Ultrafast signatures of spin and orbital order in antiferromagnetic α-Sr2CrO4

We used femtosecond optical spectroscopy to study ultrafast spin and orbital ordering dynamics in the antiferromagnetic Mott insulator α-Sr2CrO4. This chromate system possesses multiple spin and orbital ordered phases, and therefore could enable us to study the unique interplay between these collective phases through their non-equilibrium response to photoexcitation. Here, by varying the pump photon energy, we selectively drove inter-site spin hopping between neighboring Cr t2g orbitals and charge transfer-type transitions between oxygen 2p and Cr eg orbitals. The resulting transient reflectivity dynamics revealed temperature-dependent anomalies across the Neel temperature for spin ordering as well as the transition temperatures linked to different types of orbital order. Our results reveal distinct relaxation timescales for spin and orbital orders in α-Sr2CrO4 and provide experimental evidence for the phase transition at TO, possibly related to antiferro-type orbital ordering.

Unlocking coherent control of ultrafast plasmonic interaction

Striking a metallic nanostructure with a short and intense pulse of light excites a complex out-of-equilibrium distribution of electrons that rapidly interact and lose their mutual coherent motion. Due to the highly nonlinear dynamics, the photo-excited nanostructures may further emit energetic photons beyond the spectrum of the incident beam, where the shortest pulse duration is traditionally expected to induce the greatest nonlinear emission. Here, we coherently control these photo-induced extreme ultrafast dynamics by spectrally shaping a sub-10 fs pulse within the timescale of coherent plasmon excitations. Contrary to the common perception, we show that stretching the pulse to match its internal phase with the plasmon-resonance increases the second-order nonlinear emission by > 25%. The enhancement is observed only when shaping extreme-ultrashort pulses (< 20 fs), thus signifying the coherent electronic nature as a crucial source of the effect. We provide a detailed theoretical framework that reveals the optimal pulse shapes for enhanced nonlinear emission regarding the nanostructures’ plasmonic-resonances. The demonstrated truly-coherent plasma control paves the way to engineer rapid out-of-equilibrium response in solids state systems and light-harvesting applications.

An Analytical Spectral Model for Infragravity Waves over Topography in Intermediate and Shallow Water under Non-breaking Conditions

The theoretical model for group-forced infragravity (IG) waves in shallow water is not well established for non-breaking conditions. In the present study, analytical solutions of the group-forced IG waves at (, hx =bottom slope, Δk =group wavenumber, h =depth) in intermediate water and at in shallow water are derived separately. In case of off-resonance (, where is the resonant departure parameter, cg = group speed) in intermediate water, additional IG waves in quadrature with the wave group forcing (hereinafter as the non-equilibrium response or component) are induced at relative to the equilibrium bound IG wave solution of Longuet-Higgins and Stewart (1962) in phase with the wave group. The present theory indicates that the non-equilibrium response is mainly attributed to the spatial variation of the equilibrium bound IG wave amplitude instead of group-forcing. In case of near-resonance () in shallow water, however, both the equilibrium and non-equilibrium components are at the leading order. Based on the nearly-resonant solution, the shallow water limit of the local shoaling rate of bound IG waves over a plane sloping beach is derived to be ~ h−1 for the first time. The theoretical predictions compare favorably with the laboratory experiment by Van Noorloos (2003) and the present numerical model results using SWASH. Based on the proposed solution, the group-forced IG waves over a symmetric shoal are investigated. In case of off-resonance, the solution predicts a roughly symmetric reversible spatial evolution of the IG wave amplitude, while in cases of near- to full- resonance the IG wave is significantly amplified over the shoal with asymmetric irreversible spatial evolution.

Surface-response functions obtained from equilibrium electron-density profiles

Surface-response functions are one of the most promising routes for bridging the gap between fully quantum-mechanical calculations and phenomenological models in quantum nanoplasmonics. Among all currently available recipes for obtaining such response functions, the use of ab initio methods remains one of the most conspicuous trends, wherein the surface-response functions are retrieved via the metal’s non-equilibrium response to an external time-dependent perturbation. Here, we present a complementary approach to approximate one of the most appealing surface-response functions, namely the Feibelman d-parameters, yield a finite contribution even when they are calculated solely with the equilibrium properties of the metal, described under the local-response approximation (LRA) but with a spatially varying equilibrium electron density, as input. Using model calculations that mimic both spill-in and spill-out of the equilibrium electron density, we show that the obtained d-parameters are in qualitative agreement with more elaborate, but also more computationally demanding, ab initio methods. The analytical work presented here illustrates how microscopic surface-response functions can emerge out of entirely local electrodynamic considerations.

Ancient warming pushed wetlands across biogeochemical tipping points

&lt;p&gt;Ancient peat deposits provide valuable and complementary insight into the biogeochemical response of wetlands to climate perturbations, including potential tipping points in such systems. The combination of temperature (GDGTs) and hydrology (leaf wax hydrogen isotopic compositions) proxies with qualitative proxies for methanogenesis (archaeal lipid abundances) and methanotrophy (bacterial lipid carbon isotopic compositions) has revealed dramatic perturbations to the carbon cycle during transient warming events, including the Palaeocene Eocene Thermal Maximum.&amp;#160; Bacterially-derived hopanes in at least two PETM-spanning lignite sequences record negative carbon isotope excursions of near-unprecedented magnitude in response to rapid global warming.&amp;#160; The warming &amp;#8211; either directly or indirectly &amp;#8211; clearly caused a fundamental reorganisation of the carbon cycle in those ancient wetlands. Intriguingly however, these excursions persist for a far shorter duration than the PETM warming. Similarly, hopane &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C values in lignites of the Early Eocene Climate Optimum, the warmth of which was reached more gradually, are similar to those of today. This suggests that these unusually isoptopically light hopanoids represent a transient disruption to the methane cycle associated with a climate perturbation rather than an equilibrium response to warmer temperatures.&amp;#160; Such an interpretation is consistent with Deglacial and Holocene peat-derived records, in which hopane &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C values exhibit large responses to transient drying events and modest responses to longer-term change. Such findings could have implications for future climate change feedbacks, with the wetland methane cycle being particularly sensitive to the rate of climatic change.&lt;/p&gt;

