Local Dynamical Processes Research Articles

A case study on more recent heat wave occurred in South Africa, based on background weather synoptic and dynamic characteristics analysis

This study investigates the characteristics of the more recent heat wave episode in South Africa during January 2023. The evaluation of several meteorological parameters using different reanalysis models and observational datasets have demonstrated that the domination of the anticyclonic pattern over the study area associated with a omega-blocking high. The dominant subtropical Botswana subtropical high along with the low-level omega blocking high pressure over South Africa is one of the main factors for the abnormally hot weather event. The upper-level anomaly wind analysis illustrates the weakening of the zonal wind accompanied by the Rossby waves meridionally stretching. Also, this is correlated to abnormal both tropical easterly and southern westerly jets meandering around an omega-blocking pattern weather system over South Africa which causes warm air mass trapping over the study region. The outcome model results prove the anomalies of the surface higher temperature happened close to the center of the blocking high, where an intensified southward shift of the easterly tropical jet along with the northward shift (jet entrance) of an intensified westerly jet formed two strong cores creating confluent. This research also shows that the January heat wave is demonstrated by an anomalous upper tropospheric anticyclonic inflow (southern hemisphere) causing the strong subsidence, resulting in the surface temperature increase. In comparison with the heat wave event in January 2016, the current study displays the high impact of the internal and local dynamical processes. Also, the current case study addressed in drier condition with less health risk than the previous case study noticed in 2016.

Convection-permitting climate models offer more certain extreme rainfall projections

Extreme precipitation events lead to dramatic impacts on society and the situation will worsen under climate change. Decision-makers need reliable estimates of future changes as a basis for effective adaptation strategies, but projections at local scale from regional climate models (RCMs) are highly uncertain. Here we exploit the km-scale convection-permitting multi-model (CPM) ensemble, generated within the FPS Convection project, to provide new understanding of the changes in local precipitation extremes and related uncertainties over the greater Alpine region. The CPM ensemble shows a stronger increase in the fractional contribution from extreme events than the driving RCM ensemble during the summer, when convection dominates. We find that the CPM ensemble substantially reduces the model uncertainties and their contribution to the total uncertainties by more than 50%. We conclude that the more realistic representation of local dynamical processes in the CPMs provides more reliable local estimates of change, which are essential for policymakers to plan adaptation measures.

High-speed mapping of surface charge dynamics using sparse scanning Kelvin probe force microscopy

Unraveling local dynamic charge processes is vital for progress in diverse fields, from microelectronics to energy storage. This relies on the ability to map charge carrier motion across multiple length- and timescales and understanding how these processes interact with the inherent material heterogeneities. Towards addressing this challenge, we introduce high-speed sparse scanning Kelvin probe force microscopy, which combines sparse scanning and image reconstruction. This approach is shown to enable sub-second imaging (>3 frames per second) of nanoscale charge dynamics, representing several orders of magnitude improvement over traditional Kelvin probe force microscopy imaging rates. Bridging this improved spatiotemporal resolution with macroscale device measurements, we successfully visualize electrochemically mediated diffusion of mobile surface ions on a LaAlO3/SrTiO3 planar device. Such processes are known to impact band-alignment and charge-transfer dynamics at these heterointerfaces. Furthermore, we monitor the diffusion of oxygen vacancies at the single grain level in polycrystalline TiO2. Through temperature-dependent measurements, we identify a charge diffusion activation energy of 0.18 eV, in good agreement with previously reported values and confirmed by DFT calculations. Together, these findings highlight the effectiveness and versatility of our method in understanding ionic charge carrier motion in microelectronics or nanoscale material systems.

