A strategy for the design of skyrmion racetrack memories

Magnetic storage based on racetrack memory is very promising for the design of ultra-dense, low-cost and low-power storage technology. Information can be coded in a magnetic region between two domain walls or, as predicted recently, in topological magnetic objects known as skyrmions. Here, we show the technological advantages and limitations of using Bloch and Neel skyrmions manipulated by spin current generated within the ferromagnet or via the spin-Hall effect arising from a non-magnetic heavy metal underlayer. We found that the Neel skyrmion moved by the spin-Hall effect is a very promising strategy for technological implementation of the next generation of skyrmion racetrack memories (zero field, high thermal stability, and ultra-dense storage). We employed micromagnetics reinforced with an analytical formulation of skyrmion dynamics that we developed from the Thiele equation. We identified that the excitation, at high currents, of a breathing mode of the skyrmion limits the maximal velocity of the memory

The Impact of an Intense Cyclone on Short-Term Sea Ice Loss in a Fully Coupled Atmosphere-Ocean-Ice Model

AbstractArctic cyclones may be associated with periods of locally enhanced sea ice loss during the summer, and some studies have found that an intense cyclone in August 2012 resulted in a rapid sea ice retreat. This study uses a coupled atmosphere‐ocean‐ice model (Navy‐ESPC) to explore the relationship between the 2012 cyclone and short‐term sea ice melting. There are two mechanisms of cyclone‐induced melting in Navy‐ESPC: turbulent mixing of a warm layer located at 15‐ to 35‐m depth increases bottom melting and warm air advection by the strong surface winds increases surface melting. Although the rate of sea ice melt is substantially increased in association with the cyclone, this effect is confined to a relatively small region and only lasts for a few days. There is no clear signature of the cyclone on the overall Arctic sea ice extent in Navy‐ESPC

Ni Catalysts Supported Over TiO2, SiO2 and ZrO2 for the Steam Reforming of Glycerol

A 72-year-old man was admitted with one blade of a huge pair of shears in his left thorax. His hemodynamics deteriorated due to life-threatening vascular lesions. An urgent thoracotomy revealed several injuries to the intercostal vessels and left apical inferior lung lobe. The blade tip was stuck in the posterior chest wall, 2 cm adjacent to the descending aorta. The blade was removed, the lung was sutured, and the patient made a good recovery

Ni Catalysts Supported Over TiO2, SiO2 and ZrO2 for the Steam Reforming of Glycerol

Ni-based catalysts supported on TiO2, ZrO2 and SiO2 (in the form of mesoporous Santa Barbara Amorphous 15 (SBA-15) and amorphous dense nanoparticles), were employed in the steam reforming of glycerol. Each sample was prepared by liquid phase synthesis of the support followed by impregnation with the active phase and calcination at 8008C or by direct synthesis through flame pyrolysis. Many techniques have been used to assess the physical chemical properties of both the fresh and spent catalysts, such as atomic absorption, N2 adsorption/desorption, XRD, SEM, TEM, temperature-programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS), Micro-Raman and FTIR spectroscopy. The samples showed different textural, structural and morphological properties,as well as different reducibility and thermal resistance depending on the preparation method and support. Some of these properties were tightly bound to catalyst performance, in terms of H2 productivity and stability towards coking and sintering. A key parameter was the metal\u2013support interaction, which strongly depended on the preparation procedure. In particular, the stronger the interaction, the more stable the metallic Ni clusters, which in turn lead to a higher catalytic activity and stability. Surface acidity was also taken into account, in which the nature of the acid sites was differentiated (silanols, titanols or Lewis acid sites). The characterisation of the spent catalysts also allowed us to interpret the deactivation process. The formation of multi-walled nanotubes was observed for every sample, though it was only in some cases that this led to severe deactivatio

Kaolinite-based zeolites synthesis and their application in CO2 capture processes

In light of the urgent need of reducing the atmospheric CO2 emissions, the use of low-cost adsorbents, that exhibit a high affinity and CO2 adsorption capacity, is a promising method from the economic and environmental point of view to separate CO2 from the flue gas emitted from large sources of emissions like power-fueled plants. Clay minerals are low-cost raw materials with high availability all over planet and great versatility in the fields of adsorption and catalysis processes. The present study pretends to elucidate the link between the reaction conditions during the synthesis of the zeolite from kaolinite and its CO2 adsorption capacity. For that purpose, the type A zeolite was synthesized via hydrothermal process in alkaline solution using metakaolinite as a starting material. The metakaolinite was obtained by calcination of kaolinite at 600 degrees C and some parameters such as temperature and synthesis time were modified to optimize the synthesis aiming for a high CO2 adsorption capacity adsorbent. Synthesized materials were characterized by X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), N-2 adsorption-desorption at -196 degrees C and CO2 adsorption at 0 degrees C (up to 10 bars) isotherms and Nuclear Magnetic Resonance of solids (NMR). In addition, the adsorption capacity of CO2 was evaluated by means of CO2 adsorption-desorption isotherms at 25 degrees C up to atmospheric pressure. The obtained results indicated that synthesized zeolite 4A can be successfully prepared from natural kaolinite (via metakaolinization) at 100 degrees C for 48 h under alkaline conditions, showing chemical and physical properties similar to that of the commercial 4A zeolite

Antiferromagnetic interlayer exchange coupled Co₆₈B₃₂/Ir/Pt multilayers

Synthetic antiferromagnetic structures can exhibit the advantages of high velocity similarly to antiferromagnets with the additional benefit of being imaged and read-out through techniques applied to ferromagnets. Here, we explore the potential and limits of synthetic antiferromagnets to uncover ways to harness their valuable properties for applications. Two synthetic antiferromagnetic systems have been engineered and systematically investigated to provide an informed basis for creating devices with maximum potential for data storage, logic devices, and skyrmion racetrack memories. The two systems considered are (system 1) CoB/Ir/Pt of N repetitions with Ir inducing the negative coupling between the ferromagnetic layers and (system 2) two ferromagnetically coupled multilayers of CoB/Ir/Pt, coupled together antiferromagnetically with an Ir layer. From the hysteresis, it is found that system 1 shows stable antiferromagnetic interlayer exchange coupling between each magnetic layer up to N = 7. Using Kerr imaging, the two ferromagnetic multilayers in system 2 are shown to undergo separate maze-like switches during hysteresis. Both systems are also studied as a function of temperature and show different behaviors. Micromagnetic simulations predict that in both systems the skyrmion Hall angle is suppressed with the skyrmion velocity five times higher in system 1 than system 2

“Silica and zirconia supported catalysts for the low-temperature ethanol steam reforming"

Ethanol steam reforming has been investigated in the low temperature range, focusing not only on H2pro-ductivity, but also on catalyst stability, very critical parameters under such conditions. Different supports(SiO2and ZrO2), active phases (Ni, Co, Cu) and reaction temperature (300–500◦C) have been employed.Ni confirmed the best performing active phase to promote ethanol decomposition and reforming alreadyat low reaction temperature. However, stability towards coking remains a key problem. The supportplays a key role from this point of view. Indeed, the stabilization of the active phase in very dispersedform allowed to reach stable catalyst performance with time-on-stream. SiO2, thanks to no Lewis acidityand sufficiently strong metal–support interaction, demonstrated an interesting support for Ni under theselected operating condition

The peopling of the last Green Sahara revealed by high-coverage resequencing of trans-Saharan patrilineages

Little is known about the peopling of the Sahara during the Holocene climatic optimum, when the desert was replaced by a fertile environment