Strong Fluctuations Research Articles

Masks Down: Diplomacy and Regime Stability in the Post‐Covid‐19 Era

Natural disasters can create peaceful diplomatic interactions between conflicting parties, be they warring states or warring domestic factions. Advocates of “disaster diplomacy” argue that while events such as epidemics, earthquakes, floods, windstorms, and tsunamis result in human tragedies, they also generate opportunities for international cooperation, even between enemies. Conversely, natural disasters can also create rifts between friends and allies. Case studies of individual disasters show that while these events sometimes facilitate diplomatic efforts, they may also emphasize existing differences, creating rifts and exacerbating conflicts. The Covid-19 pandemic represents a unique opportunity to test the disaster diplomacy hypothesis on a rare global health crisis that affected many nations of various regime types and with various relations between them. We argue that pandemics and large-scale emergencies can change the rules of the diplomatic game by exposing states’ genuine interests while disregarding international community norms. As such, the Covid-19 pandemic is tearing off the masks from states’ faces, opening paths to cooperation with unexpected partners while creating rifts between yesterday’s allies. We thus argue that post-Covid-19 diplomacy may be characterized by previously rare tendencies such as “trading with the enemy” on the one hand and abandonment of international agreements on the other. Moreover, on the domestic front, such crises tend to exhibit strong fluctuations in regime type, with a clear shift toward populist parties. Additionally, this article provides two alternative explanations for these phenomena and offers an in-depth analysis of two case studies.

Excellent Barocaloric Effect by Modulating Geometrical Frustrations in Mn3Pt.

Barocaloric materials hold great promise for next-generation solid-state cooling devices because of their green and efficient cooling performance. The insights into low-pressure-driven barocaloric materials are expected to pave the way for the widespread application of barocaloric refrigeration technology. Here, we reveal the low-pressure-driven large barocaloric effect (BCE) modulated by geometrical frustrations in Mn3Pt. The highest sensitivity to pressure of Mn3Pt in metal BCE materials results in an excellent temperature-change strength of 9.77 K 100-1 MPa-1. Neutron powder diffraction and first-principles calculations point out the dual effect of geometrical frustration on modulating the unusual BCE, which not only induces giant volume expansion by inspiring strong spin fluctuation and magnetic moment but also enhances the sensitivity of magnetic phase transition. The model of the dual effect of geometrical frustration in magnets with geometrical frustration is established, which will promote the research progress of barocaloric refrigeration devices.

Optical diagnostics of vacuum arcs in the process of DC interruption

Abstract Vacuum circuit-breakers (VCBs) are commonly used in emerging mechanical DC circuit-breakers. The electrical performance of VCBs in DC interruption duties has been extensively investigated, but basic physics such as the excitation temperature of plasma species, electron/vapor densities and emission of droplets in such applications were rarely reported. In this paper, we focus on how the short high frequency (HF) current pulse affects erosion of electrodes as well as generation of flying droplets by using laser shadow photography. Spectroscopy was adopted to obtain spectra and calculate the excitation temperature of CuI. Shack–Hartmann wavefront sensors were applied to measure neutral and electron density, in tests where di/dt, breaking current and the direction of the injected HF current varied. Indeed, the in-phase injection of the HF current caused an intense arc, but the pulse was too short to make either the cathode or anode melt. Since the plasma is in a nonequilibrium state, the excitation temperature of CuI is relatively low. Electron densities in different tests all approach similar values right before current zero. Neutral densities show strong fluctuation and independence on instantaneous current.

