Initial Structure Research Articles

Gradient estimates of the solution to the Cauchy problem for degenerate parabolic equations with nonpower nonlinearities

ABSTRACT We prove the uniform gradient estimates of the nonnegative solution to the Cauchy problem for quasilinear degenerate parabolic equations with nonpower nonlinearity. The large-time estimates in terms of initial data mass and nonlinearity structure were obtained. In the particular case, when the nonlinearity of the equation is power like, then our result coincides with well-known optimal bound.

ReaxFF Simulation of Pyrolysis Behaviors of Polysiloxane Precursors with Different Carbon Content

Polymer-derived ceramics are a promising class of high-temperature materials. This work uses LAMMPS and reactive force field (ReaxFF) energy potential to first-time quantify the atomic evolution of the polymer-to-ceramic conversion. Three different polymer structures are selected based on initial carbon content and molecular structure differences. From these simulations, the ceramic composition, yield, atomic structure, bond change, and radial distribution function (RDF) are comprehensively analyzed and provided data that are not available otherwise. The ceramic compositions correlate with the polymer compositions. The C-rich precursor forms C–C bonds through Si–O, Si–C, and C–H bond losses while less C-rich polymers have no significant C–C bond formation during C–H bond loss. The end structures have vastly different Si–O-rich and C-rich domain sizes, which cannot be observed by any bulk analysis. For the first time, H presence and cluster separation are shown to be determined by the polymer molecular structure. The RDF results show that higher pyrolysis temperature leads to more C–C bond formation. Even at 2100 K, C–H bonds are still prevalent and there is no long-range ordering. Such fundamental understanding provides new knowledge about polymer atomic evolution to silicon oxycarbide (SiOC) ceramics.

Memory-dictated dynamics of single-atom Pt on CeO2 for CO oxidation

Single atoms of platinum group metals on CeO2 represent a potential approach to lower precious metal requirements for automobile exhaust treatment catalysts. Here we show the dynamic evolution of two types of single-atom Pt (Pt1) on CeO2, i.e., adsorbed Pt1 in Pt/CeO2 and square planar Pt1 in PtATCeO2, fabricated at 500 °C and by atom-trapping method at 800 °C, respectively. Adsorbed Pt1 in Pt/CeO2 is mobile with the in situ formation of few-atom Pt clusters during CO oxidation, contributing to high reactivity with near-zero reaction order in CO. In contrast, square planar Pt1 in PtATCeO2 is strongly anchored to the support during CO oxidation leading to relatively low reactivity with a positive reaction order in CO. Reduction of both Pt/CeO2 and PtATCeO2 in CO transforms Pt1 to Pt nanoparticles. However, both catalysts retain the memory of their initial Pt1 state after reoxidative treatments, which illustrates the importance of the initial single-atom structure in practical applications.

The Effects of Time-Averaging on Archaeological Networks

It is well recognized that time-averaging of archaeological deposits results in significant biases in interpretations of the archaeological record. In this study, we investigate the biases introduced by time-averaging in the study of social and economic networks from the archaeological record. Using three different archaeological network datasets, we combine network slices from multiple periods to mimic the effects of time-averaging to understand how the palimpsest nature of the archaeological record affects our interpretations of the network. The results of our analysis indicate that time-averaging reduces the fidelity of network interpretations compared to the non-time-averaged networks when analyzing network or node properties. Our results also showed that the effects of time-averaging are highly dependent on initial network structures. This makes it difficult to establish general rules for how to interpret time-averaged networks in archaeology. However, our study shows that it is of paramount importance that archaeologists are aware of these biases and evaluate the reliability of their data accordingly.

The Interaction of Factor Xa and IXa with Non-Activated Antithrombin in Michaelis Complex: Insights from Enhanced-Sampling Molecular Dynamics Simulations.

