Local Fluctuations Research Articles

Long term environmental variability modulates the epigenetics of maternal traits of kelp crabs in the coast of Chile

The methylation of DNA is an environmentally inducible epigenetic mechanism reflecting the short‐term ecological and environmental background of populations. Marine invertebrate populations, which spread along a latitudinal cline, are particularly suitable for profiling DNA methylation, due to the heterogenous environmental conditions experienced. We used the MSAP (Methylation Sensitive Amplified Polymorphism) technique to investigate the natural variation in DNA methylation of different female’s tissues (muscle, gonads, and gills) and early-stage eggs from five populations of the kelp crab Taliepus dentatus, distributed along a latitudinal cline in the coast of Chile. We assessed whether, (1) the distribution of DNA methylation profiles can be associated with the temporal variability of long term (18 years) climatologies (sea surface temperature, turbidity and productivity) and (2) the epigenetic diversity of eggs is related to the population-level phenotypic variability of several maternal investment traits (egg volume, egg weight, egg lipids and fecundity). The DNA methylation of eggs correlated positively and negatively with the long term variability in productivity and sea surface temperature, respectively. Furthermore, the diversity of DNA methylation of eggs correlated positively with the population-level phenotypic variability of several maternal investment traits, suggesting a key role of epigenetic mechanisms in generating phenotypic variability at population level for this species. We provide evidence of a strong link between the temporal variability of long term climatologies with the epigenetic profiles of key early ontogenetic traits associated with the maternal investment of kelp crabs. These modulating mechanisms can hence contribute early to phenotypic variability at population levels in response to local and past environmental fluctuation.

Fatigue-Induced Surface Modification of Zr-Based Metallic Glass under Environmental Conditions.

Metallic glass (MG), an intrinsic heterogeneous structure at the atomic scale, is one of the promising engineering materials with intriguing physical properties. MG often suffers from the fatigue issue caused by the repetitive mechanical loading, but it is still elusive how the local heterogeneity evolves and affects the macroscale fatigue and deformation against bulky external stress. In this study, we investigate the fatigue effect in Zr-Cu-Al ribbon using a bending fatigue method. We used scanning probe microscopy (SPM) in parallel with X-ray diffraction and X-ray photoelectron spectroscopy to figure out the loading effect on the local heterogeneities. The spatially resolved SPM images show that there is a local fluctuation of mechanical and electrical properties on the fatigued side along with morphological deformation compared to the unloaded side. Approaching the broken edge where the fatigue failure occurs, the decaying tendency is not only more dominant but also accelerated by surface oxidation of the fatigued regions. Our study provides a useful guideline on how to monitor structural changes of MGs under fatigue conditions in service and will open a door toward commercialization of high-performance structural engineering materials.

Topography and rainfall coupled landscape evolution of the passive margin of Sahyadri (Western Ghats), India

The passive margin of the Indian peninsula, revered as Sahyadri (Western Ghats) from time immortal, stretches along the western margin of the Indian Craton. It acts as an orographic barrier, and the frontal part of this continental-scale escarpment receives most of the rainfall, whereas the plateau top remains dry; this makes a case to study the processes of landform evolution in a climatically active and tectonically quiescent region. In our study, we demonstrated the modification of the Sahyadri with the annual forcing of the Indian Summer Monsoon (ISM). Seven major perennial river basins having higher drainage density and flowing on a lithologically varied terrain were studied using the SRTM 30 m data. The morphometric studies carried out in these basins, and the topographical analyses of the region offer the development of drainage systems on varied lithological terrain with diverse geological history. We demonstrated how the drainage basin erosion is moderated by the headward erosion by the streams as forced by the runoff water, probably by local base-level fluctuations and the forcing of ISM. The modification of the basin margin, i.e., drainage divide migration, is primarily affected by precipitation, whereas the lithological and structural factors have a second-order control on the overall retreat of the water divide.

Analysis method for calculating radial correlation length of electron temperature turbulence from correlation electron cyclotron emission radiometer.

