We investigate the physical properties of silicene with both staggered sublattice potential and magnetization by using Kubo formalism, the latter arises from the magnetic proximity effect by depositing Fe atoms to silicene or depositing silicene on an appropriate ferromagnetic insulator. Based on the low-energy continuum model of the system where inversion symmetry is broken, we show that the system exhibits spin half metal state when staggered sublattice potential is in the same magnitude with mean and staggered magnetization. Besides, Hall conductivity and magnetic moment are all valley dependent, so we investigate the valley Hall effect of the system further by considering magnetization exclusively. This means carriers in different valleys turning into opposite directions transverse to an in-plane electric field. At last, we prove these results by investigating Berry curvature that characterizing Hall transport, which is also valley dependent. These effects can be used to generate valley-polarized currents solely by magnetization, forming the basis for the valley-based electronics applications.
Poquita-Du, Rosa Celia; Quek, Zheng Bin Randolph; Jain, Sudhanshi Sanjeev; Schmidt-Roach, Sebastian; Tun, Karenne; Heery, Eliza C.; Chou, Loke Ming; Todd, Peter A.; Huang, Danwei(Marine Biodiversity, Springer Nature, 2019-02-21)[Article]
Coral reefs worldwide are facing multiple severe stressors leading to ecosystem degradation, but local extinctions of species are not well documented. Here, we track the diversity of Pocilloporidae Gray, 1840 coral species—many of which are known to be sensitive to environmental disturbances—on Singapore reefs through time, integrating information from taxonomically verified museum specimens, careful examination of the literature, and DNA sequences. We found that more Pocilloporidae species were detected in the past than at present. A total of five species were historically recorded under Pocillopora Lamarck, 1816; Seriatopora Lamarck, 1816; and Stylophora Schweigger, 1820. Among the five species, only Pocillopora acuta Lamarck, 1816 appears to remain on Singapore reefs. The absence of Seriatopora for over half a century and the recent losses of Stylophora and the other species of Pocillopora are likely caused by habitat loss and other stressors associated with coastal urbanization, which have been further exacerbated by recent bleaching events.
We study localization occurring during high-speed shear deformations of metals leading to the formation of shear bands. The localization instability results from the competition between Hadamard instability (caused by softening response) and the stabilizing effects of strain rate hardening. We consider a hyperbolic–parabolic system that expresses the above mechanism and construct self-similar solutions of localizing type that arise as the outcome of the above competition. The existence of self-similar solutions is turned, via a series of transformations, into a problem of constructing a heteroclinic orbit for an induced dynamical system. The dynamical system is in four dimensions but has a fast–slow structure with respect to a small parameter capturing the strength of strain rate hardening. Geometric singular perturbation theory is applied to construct the heteroclinic orbit as a transversal intersection of two invariant manifolds in the phase space.
Ternary organic solar cells (TSCs) contain a single three-component photoactive layer with a wide absorption window, which is obtained without the need for multiple stacks. Subsequently, TSCs have attracted great interest in the photovoltaics field. Through careful selection of the three (or more) active components that form the photoactive layer, all photovoltaic parameters can be simultaneously enhanced within a TSC — a strategy that has resulted in record efficiencies for single-junction solar cells. In this Review, we outline key developments in TSCs, with a focus on the central role of the third component in achieving record efficiencies. We analyse the effects of the third component on the nanomorphology of the bulk heterojunction and the photovoltaic parameters of TSCs. Moreover, we discuss the charge-transfer and/or energy-transfer mechanisms and nanomorphology models that govern the operation of TSCs. We consider both polymer and small-molecule donors as well as fullerenes and recently developed non-fullerene acceptors. In addition, we summarize the recent success of TSCs in mitigating the stability issues of binary solar cells. Finally, we provide a perspective on the advantages of ternary blends and suggest design strategies for highly efficient and stable devices for commercial photovoltaics.
Putra, Wira; Hakiki, Farizal(Journal of Petroleum Exploration and Production Technology, Springer Nature, 2019-03-05)[Article]
Microbial enhanced oil recovery (MEOR) is a method that utilises bacteria or bioproducts to increase oil recovery at the tertiary stage. Clostridium sp. produces biosurfactant that alters rock–fluid properties and increases oil detachment. The interaction between bacteria and surfactant is interesting relation to study. We revisit and develop models for biosurfactant-producing bacteria’s growth and the interfacial tension (IFT) response. The biosurfactant-producing bacteria growth model (BBG model) mimics the predator–prey interaction and the IFT response model derived from analogy. Both models form an integrated model called coupled-simultaneous model. We deliver the suitability of these models to experimental datasets by conducting parameter estimation. The decreased number of parameter in BBG model is with the help of rate estimation model. It estimates the bacteria growth rate and biosurfactant production rate. This research introduces a graphical method to narrow parameters initial guess in the IFT model. The method comes with a proposed index to compare surfactant performance called as surfactant performance index (SPI). The paper exposes the logic of each parameter, physics behind the models, and addresses the mathematical artefacts. The significant findings are valuable to anticipate bacterial performance for MEOR.
Unsaturated carbon–carbon bonds are one of the most common and important structural motifs in many organic molecules, stimulating the continuous development of general, efficient and practical strategies for their functionalization. Here, we report a one-pot difunctionalization of alkynes via a photoredox/nickel dual-catalysed three-component cross-coupling reaction under mild conditions, providing access to a series of highly important tri-substituted alkenes. Notably, in contrast to traditional methods that are based on the steric hindrance of the substrates to control the reaction selectivity, both E- and Z-isomers of tri-substituted alkenes, which are often energetically close, can be obtained by choosing an appropriate photocatalyst with a suitable triplet state energy. Beyond the immediate practicality of this transformation, this newly developed methodology might inspire the development of diverse and important one-pot functionalizations of carbon–carbon multiple bonds via photoredox and transition-metal dual-catalysed multicomponent reactions.