Understanding allochthonous marine litter in a Protected Area in the Amazon Coast

Studies on international waste on the Amazon coast are lacking, leaving a substantial knowledge gap concerning the socioeconomic, cultural, and environmental repercussion of this issue. In this context, the objective of this study is to comprehensively characterize and trace the origins of allochthonous litter discovered on a beach situated within a Protected Area. Given this, the hypothesis of this study is that the international litters comes from vessels operating in the region. A total of 384 containers were collected, originating from 36 countries, with those located in Asia and Africa showing the highest prevalence. Among the bottles with identified expiration dates, 76 % are newly arrived, confirming our hypothesis. The presence of older waste may result from a combination of the absence of beach cleaning public services and local dynamic processes. While international engagement is necessary, local communities, along with the scientific community, have taken proactive measures to address the problem.

Revealing Local Structure and Dynamics in Li-Salt Electrolytes Using Dielectric Relaxation Spectroscopy

Understanding the interplay between local structure and dynamics is critical for establishing design rules for advanced ion-conducting electrolytes. In this work, a set of Li-salt in liquid electrolytes is studied using dielectric relaxation spectroscopy (DRS) to examine correlations between several electrolyte properties, including conductivity, dielectric relaxation time and strength, ionicity, and viscosity. These properties were evaluated by changing ion concentration, solvent type, and anion type. DRS was used to identify relaxation processes associated with the solvent and different ion-solvent coordinating structures, and the dielectric properties are reported for the first time for a majority of these systems. The behavior of viscosity and conductivity were shown to change similarly with concentration when accounting for the local coordinating environment, regardless of the salt or solvent type. τα, the dielectric relaxation time of the solvent-ion complexes, is shown to be independent of ion content at low salt concentrations, when solvent separated ion pairs are the dominant ion-solvent complex. However, at high ion concentrations, a new relationship, a power-law dependence, was identified between molar conductivity and τα, as well as viscosity and τα, demonstrating that the dependence of molar conductivity or viscosity on τα is controlled in part by the solvent type, due to variation in shielding between contact ion pairs and aggregates. In contrast, there was not a clear change in the dependence of molar conductivity or viscosity on τα with changing anion. Furthermore, the effective dipole moments of the ion-solvent complexes were determined, and found to decrease with increasing ion concentration, as contact ion pairs and aggregates form. This systematic analysis of the wide range of Li-salts and solvents, and discussion of relations between different local structures and dynamic processes that contribute to conductivity, helps lay a foundation for the design of new liquid electrolytes.

Slab gliding, a hidden factor that induces irreversibility and redox asymmetry of lithium-rich layered oxide cathodes

Lithium-rich layered oxides, despite their potential as high-energy-density cathode materials, are impeded by electrochemical performance deterioration upon anionic redox. Although this deterioration is believed to primarily result from structural disordering, our understanding of how it is triggered and/or occurs remains incomplete. Herein, we propose a theoretical picture that clarifies the irreversible transformation and redox asymmetry of lithium-rich layered oxides by introducing a series of global and local dynamic structural evolution processes involving slab gliding and transition-metal migration. We show that slab gliding plays a key role in trigger/initiating the structural disordering and consequent degradation of the anionic redox reaction. We further reveal that the ‘concerted disordering mechanism’ of slab gliding and transition-metal migration produces spontaneously irreversible/asymmetric lithiation and de-lithiation pathways, causing irreversible structural deterioration and the asymmetry of the anionic redox reaction. Our findings suggest slab gliding as a crucial, yet underexplored, method for achieving a reversible anionic redox reaction.

Mineralogy of indium mineralization in the Dajing Sn-Cu polymetallic deposit in Inner Mongolia