The radial correlation length (Lr) is one of the essential quantities to measure in order to more fully characterize and understand turbulence and anomalous transport in magnetic fusion plasmas. The analysis method for calculating Lr of electron temperature (Te) turbulence from correlation electron cyclotron emission (correlation ECE or CECE) radiometer measurements has not been fully developed partly due to the fact that the turbulent electron temperature fluctuations are generally imbedded in much larger amplitude thermal noise, which leads to a greatly reduced cross correlation coefficient (ϱ) between two spatially separated ECE signals. This work finds that this ϱ reduction factor due to thermal noise is a function of the local relative temperature fluctuation power and CECE system bandwidths of intermediate and video frequencies, independent of radial separations. This indicates that under the approximation of constant relative temperature fluctuation power for a small radial range of local CECE measurements, the original shape of ϱ as a function of radial separation without thermal noise is preserved in the CECE data with thermal noise present. For Te turbulence with a Gaussian radial wavenumber spectrum, a fit function using the product of Gaussian and sinusoidal functions is derived for calculating Lr. This analysis method has been numerically tested using simulated ECE radiometer data over a range of parameters. Using this method, the experimental temperature turbulence correlation length Lr in a DIII-D L-mode plasma is found to be ∼10 times the local ion gyroradius.

Atomistic understanding of incipient plasticity in BCC refractory high entropy alloys

Understanding the incipient plastic behavior of refractory high-entropy alloys (RHEAs) is crucial for their high-temperature applications. In this study, the initial dislocation nucleation and motion mechanisms in the TaTiZrV RHEA and their dependence on temperature were investigated upon nanoindentation by molecular dynamics (MD) simulations. Compared with the high stress-driven homogeneous nucleation criterion in pure BCC metals, the Zr-V short-range orders in the RHEA facilitate preferential inhomogeneous nucleation at low stress. The local compositional fluctuation not only causes intermittent slipping of screw dislocations by the trapping-detrapping mechanism but also severely reduces the moving rate of edge dislocations. In particular, the initial dislocation nucleation in the RHEA becomes more difficult with the increasing temperature. Based on the competitive mechanism between multiple-element-induced lattice distortion and point-defect-induced lattice distortion, the reason for their excellent retained mechanical properties at high temperatures was revealed. This study would provide theoretical support for the development of RHEAs in high-temperature technological applications.

Feasibility study of a high spatial and time resolution beam emission spectroscopy diagnostic for localized density fluctuation measurements in Lithium Tokamak eXperiment-β (LTX-β).

Trapped electron mode (TEM) is the main source of turbulence predicted for the unique operation regime of a flat temperature profile under low-recycling conditions in the LTX-β tokamak, while ion temperature gradient driven turbulence may also occur with gas fueling from the edge. To investigate mainly TEM scale density fluctuations, a high spatial and time resolution 2D beam emission spectroscopy (BES) diagnostic is being developed. Apart from spatially localized density turbulence measurement, BES can provide turbulence flow and flow shear dynamics. This BES system will be realized using an avalanche photodiode-based camera and narrow band interference filter. The system can acquire data at 2MHz. Simulations with the Simulation of Spectra (SOS) code indicate that a high signal to noise ratio can be achieved with the proposed system. This will enable sampling the density fluctuations at this high time resolution. The design considerations and system optimization using the SOS code are presented.

Evidence of specialized resource exploitation by Modern Humans in Western Iberia associated to Pleistocene and Holocene extreme environmental conditions

Throughout prehistory, landscapes were repeatedly subjected to both global and localized climatic fluctuations that changed the regional environments where human groups lived. This instability demanded constant adaptation and, as a result, the functionality of some sites changed over time.In this light, the western coast of Iberia represents an exceptional case study due to the proximity between at least some oceanic cores and archaeological sites, which should facilitate an accurate reconstruction of the relationships between paleoenvironmental conditions and the coeval patterns of human behavior. This region, and in particular the valley of the River Lis, is marked by wide exposed plateaus cut by narrow and deep canyons. In this paper we present the stratigraphic, archaeometric, technological and archaeobotanical record of Poço Rock Shelter, located in one of these canyons, which hints at the human responses to such changes, and discuss the link between its Solutrean and Epipaleolithic occupations to specific activities. During the coldest part of the Last Glacial Maximum, we hypothesize that there was intensive exploitation of a chert outcrop above the roof to produce blades and Solutrean tips. Later, during Bond Event 6, after that outcrop had been exhausted, there was intensive consumption of shellfish gathered between the mouth of the canyon and the sea. We hypothesize that these strikingly different roles demonstrate how hunter-gatherers adapted to local conditions, and exploited specific resources, promising to provide a better understanding about its functional role during specific extreme climate events.