The interaction between coagulation factors Xa and IXa and the activated state of their inhibitor, antithrombin (AT),have been investigated using X-ray diffraction studies. However, only mutagenesis data are available for non-activated AT. Our aim was to propose a model based on docking and advanced-sampling molecular dynamics simulations that can reveal the conformational behavior of the systems when AT is not binding a pentasaccharide. We built the initial structure for non-activated AT-FXa and AT-FIXa complexes using HADDOCK 2.4. The conformational behavior was studied using Gaussian accelerated molecular dynamics simulations. In addition to the docked complexes, two systems based on the X-ray structures were also simulated, with and without the ligand. The simulations revealed large variability in conformation for both factors. In the docking-based complex of AT-FIXa, conformations with stable Arg150-AT interactions can exist for longer time periods but the system also has a higher tendency for reaching states with very limited interaction with the "exosite" of AT. By comparing simulations with or without the pentasaccharide, we were able to gain insights into the effects of conformational activation on the Michaelis complexes. RMSF analysis and correlation calculations for the alpha-carbon atoms revealed important details of the allosteric mechanisms. Our simulations provide atomistic models for better understanding the conformational activation mechanism of AT against its target factors.

Internal tensile properties of characteristic zones in the electron beam weldment of TC17 titanium alloy

The internal tensile deformation of the individual base metal zone (BM), heat-affected zone (HAZ), and fusion zone (FZ) in a titanium alloy (Ti–5Al–2Sn–2r–4Mo–4Cr, wt.%) electron beam welding (EBW) joint is investigated. The ultimate strength of BM with a bimodal microstructure is 1047.5 MPa, and the elongation to fracture is 9.8%. HAZ is distinguished by the formation of a ghost structure with a hierarchical cluster structure within the initial αP grains, while the embedded αs laths dissolve in the matrix and relatively coarsening β grains are generated. During tension, the ghost structures strongly inhibit and deflect slip initiation and extension in the relatively coarsening β matrix. The competitive balance between strengthening from the ghost structure and weakening from the coarsening matrix dominates the mechanical properties of the HAZ, which then induces a hybrid fracture. The needle-shaped thermal martensite that formed during EBW causes the FZ to fail prematurely. The microstructural evolution of HAZ and FZ decreases their mechanical properties. This research may shed some light on the mechanical enhancement of titanium alloys by utilizing the multiple αL laths precipitated within the initial αP structure associated with the bimodal matrix.

Solvation of magnesium chloride dimer in water: The case of anionic and neutral clusters.

The structures of magnesium chloride dimer-water clusters, (MgCl2)2(H2O)n-/0, were investigated with size-selected anion photoelectron spectroscopy and theoretical calculations to understand the dissolution of magnesium chloride in water. The most stable structures were confirmed by comparing vertical detachment energies (VDEs) with the experimental measurements. A dramatic drop of VDE at n = 3 has been observed in the experiment, which is in accordance with the structural change of (MgCl2)2(H2O)n-. Compared to the neutral clusters, the excess electron induces two significant phenomena in (MgCl2)2(H2O)n-. First, the planar D2h geometry can be converted into a C3v structure at n = 0, making the Mg-Cl bonds easier to be broken by water molecules. More importantly, a negative charge-transfer-to-solvent process occurs after adding three water molecules (i.e., at n = 3), which leads to an obvious deviation in the evolution of the clusters. Such electron transfer behavior was noticed at n = 1 in monomer MgCl2(H2O)n-, indicating that the dimerization between two MgCl2 molecules can make the cluster more capable of binding electron. In neutral (MgCl2)2(H2O)n, this dimerization provides more sites for the added water molecules, which can stabilize the entire cluster and maintain its initial structure. Specifically, filling the coordination number to be 6 for Mg atoms can be seen as a link between structural preferences in the dissolution of the monomers, dimers, and extended bulk-state of MgCl2. This work represents an important step forward into fully understanding the solvation of MgCl2 crystals and other multivalent salt oligomers.