Benthic response to the strong Silurian climatic fluctuations—implications from Gotland (Sweden)

Climatically the Silurian was a most unstable period, as it is shows several strong δ13C excursions, with the Lau excursion being the strongest short-lived positive δ13C excursion of the entire Phanerozoic. The causes of these excursions remain a topic of debate. In order to determine how benthic communities responded to these climatic perturbations, a microfacies analysis of carbonate rocks from the Silurian period (Late Telychian to the uppermost Ludfordian) of Gotland was conducted. The development of reefs was significantly enhanced during periods characterized by carbon isotope excursions, compared to time intervals without. In periods of elevated δ13C values (≥ 3 ‰) the abundance of bryozoans and microbes increases, and in some areas, they form reefs (bryostromatolites), while corals and stromatoporoids were the main reef builders in periods of lower isotope ratios (0–3 ‰). Furthermore, a significant increase of phosphatic components, gypsum pseudomorphs and the microproblematicum Palaeomicrocodium is observed in times of increased isotope ratios. A model is proposed that explains the changes in the benthic communities over time. It is based on previously published models and explains the geochemical processes from coastal areas to the open ocean. Changes are assumed from a humid climate in times without isotope excursions to an arid climate in times of isotope excursions. It emphasizes processes that may have led to the strong δ13C shifts during the Silurian period, and includes the phosphorus cycle in sea water as an important factor in the development of the benthic communities.

Stopover by migrant Montagu's Harriers in the Thar Desert is determined by vegetation greenness and grasshopper abundance but not locust outbreaks

Food availability is an important criterion for migrant birds' decision to stay or leave a stopover site. This can vary depending on the conditions at the site. The Thar Desert of the Indian subcontinent is a major stopover area for birds wintering further south in the region. The desert is also prone to stochastic outbreaks of desert locusts that often coincide with the stopover time of migrating birds. Between 2017 and 2022, we tracked nine tagged Montagu's Harriers (Circus pygargus) using PTT and GPS-GSM transmitters to determine if the stopover duration at stopover sites in the desert is influenced by the availability of migratory locusts or resident grasshoppers and the strategies the birds employ, such as, foraging over a wide area or multiple sites to ensure refuelling during stopover. The mean stopover duration during the 2019 peak locust outbreak was 12 days compared to 18 days in other years. Birds did not track locust occurrence deliberately and preferred to stopover at the same sites each year, irrespective of locust outbreaks. The stopover duration at stopover sites appears to be linked to arrival date, vegetation greenness (NDVI) and marginally to grasshopper abundance. We conclude that the stochastic availability of locusts at stopover sites may provide only an opportunistic source of abundant food for migrant harriers and does not seem to affect their stopover duration. Instead, they choose a more stable strategy of relying on resident grasshoppers, less prone to strong fluctuations in abundance and distribution at the stopover sites.

Buscando Luciérnagas: findings on Mexican fireflies from an 8-year virtual citizen science project.

Fireflies are charismatic and conspicuous animals that often evoke childhood memories, which make firefly watching an emotional and even transformative experience. Citizen science projects have the potential to enhance transformative interactions with nature. Like many insects, firefly populations are declining due to land-use change, urbanization and watershed pollution, but ecological data for this group is scarce, particularly in Mexico. Virtual Citizen Science (VCS) initiatives can serve as a scientific instrument, yield reliable and relevant scientific data, and may also offer a platform to promote broader educational outcomes. We established a VCS project to document fireflies through a Facebook page named Buscando Luciernagas with the following hashtag in every post #veobrillar in 2015. After seven years we complied the gathered data and analyzed the results. We had 647 reports in total, with strong fluctuations from year to year that were correlated with the number of posts and publicity we made each year. The largest number of sightings (319) occurred in 2021, coinciding with a change in our reporting format. Most of the reports came from central Mexico (91.5%), but we had reports from eight states and also received some international reports from nine different countries. Fireflies were most frequently seen in habitats characterized as grasslands (35%) or forests (27%), followed by gardens (17%), vacant lots (9%) and parks (5%) but also paved areas and agricultural lands were reported (3% each). Most citizen scientists reported few fireflies, 1-5 individuals (31%) while only 11% reported more than 50 fireflies per sighting. Our study can serve as a preliminary approach to explore more focused research areas in the future. For example, in areas with no sightings, we could reach out to specific local people to corroborate that there are no fireflies in the region, or in areas with high sightings we could promote conservation measures. Notably, we found it intriguing to discover numerous sightings of fireflies in urban areas, which could offer a potential avenue for further research in urban ecology.

