Short Time Scales Research Articles

Early flowering enhances performance among conspecifics.

Timing plays a crucial role in plant survival as it determines the environmental conditions during which each phenophase develops. In Mediterranean regions, with high temperatures and low precipitation during summer, the timing of flowering may impact plant performance. Different species avoid harsh abiotic conditions by flowering weeks or months earlier than others. On a shorter time scale, conspecifics that flower just a few days earlier may also gain biotic advantages, such as reduced competition for nutrients or pollinators. We propose that earlier flowering, whether by days for conspecifics or by weeks to months for different species, allows plants to avoid biotic and abiotic stress, respectively, leading to increased reproductive success and growth. We hypothesize that: (i) earlier-flowering species will have higher growth and reproductive success than other species co-occurring in the community, and (ii) earlier-flowering conspecifics will show higher growth and reproductive success than the average of their co-occurring conspecifics. A field study was conducted in SE Spain using 98 co-occurring individuals of four species. We monitored phenology, water loss, and growth over a growing season and estimated relative individual reproduction. Early-flowering species did not show higher relative reproduction than late, co-occurring flowering species, although they differed in water loss. However, early-flowering conspecifics had higher growth and relative reproduction than later-flowering conspecifics, but did not differ in water loss. Our results suggest that early flowering might reduce intraspecific competition among conspecifics, rather than enhance performance of those species that avoid harsh summer conditions (high temperatures and low precipitations).

El Niño-Southern Oscillation signals imprinted in stalagmite δ18O from 2005 to 2017

El Niño-Southern Oscillation (ENSO) is essential to the annual rainfall in the Pacific Rim, causing frequent floods and droughts in these regions. However, its relationship with precipitation in southeastern China on the interannual timescale remains uncertain. Here we reconstruct an ultra-high-resolution hydroclimate record from 2005AD to 2017AD using 301 sets of δ18O data, U/Th dates, and annual-layer counting on a stalagmite MG2 from Meiguang Cave, Jiangxi Province, southeastern China. We find that both calcite and precipitation δ18O records have negative correlations with local rainfall amount, with heavier rainfall correlating with negative excursions of δ18O, supporting the rainfall amount effects on calcite and precipitation δ18O signals on the seasonal timescale. On the interannual timescale, La Niña (El Niño) years are followed by positive (negative) rainfall years and decreased (increased) MG2 δ18O values, and all records have ∼3-year cyclicity. The antiphased correlation of medium coefficiency of the Southern Oscillation Index (SOI) with both precipitation δ18O and MG2 δ18O records implies that ENSO could modulate the calcite δ18O signals in the monsoonal region of China through circulation effects. Therefore, we suggest that changes in cave δ18O values in China can be controlled by both rainfall amount and circulation effects related with the ENSO activities, which provides a good reference for the paleoclimate studies on short timescales.

Earth system responses to different levels of greenhouse gas emissions mitigation

Anthropogenic carbon dioxide (CO2) emissions are the main driver of climate change, with global warming increasing almost linearly with cumulative CO2 emissions. Hence, future warming will primarily result from future emissions of CO2 with contributions from other greenhouse gases (mostly CH4 and N2O) and aerosols. Climate projections of the 21st century, such as those assessed by the IPCC, are provided from comprehensive climate models, also called Earth System models, driven by scenarios of the 21st century evolution of emissions from those climate forcers. While it seems now inevitable that the world will reach 1.5°C of warming above pre-industrial levels by the early 2030s, the extent to which we exceed this warming level and how quickly we may be able to reduce temperatures again depends strongly on global activity taken now to limit emissions. In this paper, we review the current understanding on Earth system changes under two highly contrasted possible future worlds. We first focus on high-end scenarios, where anthropogenic emissions continue to increase over the course of the 21st century, leading to large warming levels, associated impacts on all components of the Earth System, and increased risks of triggering tipping points. We then assess low-end scenarios, where anthropogenic emissions rapidly decline, reaching net zero and potentially becoming net negative before the end of the 21st century. Such “overshoot” scenarios lead to a peak in global warming followed by a slow decline in global temperature, with some degree of reversibility in the global carbon cycle and key Earth system components. We also review paleoclimatic information relevant to these two contrasting future worlds. Paleoclimate evidence for geo-biosphere interactions shows that stabilizing feedbacks operate on millennial or longer timescales, whereas destabilizing feedbacks and tipping cascades occurred also on shorter timescales.