Coaching for winning or holistic athlete development, or both? Validation of the two-dimensional Identity of Sport Coaches Scale (2-DISCS)

Coaches face the pressures of producing desired sport outcomes for athletes and teams and developing their athletes as holistic individuals. As a result, coaches may invest different amounts of time, passion, and effort in fostering different outcomes for athletes, including winning and holistic development, and thus view themselves as primarily oriented toward winning or holistic athlete development, or both. The purpose of this study was to develop and validate the Two-Dimensional Identity of Sport Coaches Scale (2-DISCS) designed to measure winning-centered and holistic development-centered coaching identities. The scale was developed using the 4Cs framework. Following literature review, an item pool was developed and submitted for content validation. Then, items were tested with collegiate coaches. In Study 1 (N = 946), initial factor structure was examined through confirmatory factor analysis. In Study 2 (N = 380), psychometric properties of the items were further assessed through confirmatory factor analysis. Results confirmed the two-factor structure. Measurement invariance was established across gender, NCAA Division, and position. Overall, results provided evidence of factorial validity, construct validity, and reliability of the scale. The 10-item 2-DISCS is suggested as a reasonable measure of winning-centered and holistic development-centered identity of sport coaches that can be used in future studies and in practice. However, future studies should further examine the validity of the 2-DISCS. Lay summary: Coaches may view themselves primarily oriented towards winning or holistic athlete development, or both. Utilizing the 4Cs framework, here we describe the development and validation of the Two-Dimensional Identity of Sport Coaches Scale (2-DISCS), a 10-item scale designed for coaches to measure winningcentered and holistic development-centered coaching identities.

Device Simulation of Highly Stable and 29% Efficient FA0.75MA0.25Sn0.95Ge0.05I3-Based Perovskite Solar Cell.

A new type of perovskite solar cell based on mixed tin and germanium has the potential to achieve good power conversion efficiency and extreme air stability. However, improving its efficiency is crucial for practical application in solar cells. This paper presents a quantitative analysis of lead-free FA0.75MA0.25Sn0.95Ge0.05I3 using a solar cell capacitance simulator to optimize its structure. Various electron transport layer materials were thoroughly investigated to enhance efficiency. The study considered the impact of energy level alignment between the absorber and electron transport layer interface, thickness and doping concentration of the electron transport layer, thickness and defect density of the absorber, and the rear metal work function. The optimized structures included poly (3,4-ethylenedioxythiophene)polystyrene sulfonate (PEDOT:PSS) as the hole transport layer and either zinc oxide (ZnO) or zinc magnesium oxide (Zn0.7Mg0.3O) as the electron transport layer. The power conversion efficiency obtained was 29%, which was over three times higher than the initial structure. Performing numerical simulations on FA0.75MA0.25Sn0.95Ge0.05I3 can significantly enhance the likelihood of its commercialization. The optimized values resulting from the conducted parametric study are as follows: a short-circuit current density of 30.13 mA·cm-2), an open-circuit voltage of 1.08 V, a fill factor of 86.56%, and a power conversion efficiency of 28.31% for the intended solar cell.

Morphology Changes of Cu2O Catalysts During Nitrate Electroreduction to Ammonia**

AbstractThis manuscript reports the electrosynthesis of ammonia from nitrate catalysed Cu derived from Cu2O materials. Cu2O (111) and (100) preferential grain orientations were prepared through electrodeposition. Cu derived from Cu2O (111) is more active and selective for ammonia formation than Cu2O (100) derived Cu. The highest faradaic efficiency (FE) was achieved for both catalysts at −0.3 V vs RHE, with Cu derived from Cu2O (111) reaching up to 80 %. Additional measurements with quasi‐in situ X‐ray photoelectron spectroscopy and in situ Raman spectroscopy revealed that Cu0 is the active phase during the reaction. The stability of the catalysts was examined by ex situ methods such as SEM, XRD and ICP elemental analysis. The catalysts underwent severe morphological changes as a function of the applied potential and the reaction time, most likely due to the dissolution and redeposition of Cu. After 3 hours of reaction, the entire surface of the catalysts was reconstructed into nanoneedles. The FE after 3 hours remained higher for the Cu derived from Cu2O (111), suggesting that the activity is dependent on the initial structure and the different rates of dissolution and re‐deposition.

