Observation of magnetic droplets in magnetic tunnel junctions

Magnetic droplets, a class of highly nonlinear magnetodynamic solitons, can be nucleated and stabilized in nanocontact spin-torque nano-oscillators. Here we experimentally demonstrate magnetic droplets in magnetic tunnel junctions (MTJs). The droplet nucleation is accompanied by power enhancement compared with its ferromagnetic resonance modes. The nucleation and stabilization of droplets are ascribed to the double-CoFeB free-layer structure in the all-perpendicular MTJ, which provides a low Zhang-Li torque and a high pinning field. Our results enable better electrical sensitivity in fundamental studies of droplets and show that the droplets can be utilized in MTJ-based applications and materials science.

Strategies of Sino-American Rivalry in Africa: From 2000 to COVID-19

In this article it is argued that Sino-American rivalry in Africa is based on competing strategies utilized by each power to enhance their interests and bilateral ties on the continent, as well to try and outdo each other in image projection and overall influence expansion. These strategies of rivalry and power enhancement revolve around promoting close military ties and transactions on the continent; the framing of the continent in the language of securitization and strategic importance; and the perennial utilization of discourse or narrative that frames the other as detrimental to the interests of African states. These strategies of containing the others power preponderance or influence have expanded to include what is now referred to as vaccine diplomacy on the part of China, and during the Trump Administration the raising of loud alarm bells of China trying to dispossess Africa through what could be referred to as the debt trap. The consequences of these competing strategies enhance the following: authoritarianism in some key African states; increased jihadism in some regions of Africa as a reaction to the presence of the two major powers on the continent; weapons implicated in state violence and war crimes; and less money available for development as a result of resources being diverted to militarization. The ongoing pandemic will add another dimension to the US - China rivalry as both powers try to project an image of being the most concerned about Africa on as it relates to combating the virus.

Grey Wolf Optimizer-Based Array Reconfiguration to Enhance Power Production from Solar Photovoltaic Plants under Different Scenarios

The extraction of maximum power is a big challenge in solar photovoltaic-based power plants due to varying atmospheric and meteorological parameters. The concept of array reconfiguration is applied for the maximum power extraction in solar PV plants. Using this approach, the occurrence of multiple peaks in P-V and I-V characteristics during partial shade can be smoothened and reduced significantly. Partial shading due to the movement of the cloud is considered in the research. The cloud movement mainly because of velocity and wind direction is used for creating various shading conditions. The main focus is to reduce the power losses during partial shading using a nature-inspired optimization approach to reconfigure the array for different types of shading conditions. A grey wolf optimizer-based bridge-linked total cross-tied (GWO-BLTCT) configuration is proposed in this paper. The performance of the proposed topology is compared with standard and hybrid topologies, namely, series-parallel, total cross-tied, BLTCT, and SuDoKu-BLTCT, based on performance indicators such as fill factor, performance ratio, power enhancement, and power loss. The proposed GWO-BLTCT outperforms the remaining topologies due to the least power loss and high fill factor. It also has the highest average power enhancement and performance ratio with 23.75% and 70.02% respectively.

Optimization of a Novel Hybrid Wind Bio Battery Solar Photovoltaic System Integrated with Phase Change Material

The intermittent nature of renewable sources, such as solar and wind, leads to the need for a hybrid renewable energy system (HRES) that can provide uninterrupted and reliable energy to a remote and off-grid location with the use of a biogas generator and battery. In the present study, conventional PV panels have been integrated with phase change material (PCM) for power enhancement. In addition, various configurations (i. PV-Wind-Battery system, ii. PV-PCM-Wind-Battery, iii. PV-Wind-Biogas-Battery and iv. PV-PCM-Wind-Biogas-Battery) have been compared for the hot and humid climatic location of Chennai, India. Optimization has been carried out to minimize the cost of energy and the net present cost has also been computed. It has been found that the integration of PCM with the PV-Wind-Biogas-Battery-based off-grid system results in savings of USD 0.22 million in terms of net present cost and reduces the cost of energy from USD 0.099/kWh to USD 0.094/kWh. Similarly, for another off-grid HRES configuration of PV-Wind-Battery, the integration of PCM results in savings of USD 0.17 million, and reduces the cost of energy from USD 0.12/kWh to USD 0.105/kWh.