Revisit the γ-Ray Flare Associated with Blazar Mrk 421

A Very High-energy (VHE) flare was observed by Major Atmospheric Gamma Imaging Cherenkov Telescopes on MJD 57788. This VHE flare was characterized by increased VHE flux and short timescales. In this study, we used one-zone synchrotron self-Compton, two-zone, and spine/layer models to explore this VHE flare’s origin. The results indicate that this γ-ray flare can be explained by Inverse Compton Scattering radiation from the layer contributed gamma radiation and results in the γ-ray flare in a different way than the two-zone model. The difference between the two models lies in the performance of spectral energy distribution after γ-ray flare as well as a possible difference in the timescales of the flare.

The influence of SC-CO2 on the shales’ fracture behavior described by using ultra-fast time resolution method and the damage fracture constitutive model: A case study of the Cretaceous Qingshankou formation in Gulong Depression, Songliao Basin, NE China

Supercritical CO2 (SC-CO2), as an innovative non-aqueous fracturing fluid, has gained extensive application in arid regions. However, its influence on the fracture propagation behavior of shale in very short timescales remains poorly understood. Therefore, a series of three-point bending tests were conducted on shale samples with 0°-90° bedding inclinations. To describe the influence of water-heat-SC-CO2 treatment, a damage fracture constitutive model based on a normal distribution was developed. The theoretical fitting curves of this constitutive model agree well with the experimental results. The whole crack propagation processes were captured using the ultra-fast time resolution method, achieving a time resolution of fast to 15 ps. Identical three-point bending tests were repeated after subjecting the shale samples to water-heat-SC-CO2 treatment for 48 h. The experimental results reveal that after the water-heat-SC-CO2 treatment, there were significant changes in the key mechanical parameters of shale samples. Moreover, the influence of water-heat-SC-CO2 was observed to increase progressively with the bedding inclinations. And by combining the image captured by the ultra-fast time resolution method with this constitutive model, the fracture behavior change of the shale sample after water-heat-SC-CO2 treatment predominantly is affected by the weak planes of shale, with negligible influence on the matrix.

The future of offshore wind power production: Wake and climate impacts

Rapid deployment of offshore wind is expected within the coming decades to help meet climate goals. With offshore wind turbine lifetimes of 25–30 years, and new offshore leases spanning 60 years, it is vital to consider long-term changes in potential wind power resource at the farm planning stage. Such changes may arise from multiple sources, including climate change, and increasing wake-induced power losses. In this work, we investigate and compare these two sources of long-term change in wind power, for a case study consisting of 21 wind farms within the German Bight. Consistent with previous studies, we find a small but significant reduction in wind resource due to climate change by the end of the 21st century under the high-emission RCP8.5 scenario, compared with a historical period, with a mean power reduction (over an ensemble of seven climate models) of 2.1%. To assess the impact of wake-induced losses due to increasingly dense farm build-out, we model wakes within the German Bight region using an engineering wake model, under various stages of (planned) build-out corresponding to the years 2010–2027. By identifying clusters of wind farms, we decompose wake effects into long-range (inter-cluster), medium-range (intra-cluster) and short-range (intra-farm) effects. Inter-cluster wake-induced losses increase from 0 for the 2010 scenario to 2.5% for the 2027 scenario, with intra-cluster losses also increasing from 0 to 4.3%. Intra-farm losses are relatively constant, at around 13%. While the evolution of wake effects therefore outweighs the climate effect, and impacts over a shorter timescale, both factors are significant. We also find evidence of an interaction between the climate and wake effects. Both climate change and evolving wake effects must therefore be considered within resource assessment and wind farm planning.

