Surface spin dynamics of antiferromagnetically coupled frustrated triangular films

Results are presented for spin-wave dispersions in geometrically frustrated stacked triangular antiferromagnets with a thin film or semi-infinite geometry having either zero, easy-plane, or easy-axis anisotropy. Surface effects on the equilibrium spin configurations and excitation spectrum are investigated for the case of antiferromagnetically coupled films, serving to extend previous results on ferromagnetically coupled layers [E. Meloche et al., Phys. Rev. B 74, 094424 (2006)]. An operator equation of motion formalism is applied to systems which are quasi-one and quasi-two dimensional in character. In contrast to the case of ferromagnetically coupled films the new results show surface modes that are well separated in frequency from bulk excitations. Magnetic excitations in thin films with an even or an odd number of layers show qualitatively different behavior. These results are relevant for a wide variety of stacked triangular antiferromagnetics materials.Comment: 24 pages, 9 figure

The dynamics of soil aggregate breakdown in water in response to landuse as measured with laser diffraction technique

The Mastersizer 2000G (Malvern Instruments) Diffraction Instrument was used to assess and quantify the breakdown of soil aggregates and compute wet aggregate stability indices. The study was aimed at evolving a novel rapid method of determining soil aggregate stability. Bulk surface (0-15 cm) soil samples were collected under 5 different land uses in the Teaching and Resrach Farm of Obafemi Awolowo University, Ile-Ife, Nigeria. About 0.5g of the soils aggregates (0.5 -1 mm diameter) were evaluated in the laser diffractometer with the stirrer operated at 500 rpm and the pump at 1800 rpm. The different size aggregates and particles of sand silt and clay were quantified periodically. Water stable aggregates greater than 250 m (WSA>250), water stable aggregates less than 250 m (WSA<250), water dispersible clay index (WDI), and mean volume diameter (MVD) among others were computed from the laser diffraction data. The values were compared with the classical Yoder wet sieving technique. The WSA>250 was significantly higher on the soils under Forest (FR), Cacao (CC), Teak (TK) and Oil Palm (OP) plantations, while it was significantly lowest under no-tillage (NT) and continuous cultivation (CT). The pasture (PD) was not significantly different from either the cultivated and the non-cultivated soils. Conversely, the WSA<250 and water dispersible clay index was highest in the cultivated soils (CT and NT) and lowest in the non-cultivated soils (FR, TK, CC and OP) while the PD was in-between. The MVD also followed a similar trend as the WSA>250. The wet sieving water stable aggregates index (WSI>250) was significantly correlated with WSA>250 (r = 0.75), MVD (r = 0.75), WDI (r = -0.68) and WSA<250 (r = - 0.73). All the laser diffraction measured aggregation indices were significantly correlated with the organic matter contents of the soils. Thus the laser diffraction promises a rapid and comprehensive method of evaluation of soil aggregate stability

Two-stage capacity optimization approach of multi-energy system considering its optimal operation

With the depletion of fossil fuel and climate change, multi-energy systems have attracted widespread attention in buildings. Multi-energy systems, fuelled by renewable energy, including solar and biomass energy, are gaining increasing adoption in commercial buildings. Most of previous capacity design approaches are formulated based upon conventional operating schedules, which result in inappropriate design capacities and ineffective operating schedules of the multi-energy system. Therefore, a two-stage capacity optimization approach is proposed for the multi-energy system with its optimal operating schedule taken into consideration. To demonstrate the effectiveness of the proposed capacity optimization approach, it is tested on a renewable energy fuelled multi-energy system in a commercial building. The primary energy devices of the multi-energy system consist of biomass gasification-based power generation unit, heat recovery unit, heat exchanger, absorption chiller, electric chiller, biomass boiler, building integrated photovoltaic and photovoltaic thermal hybrid solar collector. The variable efficiency owing to weather condition and part-load operation is also considered. Genetic algorithm is adopted to determine the optimal design capacity and operating capacity of energy devices for the first-stage and second-stage optimization, respectively. The two optimization stages are interrelated; thus, the optimal design and operation of the multi-energy system can be obtained simultaneously and effectively. With the adoption of the proposed novel capacity optimization approach, there is a 14% reduction of year-round biomass consumption compared to one with the conventional capacity design approach

Benchmarks for energy access: Policy vagueness and incoherence as barriers to sustainable electrification of the global south

© 2019 The unavailability of tangible policy benchmarks continues to mitigate against sustainable electrification in the global south. Furthermore, incoherent policy benchmarks as to what should constitute clean energy allow for varying interpretations and divergent options in electrifying households across the global south. The multiplicity of policies to deepen access to improved energy services in the global south notwithstanding, ‘success’ is not in sight until definite and uniform benchmarks guide the roll-out of electrification schemes

GEOPHYSICAL EVALUATION OF THE GROUNDWATER POTENTIAL AND AQUIFER PROTECTIVE CAPACITY IN PART OF OYE-EKITI, SOUTHWESTERN NIGERIA

