Strongly Dependent Research Articles

Batch equilibrium experiments and modeling reveal weak temperature dependence of cyclic volatile methylsiloxane sorption in soil/sediment organic carbon-water systems

The organic carbon normalized partition coefficient, KOC, describes the equilibrium distribution of a chemical between water and organic carbon in soil or sediment. It is a key parameter in evaluating chemical persistence, mass distribution, and transport using multimedia fate and transport models. Considerable uncertainty remains about the KOC values of cyclic volatile methylsiloxane (cVMS) compounds, and in particular the dependence of KOC on temperature. In this study, we used a batch equilibrium (BE) method to measure KOC values and their temperature dependence between ∼5 and 25 °C for octamethylcyclotetrasiloxane (D4) and decamethylcyclopentasiloxane (D5) with soil and sediments. Approximate log KOC values at 25 °C were 4.5–5.0 for D4 and 5.5–6.1 for D5 with different sorbents, and decreased by 0.3 log units or less at 4–5 °C. Enthalpies of sorption, ΔHOC, obtained for the different sorbents ranged from +7.2 to +16 kJ mol−1, with average values of +7.9 and +13 kJ mol−1 for D4 and D5, respectively. These values differ in magnitude and direction from those reported elsewhere based on KOC values determined by a novel dynamic purge-and-trap (PnT) method, but are consistent with predictions based on their solvation properties. A new fugacity-based multimedia model incorporating sorption/desorption kinetics was developed and used to predict concentrations in the phases of BE and PnT systems during desorption of cVMS under different experimental and ideal conditions. Model simulations suggested that KOC values for cVMS compounds derived from the PnT systems could be influenced by sorption disequilibrium between water and solids controlled by desorption rates from the particle phase to water, and subsequent losses due to volatilization and degradation. This has the potential to result in overestimation of KOC values when fitting the experimental data of cVMS mass remaining in a PnT system over time, which could explain the observed differences between the methods.

Undetected perovskite phase interference with zirconolite dissolution measurements

Zirconolite ceramics present a chemically durable host matrix for waste actinides, but zirconolite dissolution rates reported in the literature often vary significantly. Here, the release of Ca and Al from a hot isostatically pressed zirconolite (Ca0.8Zr0.9Ce0.3Ti1.6Al0.4O7.0) was shown to be predominantly driven by preferential dissolution of minor perovskite and alumina phases. Both phases were undetectable by XRD, and the perovskite was difficult to detect by SEM-EDS. Whilst the zirconolite phase exhibited no signs of alteration, dissolution of the perovskite proceeded congruently without forming a hydrated altered layer or diffusion of protons into the solid that would be indicative of an ion-exchange mechanism. The weak temperature dependence of dissolution (40, 90 and 150 °C) showed that kinetics were limited by transport and a mixed transport-surface controlled reaction for Ca and Al, respectively. A significant H2O-D2O isotope effect on dissolution was observed for Ca but not for Al at all temperatures. The former was consistent with an abated rate of hydrolysis in the absence of a contribution from diffusion, whilst the latter could be attributed to differences in the activated complex for Ca and Al release through hydrolysis. These results demonstrate the role of a secondary phase perovskite in the dissolution kinetics of zirconolite even when perovskite occurs at low concentration and evades detection by bulk techniques such as XRD. This study provides a potential explanation of variations in zirconolite ceramic dissolution rates present in the literature and provides a null result to tests of an incongruent Ca release mechanism from zirconolite.

INSPIRE: INvestigating Stellar Population In RElics – VI. The low-mass end slope of the stellar initial mass function and chemical composition

