Minimum Potential Research Articles

Living on the edge – physiological tolerance to frost and drought explains range limits of 35 European tree species

Species distribution models are key to evaluate how climate change threatens European forests and tree species distributions. However, current models struggle to integrate ecophysiological processes. Mechanistic models are complex and have high parameter requirements. Some correlative species distribution models have tried to include traits but so far have struggled to directly connect to ecophysiological processes. Here, we propose a new strategy in which species distributions are based on safety margins which represent species' proximity to their physiological thresholds. We derived frost and drought safety margins for 38 European tree species as the difference between physiological tolerance traits and local maximum stress. We used LT50 and Ψ50 as tolerance traits for frost and drought, respectively, and local minimum temperature and minimum soil water potential as maximum stress. We integrated these safety margins into a species distribution model, which tests if the probability of species presence declines rapidly when the safety margin reaches zero, when physiological stress exceeds the species' tolerance traits. Our results showed thaet 35 of the 38 studied species had their distribution explained by one or both safety margins. We demonstrated that safety‐margins‐based model can be efficiently transferred to species for which occurrence data are not available. The probability of presence dropped dramatically when the frost safety margin reached zero, whereas it was less sensitive to the drought safety margin. This differential sensitivity may be due to the more complex regulation of drought stress, especially as water is a shared resource, whereas frost is not. Our analysis provides a new approach to link species distributions to their physiological limits and shows that, in Europe, frost and drought safety margins are important determinants of species distributions.

Dynamical friction and the evolution of black holes in cosmological simulations: A new implementation in OpenGadget3

Aims. We introduce a novel sub-resolution prescription to correct for the unresolved dynamical friction (DF) onto black holes (BHs) in cosmological simulations, to describe BH dynamics accurately, and to overcome spurious motions induced by numerical effects. Methods. We implemented a sub-resolution prescription for the unresolved DF onto BHs in the OpenGadget3 code. We carried out cosmological simulations of a volume of (16 comoving Mpc)3 and zoomed-in simulations of a galaxy group and of a galaxy cluster. We assessed the advantages of our new technique in comparison to commonly adopted methods for hampering spurious BH displacements, namely repositioning onto a local minimum of the gravitational potential and ad hoc boosting of the BH particle dynamical mass. We inspected variations in BH demography in terms of offset from the centres of the host sub-halos, the wandering population of BHs, BH–BH merger rates, and the occupation fraction of sub-halos. We also analysed the impact of the different prescriptions on individual BH interaction events in detail. Results. The newly introduced DF correction enhances the centring of BHs on host halos, the effects of which are at least comparable with those of alternative techniques. Also, the correction becomes gradually more effective as the redshift decreases. Simulations with this correction predict half as many merger events with respect to the repositioning prescription, with the advantage of being less prone to leaving substructures without any central BH. Simulations featuring our DF prescription produce a smaller (by up to ~50% with respect to repositioning) population of wandering BHs and final BH masses that are in good agreement with observations. Regarding individual BH–BH interactions, our DF model captures the gradual inspiraling of orbits before the merger occurs. By contrast, the repositioning scheme, in its most classical renditions, describes extremely fast mergers, while the dynamical mass misrepresents the dynamics of the black holes, introducing numerical scattering between the orbiting BHs. Conclusions. The novel DF correction improves the accuracy if tracking BHs within their hosts galaxies and the pathway to BH- BH mergers. This opens up new possibilities for better modeling the evolution of BH populations in cosmological simulations across different times and different environments.