Antiferromagnetism and Phase Stability of CrMnFeCoNi High-Entropy Alloy.

It has long been suspected that magnetism could play a vital role in the phase stability of multicomponent high-entropy alloys. However, the nature of the magnetic order, if any, has remained elusive. Here, by using elastic and inelastic neutron scattering, we demonstrate evidence of antiferromagnetic order below ∼80 K and strong spin fluctuations persisting to room temperature in a single-phase face-centered cubic (fcc) CrMnFeCoNi high-entropy alloy. Despite the chemical complexity, the magnetic structure in CrMnFeCoNi can be described as γ-Mn-like, with the magnetic moments confined in alternating (001) planes and pointing toward the ⟨111⟩ direction. Combined with first-principles calculation results, it is shown that the antiferromagnetic order and spin fluctuations help stabilized the fcc phase in CrMnFeCoNi high-entropy alloy.

Power Semiconductor Junction Temperature and Lifetime Estimations: A Review

The lifetime of power electronic systems is the focus of both the academic and industrial worlds. Today, compact systems present high switching frequency and power dissipation density, causing high junction temperatures and strong thermal fluctuations that affect their performance and lifetime. This paper is a review of the existing techniques for the electro-thermal modelling of Mosfet and IGBT devices regarding lifetime estimation. The advantages and disadvantages of the methodologies used to achieve lifetime prediction are discussed, and their benefits are highlighted. All the factors required to predict power electronic device lifetime, including Mosfet and IGBT electrical models, the computation of power losses, thermal models, temperature measurement and management, lifetime models, mission profiles, cycle counting, and damage accumulation, are described and compared.

Linearized fluctuating hydrodynamics via random polynomials

We argue that an ensemble of backgrounds best describes hydrodynamic dispersion relations in a medium with few degrees of freedom and is therefore subject to strong thermal fluctuations. In the linearized regime, dispersion relations become describable by polynomials with random coefficients. We give a short review of this topic and perform a numerical study of the distribution of the roots of polynomials whose coefficients are of the order of a Knudsen series but fluctuate in accordance with canonical fluctuations of temperature. We find that, remarkably, the analytic structure of the poles of fluctuating dispersion relations is very different from deterministic ones, particularly regarding the distribution of imaginary parts with respect to real components. We argue that this provides evidence that hydrodynamic behavior persists, and is enhanced, by nonperturbative background fluctuations. Published by the American Physical Society 2024

A Statistical Route to Robust SERS Quantitation Beyond the Single-Molecule Level.

Single-molecule surface-enhanced Raman spectroscopy (SM-SERS) holds great potential to revolutionize ultratrace quantitative analysis. However, achieving quantitative SM-SERS is challenging because of strong intensity fluctuation and blinking characteristics. In this study, we reveal the relation P = 1 - e-α between the statistical SERS probability P and the microscopic average molecule number α in SERS spectra, which lays the physical foundation for a statistical route to implement SM-SERS quantitation. Utilizing SERS probability calibration, we achieve quantitative SERS analysis with batch-to-batch robustness, extremely wide detection range of concentration covering 9 orders of magnitude, and ultralow detection limit far below the single-molecule level. These results indicate the physical feasibility of robust SERS quantitation through statistical route and certainly open a new avenue for implementing SERS as a practical analysis tool in various application scenarios.

Numerical investigations of spatiotemporal dynamics of space-charge limited collisional sheaths

