuating productivity3. During this interval, metazoan-dominated reefs are thought to have been replaced by microbial deposits that are considered the hallmark of the Early Triassic4-7. Here we use field and microscopic investigations to document Early Triassic bioaccumulations and reefs f…