Dynamic 3D Simulation of Surface Charging on Rotating Asteroids

The surface-charging phenomenon of asteroids, mainly resulting from solar wind plasma and solar radiation, has been extensively studied. However, the influence of the asteroid’s rotation on surface charging is not yet fully understood. In this study, a neural network is established to replace numerical integration, improving the efficiency of dynamic 3D simulations. We simulate rotating asteroids and their surrounding plasma environments under various conditions, including the quiet solar wind and solar storms. Different minerals on the asteroid surface are also considered. Additionally, the effects of orbital motion and obliquity are studied for asteroids with rotation periods comparable to their orbital periods. The results show that under the typical solar wind, the maximum and minimum potentials of asteroids gradually decrease with increasing rotation periods, especially when the solar wind is obliquely incident. For asteroids with rotation periods longer than one week, this decreasing trend becomes extremely slow. During a solar storm, the solar wind plasma changes sharply, and the susceptibility of an asteroid’s surface potential to rotation is greatly pronounced. Surface minerals also play a role; plagioclase is the most sensitive mineral among those explored, while ilmenite appears indifferent to changes in rotation periods. Understanding the surface charging of asteroids under various rotation periods and angles is crucial for further research on solar wind plasma and asteroids’ surface dust motion, providing a reference for the safe landing and exploration of asteroids.

Parametrically amplified super-radiance towards hot big bang universe

We propose a mechanism of preheating stage after inflation, using a new idea of parametrically amplified super-radiance. Highly coherent state, characterized by macro-coherence of scalar field coupled to produced massless particle in pairs, is created by parametric resonance effects associated with field oscillation around its potential minimum, within a Hubble volume. The state is described effectively by the simple Dicke-type of super-radiance model, and super-radiant pulse is emitted within a Hubble time, justifying neglect of cosmic expansion. Produced particles are shown to interact to change their energy and momentum distribution to realize thermal hot big bang universe. A long standing problem of heating after inflation may thus be solved. A new dark matter candidate produced at the emergence of thermalized universe is suggested as well.

Atomic H over crystal surface: effective potential dependence on sample properties

Abstract We considered the behavior of the lowest electronic level of atomic H in a semi-infinite space bounded by a flat surface. 
We impose a third kind boundary condition on the electronic wave functions, where the boundary condition parameter models the adsorbent properties of the surface.
For the crystal surface, the double periodic function as the boundary parameter seems reasonable; therefore, this case is considered.
It is shown that there are two modes of atom adsorption on the sample surface depending on the parameters of the boundary condition. 
In the first case the effective atomic potential, considered as a function of the distance between H and the boundary plane, exhibits a well pronounced minimum at some finite distance and a relatively small effective range of interaction distances between the atoms and samples.
The second case occurs under the condition of a large positive affinity of the atomic electron to the sample boundary and low initial H-concentration inside the sample. 
In such a situation, the minimum of the effective potential is close to the sample surface, and a significant amount of energy can be emitted throughout the adsorption process.

Atomistic-informed phase field modeling of magnesium twin growth by disconnections

The nucleation and propagation of disconnections play an essential role during twin growth. Atomistic methods can reveal such small structural features on twin facets and model their motion, yet are limited by the simulation length and time scales. Alternatively, mesoscale modeling approaches (such as the phase field method) address these constraints of atomistic simulations and can maintain atomic-level accuracy when integrated with atomic-level information. In this work, a phase field model is used to simulate the disconnection-mediated twinning, informed by molecular dynamics (MD) simulations. This work considers the specific case of the growth of {101¯2} twin in magnesium. MD simulations are first conducted to obtain the orientation-dependent interface mobility and motion threshold, and to simulate twin embryo growth and collect facet velocities, which can be used for calibrating the continuum model. The phase field disconnections model, based on the principle of minimum dissipation potential, provides the theoretical framework. This model incorporates a nonconvex grain boundary energy, elasticity and shear coupling, and simulates disconnections as a natural emergence under the elastic driving force. The phase field model is further optimized by including the anisotropic interface mobility and motion threshold suggested by MD simulations. Results agree with MD simulations of twin embryo growth in the aspects of final twin thickness, twin shape, and twin size, as well as the kinetic behavior of twin boundaries and twin tips. The simulated twin microstructure is also consistent with experimental observations, demonstrating the fidelity of the model.

