Weak Energy Research Articles

From 2e- to 4e- pathway in the alkaline oxygen reduction reaction on Au(100): Kinetic circumvention of the volcano curve.

We report the free energy barriers for the elementary reactions in the 2e- and 4e- oxygen reduction reaction (ORR) steps on Au(100) in an alkaline solution. Due to the weak adsorption energy of O2 on Au(100), the barrier for the association channel is very low, and the 2e- pathway is clearly favored, while the barrier for the O-O dissociation channel is significantly higher at 0.5eV. Above 0.7V reversible hydrogen electrode (RHE), the association channel becomes thermodynamically unfavorable, which opens up the O-O dissociation channel, leading to the 4e- pathway. The low adsorption energy of oxygenated species on Au is now an advantage, and residue ORR current can be observed up to the 1.0-1.2V region (RHE). In contrast, the O-O dissociation barrier on Au(111) is significantly higher, at close to 0.9eV, due to coupling with surface reorganization, which explains the lower ORR activity on Au(111) than that on Au(100). In combination with the previously suggested outer sphere electron transfer to O2 for its initial adsorption, these results provide a consistent explanation for the features in the experimentally measured polarization curve for the alkaline ORR on Au(100) and demonstrate an ORR mechanism distinct from that on Pt(111). It also highlights the importance to consider the spin state of O2 in ORR and to understand the activation barriers, in addition to the adsorption energies, to account for the features observed in electrochemical measurements.

Energy bounds in f(R,T) gravity with anisotropic backgrounds

This research work discusses the energy bounds in [Formula: see text] gravity with an anisotropic background, where [Formula: see text] is the Ricci scalar and [Formula: see text] is the trace of the energy–momentum tensor. For our study, we consider the locally rotationally symmetric Bianchi Type-I space-time. Moreover, we calculate the field equations and find exact solutions by considering different [Formula: see text] gravity models. We investigate the graphical behavior of energy density and pressure components by considering these distinct gravity models. We further use Hubble, deceleration, jerk, and snap parameters to evaluate the viability of our models. We also perform the graphical analysis to observe the behavior of energy conditions especially null energy conditions, weak energy conditions, strong energy conditions, and dominant energy conditions. It can be noticed that all considered [Formula: see text] gravity models support the idea of the presence of exotic matter, which justifies the phenomenon of expansion of the universe.

Experimental investigation of styrene destruction by DBD plasma and its conversion pathways

AbstractThis work was devoted to the investigation of the contribution of various species in plasma to styrene decomposition. Different background gases (air, argon, nitrogen, and oxygen) and plasma reactor (in‐plasma, post‐plasma, and post‐plasma with buffer tube) were employed in this experiment. The results showed that degradation and polymerization of styrene occur simultaneously in the plasma treatment process. In the discharge zone, the bombardment of electrons and energetic particles on styrene and its degradation intermediates played a role in breaking its weak bond energy and promoting their conversion. The short‐lived reactive species with high oxidation potential in plasma were the prerequisite for complete degradation of styrene, due to its ability of breaking bonds with large bond energies, such as benzene ring. Away from the discharge zone, long‐lived reactive oxygen species further oxidized and degraded styrene, and its intermediates outside the discharge zone, promoting their mineralization.

Cosmological dynamics in f(R) gravity models through cosmographic energy conditions

A proposed f(R) functional form’s constraints caused by energy conditions are presented. Raychaudhuri’s equation and the premise that gravity is attractive are both used to derive null and strong energy conditions for the proposed f(R) gravity model. Furthermore, the weak and dominant energy conditions are established by analysing the energy conditions induced by an effective energy-momentum tensor for the f(R)-theory of gravity. The most recent estimates of the cosmographic parameters that mimic Chaplygin gas-type dark energy are used on the parameters of a pair of f(R) models as a tangible extension of the energy conditions to the Robertson-Walker universe. It is found that under the various values of the coupling parameters the proposed f(R) model satisfy null, weak and dominant energy conditions while strong energy conditions are breached. Further, constraining the coupling parameters as a result of energy conditions, our analysis shows that the proposed model accurately captures the observed cosmic acceleration, as indicated by key parameters such as the effective equation of state (ω eff ), and the deceleration parameter (q). Through a geometric analysis of cosmographic parameters, we observe deviations of f(R) gravity from the ΛCDM model. We identify distinct evolutionary pathways that resemble characteristics of either quintessence or Chaplygin gas dark energy across various epochs, indicating a dynamic rate of cosmic acceleration. Our findings highlight the significant influences of coupling parameters and initial conditions on the cosmic evolution.

