20,284 research outputs found
MEDUSA-2.0: an intermediate complexity biogeochemical model of the marine carbon cycle for climate change and ocean acidification studies
No full textMEDUSA-1.0 (Model of Ecosystem Dynamics, nutrient Utilisation, Sequestration and Acidification) was developed as an "intermediate complexity" plankton ecosystem model to study the biogeochemical response, and especially that of the so-called "biological pump", to anthropogenically driven change in the World Ocean (Yool et al., 2011). The base currency in this model was nitrogen from which fluxes of organic carbon, including export to the deep ocean, were calculated by invoking fixed C:N ratios in phytoplankton, zooplankton and detritus. However, due to anthropogenic activity, the atmospheric concentration of carbon dioxide (CO2) has significantly increased above its natural, inter-glacial background. As such, simulating and predicting the carbon cycle in the ocean in its entirety, including ventilation of CO2 with the atmosphere and the resulting impact of ocean acidification on marine ecosystems, requires that both organic and inorganic carbon be afforded a more complete representation in the model specification. Here, we introduce MEDUSA-2.0, an expanded successor model which includes additional state variables for dissolved inorganic carbon, alkalinity, dissolved oxygen and detritus carbon (permitting variable C:N in exported organic matter), as well as a simple benthic formulation and extended parameterizations of phytoplankton growth, calcification and detritus remineralisation. A full description of MEDUSA-2.0, including its additional functionality, is provided and a multi-decadal spin-up simulation (1860–2005) is performed. The biogeochemical performance of the model is evaluated using a diverse range of observational data, and MEDUSA-2.0 is assessed relative to comparable models using output from the Coupled Model Intercomparison Project (CMIP5)
Climate change and ocean acidification impacts on lower trophic levels and the export of organic carbon to the deep ocean
No full textMost future projections forecast significant and ongoing climate change during the 21st century, but with the severity of impacts dependent on efforts to restrain or reorganise human activity to limit carbon dioxide (CO2) emissions. A major sink for atmospheric CO2, and a key source of biological resources, the World Ocean is widely anticipated to undergo profound physical and – via ocean acidification – chemical changes as direct and indirect results of these emissions. Given strong biophysical coupling, the marine biota is also expected to experience strong changes in response to this anthropogenic forcing. Here we examine the large-scale response of ocean biogeochemistry to climate and acidification impacts during the 21st century for Representative Concentration Pathways (RCPs) 2.6 and 8.5 using an intermediate complexity global ecosystem model, MEDUSA-2.0. The primary impact of future change lies in stratification-led declines in the availability of key nutrients in surface waters, which in turn leads to a global decrease (1990s vs. 2090s) in ocean productivity (?6.3%). This impact has knock-on consequences for the abundance of the low trophic level biogeochemical actors modelled by MEDUSA-2.0 (?5.8%), and these would be expected to similarly impact higher trophic level elements such as fisheries. Related impacts are found in the flux of organic material to seafloor communities (?40.7% at 1000 m), and in the volume of ocean suboxic zones (+12.5%). A sensitivity analysis removing an acidification feedback on calcification finds that change in this process significantly impacts benthic communities, suggesting that a~better understanding of the OA-sensitivity of calcifying organisms, and their role in ballasting sinking organic carbon, may significantly improve forecasting of these ecosystems. For all processes, there is geographical variability in change – for instance, productivity declines ?21% in the Atlantic and increases +59% in the Arctic – and changes are much more pronounced under RCP 8.5 than the RCP 2.6 scenario
Multilevel conductance switching for a monolayer of redox-active metal complexes through various metallic contacts
No full textRedox-active metal complexes (e. g., Fe-II, Ru-II, and Co-II biphenylterpyridine) exhibiting multiple electroreduction behaviors show multilevel conductance switching through various metallic contacts, including Au, Pt/Ir, and reduced graphene oxide (rGO), in solid-state molecular junctions (e. g., a metal-molecule-metal junction). At Pt/Ir and Au contacts in the scanning tunneling microscopy (STM)-based junctions or Au/rGO film contacts in monolayer-based devices, current-voltage (I/V) characteristics have different energy distributions depending on the level of injection into the three electron affinity levels of the redox-active metal complexes. These metal complexes can be negatively charged when the energy levels between the Fermi levels of the metal contacts and the molecular reduction states are aligned, which strongly depends upon the molecular conductance states of conjugated ligands coordinated to central metal atoms. Multiple reduction states of redox-active metal complexes measured with solution-phase electrochemistry correspond to the multiple electron affinity levels of the solid-state molecular junctions, which suggests the possibility of multilevel molecular memory components
Impact of amorphous titanium oxide film on the device stability of Al/TiO2/Al resistive memory
No full textWe have investigated the role of amorphous titanium oxide film in the reliable bipolar resistive switching of Al/TiO2/Al resistive random access memory devices. As TiO2 deposition temperature decreased, a more stable endurance characteristic was obtained. We proposed that the degradation of the bipolar resistive switching property of Al/TiO2/Al devices is closely related to the imperfect migration of oxygen ions between the top insulating interface layer and the oxygen-deficient titanium oxide during the set and reset operations. In addition, the dependence of the TiO2 film thickness on the switching property was also studied. As the thickness of the film increased, a reduction in the resistance of the high resistance state rapidly appeared. We attribute the improved endurance performance of thin and low-temperature grown TiO2 devices to the amorphous state with a low film density
Uniform h-BN Thin Films Synthesized via PECVD at Low Temperatures for Volatile Switching CBRAM
No full textDielectric Engineering for Enhanced Top gate Monolayer MoS2 Transistor Using iCVD-based High-k Dielectric
No full text- …