The Great Xing’an Sn-polymetallic metallogenic belt in Inner Mongolia is a potential district for indium (In) resources, where In mineralization has been discovered in the Dajing Sn-Cu polymetallic deposit, but the occurrence of In is not well understood. In this contribution, detailed mineralogical investigations of In-bearing minerals in the Dajing Sn-Cu deposit were conducted, based on fieldwork and ore petrography, combined with whole-rock analysis, EPMA, and LA-ICP-MS. Three ore-forming stages and six types of sphalerite are distinguished. The highest In content (average 0.18 wt%) is observed in earlier exsolved sphalerite (Ia) in the Cu-Sn stage, other types of sphalerite contain relatively lower In concentration, with the average value ranging from 16 to 478 ppm. Overall, sphalerite in the Cu-Sn stage is more enriching in In than that in the Pb-Zn stage. Indium mainly occurs as solid solution in sphalerite. Other minerals such as stannite and chalcopyrite (Ia) exhibit relatively elevated In concentration (average >202 ppm). Cassiterite, pyrite, and pyrrhotite show negligible In content typically below 10 ppm. Combined with previous studies on ore-forming fluids, indium mineralization in the Dajing deposit is mainly associated with early-stage Cu-Sn fluids. The enrichment of In in sphalerite is probably attributed to the migration and diffusion of In in the Cu-Sn fluid during high-temperature conditions. Local dynamic processes (exsolution, diffusion, etc.) possibly have facilitated In mineralization in sphalerite. This study reveals the occurrence and distribution patterns of In in the Dajing deposit, promotes the recovery and utilization of In resources, and proposes new insights into the enrichment mechanisms and potential assessment of In.

Seasonal distribution of the early life stages of the small yellow croaker (Larimichthys polyactis) and its dynamic controls adjacent to the Changjiang River Estuary

AbstractThe distribution of the early life stages of Larimichthys polyactis indicates the availability of suitable spawning and nursing grounds and enables a better understanding of the distribution of its geographic subpopulations and isolation. Large‐scale quantitative ichthyoplankton surveys of L. polyactis were performed from March to July 2018, and a numerical hydrodynamic model was applied to explore the spatiotemporal distribution and habitats of L. polyactis early life stages adjacent to the Changjiang River Estuary. Two distinct early life stage distribution patterns were found. One occurred during March and April in the deep waters seaward of the Changjiang River bottom plume front, to the east and southeast of the Changjiang River Estuary. The other occurred in May and June throughout the entire water column in coastal waters to the east and north of the Changjiang River Estuary. Rising seasonal temperatures, and the local dynamic processes such as the Changjiang River plume, determined the transitions between the two distribution patterns. A potential fish larval migration route from the southern deep shelf waters to the northern coastal waters within the motor‐trawl prohibition line was suggested. This study contributes to our understanding of the mixture of habitats used by the two L. polyactis subpopulations in the southern Yellow Sea and the East China Sea.

Polar and Topographic Amplifications of Intermodel Spread of Surface Temperature in Climate Models

AbstractThe spatial pattern of intermodel spread of surface temperature (TS‐SPREAD) is similar to the absolute error of modeled surface temperature relative to observations, implying the possibility of using intermodel spread to understand the model biases. The regions with maximum TS‐SPREAD are located in the northern polar (NP) and southern polar (SP) regions, and regions with the large orographic features, such as the Tibetan Plateau (TP). We find: (a) Winter amplification exists in the TS‐SPREAD over both the NP and SP regions, but the maximum TS‐SPREAD over the TP happens during spring and summer with weak seasonality there. (b) Surface energy balance analyses show salient land‐sea contrast in the interlinkage between the physical processes. (c) Over the Arctic Ocean and the Southern Ocean, the maximum spreads of sea‐ice‐induced surface albedo appear during summer when the TS‐SPREADs are the weakest because the effect of surface albedo is offset by the heat storage in the oceans. (d) Through the interseasonal linkage of the heat storage term, i.e., the summer‐storing‐winter‐releasing of oceanic heat content, the summer surface albedo may indirectly contribute to the winter amplification of the TS‐SPREAD over the polar oceans. Such interseasonal linkage of the processes does not exist over the land areas. A method of distinguishing the roles of the local and nonlocal dynamical processes in the contribution of the clear‐sky downward longwave radiation to the TS‐SPREAD is also provided.

A Robust Neural Network for Extracting Dynamics from Electrostatic Force Microscopy Data.