Enhanced acidic hydrogen evolution reaction kinetics via nitrogen-doped iridium nanosheet with optimized hydrogen adsorption energy

The hydrogen evolution reaction (HER) is influenced by the adsorption/desorption of hydrogen intermediates on active sites. Nitrogen doping is a way to alter the electronic structure and boost the activity of metal electrocatalysts although the mechanism remains controversial. Here, nitrogen is incorporated into face-centered cubic iridium nanosheets (N-fcc-Ir-NSs) through the ammonia reduction of metastable two-dimensional pristine trigonal iridium oxide. With a nitrogen content of only 0.8 wt%, N-fcc-Ir-NSs exhibit a low overpotential of 19 mV at −10 mA cmgeo-2 and a Tafel slope of 18.6 mV dec-1 in sulfuric acid. The doped nitrogen reduces hydrogen adsorption energy by modulating the electronic structure of iridium atoms, and the combined effects of iridium sites with strong hydrogen adsorption energy and iridium sites near the nitrogen atoms with weak hydrogen adsorption energy improve the HER activity. Moreover, the presence of nitrogen causes iridium to donate more electrons to hydrogen and promotes hydrogen desorption.

Casimir wormholes in Brans–Dicke theory

In recent years there has been a growing interest in the field of wormhole physics in the presence of Casimir effect. As this effect provides negative energy density, it can be utilized as an ideal candidate for the exotic matter required for creating a traversable wormhole. In the context of modified theories of gravity such as Brans–Dicke (BD) theory (Brans and Dicke 1961 Phys. Rev. 124 925), wormhole geometries have been vastly investigated. However, the scientific literature is silent on the issue of BD wormholes in the presence of Casimir energy. Our aim in the present study is to seek for static spherically symmetric solutions representing wormhole configurations in BD theory with Casimir energy as the supporting matter. The Casimir setup we assume comprises two electrically neutral, infinitely large parallel planes placed in a vacuum. We then consider the Casimir vacuum energy density of a scalar field in such a configuration with Dirichlet and mixed boundary conditions. In the former case the corresponding Casimir force is attractive and in the latter this force is repulsive. We present exact zero tidal force wormhole solutions as well as those with non vanishing redshift function for both types of Casimir energies. The conditions on wormhole solutions along with the weak (WEC) and null (NEC) energy conditions put constraints on the values of BD coupling parameter. These constraints are also subject to the value of BD scalar field at the throat and the throat radius. We therefore find that BD wormholes in the presence of Casimir energy can exist without violating NEC and WEC (for the repulsive Casimir force). Finally, we examine the equilibrium condition for stability of the obtained solutions using Tolman–Oppenheimer–Volkoff equation.

Dual dynamic H-bonds crosslink side chains support a robust polysiloxane elastomer and its self-repairing and recycling properties

Owning excellent mechanical properties and mild repair conditions simultaneously has always been a paradox in the field of self-healing polysiloxane elastomer research. In this work, a robust polysiloxane elastomer with autonomic self-repairing at r. t. and recyclable properties was firstly designed and synthesized. The double strong H-bonds ensure the strength of the elastomer, while the urea bond with relatively weak bond energy also acts as a sacrifice bond to dissipate energy and further bolster the mechanical properties. Meanwhile the double dynamic bonds located in the side chain with stronger molecular activity ability help to get good self-healing performance. Additionally, the material that can be recycled by crushing/remolding and dissolving/remolding methods without compromising their mechanical robustness and self-repairing properties is environmentally friendly.