How well do you think you remember your personal past? French validation of the Autobiographical Recollection Test (ART) and exploration of age effect

ABSTRACT This study aimed to validate a French version of the Autobiographical Recollection Test (ART), a 21-item self-report questionnaire developed by Berntsen, D., Hoyle, R. H., & Rubin, D. C. (2019; The Autobiographical Recollection Test (ART): A measure of individual differences in autobiographical memory. Journal of Applied Research in Memory and Cognition, 8(3), 305–318) examining the subjective quality people attribute to their autobiographical memories. It measures seven distinct but correlated dimensions of memories’ quality varying between individuals: vividness, narrative coherence, reliving, rehearsal, visual imagery, scene, and life-story relevance. 373 participants aged from 18 to 87 years old were invited to complete the questionnaire by rating on a 7-point Likert scale the degree to which they agree with each item. Demographic data and information about their perception of their memory functioning and satisfaction were also collected. Confirmatory factor analysis confirmed the initial seven-factor structure of the ART. Moreover, results showed desirable psychometric properties, with good internal consistency (.94) and test-retest reliability (.83). This scale was also correlated with participants’ perception of memory functioning in daily life. However, there was no correlation with age, confirming prior studies showing that the subjective quality of autobiographical memories does not decline with age. This study thus provides proof of the good psychometric properties of the French version of the ART and promotes its use to explore the subjective quality of autobiographical memories in clinical populations.

Adsorption of 2-Mercapto-1-methylimidazole on the (√3 × 22) Reconstructed and (1 × 1) Phases of an Ordered Au(111) Electrode under Potential Control

The self-assembled monolayers (SAMs) of organosulfur compounds bearing an imidazole (Im) functional group can form hydrogen bonds with others and tailor specific interfacial structures used for CO2 reduction, biosensing, and corrosion prevention. The current study employed cyclic voltammetry and in situ scanning tunneling microscopy (STM) to address the adsorption and structure of 2-mercapto-1-methylimidazole (MMI) on the reconstructed and unreconstructed Au(111) electrodes as a function of potential. The adsorbed MMI molecule assumed the unprotonated form, allowing its S- and N-ends to bind with the Au electrode at a positive potential. Molecular resolution STM images showed an ordered Au(111)–(√21 × √21)R10.9°–MMI structure. The Au–N bond could weaken and be broken at a negative potential, leading to a disordered MMI adlayer. This restructuring event was coupled with the protonation of the Im group. These processes resulted in a sharp peak, which shifted negatively by 60 mV with an increase of 1 pH unit. MMI admolecules were desorbed at a more negative potential to unveil a pitted Au surface, resulting from etching of MMI adsorption. This feature supports the S–Au–S motif for MMI adsorbed to the Au(111) electrode, irrespective of the initial Au surface structure. The effect of MMI as an additive to the deposition bath of Ni was also explored.

Critical Assessment of Self-Consistency Checks in the All-Atom Molecular Dynamics Simulation of Intrinsically Disordered Proteins.

All atom simulations can be used to quantify conformational properties of Intrinsically Disordered Proteins (IDP). However, simulations must satisfy convergence checks to ensure observables computed from simulation are reliable and reproducible. While absolute convergence is purely a theoretical concept requiring infinitely long simulation, a more practical, yet rigorous, approach is to impose Self Consistency Checks (SCCs) to gain confidence in the simulated data. Currently there is no study of SCCs in IDPs, unlike their folded counterparts. In this paper, we introduce different criteria for self-consistency checks for IDPs. Next, we impose these SCCs to critically assess the performance of different simulation protocols using the N terminal domain of HIV Integrase and the linker region of SARS-CoV-2 Nucleoprotein as two model IDPs. All simulation protocols begin with all-atom implicit solvent Monte Carlo (MC) simulation and subsequent clustering of MC generated conformations to create the representative structures of the IDPs. These representative structures serve as the initial structure for subsequent molecular dynamics (MD) runs with explicit solvent. We conclude that generating multiple short (∼3 μs) MD simulation trajectories─all starting from the most representative MC generated conformation─and merging them is the protocol of choice due to (i) its ability to satisfy multiple SCCs, (ii) consistently reproducing experimental data, and (iii) the efficiency of running independent trajectories in parallel by harnessing multiple cores available in modern GPU clusters. Running one long trajectory (greater than 20 μs) can also satisfy the first two criteria but is less desirable due to prohibitive computation time. These findings help resolve the challenge of identifying a usable starting configuration, provide an objective measure of SCC, and establish rigorous criteria to determine the minimum length (for one long simulation) or number of trajectories needed in all-atom simulation of IDPs.