Advances in scanning probe microscopy (SPM) methods such as time-resolved electrostatic force microscopy (trEFM) now permit the mapping of fast local dynamic processes with high resolution in both space and time, but such methods can be time-consuming to analyze and calibrate. Here, we design and train a regression neural network (NN) that accelerates and simplifies the extraction of local dynamics from SPM data directly in a cantilever-independent manner, allowing the network to process data taken with different cantilevers. We validate the NN's ability to recover local dynamics with a fidelity equal to or surpassing conventional, more time-consuming, calibrations using both simulated and real microscopy data. We apply this method to extract accurate photoinduced carrier dynamics on n = 1 butylammonium lead iodide, a halide perovskite semiconductor film that is of interest for applications in both solar photovoltaics and quantum light sources. Finally, we use SHapley Additive exPlanations to evaluate the robustness of the trained model, confirm its cantilever-independence, and explore which parts of the trEFM signal are important to the network.

Molecular dynamics between amorphous and crystalline phases of e-beam irradiated piezoelectric PVDF thin films employing solid-state NMR spectroscopy

Piezoelectric bi-axially and uni-axially stretched PVDF films subjected to e-beam irradiation doses of 5 kGy, 500 kGy and 1 MGy and films not irradiated have been studied. It was found that the piezoelectric responses of both untreated and e-beam irradiated PVDF films under strain strongly depends on their initial manufacturing processing. The initial structural differences were mainly based on crystalline phase composition, notably the α to β polymorph ratio. 19F MAS Solid State NMR measurements performed with fast sample spinning (31.25 kHz) allow us to accurately determine the proportion of crystal and amorphous phases. Considering only the crystalline phases, it was concluded that the uni-axial ((β)-PVDF) film was almost composed of 100% of β-phase while the biaxially-oriented ((α-β)-PVDF) was composed of 81% β-phase and 19% of α-phase. It was also shown that the changes of local dynamic processes of PVDF chains in kHz timescale enable to reflect the degradation of both the crystalline and amorphous phases. Presence of small molecular-weight chemical compounds was evidenced by Carr–Purcell–Meiboom–Gill (CPMG) 1H MAS NMR experiment. The degradation process was in agreement with melting peak decrease registered by DSC. 19F/1H T1ρ relaxation times and analysis of cross-polarization (CP) buildup curves are discussed. Significant scatter of relaxation parameters (19F T1ρ and 1H T1ρ) suggested an important degradation of polymer structure. The 1H T1ρ values for PVDF samples irradiated at 1 MGy mainly imply chain scission mechanisms of degradation rather than cross-linking processes. SS NMR spectroscopy data supported assumption that e-beam irradiation brings flexibility to piezoelectric PVDF films which improved their piezoelectric voltage output generated by deformation up to doses of 500kGy. Above this dose range, degradations were very important and affected severely PVDF films mechanical properties.

Morphological evolution of river mouth spits: Wave effects and self-organization patterns

Sand spits as a type of common landform features, associated with wave-dominated deltas, may be influenced by self-organization processes due to shoreline instability at the downdrift flank of the delta, which forms an asymmetric plan morphology for the delta. Here, we examine the spatial-temporal variations and their controlling processes of the sand spit system at the Changhua River mouth, northwest of the South China Sea, by combining 34-year (1986–2019) satellite-derived shoreline data with an ERA5 wave hindcast dataset. The spit system is characterized by extension towards the sea, as well as recurvature towards the land, in response to dominating N-NE waves, whilst, for the sheltered coastal embayment behind the spit, echelon reverse spits have developed due to the dominating S-SW waves. The wave action is governed by a combination of the short period local marine climate of the area (monsoonal regime) and large-scale weather cycles (i.e., El Niño and La Niña), resulting in inter-seasonal and inter-annual variations of the spit neck morphology. Furthermore, the river mouth spit shows self-organization patterns at different temporal-spatial scales, as indicated by the cyclical behavior of the updrift coast, together with the stepwise formation of the echelon reverse spits. Such behavior influences the spit morphology and its rate of change. The geomorphological self-organization patterns contain the information on local dynamic processes, as well as on large scale air-sea interactions as exemplified by the ENSO events. Thus, the analysis presented in this study is valid to describe and estimate the morphological evolution of highly dynamic barrier-spit systems elsewhere, based on wave energy flux estimated by available wave parameters.