Electrostatic particle-in-cell (PIC) and direct simulation Monte Carlo (DSMC) methods are used to compare the plasma dynamics of collisionless with collisional emissive sheaths in partially ionized environments. Space-charge limited emissive sheaths submersed in a plasma with a density of ∼1017 m−3 are examined using a PIC-DSMC solver, CHAOS. Collisionless emissive sheaths with plasma domains sufficiently long (30 and 60 Debye lengths, λD) are subject to strong oscillations due to two-stream electron instability, whereas emissive sheaths in weakly collisional conditions with a short domain (15 λD) exhibit self-spike (sawtooth) oscillations in the plasma field due to the trapped charge-exchange (CEX) ion population within the virtual cathode (VC) region. The two-stream electron instability leads to strong temporal fluctuations in the total emission current, with maximum deviations of 60% and 100% from the time-averaged current for the long plasma domains, whereas CEX collisions cause strong spikes in the emission current if the domain size is short. Our PIC-DSMC simulations show for the first time that the interaction of the two types of instabilities causes the strength of the self-spike to be weakened due to the strong fluctuations caused by the two-stream instability when a sufficiently long computational domain with ion-neutral collisions is employed. By conducting a two-dimensional Fast Fourier Transform (FFT) on the collisional and collisionless sheaths with long domains, we show that the transient evolution of CEX entrapment in the VC increases frequency of sheath oscillations up to two times the ion-acoustic frequencies observed in the collisionless sheath. CEX collisions weaken the VC region and result in a total emission current more than that obtained from the collisionless case for the same domain length. With a more rarefied neutral environment of 1019 m−3 in the plasma sheath, the total emission current increases only 4% in comparison with 14% for one order of magnitude denser environment, within 20 μs. In addition, the spike period is tested with different neutral temperatures and densities. While we do not observe any self-spike in the more rarefied environment, the spike period increased from 5 to 7.5 μs when the neutral temperature is increased from 300 to 2000 K in the denser environment with the simulation time of 20 μs.

Individual bacterial cells can use spatial sensing of chemical gradients to direct chemotaxis on surfaces

Swimming bacteria navigate chemical gradients using temporal sensing to detect changes in concentration over time. Here we show that surface-attached bacteria use a fundamentally different mode of sensing during chemotaxis. We combined microfluidic experiments, massively parallel cell tracking and fluorescent reporters to study how Pseudomonas aeruginosa senses chemical gradients during pili-based ‘twitching’ chemotaxis on surfaces. Unlike swimming cells, we found that temporal changes in concentration did not induce motility changes in twitching cells. We then quantified the chemotactic behaviour of stationary cells by following changes in the sub-cellular localization of fluorescent proteins as cells are exposed to a gradient that alternates direction. These experiments revealed that P. aeruginosa cells can directly sense differences in concentration across the lengths of their bodies, even in the presence of strong temporal fluctuations. Our work thus overturns the widely held notion that bacterial cells are too small to directly sense chemical gradients in space.

Characteristics of fluctuations in the equatorial and polar directions of a compact dipole plasma driven at steady state

The fluctuations in the plasma potential (Vs̃) and electron density (Nẽ) are measured in the steady-state dipole plasma confined in a spherical vacuum chamber using a single permanent dipole magnet. Measurements are made from a radial distance r = 0.5–17 cm, from the surface of the magnet in the equatorial (θ=90°) and polar (θ=180°) directions, using a 4-pin probe setup, and have been characterized by power spectra, cross-phase, cross-coherence, induced transport, and energy spectra. The fluctuations are stronger near the surface of the dipole magnet for θ=90°, thereafter their magnitude decreases gradually with the radial distance. However, a peaked profile of potential fluctuations with the peak around r = 9 cm is observed for θ=180°. The locations of strong fluctuations are around the locations of smaller values of the electron neutral collision frequency. Frequency-resolved power spectra show that the fluctuations in the dipole plasma, predominantly, belong to the very low-frequency range. The values of cross-phase (≤45°) and |Vs̃/Te|/|Nẽ/Ne|≤1 indicate the presence of drift wave instability in both planes, where Te and Ne are equilibrium values of the electron temperature and density. The radial variation of fluctuation-induced electron flux (Γr) verifies the “inward diffusion” of electrons in the equatorial plane.