ABSTRACT The INSPIRE project has built the largest sample of ultra-compact massive galaxies (UCMGs) at 0.1 < z < 0.4 and obtained their star formation histories (SFHs). Due to their preserved very old stellar populations, relics are the perfect systems to constrain the earliest epochs of mass assembly in the Universe and the formation of massive early-type galaxies. The goal of this work is to investigate whether a correlation exists between the degree of relicness (DoR), quantifying the fraction of stellar mass formed at z > 2, and the other stellar population parameters. We use the Full-Index-Fitting method to fit the INSPIRE spectra to single stellar population (SSP) models. This allows us to measure, for the first time, the slope of the IMF, as well as stellar metallicity [M/H], [Mg/Fe], [Ti/Fe], and [Na/Fe] ratios, and study correlations between them and the DoR. Similarly to normal-sized galaxies, UCMGs with larger stellar masses have overall higher metallicities. We found a correlation between the IMF slope and the DoR, that, however, breaks down for systems with a more extended SFH. An even stronger dependency is found between the IMF and the fraction of mass formed at high-z. At equal velocity dispersion and metallicity, galaxies with a higher DoR have a larger dwarf-to-giant ratio, i.e. a bottom heavy IMF, than that of low-DoR counterparts. This might indicate that the cosmic epoch and therefore different formation scenarios influence the fragmentation of the star formation cloud and hence might be the explanation for IMF variations detected in massive ETGs.

In-plane thermal conductivity of hexagonal boron nitride from 2D to 3D

The in-plane thermal conductivity of hexagonal boron nitride (h-BN) with varying thicknesses is a key property that affects the performance of various applications from electronics to optoelectronics. However, the transition of the thermal conductivity from two-dimensional (2D) to three-dimensional (3D) h-BN remains elusive. To answer this question, we have developed a machine learning interatomic potential within the neuroevolution potential (NEP) framework for h-BN, achieving a high accuracy akin to ab initio calculations in predicting its thermal conductivity and phonon transport from monolayer to multilayers and bulk. Utilizing molecular dynamics simulations based on the NEP, we predict the thermal conductivity of h-BN with a thickness up to ∼100 nm, demonstrating that its thermal conductivity quickly decreases from the monolayer and saturates to the bulk value above four layers. The saturation of its thermal conductivity is attributed to the little change in phonon group velocity and lifetime as the thickness increases beyond four layers. In particular, the weak thickness dependence of phonon lifetime in h-BN with a nanoscale thickness results from its extremely high phonon focusing along the in-plane direction. This research bridges the knowledge gap of phonon transport between 2D and 3D h-BN and will benefit the thermal design and performance optimization of relevant applications.

Hydroxymethanesulfonate and Sulfur(IV) in Fairbanks Winter During the ALPACA Study.

Hydroxymethanesulfonate (HMS) in fine aerosol particles has been reported at significant concentrations along with sulfate under extreme cold conditions (-35 °C) in Fairbanks, Alaska, a high latitude city. HMS, a component of S(IV) and an adduct of formaldehyde and sulfur dioxide, forms in liquid water. Previous studies may have overestimated HMS concentrations by grouping it with other S(IV) species. In this work, we further investigate HMS and the speciation of S(IV) through the Alaskan Layered Pollution and Chemical Analysis (ALPACA) intensive study in Fairbanks. We developed a method utilizing hydrogen peroxide to isolate HMS and found that approximately 50% of S(IV) is HMS for total suspended particulates and 70% for PM2.5. The remaining unidentified S(IV) species are closely linked to HMS during cold polluted periods, showing strong increases in concentration relative to sulfate with decreasing temperature, a weak dependence on particle water, and similar particle size distributions, suggesting a common aqueous formation process. A portion of the unidentified S(IV) may originate from additional aldehyde-S(IV) adducts that are unstable in the water-based chemical analysis process, but further chemical characterization is needed. These results show the importance of organic S(IV) species in extreme cold environments that promote unique aqueous chemistry in supercooled liquid particles.

Early Jurassic origin of avian endothermy and thermophysiological diversity in dinosaurs