Investigations on the effect of arsenic and phosphorus atomic exchange on the origin of crystal potential fluctuations in InAsP/InP epilayers

The study investigates the anion exchange mechanism between the ad-atoms of arsenic and phosphorus followed by their inter-diffusion processes, in InAsP/InP hetero-structures grown by metal organic vapor phase epitaxy technique. The energetics and kinetics of the ad-atoms like arsenic and phosphorus are governed by the growth conditions. It has been found that the percolation of arsenic and phosphorus in the epilayer depends on various factors, such as gas-phase diffusion coefficients, surface reaction rates, misfit strain energy, bond energy, segregations, and the presence of defects and dislocations. Effects of anion exchange mechanisms on generating local crystal potential states that originated due to the local crystal bonding environment are further investigated. The magnitude of these local potential states strongly depends on the strain states associated with the layer thickness. If the difference between the potential minima is small (< 25 meV), it leads to distinct “S” shaped temperature-dependent luminescence/absorption spectra. In contrast, a large difference gives rise to two distinctive luminescence/absorption peaks. Thus, by controlling the strain states associated with the energetics and kinetics of ad-atoms like arsenic/phosphorus and layer thickness, such “S” shaped behavior can be controlled.

Self-aggregation and microhydration mechanisms of monoethanolamine: Far-infrared identification of large-amplitude hydrogen bond libration.

The strong tendency for self-aggregation together with an intriguing mechanism for the microhydration of monoethanolamine (MEA) have been explored by low-temperature far-infrared cluster spectroscopy in doped neon "quantum" matrices at 4K complemented by high-level quantum chemical modeling. In addition to the assignment of new mid-infrared perturbed intramolecular transitions, a distinct far-infrared transition is unambiguously assigned to the concerted large-amplitude hydrogen bond librational motion of the MEA homodimer. This observation confirms a global "head-to-head" intermolecular potential energy minimum associated with the formation of a compact doubly intermolecular OH⋯N hydrogen-bonded cyclic structure, where both monomeric intramolecular OH⋯N hydrogen bonds are broken upon complexation. By means of relative mixing ratio dependencies, dedicated annealing procedures, and selective complexation between MEA and isotopic H216O and H218O samples, distinct far-infrared transitions associated with large-amplitude intra-molecular hindered OH torsional motion and inter-molecular H2O librational (hindered c-type overall rotational) motion of the MEA monohydrate are furthermore assigned unambiguously for the first time. These spectroscopic observations reveal an intriguing metastable conformation, where H2O acts as a OH⋯O hydrogen bond donor to the hydroxy group instead of the amino group of MEA upon microhydration in the cryogenic neon environment, where the microhydration strengthens the intramolecular OH⋯N hydrogen bond of MEA due to hydrogen bond cooperativity.

New Insight into Quantity-Dependent Self-Assembly Pattern of Light Levitating Droplet Clusters.

It has been reported that the self-assembly pattern of light levitating droplet clusters above the hot gas-liquid interface is dependent on the quantity of droplets. However, the already-reported theoretical explanation of the quantity-dependent self-assembly pattern cannot work well when the quantity of the light levitating droplet exceeds 15. Herein, we propose a new theoretical perspective to understand the self-assembly of a light levitating droplet cluster by referring to the classical densest packing problem of identical rigid circles in a larger circle with the introduction of the minimum total potential energy principle. Amazingly, the theoretical results obtained by this new approach agree well with experimental results, even though the quantity of the light levitating droplet is up to 142. This study deepens our understanding of the quantity-dependent self-assembly pattern of the light levitating droplet clusters and provides significant inspiration for other analogous self-assembly phenomena.

Influence of temperature on the cathodic polarization behavior and calcareous deposit properties of X65 steel in sea water

PurposeThis paper aims to investigate how cathodic polarization behavior significantly affects the selection of cathodic protection parameters and the effectiveness of protecting underwater metal structures. Factors such as water depth and operating conditions impact seawater temperature, making it crucial to understand the effects of temperature on cathodic protection parameters for underwater pipelines.Design/methodology/approachIn this paper, potentiostatic polarization was carried out by three-electrode method, and morphology, X-ray diffraction and electrochemical analysis.FindingsIt was determined that the stable current densities at the minimum negative potential (−0.8 VSSC) for pipeline steel varied at different temperatures: 7°C, room temperature and 60°C. The cathodic protection potential corresponding to the lowest stable current density was observed to be −1.0 VSSC at 7°C and −0.95 VSSC at room temperature and 60°C.Originality/valueThis study elucidates the mechanisms by which different temperatures affect the protective performance of calcareous deposits and current densities.