Giant Thermoelectric Efficiency of Single-Filled Skutterudite Nanocomposites: Role of Interface Carrier Filtering.

The advantage of secondary-phase induced carrier filtering on the thermoelectric properties has paved the way for developing cost-effective, highly efficient thermoelectric materials. Here, we report a very high thermoelectric figure-of-merit of skutterudite nanocomposites achieved by tailoring interface carrier filtering. The single-filled skutterudite nanocomposites are prepared by dispersing rare-earth oxides nanoparticles (Yb2O3, Sm2O3, La2O3) in the skutterudite (Dy0.4Co3.2Ni0.8Sb12) matrix. The nanoparticles/skutterudite interfaces act as efficient carrier filters, thereby significantly enhancing the Seebeck coefficient without compromising the electrical conductivity. As a result, the highest power factor of ∼6.5 W/mK2 is achieved in the skutterudite nanocomposites. The nonuniform strain distribution near the nanoparticles due to the local lattice misfit and concentration fluctuations affect the heat carriers and thereby reduce the lattice thermal conductivity. Moreover, the three-dimensional atom probe analysis reveals the formation of Ni-rich grain boundaries in the skutterudite matrix, which also facilitates the reduction of lattice thermal conductivity. Both the factors, i.e., the reduction in lattice thermal conductivity and the enhancement of the power factor, lead to an enormous increase in ZT up to ∼1.84 at 723 K and an average ZT of about 1.56 in the temperature range from 523 to 723 K, the highest among the single-filled skutterudites reported so far.

Structural Dynamics of a Thermally Stressed Monoclonal Antibody Characterized by Temperature-Dependent H/D Exchange Mass Spectrometry.

Differential scanning calorimetry (DSC) is a standard tool for probing the resilience of monoclonal antibodies (mAbs) and other protein therapeutics against thermal degradation. Unfortunately, DSC usually only provides insights into global unfolding, although sequential steps are sometimes discernible for multidomain proteins. Temperature-dependent hydrogen/deuterium exchange (HDX) mass spectrometry (MS) has the potential to probe heat-induced events at a much greater level of detail. We recently proposed a strategy to deconvolute temperature-dependent HDX data into contributions from local dynamics, global unfolding/refolding, as well as chemical labeling. However, that strategy was validated only for a small protein (Tajoddin, N. N.; Konermann, L. Anal. Chem. 2020, 92, 10058). The current work explores the applicability of this HDX framework to the NIST reference mAb (NISTmAb), a large multidomain protein that is prone to aggregation and has three melting points. Using global fitting, we were able to model HDX profiles across the NISTmAb sequence between zero and 95 °C, and for time points between 15 s and 20 min. We uncovered the enthalpic and entropic contributions of local fluctuations that govern the conformational dynamics at low temperatures. The CH2 and CH3 domains were found to be increasingly affected by global unfolding/refolding in the vicinity of their melting points, although the transiently unfolded protein displayed significant residual protection. Global dynamics were not involved in the deuteration of the Fab domains (which have the highest melting point). Instead, global Fab unfolding was followed immediately by irreversible aggregation. Our results reveal that the thermodynamic HDX-MS strategy applied in this work is well suited for probing spatially resolved dynamics of thermally stressed large proteins such as mAbs, complementing data obtained by DSC.

Understanding the mechanisms of adhesive wear for heterogeneous materials through atomistic simulations