A fundamental question in dinosaur evolution is how they adapted to long-term climatic shifts during the Mesozoic and when they developed environmentally independent, avian-style acclimatization, becoming endothermic.1,2 The ability of warm-blooded dinosaurs to flourish in harsher environments, including cold, high-latitude regions,3,4 raises intriguing questions about the origins of key innovations shared with modern birds,5,6 indicating that the development of homeothermy (keeping constant body temperature) and endothermy (generating body heat) played a crucial role in their ecological diversification.7 Despite substantial evidence across scientific disciplines (anatomy,8 reproduction,9 energetics,10 biomechanics,10 osteohistology,11 palaeobiogeography,12 geochemistry,13,14 and soft tissues15,16,17), a consensus on dinosaur thermophysiology remains elusive.1,12,15,17,18,19 Differential thermophysiological strategies among terrestrial tetrapods allow endotherms (birds and mammals) to expand their latitudinal range (from the tropics to polar regions), owing to their reduced reliance on environmental temperature.20 By contrast, most reptilian lineages (squamates, turtles, and crocodilians) and amphibians are predominantly constrained by temperature in regions closer to the tropics.21 Determining when this macroecological pattern emerged in the avian lineage relies heavily on identifying the origin of these key physiological traits. Combining fossils with macroevolutionary and palaeoclimatic models, we unveil distinct evolutionary pathways in the main dinosaur lineages: ornithischians and theropods diversified across broader climatic landscapes, trending toward cooler niches. An Early Jurassic shift to colder climates in Theropoda suggests an early adoption of endothermy. Conversely, sauropodomorphs exhibited prolonged climatic conservatism associated with higher thermal conditions, emphasizing temperature, rather than plant productivity, as the primary driver of this pattern, suggesting poikilothermy with a stronger dependence on higher temperatures in sauropods.

Biases in Information Selection and Processing: Survey Evidence from the Pandemic

Abstract We conduct two survey experiments to study which information people choose to consume and how it affects their beliefs. In the first experiment, respondents choose between optimistic and pessimistic article headlines related to the COVID-19 pandemic and are then randomly shown one of the articles. Respondents with more pessimistic prior beliefs tend to prefer pessimistic headlines, providing evidence of confirmation bias. Additionally, respondents assigned to the less preferred article discount its information. The second experiment studies the role of partisan views, uncovering strong source dependence: news source revelation further distorts information acquisition, eliminating the role of priors in article choice.

The electron density at the midpoint of the plasmapause

The high density plasmasphere in the magnetosphere is often separated from a lower density region outside of the plasmasphere, called the plasmatrough, by a sharp gradient in electron density called the plasmapause. Here we use plasmapause events identified from electron density data from the ISEE, CRRES, Polar, and IMAGE missions, and the nonlinear genetic algorithm TuringBot, to find models for the electron density at the midpoint of the plasmapause, ne,pp. A good model for ne,pp should include dependence on L, which is the strongest dependence. But models can be improved by including weaker dependencies on the magnetic local time, MLT, the solar EUV index F10.7, and geomagnetic activity as indicated by averages of Kp and AE. The most complicated model that we present predicts ne,pp within a factor of 1.64, and is within the range of observed plasmapause densities for about 96% of our events. These models can be useful for separating plasma populations into plasmasphere-like and plasmatrough-like populations. We also make available our database of electron density measurements categorized into various populations.

Production of sub-micron-sized high-entropy alloy particles and nanoparticles via pulsed laser ablation of CrMnFeCoNi targets in water

High-entropy alloys (HEAs) are a class of materials known for their unique properties, including high strength, excellent wear resistance, and good corrosion resistance. Sub-micron- and nanosized HEA particles were fabricated via pulsed laser ablation in liquid using a Cantor alloy target. The Cr20Mn20Fe20Co20Ni20 target was immersed in pure water and ablated using a focused nanosecond-pulsed Nd: YAG laser. A dark solution containing HEA particles was obtained which was stable for about one week before agglomeration and precipitation was observed. The diameters of the obtained particles ranged from several tens of nanometers to several hundred nanometers. Increasing the laser power resulted in higher particle concentration and an increase in the intensity of UV-vis absorption spectra. Electron diffraction was used to confirm that the composition of the particles was close to that of the Cantor alloy, although the concentrations of Cr and Mn were slightly deficient. There was also a weak dependence of the composition on laser power, and all the particles also contained oxygen. Selected area electron diffraction revealed that the composition varied spatially within some particles and that they are mainly polycrystalline. This work shows that HEA particles can be quickly, safely, and effectively manufactured using liquid-based laser ablation, opening the pathway for mass manufacture and disruptive applications in, e.g., catalysis or tribology.