Introducing KICK-MEP: exploring potential energy surfaces in systems with significant non-covalent interactions.

Exploring potential energy surfaces (PES) is fundamental in computational chemistry, as it provides insights into the relationship between molecular energy, geometry, and chemical reactivity. We introduce Kick-MEP, a hybrid method for exploring the PES of atomic and molecular clusters, particularly those dominated by non-covalent interactions. Kick-MEP computes the Coulomb integral between the maximum and minimum electrostatic potential values on a 0.001 a.u. electron density isosurface for two interacting fragments. This approach efficiently estimates interaction energies and selects low-energy configurations at reduced computational cost. Kick-MEP was evaluated on silicon-lithium clusters, water clusters, and thymol encapsulated within Cucurbit[7]uril, consistently identifying the lowest energy structures, including global minima and relevant local minima. Kick-MEP generates an initial population of molecular structures using the stochastic Kick algorithm, which combines two molecular fragments (A and B). The molecular electrostatic potential (MEP) values on a 0.001 a.u. electron density isosurface for each fragment are used to compute the Coulomb integral between them. Structures with the lowest Coulomb integral are selected and refined through gradient-based optimization and DFT calculations at the PBE0-D3/Def2-TZVP level. Molecular docking simulations for the thymol-Cucurbit[7]uril complex using AutoDock Vina were performed for benchmarking. Kick-MEP was validated across different molecular systems, demonstrating its effectiveness in identifying the lowest energy structures, including global minima and relevant local minima, while maintaining a low computational cost.

Tachyonic effects on Kähler moduli stabilized inflaton potential in type-IIB/F theory

We investigate the effects of inclusion of charged tachyonic open-string scalars in the perturbative and the non-perturbative Kähler moduli stabilizations in a geometry of three intersecting magnetized D7-brane stacks in type-IIB/F theory and also study the overall influence of this process on the inflaton potential, in a hybrid inflation scenario. We find that a tachyon lowers the minimum of the inflaton potential and assists to end the inflation. For simplicity, we have included one tachyon at a time in the present work and observe that this procedure preserves the features of slow-roll plateau of the potential. An interesting observation here is that the tachyonic part of the potential can be fine-tuned to get an almost zero minimum of the potential, thereby conforming to the small experimental value of the cosmological constant.

Synthesis, Crystal Structure and Antifungal Activity of (E)-1-(4-Methylbenzylidene)-4-(3-Isopropylphenyl) Thiosemicarbazone: Quantum Chemical and Experimental Studies.

A novel (E)-1-(4-methylbenzylidene)-4-(3-isopropylphenyl) thiosemicarbazone was synthesized in a one-pot four-step synthetic route. Fourier transform infrared spectroscopy (FTIR), 1H and 13C nuclear magnetic resonances (NMR), single-crystal X-ray diffraction, and UV-visible absorption spectroscopy were utilized to confirm the successful preparation of the title compound. Single-crystal data indicated that the intramolecular hydrogen bond N(3)-H(3)···N(1) and intermolecular hydrogen bond N(2)-H(2)···S(1) (1 - x, 1 - y, 1 - z) existed in the crystal structure and packing of the title compound. Besides the covalent interaction, the non-covalent weak intramolecular hydrogen bond N(3)-H(3)···N(1) discussed by atoms in molecules (AIM) theory also functioned in maintaining the title compound's crystal structure. The strong intermolecular hydrogen bond N(2)-H(2)···S(1) (1 - x, 1 - y, 1 - z) discussed by Hirshfeld surface analysis played a major role in maintaining the title compound's crystal packing. The local maximum and minimum electrostatic potential of the title compound was predicted by electrostatic potential (ESP) analysis. The UV-visible spectra and HOMO-LUMO analysis revealed that the title compound has a low ΔEHOMO-LUMO energy gap (3.86 eV), which implied its high chemical reactivity due to the easy occurrence of charge transfer interactions within the molecule. Molecular docking and in vitro antifungal assays evidenced that its antifungal activity is comparable to the reported pyrimethanil, indicating its usage as a potential candidate for future antifungal drugs.