Analytical models of supermassive black holes in galaxies surrounded by dark matter halos

In this Letter, we present five analytical models in closed forms, each representing a supermassive black hole (SMBH) located at the center of a galaxy surrounded by dark matter (DM) halo. The density profile of the halo vanishes inside twice the Schwarzschild radius of the hole and satisfies the weak, strong, and dominant energy conditions. The spacetime are asymptotically flat, and the difference among the models lies in the slopes of the density profiles in the spike and regions far from the center of the galaxy. Three of them represent cusp models, whereas the other two represent core models. With the well-known (generalized) Newman-Janis algorithm, rotating SMBHs with DM halos can be easily constructed from these models.

Analyzing the Einstein cubic gravity black hole for weak gravitational lensing, quasi-periodic oscillations, effective force, and emission energy

Analyzing the Einstein cubic gravity black hole for weak gravitational lensing, quasi-periodic oscillations, effective force, and emission energy

Membrane models as a means of propulsion in general relativity: super-luminal warp-drive that satisfies the weak energy condition

Presented are toy-models for sub-luminal and super-luminal warp-drives in 3+1 dimensions. The models are constructed in a chimeric manner—as different bulk space-times separated by thin membranes. The membranes contain perfect-fluid-like stress-energy tensors. The Israel junction conditions relate this stress-energy to a jump in extrinsic curvature across the brane, which in turn manifests as apparent acceleration in the bulk space-times. The acceleration on either side of the brane may be set individually by choice of model parameters. The Weak Energy Condition (WEC) is shown to be satisfied everywhere in both models. Although the branes in these toy models are not compact, it is demonstrated that super-luminal warp-drive is possible that satisfies the WEC. Additionally, the nature of these models provides framework for speculation on a mechanism for transition from sub-luminal to super-luminal warp. It is shown that the difference in extrinsic curvature across a thin membrane can yield a positive contribution to the Landau–Raychaudhuri equation, thus providing a means to evade some super-luminal warp-drive no-go theorems. Neither quantum effects nor stability of the models is considered.

Unraveling the mysteries of wormhole formation in Rastall–Rainbow gravity: a comprehensive study using the embedding approach

The present work looks for the possible existence of static and spherically symmetric wormhole geometries in Rastall–Rainbow gravity. Since, the Rastall–Rainbow gravity model has been constructed with the combination of Rastall theory and the gravity’s rainbow formalism. Taking advantage of the Karmarkar condition for embedding class one metrics, we solve the modified field equations analytically that describe wormholes for specific choice of redshift function. For specific parameter ranges, the solution represents a traversable wormhole that exhibits the violation of null energy condition and consequently the weak energy condition also. Furthermore, we focus on the wormhole stability via adiabatic sound velocity analysis. This model establishes a strong connection between two model parameters, namely, the Rastall parameters and the Rainbow functions, and how it affects the wormhole solution.

Fate of charged wormhole structures utilizing Karmarkar approach

The purpose of this study is to elaborate on the Morris–Thorne wormhole notion by creating a detailed model of a charged wormhole shape function. The classical embedding theory, which has played a significant role in the general theory of relativity, accomplishes this objective. Here, we assume redshift function along with charge i.e. ψ(r,Q2)=Log[1+Q2r2] and Q(r)=ξr. For this particular choice, the surface redshift function remains positive and finite everywhere even for the larger range of radial coordinate r. In wormhole geometry, the violation of Null energy condition have a crucial role which leads to the exotic matter. We examined our solutions through energy bounds (Null, Weak and Strong energy bounds) to check their stable state and its viability. Interestingly, in present work we analyze that the presence of electric charge amplify the results and provides the traversable charged wormhole solutions without exotic matter near the throat in the context of general theory of relativity.