Investigation of cyclopentene + OH and cyclopentene thermal decomposition reactions

This study presents the first high-temperature measurements of cyclopentene+OH→k1Products reaction over 856 – 1258 K and 1.03 – 4.33 bar. The determined rate coefficients of k1 exhibited Arrhenius temperature dependence with an activation energy ∼ 3.3 kcal mol−1 and negligible pressure dependence. Rate coefficients of OH + cyclopentene are faster than OH + 1-pentene but comparable to OH + 2-pentene, highlighting the significance of allylic CH bonds in these reactions. At 1258 K, our rate coefficient is ∼ 30 % slower than the average room-temperature measurement, indicating the role of OH-addition pathways at low temperatures. Site-specific rate coefficients and branching ratios are determined, with H-abstraction at the allylic CH site accounting for ∼68 % of the reaction and alkylic CH bond contributing ∼22 %. Our measured k1 may be given as (unit: cm3molecule−1s−1):k1=1.64×10−10e(−1660T)Cyclopentene decomposition reaction (cyclopentene→k2cyclopentadiene+H2) is studied over 1186–1472 K and 1.17 – 1.38 bar. Time-resolved yields of the product, cyclopentadiene, are monitored using a sensitive UV laser diagnostic near 220 nm. Absorption cross-sections of cyclopentadiene, measured in two separate mixtures, showed weak positive temperature dependence (8.7 – 9.8 × 10−18 cm2molecule−1) over 961 – 1326 K. Our rate coefficients of k2 exhibited a positive Arrhenius temperature dependence with an activation energy of ∼ 54.7 kcal mol−1. At 1300 K, the decomposition of cyclopentene proceeds 5.5 and 28 times faster than that of cyclopentadiene and cyclopentane, respectively. Our measured k2 may be expressed as (unit: s−1):k2=2.55×1012e(−27,527.6T)The pentagonal structure of cyclopentene influences its H-abstraction and decomposition reactions distinctively. While H-abstraction by OH follows a mechanism akin to cyclohexene and linear alkenes, with comparable rate coefficients at allylic CH bonds, the penta-ring structure significantly impacts the decomposition mechanism. Cyclopentene decomposition predominantly produces cyclopentadiene and H2 in a ring-conserving manner, differing from the cleavage of allylic-alkylic CC bonds in the decompositions of 1-alkenes and cyclohexene.

Deviation inequalities for dependent sequences with applications to strong approximations

In this paper, we give precise rates of convergence in the strong invariance principle for stationary sequences of bounded real-valued random variables satisfying weak dependence conditions. One of the main ingredients is a new Fuk-Nagaev type inequality for a class of weakly dependent sequences. We describe also several classes of processes to which our results apply.

A novel eco-friendly and economical approach of bamboo colorization through biomimetic polymerization of dopamine melanin inspired by photonic microstructure of bird plumage

Bamboo is a low-carbon, sustainable, and versatile substitute for many synthetic materials, but limited variety of color restricts bamboo's decoration performance and added value. Traditional chemical colorization suffers poor generality, massive resource consumption, low colorfastness, high pollution, and remarkable damage to bamboo. This research pioneered an eco-friendly, economical approach to tailor bamboo color while keeping natural texture. Through a facile, mild modification by dopamine (a tyrosine derivative), its biomimetic polymerization endowed bamboo surface with a double-layered polydopamine melanin system mimicking morphology and composition of (keratin layer)/(melanin granules) microstructure of colorful bird plumage. Chromatic-optical and microstructural characterizations showed that polydopamine system's upper layer was nanoscale ∼ submicronscale (thickness 55∼215 nm) film bestowing on bamboo structural colors through thin-film interference. All colors at visible wavelength could be formed through controlling film thickness by adjusting dopamine concentration. Thicker film was more continuous and smoother, while thinner film was stabler. Polydopamine system's lower layer was micronscale (thickness 1.2∼4.4 μm) aggregate of particles enhancing color saturation through suppressing light scattering. Amorphous arrangement of polydopamine system made structural colors on bamboo display weak angle dependence. Physicochemical characterizations proved that bamboo featured non-covalent interaction with deposited polydopamine, which never destroyed bamboo's crystalline structure. Structural colors on bamboo exhibited satisfactory stability in long-term exposure and mechanical washing tests. Overall, proposed colorization was confirmed eco-friendly, convenient, and effective, thus contributing novel ideas to cleaner production in bamboo utilization.