Enrichment of dissolved metal(loid)s and microbial organic matter during transit of a historic mine drainage system

Water quality degradation by decommissioned mining sites is an environmental issue recognized globally. In the Ore mountains of Central Europe, a wide array of contaminants is released by abandoned under- and aboveground mining sites threatening the quantity and quality of surface and groundwater resources. Here, we focus on the less-explored internal pollution processes within these mines involving organic carbon and microorganisms in trace metal(loid)s mobilization processes. Over an 18-month period, we conducted hydrological and biogeochemical monitoring at the Reiche Zeche mine, a former lead-zinc-silver mine, in Germany, reaching 230 meters below ground, well below the critical zone. Our results show strong seasonal fluctuations in water availability, concentrations of metal(loid)s, pH, and dissolved organic matter (DOM) components across multiple depths. Excess metal(loid) presence during high flow conditions indicated mobilization behavior deviating from conservative dilution. Our findings reveal strong positive correlations between metal(loid) variability and pH (0.894), and between metal(loid) variability and the DOM fluorescent component C2 (-0.910), a proxy for microbial activity. Accordingly, the microbial processes may significantly contribute to the observed metal(loid) composition and fluxes. By elucidating the intricate roles of hydrological and biogeochemical factors in trace metal(loid) mobilization, our research offers a comprehensive framework for improving mine water management and remediation, potentially informing global environmental policies and sustainable mining practices.

Long-lived isospin excitations in magic-angle twisted bilayer graphene.

Numerous correlated many-body phases, both conventional and exotic, have been reported in magic-angle twisted bilayer graphene (MATBG)1-24. However, the dynamics associated with these correlated states, crucial for understanding the underlying physics, remain unexplored. Here we combine exciton sensing and optical pump-probe spectroscopy to investigate the dynamics of isospin orders in MATBG with WSe2 substrate across the entire flat band, achieving sub-picosecond resolution. We observe remarkably slow isospin dynamics in a broad filling range around ν = 2 and between ν = -3 and -2, with lifetimes of up to 300 ps that decouple from the much faster cooling of electronic temperature (about 10 ps). This non-thermal behaviour demonstrates the presence of abnormally long-lived modes in the isospin degrees of freedom. This observation, not anticipated by theory, implies the existence of long-range propagating collective modes, strong isospin fluctuations and memory effects and is probably associated with an intervalley coherent or incommensurate Kekulé spiral ground state. We further demonstrate non-equilibrium control of the isospin orders previously found around integer fillings. Specifically, through ultrafast manipulation, it can be transiently shifted away from integer fillings. Our study demonstrates a unique probe of collective excitations in MATBG and paves the way for actively controlling non-equilibrium phenomena in moiré systems.

Sparsity-Independent Lyapunov Exponent in the Sachdev-Ye-Kitaev Model.

The saturation of a recently proposed universal bound on the Lyapunov exponent has been conjectured to signal the existence of a gravity dual. This saturation occurs in the low-temperature limit of the dense Sachdev-Ye-Kitaev (SYK) model, N Majorana fermions with q body (q>2) infinite-range interactions. We calculate certain out-of-time-order correlators (OTOCs) for N≤64 fermions for a highly sparse SYK model and find no significant dependence of the Lyapunov exponent on sparsity up to near the percolation limit where the Hamiltonian breaks up into blocks. This provides strong support to the saturation of the Lyapunov exponent in the low-temperature limit of the sparse SYK. A key ingredient to reaching N=64 is the development of a novel quantum spin model simulation library that implements highly optimized matrix-free Krylov subspace methods on graphical processing units. This leads to a significantly lower simulation time as well as vastly reduced memory usage over previous approaches, while using modest computational resources. Strong sparsity-driven statistical fluctuations require both the use of a much larger number of disorder realizations with respect to the dense limit and a careful finite size scaling analysis. The saturation of the bound in the sparse SYK points to the existence of a gravity analog that would enlarge substantially the number of field theories with this feature.

Effect of Waiting Period on Initial Adverse Vaginal Microbiome Composition in IVF-ICSI Patients.