The influence of particle surface oxidation treatment on microstructure and mechanical behavior of 3D-SiCp/A356 interpenetrating composites fabricated by pressure infiltration technique

In this work, the 3D-SiCp/A356 composites with interpenetrating microstructure were prepared by pressure infiltration of A356 aluminum alloy into a porous 3D-SiC ceramic preform, which served as reinforcement. The effects of the surface oxidation treatment of the SiC particles on microstructure, thermal expansion coefficient, and bending strength of as-fabricated composites were investigated. The results revealed that the initial structure of the 3D-SiC ceramic preform could be retained after pressure infiltration, the pores of the preform were filled with A356 aluminum alloy, and the particles were uniformly distributed in the A356 matrix alloy. The thermal expansion coefficient of the SiC/A356 composite reinforced by oxidized SiC particles was lower than that of the unoxidized SiC particle-reinforced composite. It increased with increasing temperature for both, eventually reaching maxima at 420 °C and 350 °C, respectively, and decreased thereafter. However, a rapid decrease in the thermal expansion coefficient was evident at 565 °C because of the over-burning of the A356 aluminum matrix. In particular, the surface oxidation treatment of SiC particles changed the nature of bonding between SiC and Al, which reduced the strength of the composites. As a result, the bending strength of the unoxidized SiC particle-reinforced composite was approximately twice that of the oxidized SiC particle-reinforced composite. Additionally, the bending strength values of the SiC–Al showed an obvious anisotropic behavior. The bending strength measured by loading parallel to the infiltration direction was 2.5 times larger than that of a perpendicular loading.

Slow myosin heavy chain 1 is required for slow myofibril and muscle fibre growth but not for myofibril initiation

Slow myosin heavy chain 1 (Smyhc1) is the major sarcomeric myosin driving early contraction by slow skeletal muscle fibres in zebrafish. New mutant alleles lacking a functional smyhc1 gene move poorly, but recover motility as the later-formed fast muscle fibres of the segmental myotomes mature, and are adult viable. By motility analysis and inhibiting fast muscle contraction pharmacologically, we show that a slow muscle motility defect persists in mutants until about 1 month of age. Breeding onto a genetic background marking slow muscle fibres with EGFP revealed that mutant slow fibres undergo terminal differentiation, migration and fibre formation indistinguishable from wild type but fail to generate large myofibrils and maintain cellular orientation and attachments. In mutants, initial myofibrillar structures with 1.67 ​μm periodic actin bands fail to mature into the 1.96 ​μm sarcomeres observed in wild type, despite the presence of alternative myosin heavy chain molecules. The poorly-contractile mutant slow muscle cells generate numerous cytoplasmic organelles, but fail to grow and bundle myofibrils or to increase in cytoplasmic volume despite passive movements imposed by fast muscle. The data show that both slow myofibril maturation and cellular volume increase depend on the function of a specific myosin isoform and suggest that appropriate force production regulates muscle fibre growth.