When two rough surfaces slide against each other, two main behaviors can be observed at the asperity level: A ductile behavior where the asperities tend to smooth out or a brittle behavior where the asperities detach and form debris. Recently, a critical length scale controlling the transition between both behaviors was identified. Its formulation depends only on material properties and a geometrical factor (of the order of unity). This finding was achieved thanks to molecular dynamics (MD) simulations with hardness-tunable interatomic potentials. However, the materials studied so far have been homogeneous. Here, the work is extended to a class of simple heterogeneous materials with random fluctuations of their properties. A comparative study of the heterogeneous materials against an equivalent homogeneous material is conducted to study the influence of the local variations on the global behavior. It is found that the critical junction size formula works well for hard materials up until a certain ductility threshold after which a third behavior, mixing shear localization and mode II crack opening, appears. There is a transition zone, larger for the heterogeneous material, from the ductile to the brittle behaviors due to local fluctuations and non-deterministic nature of finite temperature atomistic simulations. Local fluctuations render the heterogeneous material weaker than the equivalent homogeneous material and thus, following the critical junction size formula, should lower the probability of forming debris. While this effect can be observed in the single asperity simulations, its magnitude is lower than expected, hinting at the dichotomic effect of local variations: while they increase the overall ductility, they also create particularly brittle areas prone to crack nucleation.

Freestream Turbulence Effects on the Aerodynamics of an Oscillating Square Cylinder at the Resonant Frequency

Flow past a bluff body in freestream turbulence can substantially change the flow behaviour compared to that in smooth inflow. This paper presents the study of wake flow and aerodynamics of an oscillating square cylinder at the resonant frequency in freestream turbulence, with the integral length not greater than the cylinder side and the turbulence intensity not greater than 10%. Large eddy simulations (LES) in the Cartesian grid using the Immersed Boundary Method (IBM) technique embedded in a FVM solver, together with an efficient synthetic turbulent inflow generator implemented in an in-house parallel FORTRAN code are used for the study. The results are compared with those for smooth inflow, and relevant data published in the literature. The key findings are: the freestream turbulence conditions evidently reduces the local turbulent scales and fluctuations in the shear layer compared to in smooth flow, as small scale freestream turbulence breaks down cylinder-generated larger scale eddies and weakens them; but does not evidently affect the vortex shedding frequency, or the length of the recirculation region behind the cylinder. This suggests negligible change of drag coefficient compared to in smooth inflow. Moreover, this is because the vortex shedding is dominated by the forced oscillation at the resonance frequency, and the turbulence intensity is small.

Cortical response variability is driven by local excitability changes with somatotopic organization

Identical sensory stimuli can lead to different neural responses depending on the instantaneous brain state. Specifically, neural excitability in sensory areas may shape the brain´s response already from earliest cortical processing onwards. However, whether these dynamics affect a given sensory domain as a whole or occur on a spatially local level is largely unknown. We studied this in the somatosensory domain of 38 human participants with EEG, presenting stimuli to the median and tibial nerves alternatingly, and testing the co-variation of initial cortical responses in hand and foot areas, as well as their relation to pre-stimulus oscillatory states. We found that amplitude fluctuations of initial cortical responses to hand and foot stimulation – the N20 and P40 components of the somatosensory evoked potential (SEP), respectively – were not related, indicating local excitability changes in primary sensory regions. In addition, effects of pre-stimulus alpha (8-13 Hz) and beta (18-23 Hz) band amplitude on hand-related responses showed a robust somatotopic organization, thus further strengthening the notion of local excitability fluctuations. However, for foot-related responses, the spatial specificity of pre-stimulus effects was less consistent across frequency bands, with beta appearing to be more foot-specific than alpha. Connectivity analyses in source space suggested this to be due to a somatosensory alpha rhythm that is primarily driven by activity in hand regions while beta frequencies may operate in a more hand-region-independent manner. Altogether, our findings suggest spatially distinct excitability dynamics within the primary somatosensory cortex, yet with the caveat that frequency-specific processes in one sub-region may not readily generalize to other sub-regions.

Unveiling deep-sea habitats of the Southern Ocean-facing submarine canyons of southwestern Australia