Impacts of atmospheric and oceanic factors on monthly and interannual variations of polynya in the East Siberian Sea and Chukchi Sea

As a key region of Northeast Passage, the polynya along the Siberian coast in the East Siberian and Chukchi Seas is important to local dynamic and thermodynamic processes, sea ice production and marine ecosystem. The detailed variations of polynya and the contributions of atmospheric and oceanic factors to the polynya have not been explored quantitatively. AMSR-E satellite data from January to April during the period 2003–2011 were used to study the impacts of wind stress and ocean heat transport on variations of polynya in the East Siberian Sea and Chukchi Sea. The study region was divided into six domains. Four sets of AMSR-E data with resolutions of 6.25 km and 12.5 km were compared based on two algorithms of sea ice concentration (referred to as 6.25 km-IC and 12.5 km-IC) and sea ice thickness (referred to as 6.25 km-h and 12.5 km-h). The monthly and yearly polynya areas in the four cases and six domains had remarkable differences. The two cases of 6.25 km-h and 12.5 km-h had larger areas of polynya than the other two cases of 6.25 km-IC and 12.5 km-IC. The difference in polynya area between the 6.25 km-h and 12.5 km-h cases was much smaller than the difference between the 6.25 km-IC and 12.5 km-IC cases. The study of atmospheric and oceanic mechanisms on polynya is influenced significantly by the sensitivity of polynya areas. In general, the impact of wind stress and ocean heat transport on the polynyas had noticeable monthly and interannual variations and was dependent on the locations of the polynyas. The alongshore and offshore wind had stronger correlations with the polynya area than ocean heat transport. Although the higher resolution (6.25 km) AMSR-E data are best for the study of atmospheric and oceanic impacts on polynya area, the coarse resolution (12.5 km) AMSR-E data based on sea ice thickness can also be used. Wind direction dominated the polynya area in the East Siberian Sea and wind speed dominated the polynya area in the Chukchi Sea. The variation in ocean heat transport was influenced mainly by variation in volume transport rather than variation in water temperature.

Why is the November Siberian High Intensity More Predictable by NCEP-CFSv2 Model?

As a critical system of the East Asian winter monsoon, the Siberian high has an important impact on the winter weather and climate anomalies in Eurasia. Using the National Center for Environment Prediction-Climate Forecast System version 2 (NCEP-CFSv2), this study comprehensively evaluates the seasonal and monthly prediction of the Siberian high intensity during the winter time (November to February). Results show that the NCEP-CFSv2 model can skillfully predict the Siberian high intensity only in November, the reasons for which are that the local thermal process, dynamic process, and Siberian snow cover extent mainly affect the Siberian high intensity in November. In terms of the thermal process, the NCEP-CFSv2 can better reproduce the Siberian high intensity in November and its related surface soil temperature, upward long-wave radiation, and other thermal factors in Siberia. In terms of the dynamic process, the NCEP-CFSv2 can better reproduce the Siberian high strength in November, which is associated with the low-level tropospheric divergent circulation and the sinking movement of the upper and middle layers in the Siberian area. The model also reproduces the relationship between the snow cover extent over Siberia and the Siberian high intensity in November. The thermodynamic process of the Siberian high and snow cover extent in the area are predictability sources of the Siberian High intensity in November, and the NCEP-CFSv2 can reasonably reproduce these predictability sources in November.