Characteristics of the Mediterranean Cyclone IANOS in Convection‐Permitting Simulations: Unraveling Model Sensitivity to Microphysics and Cumulus Parameterization

AbstractThis study quantified the relative impact of microphysics parameterization (MP) and cumulus parameterization (CP) schemes on storm prediction using a non‐hydrostatic weather research and forecasting model for an intense Medicane: IANOS. All the simulations agreed with the main observed characteristics of this storm, with some discrepancies in magnitude and location, which vary with CP and MP schemes. These discrepancies were larger during the mature phase of the storm. In the CP‐on simulations, the non‐scale aware Kain–Fritsch (KF) scheme typically resulted in higher precipitation, while the Betts‐Miller‐Janjic (BMJ) scheme led to lower precipitation compared to the CP‐off simulations (C0). The tendency of the KF scheme to consume available convective potential energy at a relatively high rate (i.e., short time scale) resulted in high mass fluxes and latent heat release, leading to strengthened convective activity and, hence, precipitation. The multi‐scale aware (MSKF) substantially reduces the precipitation compared to KF due to the reduced contribution of convective scale precipitation. It also modulates the spatial structure precipitation compared to KF, especially light precipitation over the outer bands, and the contribution of grid‐scale precipitation to total precipitation. KF shows the lowest contribution, around 50%, whereas BMJ exhibits a slightly higher contribution, and MSKF versions nearly reach 100%, making it closer to CP‐off. The improved performance in MSKF compared to KF highlights the importance of MSKF convection parameterization for gray zone (~1–4 km) simulation. The persistent discrepancy in landfall location in CP‐on and CP‐off simulation underscored the need of further investigating other physics parameterizations and dynamical mechanisms.

Parental Monitoring, Parental Knowledge, and the Occurrence of Potentially Traumatic Events in Adolescence.

Parental monitoring and knowledge of their teens' activities might enable parents to keep teens safe, reducing the risk of potentially traumatic events. This paper investigated that possibility using a large, nationwide sample of 11,880 early adolescent teens followed longitudinally from ages 10-11 to 13-14years old. At annual assessments, teens completed measures of parental monitoring/knowledge and of potentially traumatic events. Data were analyzed using multilevel models to separate between- and within-family associations. Because within-family associations cannot be explained by the many systematic differences between families with low vs. high monitoring, they comprise more rigorous evidence of a potential causal relationship. We tested both concurrent associations between monitoring/knowledge and PTEs and prospective associations over 12months. At the between-family level, every tested association was significant (p < .001): greater monitoringand/orknowledge predicted fewer PTEs. However, at the within-family level, few associations were significant. Greater knowledge (p = 0.005) or combined monitoring/knowledge (p = 0.01) predicted fewer PTEs concurrently, but greater monitoring alone did not (p = 0.14). No prospective within-family associations were statistically significant. We replicated this pattern of findings in a different set of observations from the same sample, using different measures of each construct. We conclude that most of the apparent association between parental monitoring/knowledge and PTEs is explained by confounding factors, rather than a causal relationship. However, we found some evidence supporting a causal link in models of concurrent associations, suggesting any causal relationship between monitoring/knowledge and PTEs may unfold over shorter timescales.

Enzyme kinetics simulation at the scale of individual particles.

Enzyme-catalyzed reactions involve two distinct timescales: a short timescale on which enzymes bind to substrate molecules to produce bound complexes and a comparatively long timescale on which the molecules of the complex are transformed into products. The uptake of the substrate in these reactions is the rate at which the product is made on the long timescale. Models often only consider the uptake to reduce the number of chemical species that need to be modeled and to avoid explicitly treating multiple timescales. Typically, the uptake rates cannot be described by mass action kinetics and are traditionally derived by applying singular perturbation theory to the system's governing differential equations. This analysis ignores short timescales by assuming that a pseudo-equilibrium between the enzyme and the enzyme-bound complex is maintained at all times. This assumption cannot be incorporated into current particle-based simulations of reaction-diffusion systems because they utilize proximity-based conditions to govern the instances of reactions that cannot maintain this pseudo-equilibrium for infinitely fast reactions. Instead, these methods must directly simulate the dynamics on the short timescale to accurately model the system. Due to the disparate timescales, such simulations require excessive amounts of computational time before the behavior on the long timescale can be observed. To resolve this problem, we use singular perturbation theory to develop a proximity-based reaction condition that enables us to ignore all fast reactions and directly reproduce non-mass action kinetics at long timescales. To demonstrate our approach, we implement simulations of a specific third order reaction with kinetics reminiscent of the prototypical Michaelis-Menten system.