Analysis of a detailed multi-stage model of stochastic gene expression using queueing theory and model reduction

We introduce a biologically detailed, stochastic model of gene expression describing the multiple rate-limiting steps of transcription, nuclear pre-mRNA processing, nuclear mRNA export, cytoplasmic mRNA degradation and translation of mRNA into protein. The processes in sub-cellular compartments are described by an arbitrary number of processing stages, thus accounting for a significantly finer molecular description of gene expression than conventional models such as the telegraph, two-stage and three-stage models of gene expression. We use two distinct tools, queueing theory and model reduction using the slow-scale linear-noise approximation, to derive exact or approximate analytic expressions for the moments or distributions of nuclear mRNA, cytoplasmic mRNA and protein fluctuations, as well as lower bounds for their Fano factors in steady-state conditions. We use these to study the phase diagram of the stochastic model; in particular we derive parametric conditions determining three types of transitions in the properties of mRNA fluctuations: from sub-Poissonian to super-Poissonian noise, from high noise in the nucleus to high noise in the cytoplasm, and from a monotonic increase to a monotonic decrease of the Fano factor with the number of processing stages. In contrast, protein fluctuations are always super-Poissonian and show weak dependence on the number of mRNA processing stages. Our results delineate the region of parameter space where conventional models give qualitatively incorrect results and provide insight into how the number of processing stages, e.g. the number of rate-limiting steps in initiation, splicing and mRNA degradation, shape stochastic gene expression by modulation of molecular memory.

The impact of left-behind experience on urban identity of new-generation migrant workers.

We investigate the impact of left-behind experiences on the urban identity of new-generation migrant workers using data from the 2017 China Migrants Dynamic Survey. The results show the following: (1) The left-behind experience is an important factor undermining the urban identity of new-generation migrant workers, and the conclusion remains consistent after robustness checks, such as propensity score matching. (2) Left-behind experiences of both parents away from home had the most significant negative impact on urban identity. (3) The results of the mechanism tests indicate that the left-behind experience exerts an adverse impact on urban identity through the pathways of poorer physical health, more frequent migration, more challenging job search, and stronger dependence on preexisting social networks. The findings of this study also offer policy suggestions for promoting the urban identity of new-generation migrant workers.

Topological semimetal interface resistivity scaling for vertical interconnect applications

In this work, we explore the electron scattering characteristics at interfaces between normal metals and topological semimetals in bulk as well as in thin film structures. We consider Cu/Ta and CoSi/Ta as representative metal/metal and topological semimetal/metal interface structures, respectively. For bulk interface structures, we find that metal/topological semimetal interfaces have roughly 20× higher interfacial resistivity than normal metal/metal interfaces primarily due to the low electronic density of states, the Fermi level in bulk topological semimetals. For thin films, we find that normal metal/metal interfacial resistivity shows a weak dependence on film thickness and is generally close to the corresponding bulk value. Interfaces between surface-conduction dominated topological semimetals, such as CoSi and normal metals in thin films, however, show decreasing interfacial resistivity with decreasing film thickness. This apparent reduction in interface resistivity originates from the surface-dominated transport, where the total transmission across the interface varies little with reduced film thickness, yielding an effective increase in interface conductivity at smaller dimensions. These results suggest that topological semimetals may be attractive candidates for next-generation interconnect materials with critically small dimensions where interfaces with other metals are ubiquitous.

Study on Water Splitting of the 214-Type Perovskite Oxides LnSrCoO4 (Ln = La, Pr, Sm, Eu, and Ga).

We present a study on the electrocatalysis of 214-type perovskite oxides LnSrCoO4 (Ln = La, Pr, Sm, Eu, and Ga) with semiconducting-like behavior synthesized using the sol-gel method. Among these five catalysts, PrSrCoO4 exhibits the optimal electrochemical performance in both the oxygen evolution reaction and the hydrogen evolution reaction, mainly due to its larger electrical conductivity, mass activity, and turnover frequency. Importantly, the weak dependency of LSV curves in a KOH solution with different pH values, revealing the adsorbate evolving mechanism in PrSrCoO4, and the density functional theory (DFT) calculations indicate that PrSrCoO4 has a smaller Gibbs free energy and a higher density of states near the Fermi level, which accelerates the electrochemical water splitting. The mutual substitution of different rare-earth elements will change the unit-cell parameters, regulate the electronic states of catalytic active site Co ions, and further affect their catalytic performance. Furthermore, the magnetic results indicate strong spin-orbit coupling in the electroactive sites of Co ions in SmSrCoO4 and EuSrCoO4, whereas the magnetic moments of Co ions in the other three catalysts mainly arise from the spin itself. Our experimental results expand the electrochemical applications of 214-type perovskite oxides and provide a good platform for a deeper understanding of their catalytic mechanisms.