The hydrodynamics of inverse phase transitions

First order phase transitions are violent phenomena that occur when the state of the universe evolves abruptly from one vacuum to another. A direct phase transition connects a local vacuum to a deeper vacuum of the zero-temperature potential, and the energy difference between the two minima manifests itself in the acceleration of the bubble wall. In this sense, the transition is triggered by the release of vacuum energy. On the other hand, an inverse phase transition connects a deeper minimum of the zero-temperature potential to a higher one, and the bubble actually expands against the vacuum energy. The transition is then triggered purely by thermal corrections. We study for the first time the hydrodynamics and the energy budget of inverse phase transitions. We find several modes of expansion for inverse bubbles, which are related to the known ones for direct transitions by a mirror symmetry. We finally investigate the friction exerted on the bubble wall and comment on the possibility of runaway walls in inverse phase transitions.

Experimental investigation of the influence of ZnO–CuO nanocomposites on interfacial tension, contact angle, and oil recovery by spontaneous imbibition in carbonate rocks

Researchers have recently focused on applying various nanoparticles/nanocomposites to improve the recovery factor from oil reservoirs. In this study, a new enhanced oil recovery agent, i.e., a ZnO–CuO (ZCO) nanocomposite, was synthesized, and its physicochemical properties are investigated by the scanning electron microscope, Fourier transform infrared spectrometer, Brunauer–Emmett–Teller, X-ray diffraction, and energy diffraction x-rays. The impact of ZCO and ZnO on interfacial tension, wettability change, and zeta potential tests has also been investigated under reservoir conditions. 0.1 weight percent (wt.%) of ZnO and ZCO in injection fluid, which minimizes contact angle and maximizes stability (i.e., minimum zeta potential), has been determined as the optimum concentration. The contact angle and zeta potential at this optimum concentration of ZnO and ZCO are 50.83°, 35.69° and −31.38, −35.65 mV, respectively. Then, the spontaneous imbibition using ZnO- and ZCO-based nanofluids with the optimum concentration is applied to monitor the recovery factor. The 22.5 day-long imbibition operation utilizing base fluid (without nanomaterials), ZnO, and ZCO retrieved 24.95%, 35.74%, and 52.01% of the oil, respectively. Overall, we concluded that injecting the ZCO-based nanofluids in carbonate porous media efficiently improves rocks and fluid parameters and enhances oil recovery.

Induced domain walls of QCD axion, and gravitational waves

We show that heavy axion domain walls induce domain walls of the QCD axion through a mixing between the heavy axion and the QCD axion, even when the pre-inflationary initial condition is assumed for the QCD axion. The induced domain walls arise because the effective θ parameter changes across the heavy axion domain walls, shifting the potential minimum of the QCD axion. When the heavy axion domain walls collapse, the induced QCD axion domain walls collapse as well. This novel mechanism for producing the QCD axions can explain dark matter even with the axion decay constant as small as 𝒪(109) GeV. In particular, this scenario requires domain wall collapse near the QCD crossover, potentially accounting for the stochastic gravitational wave background suggested by recent pulsar timing array observations, including NANOGrav. Using this mechanism, it is also possible to easily create induced domain walls for string axions or axions with a large decay constant, which would otherwise be challenging. We also comment on the implications for cosmic birefringence using induced axion domain walls.

Theoretical Investigation on Proton Transfer Directionality and Dynamics Behavior of 3-(Benzo[d]thiazol-2-yl)-2-hydroxy-5-methoxybenzaldehyde with Two Asymmetric Proton Acceptors.