Turnover of retroelements and satellite DNA drives centromere reorganization over short evolutionary timescales in Drosophila.

Centromeres reside in rapidly evolving, repeat-rich genomic regions, despite their essential function in chromosome segregation. Across organisms, centromeres are rich in selfish genetic elements such as transposable elements and satellite DNAs that can bias their transmission through meiosis. However, these elements still need to cooperate at some level and contribute to, or avoid interfering with, centromere function. To gain insight into the balance between conflict and cooperation at centromeric DNA, we take advantage of the close evolutionary relationships within the Drosophila simulans clade-D. simulans, D. sechellia, and D. mauritiana-and their relative, D. melanogaster. Using chromatin profiling combined with high-resolution fluorescence in situ hybridization on stretched chromatin fibers, we characterize all centromeres across these species. We discovered dramatic centromere reorganization involving recurrent shifts between retroelements and satellite DNAs over short evolutionary timescales. We also reveal the recent origin (<240 Kya) of telocentric chromosomes in D. sechellia, where the X and fourth centromeres now sit on telomere-specific retroelements. Finally, the Y chromosome centromeres, which are the only chromosomes that do not experience female meiosis, do not show dynamic cycling between satDNA and TEs. The patterns of rapid centromere turnover in these species are consistent with genetic conflicts in the female germline and have implications for centromeric DNA function and karyotype evolution. Regardless of the evolutionary forces driving this turnover, the rapid reorganization of centromeric sequences over short evolutionary timescales highlights their potential as hotspots for evolutionary innovation.

Transcriptomic sexual conflict at two evolutionary timescales revealed by experimental evolution in Caenorhabditis elegans.

Sex-specific regulation of gene expression is the most plausible way for generating sexually differentiated phenotypes from an essentially shared genome. However, since genetic material is shared, sex-specific selection in one sex can have an indirect response in the other sex. From a gene expression perspective, this tethered response can move one sex away from their wildtype expression state and potentially impact many gene regulatory networks. Here, using experimental evolution in the model nematode Caenorhabditis elegans, we explore the coupling of direct sexual selection on males with the transcriptomic response in males and females over microevolutionary timescales to uncover the extent to which post-insemination reproductive traits share a genetic basis between the sexes. We find that differential gene expression evolved in a sex-specific manner in males, while in females indirect selection causes an evolved response. Almost all differentially expressed genes were downregulated in both evolved males and females. Moreover, 97% of significantly differentially expressed genes in males and 69% of significantly differentially expressed genes in females have wildtype female-biased expression profile. Changes in gene expression profiles were likely driven through trans-acting pathways that are shared between the sexes. We found no evidence that the core dosage compensation machinery was impacted by experimental evolution. Together these data suggest a de-feminization of the male transcriptome and masculinization of the female transcriptome driven by direct selection on male sperm competitive ability. Our results indicate that on short evolutionary timescales sexual selection can generate putative sexual conflict in expression space.

Mathematical modeling of ozone decomposition processes in wastewater treatment: A lumped kinetic approach with initial ozone demand

Ozone-based processes involve complex reaction networks and exhibit matrix-dependent decomposition patterns when dosed to wastewater effluents. Existing models for ozone decomposition are either too complex or not sufficiently descriptive of the regime manifested during initial ozone demand and decay. Models incorporating detailed reactions have shown limited applicability due to the high number of initial states and state variables involved. This study introduces a new mathematical model that balances accuracy and complexity in describing the main phases of ozone decomposition in secondary wastewater effluents. Specifically, a simplified model is proposed based on lumped variables, including initial ozone demand, two classes of organic matter (slow and fast reacting), radical forming (and ozone-decomposing) compounds, radical scavengers, and a hypothetical target contaminant. Results revealed that the model can predict with reasonable accuracy both the rapid initial ozone demand (occurring at very short timescales <10 s) and the slower ozone decomposition processes (occurring at longer timescales >30 s). A global sensitivity analysis was also conducted to further model refinement and simplification, which led to the elimination of three reactions connected to the generation and consumption of radicals (threshold |RXY| ≥ 0.05). Satisfactorily low residual values (RMSE≤7·10−6 M) were observed in all cases. Finally, the adequacy of the model was further tested against an independent set of ozone decomposition experiments obtained from the literature, confirming its suitability in describing ozone decomposition in secondary wastewater effluents with initial ozone demand.