Phase Transformations in Feldspar Group Minerals with Paracelsian Topology under High Temperature and High Pressure

Abstract—Feldspar group minerals (feldspars) form up to 60 vol.% of the Earth’s crust. The knowledge of their stability under extreme conditions (high-pressure and high-temperature) allow to better understand the processes, that occur in the subduction and collision processes. This review focuses on the behavior of feldspars with paracelsian topology (seven mineral species: three borosilicates, two aluminosilicates and two beryllophosphates) at elevated temperatures and pressures. Partly, new data on high-temperature behavior of paracelsian BaAl2Si2O8 (based on in situ high-temperature powder X-ray diffraction) provided. The high-temperature studies of 5 feldspar minerals with paracelsian topology (danburite, maleevite, pekovite, paracelsian, slawsonite) revealed that all of them are stable at least up to 800 °C. Among all of them only paracelsian undergoes polymorphic transition (at 930 °C), whereas all other minerals decompose or amorphisize. The structural deformations of these minerals demonstrate the different anisotropy degree upon heating, whereas the average volume expansion is similar for all of them (αV = 23 × 10–6 ºC–1). High-pressure behavior was studied for six of seven minerals with paracelsian topology (danburite, meleevite, pekovite, paracelsian, slawsonite, hurlbutite). The studied minerals undergo transformations with the stepwise increasing of coordination number of frame-forming cations from 4 to 5 and 6 upon compression The discovering of unusual structural units under extreme conditions (e.g., fivefold-coordinated polyhedral) can influence on the concentration and transport processes of trace elements that should be taken into account when interpreting geochemical and geophysical data. The crystal structure stability range of studied minerals highly depends on the chemical composition of frame-forming cations: aluminosilicates are the least stable and undergo the phase transitions below 6 GPa; borosilicates preserve their initial crystal structure up to ~20 GPa; beryllium phosphates do not undergo phase 2 transformations up to 75 GPa. It has been shown that transformations pathway of isostuctural compounds highly depends on the chemical composition of both extraframework and frame-forming cations that involves the difficulties with predictions of their behavior under extreme conditions.

New Isocoumarin and Pyrone Derivatives from the Chinese Mangrove Plant Rhizophora mangle-Associated Fungus Phomopsis sp. DHS-11.

Mangrove-associated fungi are important sources for the discovery of new bioactive natural products. Three new isocoumarins (1-3) and one new pyrone derivative (4) were isolated from the ethyl acetate extract of the fermentation broth of the mangrove endophytic fungus Phomopsis sp. DHS-11. Nuclear magnetic resonance (NMR) spectroscopy (one-dimensional and two-dimensional) and mass spectrometry were used to determine the structures of these new compounds. The absolute configurations for the new isocoumarins 1-3 were determined by comparing their experimental and calculated electronic circular dichroism (ECD) spectra, while the configuration for the new pyrone-derivative 4 was tentatively solved by comparison of its 13C NMR data with reported data. In the biological activity test, compounds 1 and 3 showed cytotoxic activity against HeLa cells with IC50 values of 11.49 ± 1.64 µM and 8.70 ± 0.94 µM, respectively. The initial structure and activity relationship (SAR) analysis revealed that the length of the side chain at C-3 for isocoumarin-type compounds 1-3 could affect the cytotoxicity against HeLa cells. Compound 4 exhibited cytotoxic activities against human hepatoma cells HepG2 with an IC50 value of 34.10 ± 2.92 µM. All compounds have no immunosuppressive activity.

How to design platform ecosystems by intrapreneurs: Implications from action design research on IoT-based platform

The recent technological evolution of the Internet of Things (IoT) and data sciences has created opportunities for intrapreneurs in non-platform firms to expand their businesses into platform ecosystem-related businesses. However, previous studies have typically focused on cases involving entrepreneurs. This study aims to clarify how intrapreneurs’ design for platform ecosystems could be different from that of entrepreneurs. We conducted an action design research (ADR) project in collaboration with a company for 29 months, and designed a platform ecosystem structure based on technological platforms related to radio frequency identifiers (RFID). Our main contribution is the following six-step process that describes how intrapreneurs design platform ecosystems: (1) designing an initial ecosystem structure based on platform ecosystem concepts and certain concepts related to the targeted market; (2) analyzing past business cases; (3) making the ecosystem structure into concrete shape; (4) verifying its validity; (5) elaborating the ecosystem structure; and (6) proposing the designed ecosystem business. Our findings highlight the differences between intrapreneurs’ and entrepreneurs’ designs of the ecosystem. First, when the design processes are underway, the direction of the design of the ecosystem needs to be flexibly modified to align with the strategy of the firm. Second, evidence for the success of the proposed platform ecosystem is required to reduce uncertainty and clarify the legitimacy of the proposition. Third, the structure of a platform ecosystem designed by intrapreneurs becomes a style that supports the existing businesses and networks of the firm.