A detailed theoretical investigation on the excited state intramolecular proton transfer (ESIPT) directionality and dynamics behavior of 3-(benzo[d]thiazol-2-yl)-2-hydroxy-5-methoxybenzaldehyde (BTHMB) with two unsymmetric proton acceptors (N and O2) has been performed. The hydrogen bond O1-H···N in BTHMB-a formed by the O1-H group with the N atom or O1-H···O2 in BTHMB-b formed by the O1-H group with the O2 atom is enhanced upon photoexcitation, and the strength of the O1-H···N bond is stronger, which will drive the O1-H proton to the N atom. Potential energy curves further confirm that ESIPT occurs in the N atom because of the smaller energy barrier (0.39 kcal/mol). Results of dynamics simulations manifest that no surface hopping exists between the S0 and S1 states within 300 fs, and ESIPT time constants of BTHMB-a and BTHMB-b are 48 and 151 fs, respectively. While the reverse ESIPT is observed in BTHMB-b at 294 fs, implying that the O1-H proton is transferred to the N atom instead of the O2 atom. The consistency of the calculated absorption (390 nm) and fluorescence spectra (443 and 602 nm) of BTHMB-a with the experimental values (390, 410, and 605 nm) confirms this conclusion again. The charge distribution analysis shows that the charge on the proton acceptors increases, and the O2 atom has higher electronegativity because it has more negative charges. The minimum surface electrostatic potential on the N atom in BTHMB-b correlating with the pKb value is -47.38 kcal/mol, indicating that the N atom has strong basicity. Therefore, the basicity of the N atom dominates the ESIPT process rather than the electronegativity of the O2 atom.

Effect of Leaving Centrosymmetric Character on Spectral Properties in Mono-, Bi-, and Triphotonic Absorption Spectroscopies.

Numerical simulations of the absorption bands of photoswitch E-o-tetrafluoroazobenzene in DMSO solution under one-, two-, and three-photon absorption conditions combined with the analysis of the behavior of transition probability under distortion of planarity reveal many similarities between the mono- and triphoton spectroscopic behaviors with a two-photon spectrum being set apart. The position of the absorption peak for the studied nπ* and ππ* transitions appears shifted to lower energies (longer wavelengths) than the conventional estimate based on vertical excitation from the ground-state potential energy minimum.

A light QCD axion with hilltop misalignment

We study the cosmological evolution of a light QCD axion and identify the parameter space to obtain the correct relic dark matter abundance. The axion potential is flattened at the origin, corresponding to the only minimum, while it is unsuppressed at π. These potential features arise by assuming a mirror sector with the strong CP phase θ¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\overline{\ heta} $$\\end{document} shifted by π compared to the SM sector, which allows the mirror axion potential to be tuned against the usual QCD axion potential. Before the QCD phase transition, assuming the mirror sector is decoupled and much colder than the SM thermal bath, the mirror sector potential dominates, causing the axion to initially roll to a temporary minimum at π. However, after the QCD phase transition, the potential minimum changes, and the axion relaxes from the newly created “hilltop” near π to the CP-conserving minimum at the origin. As the axion adiabatically tracks this shift in the potential minimum through the QCD phase transition, with non-adiabatic evolution near π and 0, it alters the usual prediction of the dark matter abundance. Consequently, this “hilltop” misalignment mechanism opens new regions of axion parameter space, with the correct relic abundance while still solving the strong CP problem, that could be explored in future experiments.

Stress fields at skin-stringer junctions in composite aircraft fuselages

This paper presents a semi-analytical analysis approach for the determination of stress fields in the vicinity of skin-stringer junctions in stiffened composite panels. The situation considered in this paper is representative for a typical stiffened panel in a modern composite aircraft fuselage. The analysis method employs a two-tier approach employing a global model based on CLPT on the one hand, and a local approach on the other hand in the form of a layerwise displacement formulation. This allows for the detailed computation of the stress concentrations in the vicinity of the skin-stringer junction. The layerwise formulation utilizes a discretization of the laminate layers into mathematical layers. The principle of the minimum of the total elastic potential yields the governing equations of the given problem, and an exponential approach leads to a quadratic eigenvalue problem that can be solved numerically. The analysis method shows excellent accuracy of the stress results in comparison with comparative finite element computations at a fraction of the computational time and effort that is required for numerical analyses.