In the real word, temporal data can be found in many applications, and it is rapidly increasing nowadays. It is urgently important and challenging to manage and operate big temporal data efficiently and effectively, due to the large volume of big temporal data and the real-time response requirement. Processing big temporal data using a distributed system is a desired choice, since a single-machine based system usually has the limited computing ability. Nevertheless, existing distributed systems or methods either are disk-based solutions, or cannot support native queries, which may not well meet the demands of low latency and high throughput. To attack these issues, this article suggests a new approach to handle big temporal data. Our approach is an In-memory based Two-level Index Solution in Spark, dubbed as ITISS. The proposed framework of our solution is easily understood and implemented, but without loss of effectiveness and efficiency. Based on the proposed framework, this article develops targeted algorithms for handling time travel, temporal aggregation, and temporal join queries, respectively. We have implemented our framework in Apache Spark, extended the Apache Spark SQL to support declarative SQL interface that enables users to perform temporal queries with a few lines of SQL statements, and conducted extensive experiments to verify the performance of our solution. The experimental results, based on both real and synthetic datasets, consistently demonstrate that our proposed solution is efficient and competitive for processing big temporal data.
Castro, Daniela; Huser, Raphaël; Rue, Haavard(Journal of Agricultural, Biological and Environmental Statistics, Springer Nature, 2019-07-23)[Article]
Renewable sources of energy such as wind power have become a sustainable alternative to fossil fuel-based energy. However, the uncertainty and fluctuation of the wind speed derived from its intermittent nature bring a great threat to the wind power production stability, and to the wind turbines themselves. Lately, much work has been done on developing models to forecast average wind speed values, yet surprisingly little has focused on proposing models to accurately forecast extreme wind speeds, which can damage the turbines. In this work, we develop a flexible spliced Gamma-Generalized Pareto model to forecast extreme and non-extreme wind speeds simultaneously. Our model belongs to the class of latent Gaussian models, for which inference is conveniently performed based on the integrated nested Laplace approximation method. Considering a flexible additive regression structure, we propose two models for the latent linear predictor to capture the spatio-temporal dynamics of wind speeds. Our models are fast to fit and can describe both the bulk and the tail of the wind speed distribution while producing short-term extreme and non-extreme wind speed probabilistic forecasts. Supplementary materials accompanying this paper appear online.
Mollica, Nathaniel R.; Cohen, Anne L.; Alpert, Alice E.; Barkley, Hannah C.; Brainard, Russell E.; Carilli, Jessica E.; De Carlo, Thomas Mario; Drenkard, Elizabeth J.; Lohmann, Pat; Mangubhai, Sangeeta; Pietro, Kathryn R.; Rivera, Hanny E.; Rotjan, Randi D.; Scott-Buechler, Celina; Solow, Andrew R.; Young, Charles W.(Coral Reefs, Springer Nature, 2019-05-02)[Article]
Ocean warming is negatively impacting coral reef ecosystems and considerable effort is currently invested in projecting coral reef futures under 21st century climate change. A limiting factor in these projections is lack of quantitative data on the thermal thresholds of different reef communities, due in large part to spatial and temporal gaps in bleaching observations. Here we apply a coral bleaching proxy, skeletal stress bands, to reconstruct the history of bleaching on eight coral reefs in the central equatorial Pacific (CEP) and use this information to constrain the thermal thresholds of their coral communities. First, three genera of massive corals collected on both Pacific and Caribbean reefs are used to derive a calibration between the proportion of corals that form stress bands during a bleaching event, and the total observed bleaching incidence in the community of mixed coral taxa. The correlation is highly significant, indicating that stress bands in massive corals reflect community-level bleaching severity (R2 = 0.945, p < 0.001). We applied the calibration to stress band records from eight Pacific reefs, reconstructing their bleaching histories over the period 1982 to 2015. A percentile-based method of estimating thermal stress (Degree Heating Weeks) for CEP reefs was developed and applied. Comparing the level of thermal stress experienced by each coral community during each event with the reconstructed bleaching response, we characterized the thermal sensitivities of each reef community and quantified the thermal threshold (b½) at which 50% of the coral community bleached. Our analysis reveals a unique non-linear thermal response curve for each reef. The most thermally tolerant reefs in the study (Jarvis and Kanton Islands) experienced 50% bleaching at seven to nine times more thermal stress than did the least resistant reef in the study (Maiana Island). An exploration of the potential drivers of thermal tolerance revealed a strong correlation between b½ and the history of thermal stress events in each reef system. Thermal tolerance was also correlated with concentrations of dissolved inorganic nitrate in the water column and with estimates of coral energetic reserve.
We present an investigation of the dynamic behavior of an electrostatically actuated resonant structure, resonator, under the simultaneous excitation of primary and subharmonic resonances. A comprehensive analytical solution is obtained via the method of Multiple Time Scales (MTS), which is applicable for generic electrostatic loading cases. Results using different MTS scaling methods in the equations of motion and loading conditions are compared. These results are further verified against results obtained using direct time integration of the equation of motion. It is observed that for a generic parallel-plate electrostatic loading case, the direct forcing component at the excitation frequency, and the direct and parametric excitation components at double the excitation frequency must be considered for accurate prediction of the structure’s response. Further, the case of simultaneous excitations of primary and subharmonic resonance, where both excitations are of comparable strength, is examined under various electrostatic loading conditions. We show mixed behaviors of the resonator transiting from a subharmonic-dominated response, characterized by the sudden jumps in amplitude and smaller monostable regime, to primary-dominated response exhibiting gradual amplitude increase and larger monostable regimes. This transition behavior can be potentially used for applications, such as electrometers.
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