Electrical Resistivity and Phase Evolution of Fe–N Binary System at High Pressure and High Temperature

Partitioning experiments and the chemistry of iron meteorites indicate that the light element nitrogen could be sequestered into the metallic core of rocky planets during core–mantle differentiation. The thermal conductivity and the mineralogy of the Fe–N system under core conditions could therefore influence the planetary cooling, core crystallization, and evolution of the intrinsic magnetic field of rocky planets. Limited experiments have been conducted to study the thermal properties and phase relations of Fe–N components under planetary core conditions, such as those found in the Moon, Mercury, and Ganymede. In this study, we report results from high-pressure experiments involving electrical resistivity measurements of Fe–N phases at a pressure of 5 GPa and temperatures up to 1400 K. Four Fe–N compositions, including Fe–10%N, Fe–6.4%N, Fe–2%N, and Fe–1%N (by weight percent), were prepared and subjected to recovery experiments at 5 GPa and 1273 K. These experiments show that Fe–10%N and Fe–6.4%N form a single hexagonal close-packed phase (ɛ-nitrides), while Fe–2%N and Fe–1%N exhibit a face-centered cubic structure (γ-Fe). In separate experiments, the resistivity data were collected during the cooling after compressing the starting materials to 5 GPa and heating to ~1400 K. The resistivity of all compositions, similar to the pure γ-Fe, exhibits weak temperature dependence. We found that N has a strong effect on the resistivity of metallic Fe under rocky planetary core conditions compared to other potential light elements such as Si. The temperature-dependence of the resistivity also revealed high-pressure phase transition points in the Fe–N system. A congruent reaction, ε ⇌ γ’, occurs at ~673 K in Fe–6.4%N, which is ~280 K lower than that at ambient pressure. Furthermore, the resistivity data provided constraints on the high-pressure phase boundary of the polymorphic transition, γ ⇌ α, and an eutectoid equilibrium of γ’ ⇌ α + ε. The data, along with the recently reported phase equilibrium experiments at high pressures, enable construction of a phase diagram of the Fe–N binary system at 5 GPa.

Asymptotic normality of spectral means of Hilbert space valued random processes

A variety of statistics for functional time series allows for a representation as weighted average of corresponding periodogram operators over the frequency domain. We study consistency and asymptotic normality of such spectral mean estimators under mild assumptions. We show that weak convergence of these estimators can be deduced from the (joint) weak convergence of the sample autocovariance operators. The latter is established for a large class of weakly dependent functional time series, which admit expansions as Bernoulli shifts and the weak dependence is quantified by the condition of L4-m-approximability.

Probing Turbulent Scattering Effects on Suprathermal Electrons in the Solar Wind: Modeling, Observations, and Implications

This study explores the impact of a turbulent scattering mechanism, akin to those influencing solar and galactic cosmic rays propagating in the interplanetary medium, on the population of suprathermal electrons in the solar wind. We employ a Fokker–Planck equation to model the radial evolution of electron pitch angle distributions under the action of magnetic focusing, which moves the electrons away from isotropy, and of a diffusion process that tends to bring them back to it. We compare the steady-state solutions of this Fokker–Planck equation with data obtained from the Solar Orbiter and Parker Solar Probe missions and find a remarkable agreement, varying the turbulent mean free path as the sole free parameter in our model. The obtained mean free paths are of the order of the astronomical unit, and display weak dependence on electron energy within the 100 eV–1 keV range. This value is notably lower than Coulomb collision estimates but aligns well with observed mean free paths of low-rigidity solar energetic particle events. The strong agreement between our model and observations leads us to conclude that the hypothesis of turbulent scattering at work on electrons at all heliospheric distances is justified. We discuss several implications, notably the existence of a low Knudsen number region at large distances from the Sun, which offers a natural explanation for the presence of an isotropic “halo” component at all distances from the Sun—electrons being isotropized in this distant region before traveling back into the inner part of the interplanetary medium.

Sparse-penalized deep neural networks estimator under weak dependence

Sparse-penalized deep neural networks estimator under weak dependence