Magnetic field draping around clumpy high-velocity clouds in galactic halo

ABSTRACT Throughout the passage within the Galactic halo, high-velocity clouds (HVCs) sweep up ambient magnetic fields and form stretched and draped configurations of magnetic fields around them. Many earlier numerical studies adopt spherically symmetric uniform-density clouds as initial conditions for simplicity. However, observations demonstrate that HVCs are clumpy and turbulent. In this paper, we perform 3D magnetohydrodynamic simulations to study the evolution of clouds with initial density distributions described by power-law spatial power spectra. We systematically study the role of (i) the initial density structure, (ii) halo magnetic fields, and (iii) radiative cooling efficiency upon infalling HVCs. We find that (i) the clouds’ density structure regulates mixing and mass growth. Uniform clouds grow from the onset of the simulations, while clumpy clouds initially lose gas and then grow at later times. Along the same lines, the growth curve of clumpy clouds depends on the slope of the initial density power spectra. (ii) Magnetic fields suppress hydrodynamic instabilities and the growth of small-scale structures. As a result, magnetized clouds develop long filaments extended along the streaming direction, whereas non-magnetized clouds are fragmented into many small clumps. (iii) Efficient cooling keeps the main cloud body more compact and produces decelerated dense clumps condensed from the halo gas. This work potentially helps us understand and predict the observed properties of HVCs such as the detectability of magnetized clouds, the presence of decelerated HI structures associated with HVC complexes and small-scale features, and a possible link between the origin and the fate of HVCs.

Contrasting demographic responses to size‐selective harvesting among neighbouring wild fish populations

Abstract Sustainable harvesting of wild populations relies on evidence‐based knowledge to predict harvesting outcomes for species and the ecosystems they inhabit. Although harvesting may elicit compensatory density‐dependence, it is generally size‐selective, which induces additional pressures that are challenging to forecast. Furthermore, responses to harvest may be population‐specific and whether generalizable patterns exist remains unclear. Taking advantage of Parks Canada's mandate to remove introduced brook trout Salvelinus fontinalis to restore alpine lakes in Canadian parks, we experimentally applied standardized size‐selective harvesting rates (the largest ~64% annually) for three consecutive summers in five populations with different initial size structures. Four unharvested populations were used as controls. At reduced densities, harvested and control populations exhibited similar density‐dependent increases in specific growth, juvenile survival and earlier maturation. However, size‐selective harvesting simultaneously induced changes to size and age structure that contrasted among harvested populations. Average body length decreased in three of five harvested populations, whereas it tended to increase in control populations over the 3 years. We also detected contrasting, population‐specific changes in body length variability and ultimately in length‐ and age‐at‐harvest in harvested populations but not controls. Overall, populations with smaller, more homogeneous body sizes, and living at high densities were most resilient to size‐selective harvesting, exhibiting the smallest change in size‐at‐age. In contrast, large‐bodied populations exhibited more substantial size‐structure changes following selective harvesting: large‐bodied populations experienced either stabilizing or disruptive pressures, when initial length variability was high or low, respectively. Synthesis and application. Our results show that within species, size‐selective harvesting inherently leads to more risk and uncertainty when harvesting populations with larger and more varied body sizes than smaller‐bodied populations with less range in body size. Our study supports prioritizing regulations that protect harvested populations with larger and more varied body sizes. Such a management strategy would reduce the likelihood of eliciting unpredictable or undesirable demographic changes to fish populations with these attributes.