The Variability of Persistent Radio Sources of Fast Radio Bursts

Over 700 bright millisecond-duration radio transients, known as fast radio bursts (FRBs), have been identified to date. Nevertheless, the origin of FRBs remains unknown. Two repeating FRBs (FRB 20121102A and FRB 20190520B) have been verified to be associated with persistent radio sources (PRSs), making them the best candidates to study the nature of FRBs. Monitoring the variability in PRSs is essential for understanding their physical nature. We conducted 22 observations of the PRSs linked to FRB 20121102A and FRB 20190520B using the Karl G. Jansky Very Large Array, to study their variability. We have observed significant flux variability for the PRSs of FRB 20121102A and FRB 20190520B, with a confidence level exceeding 99.99%, based on the observations covering the longest timescale recorded to date. The observed variability of the two PRSs exhibits no significant difference in amplitude across both short and long timescales. We found that the radio-derived star formation rates of the two FRB hosts are significantly higher than those measured by the optical H α emissions, indicating that their host galaxies are highly obscured or most radio emissions are not from star formation processes. The observed timescale of PRS flux evolution constrained the magnetic field of FRB 20121102A with B ∥ ≳ 1 mG and FRB 20190520B with B ∥ ≳ 0.1 mG.

A stochastic population model for the impact of cancer cell dormancy on therapy success

Therapy evasion – and subsequent disease progression – is a major challenge in current oncology. An important role in this context seems to be played by various forms of cancer cell dormancy. For example, therapy-induced dormancy, over short timescales, can create serious obstacles to aggressive treatment approaches such as chemotherapy, and long-term dormancy may lead to relapses and metastases even many years after an initially successful treatment.In this paper, we focus on individual cancer cells switching into and out of a dormant state both spontaneously as well as in response to treatment. We introduce an idealized mathematical model, based on stochastic agent-based interactions, for the dynamics of cancer cell populations involving individual short-term dormancy, and allow for a range of (multi-drug) therapy protocols. Our analysis – based on simulations of the many-particle limit – shows that in our model, depending on the specific underlying dormancy mechanism, even a small initial population (of explicitly quantifiable size) of dormant cells can lead to therapy failure under classical single-drug treatments that would successfully eradicate the tumour in the absence of dormancy. We further investigate and quantify the effectiveness of several multi-drug regimes (manipulating dormant cancer cells in specific ways, including increasing or decreasing resuscitation rates or targeting dormant cells directly). Relying on quantitative results for concrete simulation parameters, we provide some general basic rules for the design of (multi-)drug treatment protocols depending on the types and processes of dormancy mechanisms present in the population.

Unveiling dust, molecular gas, and high star-formation efficiency in extremely UV bright star-forming galaxies at z ~ 2.1-3.6

We analysed the Atacama Large Millimetre/submillimetre Array (ALMA) far-infrared (FIR), 1.3 mm, dust continuum and CO emission of 12 starburst galaxies at $z 2.1-3.6$ selected for their extreme brightness in the rest-frame UV, with absolute magnitudes of $-23.4$ to $-24.7$. We also analysed their Very Large Telescope (VLT) High Acuity Wide field $K$-band Imager (HAWK-I) $H$- and s $-band images. The targeted galaxies are characterised by negligible dust attenuations with blue UV spectral slopes ($-2.62$ to $-1.84$), very young stellar populations of $ 10$ Myr, and powerful starbursts with a high mean specific star-formation rate of $ $, placing them $ 1.5$ dex above the main sequence at similar redshifts and stellar masses stars odot $). The FIR dust continuum emission revealed in nine galaxies gives IR luminosities of $(5.9-28.3) L_ odot $, with six galaxies remaining dominated by unobscured UV star-formation rates, and high dust masses barely produced by supernovae within the 10 Myr timescale. The CO emission detected in eight galaxies leads to molecular gas masses higher than stellar masses, with the mean molecular gas mass fraction as high as $82&lt;!PCT!&gt;$. The corresponding star-formation efficiencies reach $ 40$&lt;!PCT!&gt;, with amazingly short molecular gas depletion timescales between less than 13 Myr and 71 Myr. These unique properties never reported in previously studied galaxies highlight that these galaxies are likely caught at the very beginning of their stellar mass build-up and undergo a very efficient and fast conversion of gas into stars that can only result from the gas collapse within a very short free-fall time. We find that the feedback-free starburst model seems to be able to explain the formation of these galaxies. To reconcile the co-spatial FIR dust emission with the UV-bright unattenuated emission, we speculate about the presence of radiation-driven outflows that can temporarily remove dust at the location of the starburst and expel it at large distances in line with the measured high FIR effective radii (1.7 kpc to 5 kpc) in comparison to the very compact stellar radii that are a few hundreds of parsecs).