Deterioration of Li-doped phenanthroline-based charge generation layer for tandem organic light-emitting diodes

Understanding the deterioration of the charge generation layer (CGL) is an uprising issue for efficient and stable tandem organic light-emitting diodes. Here, we comprehensively investigated the change in the electrical characteristics of Li-doped CGLs according to different stress conditions and compared the stability of Li diffusion in two phenanthroline-based electron transport materials. Through current density–voltage and capacitance-frequency measurements, it was revealed that electrical stress and thermal stress affect CGL’s electrical properties differently. Moreover, the exponential trap distribution model analysis informed that the Li diffusion is expedited toward narrowing depletion width in the CGL. Diffusion of Li and thermal effect to the diffusion was experimentally observed by X-ray photoelectron spectroscopy (XPS) depth profiling. We also evaluated variations in the operating voltage of tandem devices that differed only in nCGL. Overall, Li diffusion occurs more favorably in sparse Bphen film with weak binding energy rather than closely packed BPPB film with strong binding energy, which highlights that atomic geometry and morphological characteristics are crucial for the stability of tandem devices.

Modeling of Deuteron-Induced Reactions on Molybdenum at Low Energies

The activities of the EUROfusion consortium on the development of high quality nuclear data for fusion applications include evaluations of deuteron induced reactions and related data libraries for needs of the DEMO fusion power plant and IFMIF-DONES neutron-source nuclear analyses. Molybdenum is one of the major constituents of the reference stainless steels used in critical components of these projects. While the TENDL deuteron data library was the current reference used by EUROfusion, need of its further improvement has already been pointed out. The weak binding energy of the deuteron is responsible for the high complexity of its interaction with nuclei, involving also a variety of reactions initiated by the nucleons following the deuteron breakup. Their analysis completed that of the deuteron interactions with Mo and its stable isotopes, from elastic scattering to pre-equilibrium and compound–nucleus reactions, up to 50 MeV. A particular attention has been paid to the breakup, stripping, and pick-up direct interactions which amount to around half of the deuteron total–reaction cross section. The due account of most experimental data has validated the present approach, highlighted some prevalent features, and emphasized weak points and consequently the need for modeling/evaluation upgrade.

Understanding the adsorption properties of CO2 and N2 by a typical MOF structure: Molecular dynamics and weak interaction visualization

An extensible molecular dynamics (MD) force field for a typical metal–organic framework (MOF) has been developed and verified in comparison with experimental data. The visualization of the important weak interactions based on density functional theory (DFT) calculations is performed. The dynamic process of CO2 and N2 adsorption by MOF was then studied by MD methods. The gas adsorption and desorption during temperature and pressure swing were also investigated. It is found that the structural features of MOF have an important effect on the regional range and strength of the weak interactions, and the region of the van der Waals potential surface of the MOF can determine the gas density distribution. The adsorption is dominated by van der Waals interactions on the whole and the variation of the total weak interaction energy can reflect that of the adsorbed amount. The sorption/desorption responds more slowly to temperature swing than to pressure swing.

Modifications to The Alcubierre Warp Field Metric in Anisotropic Matter and Implications to Detection of Warp Fields

The Alcubierre warp drive concept demonstrates a designed spacetime metric which enables hyperfast travel within the framework of known physics and has become one of the most widely studied spacetimes in the community. However, there has always been a singular issue with practical realization of the “warp drive” in that a large amount of matter with unattainable properties (such as negative or “exotic” matter/energy densities) are required. The negative matter-energy or “exotic” mass-energy density requirements violating the Averaged Weak and Null Energy Conditions mainly arise from solutions to the Einstein equations with little consideration of the matter content and characteristics within the metric. Recent efforts have shown that investigating details of the matter characteristics might offer new insights to practical warp field design and might lead to realizable solutions. This paper gives analysis of an anisotropic matter field solution, hypothetical applied variations to the Einstein coupling constant (via a multiplier function), and a multilayered warp bubble approach to reducing the warp field mass requirements to realizable forms and quantities. A discussion on the detection of such an advanced warp field is also given. Keywords: Alcubierre, Warp Drive, Spacetime Metric, Negative Energy, Einstein Equations, Anisotropic Matter

Infrared small target detection algorithm based on filter kernel combination optimization learning method