Counterstreaming Strahls and Heat Flux Dropouts as Possible Signatures of Local Particle Acceleration in the Solar Wind

Abstract Suprathermal electrons with energies of ∼70 eV and above are observed at 1 au as dispersionless halo electrons and magnetic field-aligned beams of strahls. For a long time, it has been thought that both populations originate only from the solar corona, and that the only active process impacting their properties in the solar wind is scattering. This view has consequently impacted the interpretation of typical patterns of pitch-angle distributions (PADs) of suprathermal electrons. Meanwhile, recent observational studies supported by numerical simulations have shown that there is an unaccounted population of electrons accelerated to suprathermal energies at reconnecting current sheets (RCSs) and 3D dynamical plasmoids (or 2D magnetic islands (MIs)) directly in the heliosphere. We present multispacecraft observations of counterstreaming strahls and heat flux dropouts in PADs within a region filled with plasmoids and RCSs unaffected by interplanetary shocks, comparing observed PAD features with those predicted by particle-in-cell simulations. We show typical PAD patterns determined by local acceleration of thermal-core electrons up to hundreds of electron volts. Resulting PAD views depend on properties and topology of particular RCSs, MIs, and plasma/magnetic field parameters. Our study suggests that solar wind-borne suprathermal electrons coexist with those of solar origin. Therefore, some of heat flux dropout and bidirectional strahl events can be explained by local dynamical processes involving magnetic reconnection. Possible implications of the results for the interpretation of the actively debated decrease in the strahl/halo relative density with heliocentric distance and puzzling features of suprathermal electrons observed at crossings of the heliospheric current sheet and cometary comas are also discussed.

Direct visualization of magnetic domain wall motion in Nd-Fe-B magnets by alternating magnetic force microscopy using Co-GdOx superparamagnetic tip

Probing the dynamic magnetic domain of permanent magnet materials under an external AC magnetic field using magnetic force microscopy is challenging as well as important to reveal their pinning sites and local magnetization processes. In this work, we develop alternating magnetic force microscopy (A-MFM) with a Co-GdOx superparamagnetic tip for observing the dynamic magnetic domain wall (DW) motion in a, b plane Nd-Fe-B sintered magnets by stimulating the magnetization of the superparamagnetic tip and Nd-Fe-B sample using an external AC magnetic field. This method enables the simultaneous measurement of DC and AC magnetic fields from the sample surface. The measurement results reveal that the DW motion does not happen until the amplitude of the external AC magnetic field reached 77 Oe0-p (zero to peak). Further increasing the external AC magnetic field strength leads to DW motion with larger movement area and stronger AC magnetic field originating from the DW motion. In addition, A-MFM images shows the pinning sites of the DW motion. The present work provides a direct and effective approach to studying the local dynamic magnetization processes of the magnetic materials on the nanometer scale.

Molecular polaritons for controlling chemistry with quantum optics.

This is a tutorial-style introduction to the field of molecular polaritons. We describe the basic physical principles and consequences of strong light-matter coupling common to molecular ensembles embedded in UV-visible or infrared cavities. Using a microscopic quantum electrodynamics formulation, we discuss the competition between the collective cooperative dipolar response of a molecular ensemble and local dynamical processes that molecules typically undergo, including chemical reactions. We highlight some of the observable consequences of this competition between local and collective effects in linear transmission spectroscopy, including the formal equivalence between quantum mechanical theory and the classical transfer matrix method, under specific conditions of molecular density and indistinguishability. We also overview recent experimental and theoretical developments on strong and ultrastrong coupling with electronic and vibrational transitions, with a special focus on cavity-modified chemistry and infrared spectroscopy under vibrational strong coupling. We finally suggest several opportunities for further studies that may lead to novel applications in chemical and electromagnetic sensing, energy conversion, optoelectronics, quantum control, and quantum technology.

Contrastive Influence of ENSO and PNA on Variability and Predictability of North American Winter Precipitation

Abstract In this work, the roles of El Niño–Southern Oscillation (ENSO) in the variability and predictability of the Pacific–North American (PNA) pattern and precipitation in North America in winter are examined. It is noted that statistically about 29% of the variance of PNA is linearly linked to ENSO, while the remaining 71% of the variance of PNA might be explained by other processes, including atmospheric internal dynamics and sea surface temperature variations in the North Pacific. The ENSO impact is mainly meridional from the tropics to the mid–high latitudes, while a major fraction of the non-ENSO variability associated with PNA is confined in the zonal direction from the North Pacific to the North American continent. Such interferential connection on PNA as well as on North American climate variability may reflect a competition between local internal dynamical processes (unpredictable fraction) and remote forcing (predictable fraction). Model responses to observed sea surface temperature and model forecasts confirm that the remote forcing is mainly associated with ENSO and it is the major source of predictability of PNA and winter precipitation in North America.