Background/Objectives: In this observational prospective cohort study, conducted at the Fertility Centre of the University Hospital, Duesseldorf Germany, the spontaneous reversal capacity and the effect of waiting time on an adverse vaginal microbiome profile in subfertile patients were investigated. Methods: Vaginal swabs of 76 patients were obtained before starting a fertility treatment using a commercially available test to perform a microbiome analysis. Patients with a favorable microbiome profile ("medium" or "high profile") according to the manufacturer's algorithm proceeded with the fertility treatment. Patients with an unfavorable microbiome profile ("low profile") postponed their fertility treatment and were sampled up to four times in each successive cycle or until a shift to a more favorable profile was detected. Results: Initially, 54/76 subjects had a high or medium profile and 23/76 had a low profile. Within 3 months, 75% of patients with an initial low profile shifted to a more favorable profile (7/23 dropouts). The presence of Lactobacillus crispatus in the initial sample was associated with a higher likelihood of a spontaneous shift to a more favorable profile. Conclusions: The vaginal microbiome is subject to strong fluctuations. Even an unfavorable microbiome profile can develop into a favorable microbiome profile within a few months without treatment.

Static magnetic order with strong quantum fluctuations in spin-1/2 honeycomb magnet Na2Co2TeO6

Kitaev interactions, arising from the interplay of frustration and bond anisotropy, can lead to strong quantum fluctuations and, in an ideal case, to a quantum-spin-liquid state. However, in many nonideal materials, spurious non-Kitaev interactions typically promote a zigzag antiferromagnetic order in the d-orbital transition-metal compounds. Here, by combining neutron scattering with muon-spin rotation and relaxation techniques, we provide mechanism insights into the exotic properties of Na2Co2TeO6, a candidate material of the Kitaev model. Below TN, the zero-field muon-spin relaxation rate becomes almost constant (~0.45 μs−1). We attribute this temperature-independent relaxation rate to the strong quantum fluctuations, as well as to the frustrated Kitaev interactions. As the magnetic field increases, neutron scattering data indicate a broader spin-wave excitation at the K-point. Therefore, quantum fluctuations seem not only robust but are even enhanced by the applied magnetic field. Our findings provide valuable hints for understanding the onset of the quantum-spin-liquid state in Kitaev materials.

Vortex inverted pin beams: mitigation of scintillations in strong atmospheric turbulence.

We recently introduced a new class of optical beams with a Bessel-like transverse profile and increasing beam width during propagation, akin to an "inverted pin." Owing to their specially engineered distribution, these beams have shown remarkable performance in atmospheric turbulence. Specifically, inverted pin beams (PBs) were found to have a reduced scintillation index as compared to collimated or focused Gaussian beams as well as other types of pin beams especially in moderate to strong turbulence. In this work, we demonstrate that inverted pin beams carrying orbital angular momentum (OAM) can further suppress intensity scintillations in moderate to strong irradiance fluctuation conditions. Our results can be useful in improving the performance and link availability of free-space optical communication systems.

Fluctuation effects in superconducting nanowires under electric field

This study applies the time-dependent Ginzburg–Landau (TDGL) theory with thermal noise to analyze the thermoelectric and transport properties of superconducting Sn nanowires, focusing on the thermopower (αxx) and the phase transition characteristics in the S-shaped J-E curves. We observe significant contributions from superconducting Cooper pairs, which remain nonzero above the critical temperature (Tc), indicating residual superconductivity due to strong thermal fluctuations. The S-like shape in the J-E curves is attributed to a dynamical instability transition temperature (T∗) at approximately 2.9 K, where thermal fluctuations dominate. Furthermore, we compare the resistance in the linear response to experimental data for Sn nanowires both below and above Tc. Below Tc, the resistance sharply decreases, reflecting the robust superconducting state, while above Tc, it increases, aligning with normal state behavior. In nonlinear response case, our results indicate that high electric fields can be effectively used to suppress order-parameter fluctuations and the electrical conductivity in superconducting nanowires. The findings provide critical insights into the thermoelectric behavior and phase transitions in Sn nanowires, highlighting the importance of Cooper pair dynamics in shaping the transport properties of one-dimensional superconductors. This understanding is essential for the development of advanced nanoelectronic devices leveraging these unique superconducting properties.