Variations over 20 Years in Vegetation Dynamics and Its Coupled Responses to Individual and Compound Meteorological Drivers in Sichuan Province, China

This study presents an innovative investigation into the spatiotemporal dynamics of vegetation growth and its response to both individual and composite climatic factors. The Normalized Difference Vegetation Index (NDVI), derived from SPOT satellite remote sensing data, was employed as a proxy for vegetation growth. Multiple analytical methods, including the coefficient of variation, Mann–Kendall trend analysis, and Hurst index, were applied to characterize the spatiotemporal patterns of the NDVI in Sichuan Province from 2000 to 2020. The Standardized Precipitation Evapotranspiration Index (SPEI) was calculated using monthly precipitation and temperature data from 45 meteorological stations to examine the influence of composite climatic factors on vegetation growth, while the time lag effects between the NDVI and various climatic variables were also explored. Our findings unveil three key insights: (1) Vegetation coverage in Sichuan Province exhibited an overall increasing trend, with the highest NDVI values in summer and the lowest in winter. Significant NDVI fluctuations were observed in spring in the western Sichuan plateau and in winter in northern, eastern, and southern Sichuan. (2) A significant upward trend in the NDVI was detected across Sichuan Province, except for Chengdu Plain, where a downward trend prevailed outside the summer season. (3) On shorter time scales, the NDVI was positively correlated with precipitation, temperature, and the SPEI, with a one-month lag. The response of the NDVI to sunlight duration showed a two-month lag, with the weakest correlation and a five-month lag in western Sichuan. This research advances our understanding of the complex interactions between vegetation dynamics and climatic factors in Sichuan Province and provides valuable insights for predicting future vegetation growth trends.

Waves in Earth's core and geomagnetic field forecast

We use advanced numerical geodynamo series to derive a reduced stochastic model of the dynamics at the surface of Earth's core. Considering order 3 autoregressive (AR-3) processes allows to replicate the simulated spatiotemporal spectrum over a broad range of time-scales, spanning millennia to a fraction of year, including the cut-off found for periods shorter than approximately 2 years and associated with magnetic dissipation. We show how to derive such a forward model from a variety of input simulation series, and present its implementation into the pygeodyn data assimilation algorithm, based on a sequential ensemble method. The updated scheme is applied to perform magnetic field hindcasts and core flow reanalyses. For all observable length-scales, the rate of change of the observed magnetic field is most of the time accounted for within the spread of the forward model trajectories. AR-3 predictions on average supersede by about 35 % linear extrapolations on short (2 yr) time-scales, reducing high-frequency spurious variations in reanalysed flow motions. This improvement is reduced to ≈10% for 5 yr increments, with a large variability from one epoch to the other depending on the overall curvature of the magnetic field evolution. We perform a reanalysis over the period 1880–2023 covered by observatory and satellite records. We find enhanced kinetic energy in three period ranges around 12.5, 6.5 and 3.5 years. At all three periods, fluid motions share geometrical properties compatible with quasi-geostrophic magneto-Coriolis waves: equatorial symmetry, larger amplitude near the equator, flow dominated by low azimuthal wave number and modulated in longitude, phase speed much faster than the fluid velocity and decreasing with the period. At 6.5 yr period we trace back to the mid-1990's the patterns previously detected from satellite data. We also find in the 1960–70's a similar wave-train, possibly in link with the 1969 geomagnetic jerk. The AR-3 model, in conjunction with early satellite records, likely helps isolate such coherent features on interannual time-scales. Similar wave-like motions also show up at 3.5 yr period around 1970 and during the past decades. At periods around 12.5 yr we detect recurrent patterns starting as far back as 1920, and modulated over decadal time-scales. Our results show growing evidence for core dynamics governed by the presence of hydro-magnetic waves over a wide range of periods. This may allow deterministic and/or empirical descriptions of the signal that may help sound deep Earth's properties, and improve predictions of the magnetic field evolution.