Micronekton distributions and assemblages at two shallow seamounts of the south-western Indian Ocean: Insights from acoustics and mesopelagic trawl data

Micronekton distributions and assemblages were investigated at two shallow seamounts of the south-western Indian Ocean using a combination of trawl data and a multi-frequency acoustic visualisation technique. La Pérouse seamount (summit depth ~60 m) is located on the outskirts of the oligotrophic Indian South Subtropical Gyre (ISSG) province with weak mesoscale activities and low primary productivity all year round. The “MAD-Ridge” seamount (thus termed in this study; ~240 m) is located in the productive East African Coastal (EAFR) province with high mesoscale activities to the south of Madagascar. Higher micronekton species richness was recorded at MAD-Ridge compared to La Pérouse. Resulting productivity at MAD-Ridge seamount was likely due to the action of mesoscale eddies advecting productivity and larvae from the Madagascar shelf rather than local dynamic processes such as Taylor column formation. Mean micronekton abundance/biomass, as estimated from mesopelagic trawl catches, were lower over the summit compared to the vicinity of the seamounts, due to net selectivity and catchability and depth gradient on micronekton assemblages. Mean acoustic densities in the night shallow scattering layer (SSL: 10–200 m) over the summit were not significantly different compared to the vicinity (within 14 nautical miles) of MAD-Ridge. At La Pérouse and MAD-Ridge, the night and day SSL were dominated by common diel vertically migrant and non-migrant micronekton species respectively. While seamount-associated mesopelagic fishes such as Diaphus suborbitalis (La Pérouse and MAD-Ridge) and Benthosema fibulatum performed diel vertical migrations (DVM) along the seamounts’ flanks, seamount-resident benthopelagic fishes, including Cookeolus japonicus (MAD-Ridge), were aggregated over MAD-Ridge summit. Before sunrise, mid-water migrants initiated their vertical migration from the intermediate to the deep scattering layer (DSL, La Pérouse: 500–650 m; MAD-Ridge: 400–700 m) or deeper. During sunrise, the other taxa contributing to the night SSL exhibited a series of vertical migration events from the surface to the DSL or deeper until all migrants have reached the DSL before daytime. Possible mechanisms leading to the observed patterns in micronekton vertical and horizontal distributions are discussed. This study contributes to a better understanding of how seamounts influence the DVM, horizontal distribution and community composition of micronekton and seamount-associated/resident species at two poorly studied shallow topographic features in the south-western Indian Ocean.

Loschmidt echo of local dynamical processes in integrable and non integrable spin chains

We consider a local instantaneous quantum dynamical process (QDP) that disturbs the background unitary Hamiltonian dynamics of a spin chain. We consider both a non-unitary incoherent QDP and a coherent unitary QDP intervention of the dynamical evolution of the spin chain. To track the effect of QDP on the dynamics, we investigate the Loschmidt echo, which is quite sensitive to whether the background dynamics is integrable or not. For the integrable case, namely the Heisenberg model, the Loschmidt echo depends on the parameters corresponding to the QDP as well as the time of occurrence of QDP. The probability of reviving the system to its initial state is higher for non-unitary/incoherent QDPs occurring at large time intervals. In the case of a unitary/coherent QDP, some amount of the probability of reviving the state is lost. For the non-integrable background dynamics we consider a kicked Harper model. It exhibits a decaying behaviour when contrasted with integrable dynamics. The decay rate is slower when the corresponding classical Hamiltonian is non-chaotic.