Adult zebrafish anaesthesia: a study of efficacy and behavioural recovery of different anaesthetics

The use of proper anaesthesia in zebrafish research is essential to ensure fish welfare and data reliability. However, anaesthesia long-term side effects remain poorly understood. The purpose of this study was to assess anaesthesia quality and recovery in adult zebrafish using different anaesthetic protocols and to determine possible long-term effects on the fish activity and anxiety-like behaviours after anaesthesia.Mixed sex adult AB zebrafish were randomly assigned to 5 different groups (control, 175mg/L MS222, 45 mg/L clove oil, 2 mg/L etomidate and 5mg/L propofol combined with 150mg/L lidocaine) and placed in the respective anaesthetic bath. Time to lose the equilibrium, response to touch and to tail pinch stimuli, and recovery after anaesthesia administration were evaluated. In addition, after stopping anaesthesia, respiratory rate, activity and anxiety-like behaviours in the novel tank test were studied.Overall, all protocols proved to be adequate for zebrafish anaesthesia research as they showed full recovery at 1h, and only etomidate had minor effects on fish behaviour in the novel tank, a validated test for anxiety.

Non-equilibrium response and slow equilibration in hard disk systems

The relaxation from a non-equilibrium state to the equilibrium depends on the methodologies and initial conditions. To investigate the microscopic mechanisms of equilibration systematically, we focus on the non-equilibrium response during the equilibration process induced by a disturbance of the homogeneous expansion of the simple hard disk systems. Large scale simulations by event-driven molecular dynamics revealed that an anomalous slow equilibration toward the liquid states emerges when starting from the co-existence phase. The origin of the slow decay mechanism is investigated using the probability distribution of local density and orientational order parameter.Their inhomogeneities seem to cause the anomalous slow equilibration.

Time Scales and Mechanisms for the Tropical Pacific Response to Global Warming: A Tug of War between the Ocean Thermostat and Weaker Walker

Different oceanic and atmospheric mechanisms have been proposed to describe the response of the tropical Pacific to global warming, yet large uncertainties persist on their relative importance and potential interaction. Here, we use idealized experiments forced with a wide range of both abrupt and gradual CO2 increases in a coupled climate model (CESM) together with a simplified box model to explore the interaction between, and time scales of, different mechanisms driving Walker circulation changes. We find a robust transient response to CO2 forcing across all simulations, lasting between 20 and 100 years, depending on how abruptly the system is perturbed. This initial response is characterized by the strengthening of the Indo-Pacific zonal SST gradient and a westward shift of the Walker cell. In contrast, the equilibrium response, emerging after 50–100 years, is characterized by a warmer cold tongue, reduced zonal winds, and a weaker Walker cell. The magnitude of the equilibrium response in the fully coupled model is set primarily by enhanced extratropical warming and weaker oceanic subtropical cells, reducing the supply of cold water to equatorial upwelling. In contrast, in the slab ocean simulations, the weakening of the Walker cell is more modest and driven by differential evaporative cooling along the equator. The “weaker Walker” mechanism implied by atmospheric energetics is also observed for the midtroposphere vertical velocity, but its surface manifestation is not robust. Correctly diagnosing the balance between these transient and equilibrium responses will improve understanding of ongoing and future climate change in the tropical Pacific.

Decentralized Supply Chains under Random Price-Dependent Demand: Noncooperative Equilibria vs. Coordination with Cost-Sharing Contracts

It is common for a supplier to sell products to multiple retailers. In this paper, we investigate the equilibrium behavior of a decentralized supply chain with multiple retailers facing a random price-dependent demand in the additive form. Here, we consider two kinds of demand functions: the distribution of the demand depends only on the retailer’s own retail price (noncompeting retailers) and not only on his own retail price but also on that of the other retailers (competing retailers). We present appropriate wholesale price, buy-back, and lost-sales cost-sharing contracts to coordinate the total supply chain, so that when all the retailers adopt their equilibrium response, the supply chain system coordination is also achieved. Furthermore, the coalition formation among retailers is also analyzed. We find that with buy-back and lost-sales cost-sharing contracts and linear price-dependent demand function, retailers always prefer being in the grand coalition to forming any other coalition.

A Stackelberg-population competition model via variational inequalities and fixed points

In this paper, we introduce and study a new Stackelberg-population competition model which captures the desired features of both population games and Stackelberg competition model within the same framework. We obtain some characterization results for the Stackelberg-population equilibrium response set and the Stackelberg-population equilibrium leader set by using the variational inequality technique and Brouwer’s fixed point theorem. We also show an existence theorem of Nash equilibrium for Stackelbergpopulation competition model under some mild conditions. Finally, we give an example to illustrate our main results.