Features of the next reversal of the geomagnetic field

В статье обсуждаются возможность проявления очередной инверсии геомагнитного поля (ГМП) и его некоторые особенности. Дипольное поле (ДП) приблизится к нулевой отметке, которую достигнет примерно в 3500 году. С 1500 года, на фоне понижения ДП происходит рост октупольного и квадрупольного компонент ГМП и их суммы (О+К). ДП, согласно нашей модели геомагнетизма, после прохождения нулевой отметки начнет расти с обратным знаком и противодействовать (О+К) полю, понижая его уровень до нуля. В этот момент (≈ 6000 год) поле (N) будет иметь минимальную величину. Затем начнется рост ДП обратного значения (R). Инверсия закончится при достижении этим полем устойчивой величины. The possibility of a new reversal of the geomagnetic field (GMF) and some of its features are discussed. In 3500 the dipole field (DF) will become near zero. Since 1500, along with the decrease of DF, there has been an increase of the octupole and quadrupole components of the GMF as well as their sum (O+Q). According to our model of geomagnetism, after passing the zero the reversing DF will start its rise counteracting the (O+Q) field and lowering its value to zero. In about 6000 the total field DF+O+Q (N) will be minimum. After DF reaches a stable value the reversal will complete.

Nonlinear optical dynamics of 2D super-crystals of quantum Λ-emitters

We study theoretically the optical response of a 2D super-crystal of quantum Λ-emitters which are coupled by their secondary dipole field. The latter introduces a feedback into the system, the interplay of which with the intrinsic nonlinearity of emitters results in an exotic behavior of the system’s optical response, such as periodic or quasi-periodic self-oscillations and chaotic dynamics. We argue therefore that these predicted features can be promising for various nanophotonic applications.

Inferring core processes using stochastic models of the geodynamo

Summary Recent studies have represented time variations in the Earth’s axial magnetic dipole field as a stochastic process, which comprise both deterministic and random elements. To explore how these elements are affected by the style and vigour of convection in the core, as well as the core-mantle boundary conditions, we construct stochastic models from a set of numerical dynamo simulations at low Ekman numbers. The deterministic part of the stochastic model, the drift term, characterises the slow relaxation of the dipole back to its time-average. We find that these variations are predominantly accommodated by the slowest decay mode, enhanced by turbulent diffusion to enable a faster relaxation. The random part—the noise term—is set by the amplitude and timescale of variations in dipole field generation, including contributions from both velocity and internal magnetic field variations. Applying these interpretations to the paleomagnetic field suggest that reversal rates are very sensitive to rms variations in the field generation. Less than a 50 per cent reduction in rms field generation variations is sufficient to prevent reversals for the recent magnetic field.

Unified Mechanistic Understanding of CO2 Reduction to CO on Transition Metal and Single Atom Catalysts

<p>CO is the simplest product from CO₂ electroreduction (CO₂R), but the identity and nature of its rate limiting step remains controversial. Here we investigate the activity of both transition metals (TMs) and metal-nitrogen doped carbon catalysts (MNCs), and a present unified mechanistic picture of CO₂R to for both these classes of catalysts. By consideration of the electronic structure through a Newns-Andersen model, we find that on MNCs, like TMs, electron transfer to CO₂is facile, such that CO₂ (g) adsorption is driven by adsorbate dipole-field interactions. Using density functional theory with explicit consideration of the interfacial field, we find CO₂ * adsorption to generally be limiting on TMs, while MNCs can be limited by either CO₂* adsorption or by the proton-electron transfer reaction to form COOH*. We evaluate these computed mechanisms against pH-dependent experimental activity measurements on CO₂R to CO activity for Au, FeNC, and NiNC. We present a unified activity volcano that, in contrast to previous analyses, includes the decisive CO₂*and COOH* binding strengths as well as the critical adsorbate dipole-field interactions. We furthermore show that MNC catalysts are tunable towards higher activity away from transition metal scaling, due to the stabilization of larger dipoles resulting from their discrete and narrow <i>d</i>-states. The analysis suggests two design principles for ideal catalysts: moderate CO₂* and COOH* binding strengths as well as large dipoles on the CO₂*intermediate. We suggest that these principles can be exploited in materials with similar electronic structure to MNCs, such as supported single-atom catalysts, molecules, and nanoclusters, 2D materials, and ionic compounds towards higher CO₂R activity. This work captures the decisive impact of adsorbate dipole-field interactions in CO₂R to CO and paves the way for computational-guided design of new catalysts for this reaction.</p>

Unified Mechanistic Understanding of CO2 Reduction to CO on Transition Metal and Single Atom Catalysts

<p>CO is the simplest product from CO₂ electroreduction (CO₂R), but the identity and nature of its rate limiting step remains controversial. Here we investigate the activity of both transition metals (TMs) and metal-nitrogen doped carbon catalysts (MNCs), and a present unified mechanistic picture of CO₂R to for both these classes of catalysts. By consideration of the electronic structure through a Newns-Andersen model, we find that on MNCs, like TMs, electron transfer to CO₂is facile, such that CO₂ (g) adsorption is driven by adsorbate dipole-field interactions. Using density functional theory with explicit consideration of the interfacial field, we find CO₂ * adsorption to generally be limiting on TMs, while MNCs can be limited by either CO₂* adsorption or by the proton-electron transfer reaction to form COOH*. We evaluate these computed mechanisms against pH-dependent experimental activity measurements on CO₂R to CO activity for Au, FeNC, and NiNC. We present a unified activity volcano that, in contrast to previous analyses, includes the decisive CO₂*and COOH* binding strengths as well as the critical adsorbate dipole-field interactions. We furthermore show that MNC catalysts are tunable towards higher activity away from transition metal scaling, due to the stabilization of larger dipoles resulting from their discrete and narrow <i>d</i>-states. The analysis suggests two design principles for ideal catalysts: moderate CO₂* and COOH* binding strengths as well as large dipoles on the CO₂*intermediate. We suggest that these principles can be exploited in materials with similar electronic structure to MNCs, such as supported single-atom catalysts, molecules, and nanoclusters, 2D materials, and ionic compounds towards higher CO₂R activity. This work captures the decisive impact of adsorbate dipole-field interactions in CO₂R to CO and paves the way for computational-guided design of new catalysts for this reaction.</p>