Assessment of groundwater potential and aquifer protective capacity in part of Oye-Ekiti, Southwestern Nigeria using the electrical resistivity method of geophysical prospecting was carried out. The study involved Vertical Electrical Sounding (VES) technique using the Schlumberger array with current electrode spacing (AB/2) of 100 m. Thirty-one (31) VES locations were obtained with the aid of ABEM SAS 300 Resistivity Meter and plotted on the double log graph as VES curves. The VES curves were interpreted quantitatively by partialcurve matching and assisted by 1-D forward modeling using the WinResist software. The VES interpretation results (layer and thickness) were used to generate maps of the study area. A, K, H, KH, HA, QH, AA, HKH, KQH and AKH-type curves were identified in the area. The overburden thickness ranged from thick (20 to 28 m), moderate (10 to 19.9 m) to low overburden (0 to 9.9 m). The bedrock relief shows areas of moderate/high (530.1 to 558 m) and low reliefs (514 to 530m).&nbsp

Bot Canker Pathogens Could Complicate the Management of \u3ci\u3ePhytophthora\u3c/i\u3e Black Pod of Cocoa

Black pod is a major hindrance to cocoa production in Nigeria. It is caused by three different Phytophthora species with Phytophthora megakarya as the most important species in Nigeria and West African subregion. Phytophthora spp. may enhance infections by opportunistic pathogens such as members of the Botryosphaeriacea that cause branch and trunk cankers in many woody plants across the world. Botryosphaeriacea has not been reported in cocoa nor in any woody plants in Nigeria to our knowledge. In the cocoa belt of Nigeria, research and understanding on cocoa black pod and Phytophthora is limited partly because of delayed or no access to some culture media, including required antibiotics. The objectives of this study were to: (1) use locally available materials to develop media for Phytophthora isolation from infected cocoa trees and pods samples and (2) to determine if members of Botryosphaeriaceae are associated with cankers of cocoa trees infected with black pod in Ondo State. The two formulated media, clarified tomato juice agar and cocoa pod agar supported the growth of Phytophthora spp. and were used for isolation from five cocoa- producing local government areas, spanning all three senatorial districts of Ondo State. Based on morphological characteristics, four different species of Botryosphaeriaceae were identified from infected cocoa trees/pods but also from citrus and kola trees, which are similar to cocoa and usually planted in the same orchard with cocoa in Nigeria. These findings of new pathogens in cocoa and other hosts in Ondo State indicated the need for new strategies in the management of cocoa diseases in the State and across cocoa-producing areas of Nigeria

X-Ray Scattering at FeCo(001) Surfaces and the Crossover between Ordinary and Normal Transitions

In a recent experiment by Krimmel et al. [PRL 78, 3880 (1997)], the critical behavior of FeCo near a (001) surface was studied by x-ray scattering. Here the experimental data are reanalyzed, taking into account recent theoretical results on order-parameter profiles in the crossover regime between ordinary and normal transitions. Excellent agreement between theoretical expectations and the experimental results is found.Comment: 9 pages, Latex, 1 PostScript figure, to be published in Phys.Rev.

Comparative study of machine learning-based multi-objective prediction framework for multiple building energy loads

Buildings are one of the significant sources of energy consumption and greenhouse gas emission in urban areas all over the world. Lighting control and building integrated photovoltaic (BIPV) are two effective measures in reducing overall primary energy consumption and carbon emission during building operation. Due to the complex energy nature of the building, accurate day-ahead prediction of heating, cooling, lighting loads and BIPV electrical power production is essential in building energy management. Owing to the changing metrological conditions, diversity and complexity of buildings, building energy load demands and BIPV electrical power production is highly variable. This may lead to poor building energy management, extra primary energy consumption or thermal discomfort. In this study, three machine learning-based multi-objective prediction frameworks are proposed for simultaneous prediction of multiple energy loads. The three machine learning techniques are artificial neural network, support vector regression and long-short-term-memory neural network. Since heating, cooling, lighting loads and BIPV electrical power production share similar affecting factors, it is computational time saving to adopt the proposed multi-objective prediction framework to predict multiple building energy loads and BIPV power production. The ANN-based predictive model results in the smallest mean absolute percentage error while SVM-based one cost the shortest computation time

Potential of Indigenous Vegetable-Fortified Food Products for Improved Human Nutrition and Health in West Africa

The study developed and tested the acceptability of key innovative value-added products, including vegetable-fortified bread and pastry products (cookies and chinchin), using each of these three indigenous vegetables, namely Telfairia occidentalis Hook. F. (fluted pumpkin), Amaranthus virdis L. (local amaranth), and Solanum macrocarpon L. (eggplant). The bread was fortified with each of the individual dried leafy vegetables at levels of 1%, 3%, and 5%. Ogi was also fortified with the equivalent of the dried Telfaria occidentalis in the wet form at 1%, 3%, and 5%, while pastry was fortified with the only extract obtained from amaranth leafy vegetable at 1%, 3%, and 5%. Results from the MicroVeg project showed that bread fortified with 3% (w/w) dried vegetable leaf powders had higher nutritional properties. Pastry formulations that included 3% dried vegetable leaf powders had slightly lower consumer acceptability in terms of taste and color; however, due to the associated potential health benefits, consumers were willing to buy the vegetable-fortified products as replacements for the regular products. This chapter discusses the full details of the nutrition and value addition aspects of MicroVeg with empirical examples of the interventions and the potential contributions to dietary diversity and enhanced family nutrition