Here we present the outcomes of the first deep-sea remotely operated vehicle study of previously unexplored submarine canyon systems along the southwest Australian continental margin. This was conducted around: (1) the Bremer Marine Park; (2) the Mount Gabi seamount and nearby slope-shelf margin at the interface of the Southern and Indian oceans; with new information from (3) the Perth Canyon Marine Park located in the SE Indian Ocean. These canyons differ from many explored around the world in having no connectivity to continental river systems, thus little detrital input, with the Bremer systems and Mount Gabi facing the Southern Ocean which plays a key role in the global ocean circulation and climate systems. Such studies in the vast deep waters around the Australian continent are rare given the lack of local ROV capability available for research, thus little is known about these environments.Using the resources of the Schmidt Ocean Institute, we characterised the submarine topography from high-resolution bathymetric mapping, geology, physical and chemical oceanography, and provide an overview of these environments including the fauna observed and collected. We show that these Southern Ocean-influenced environments incorporate South Indian Central Water, Subantarctic Mode Water, Antarctic Intermediate Water, and Upper and Lower Circumpolar Deep Water, with Antarctic Bottom Water present in deep water just south of the Bremer canyon systems. The richness in megabenthos, especially along the steep, rocky substrates of the canyon heads and walls around the Bremer canyon systems, contrasts to the comparatively depauperate fauna of the more northerly Perth Canyon. Various corals serve as important substrates for a range of other species and often exhibit particular faunal associations. Especially notable are distinct ecological zones including a bryozoan and sponge-dominated (animal) forest on the shelf edge, spectacular coral gardens along canyon margins, and the occurrence of solitary scleractinians well below the aragonite saturation horizon. Subfossil coral deposits were discovered across all three study areas, reflecting periodic waxing and waning of deep-water Scleractinia throughout this southwest region. Extensive pre-modern assemblages at Mount Gabi contrast markedly with the sparse populations of living species and suggest that it might have once been a major coral hotspot, or whether they reflect long-term coral aggregations is yet to be determined. Nevertheless, stark differences in both living and past coral distribution patterns across our study sites point to at least localised fluctuations in Southern Ocean-derived nutrient and/or oxygen supplies to these deep-sea communities.

Schwinger boson theory of the J1, J2=J3 kagome antiferromagnet

We study the kagome antiferromagnet for quantum spin-1/2 with first J1, second J2 and third J3 neighbour exchanges, along the J2 = J3 = J line. We use Schwinger-boson mean-field theory for the precise determination of the phase diagram, and two different rewritings of the Hamiltonian to build an intuition about the origin of the transitions. The spin liquid obtained at J = 0 remains essentially stable over a large window, up to J = 1/3, because it is only weakly frustrated by the J term. Then at J = 1/2, the intermediate Z2 spin liquid condenses into a long-range chiral order because of the change of nature of local magnetic fluctuations. As a side benefit, our Hamiltonian rewriting offers an exact solution for the ground state of our model on a Husimi cactus.

Mesoscopic fluctuating domains in strontium titanate

Spatial correlation between atoms can generate a depletion in the energy dispersion of acoustic phonons. Two well known examples are rotons in superfluid helium and the Kohn anomaly in metals. Here we report on the observation of a large softening of the transverse acoustic mode in quantum paraelectric SrTiO$_3$ by means of inelastic neutron scattering. In contrast to other known cases, this softening occurs at a tiny wave vector implying spatial correlation extending over a distance as long as 40 lattice parameters. We attribute this to the formation of mesoscopic fluctuating domains due to the coupling between local strain and quantum ferroelectric fluctuations. Thus, a hallmark of the ground state of insulating SrTiO$_3$ is the emergence of hybridized optical-acoustic phonons. Mesoscopic fluctuating domains play a role in quantum tunneling, which impedes the emergence of a finite macroscopic polarisation.

Coalescence dynamics of prismatic dislocation loops due to vacancy supersaturation

Recovery processes in metals with a high defect concentration are at the heart of a structural alloy's usability in engineering applications. However, such processes take place via nonconservative mechanisms mediated by point defect diffusion and are governed by their interactions with the underlying microstructure. Indeed, one of the main challenges in studying recovery processes is their intrinsic multiscale complexity, which often negates the direct use of experimental techniques. In this Research Letter, we study the mechanism of dislocation loop coalescence in metals by simulating the interaction dynamics between vacancies and prismatic loops using a stochastic framework that seamlessly bridges point defect kinetics with dislocation mechanics. Our simulations reveal two fundamental discoveries: first, that climb processes are governed by local fluctuations that are not captured by continuum elastodiffusion models, and, second, that prismatic loops create internal traps for vacancies, leading to the formation of rings around the perimeter of the loops that affect how coalescence takes place. Our results show an excellent agreement with in situ experimental observations of loop coalescence in Fe under irradiation.