A multi-faceted view of the X-ray spectral variability in Seyfert galaxy Ark 120

Abstract Utilizing a range of techniques including multi-band light curves, softness ratio analysis, structure functions, rms spectra, cross-correlation functions, and ratios of spectra from different intervals, we present a comprehensive study of the complex X-ray spectral variability in Seyfert 1 galaxy Ark 120, through re-analyzing its six XMM-Newton observations taken between 2003 and 2014. We find a clear ``softer-when-brighter" trend in the 2--10 keV power-law component over long timescales, with this trend being timescale dependent, as it is much weaker on shorter timescales, similar to that previously detected in NGC 4051. Notably, a rare ``harder-when-brighter" trend is observed during one exposure, indicating dynamic changes in the spectral variability behavior of the power-law component. This exceptional exposure, with the spectral variability indeed marked by a power-law pivoting at an unusually low energy of $\sim$ 2 keV, suggests intricate variations in the thermal Comptonization processes within the corona. Furthermore, when the data below 2 keV are included, we identify that the soft excess component adds significant complexity to the spectral variability, such as evidenced by a transition from ``harder-when-brighter” to ``softer-when-brighter” during another single exposure.Such extra complexity arises because the variability of the soft excess sometimes follows and sometimes does not follow the changes in the power-law component.Our findings underscore the necessity of applying multiple analytic techniques to fully capture the multifaceted spectral variability of AGNs.

Observing character displacement from process to pattern in a novel vertebrate community

Ecological character displacement, whereby shifts in resource use in the presence of competing species leads to adaptive evolutionary divergence, is widely considered an important process in community assembly and adaptive radiation. However, most evidence for character displacement has been inferred from macro-scale geographic or phylogenetic patterns; direct tests of the underlying hypothesis of divergent natural selection driving character displacement in the wild are rare. Here, we document character displacement between two ecologically similar lizards (Anolis sagrei and A. cristatellus) experiencing novel contact. We identify directional selection during the incipient stages of sympatry in a new community that corresponds to repeated trait divergence across multiple established sympatric communities. By identifying the role of natural selection as character displacement unfolds, we connect how natural selection operating at short timescales may drive broader patterns of trait distributions at larger spatial and temporal scales.

Evolutionary consequences of domestication on the selective effects of new amino acid changing mutations in canids.

The domestication of wild canids led to dogs no longer living in the wild but instead residing alongside humans. Extreme changes in behavior and diet associated with domestication may have led to the relaxation of the selective pressure on traits that may be less important in the domesticated context. Thus, here we hypothesize that strongly deleterious mutations may have become less deleterious in domesticated populations. We test this hypothesis by estimating the distribution of fitness effects (DFE) for new amino acid changing mutations using whole-genome sequence data from 24 gray wolves and 61 breed dogs. We find that the DFE is strikingly similar across canids, with 26-28% of new amino acid changing mutations being neutral/nearly neutral (|s| < 1e-5), and 41-48% under strong purifying selection (|s| > 1e-2). Our results are robust to different model assumptions suggesting that the DFE is stable across short evolutionary timescales, even in the face of putative drastic changes in the selective pressure caused by artificial selection during domestication and breed formation. On par with previous works describing DFE evolution, our data indicate that the DFE of amino acid changing mutations depends more strongly on genome structure and organismal characteristics, and less so on shifting selective pressures or environmental factors. Given the constant DFE and previous data showing that genetic variants that differentiate wolf and dog populations are enriched in regulatory elements, we speculate that domestication may have had a larger impact on regulatory variation than on amino acid changing mutations.