Convergence of the KPZ Line Ensemble

Abstract In this paper we study the Kardar–Parisi–Zhang (KPZ) line ensemble under the KPZ scaling. Based on their Gibbs property, we derive quantitative local fluctuation estimates for the scaled KPZ line ensemble. This allows us to show the tightness of the scaled KPZ line ensemble. Together with the recent progress in [33], [36], and [15], the tightness result yields the conjectural convergence of the scaled KPZ line ensemble to the Airy line ensemble.

Micromorphic modeling of wave propagation in granular materials: Considering particle nonaffine micro-deformation and kinematics decomposition

The objective of this study is to develop a micromorphic model for granular materials and then apply it to investigate the wave propagation. The relationship between particle displacement and rotation is firstly decomposed and thus particle displacement and spin are adopted. The effect of the particle displacement due to particle rotation is also considered. The relative deformation tensors are introduced to describe the local fluctuation of particle kinematics. Based on micro–macro energy conservation, the constitutive relations are consequently derived. The motion equations and boundary conditions can further be obtained building on Hamilton’s principle and subsequently the dispersion equations of plane waves are derived. It is indicated that the present model can reflect sixteen dispersion curves and predict the presence of bandgaps. A further discussion on the dispersion characteristics is made. Finally, the performance of the present model is verified by comparison with existing micromorphic models and other gradient models. • A micromorphic continuum model considering nonaffine micro-deformation is developed. • The interrelation between particle displacement and rotation is decomposed. • The effects of particle spin and particle displacement induced by rotation are considered. • The dispersion relations of plane waves based on micromorphic continua are derived.

Multi-frequency angular power spectrum of the 21 cm signal from the Epoch of Reionisation using the Murchison Widefield Array

Context. The Multi-frequency Angular Power Spectrum (MAPS) is an alternative to spherically averaged power spectra, and computes local fluctuations in the angular power spectrum without need for line-of-sight spectral transform. Aims. We aimed to test different approaches to MAPS and treatment of the foreground contamination, and compare with the spherically averaged power spectrum, and the single-frequency angular power spectrum. Methods. We applied the MAPS to 110 h of data in z = 6.2 − 7.5 obtained for the Murchison Widefield Array Epoch of Reionisation experiment to compute the statistical power of 21 cm brightness temperature fluctuations. In the presence of bright foregrounds, a filter was applied to remove large-scale modes prior to MAPS application, significantly reducing MAPS power due to systematics. Results. The MAPS showed a contrast of 102–103 to a simulated 21 cm cosmological signal for spectral separations of 0−4 MHz after application of the filter, reflecting results for the spherically averaged power spectrum. The single-frequency angular power spectrum was also computed. At z = 7.5 and l = 200, we found an angular power of 53 mK2, exceeding a simulated cosmological signal power by a factor of one thousand. Residual spectral structure, inherent to the calibrated data, and not spectral leakage from large-scale modes, was the dominant source of systematic power bias. The single-frequency angular power spectrum yielded slightly poorer results compared with the spherically averaged power spectrum, having applied a spectral filter to reduce foregrounds. Exploration of other filters may improve this result, along with consideration of wider bandwidths.

Short-range magnetic order within the multiferroic erythrosiderite mineral(NH4)2FeCl5·H2O

Molecular multiferroics are receiving a large amount of interest, in part due to the ease of synthesis and their potential for tuneability. An important compound within this field is ammonium pentachloroaquaferrate(III), ${({\mathrm{NH}}_{4})}_{2}{\mathrm{FeCl}}_{5}\ifmmode\cdot\else\textperiodcentered\fi{}{\mathrm{H}}_{2}\mathrm{O}$, which has received a lot of attention due to it having both magnetic and ferroelectric transitions at 7.3 and 6.9 K, respectively. The magnetic structure is complex, with many different exchange pathways; however, to date there has been no consideration of magnetic interactions above the critical temperature. Our paper utilizes muon spin spectroscopy, inelastic neutron scattering and quasielastic neutron scattering (QENS) to show that, as one might expect for these complex magnetic systems, there is indeed evidence for short-range order above 7.3 K and this persists up to $\ensuremath{\sim}15$ K. We also highlight the sensitivity of the QENS technique to the magnetic transition and any localized fluctuations.