Infrared small target detection in complex backgrounds remains a big challenge due to its small size and weak energy, which makes it easy to be submerged in complex backgrounds. Common filtering algorithms are difficult to apply to various complex scenes and generate many false alarms and poor robustness. Therefore, this paper proposes an infrared small target detection algorithm based on filter kernel combination optimization learning method. For the sample image block use typical filter kernels and weight coefficients to calculate the combination of filtering results, and construct the loss function of the results and the true value. The optimal weight coefficients are learned using an optimization method, which effectively achieves the fusion of multiple features, then we build a sample library containing comprehensive priori information. In the implementation, an online inference method based on similarity measure is proposed to match test images with sample library image blocks to obtain optimal combination weights. By utilizing the comprehensive priori information to enhance the adaptive ability of the algorithm for various complex backgrounds. Finally, get the position of the infrared small target. The experimental results show that our algorithm has excellent detection performance for infrared small targets with complex background and low signal to clutter ratio, and the AUC value is 0.9980, which is more robust than other comparative algorithms.

Bimetallic Selenide CuFeSe2 as Mg‐Storage Material for Rechargeable Magnesium Batteries

AbstractRechargeable magnesium batteries (RMBs) are appealing alternatives for energy storage systems based on the high theoretical capacity, low price and high security of the Mg metal anode. Nevertheless, the shortage of high‐performance cathode materials severely obstructs its development. As an important conversion material, transition metal selenides, with desirable theoretical capacity and weak bond energy (Mg−Se), have attracted more attention in recent years. In this study, CuFeSe2 (CFS) nanoparticles were produced by a hydrothermal approach and its feasibility as a cathode material for RMBs was further investigated. Given the synergistic effect between Cu and Fe, the optimized CFS shows a reversible capacity of 120 mAh g−1 at 100 mA g−1, outstanding long‐term cyclability (86 mAh g−1 at 1 A g−1 after 600 cycles), and prominent rate capability (85 mAh g−1 at 1 A g−1). Density functional theory (DFT) computations conclude CFS exhibits a suitable migration barrier for Mg2+ along the tunnel of 0.92 eV. An in‐depth investigation of the mechanism demonstrates that the Mg storage process can be divided into solid solution reaction and the conversion processes by ex‐situ techniques. This work contributes to further investigate the Mg2+ storage mechanism of cathode materials for RMBs.

Atomistic analysis on implantation effects of hydrogen ions and copper ions into 4H-SiC

The microstructure evolution of 4H-SiC under the implantation of hydron ions and copper ions was investigated using molecular dynamics (MD) simulations and experimental analysis. MD models were developed to simulate the implantation of single Cu2+ and H+ ions into SiC, analyzing lattice damage, amorphous defects, and temperature distribution. H+ ion implantation resulted in a higher number of amorphous atoms compared to Cu2+ ions. The maximum atomic temperature during Cu2+ ion implantation was significantly higher (1635 K) than during H+ ion implantation (950 K), although the volume of the temperature rise region was larger in the H+ model. Cu2+ ions induced more severe lattice vibrations than H+ ions. Atom movement along regions of weak lattice binding energy was observed. The study also examined overlapping multiple ion implantations, considering ion type, initial energy, and incident angle. Cu2+ ions exhibited smaller sputtering yield, projection range, number of amorphous atoms, and energy increment compared to H+ ions. A 0° incident angle resulted in higher sputtering yield and increased amorphous structure formation due to the channeling effect, which was more pronounced in the H+ model. The experimental results demonstrate that compared to Cu2+ ions, H+ ions have a greater impact on the surface peak roughness, sub-surface damage depth, and surface damage of SiC samples. It can provide a reliable guidance for selecting process parameters and the types of ions to implant.

Self-enhanced coherent harmonic amplification in seeded free-electron lasers

High-intensity, ultrashort, fully coherent X-ray pulses hold great potential for advancing spectroscopic techniques to unprecedented levels. Here, we propose a novel scheme for generating high-brightness and femtosecond-scale soft X-ray radiation within a seeded free-electron laser (FEL) operating at MHz repetition rates. This scheme relies on the principles of self-modulation and superradiance. A relatively weak energy modulation of the pre-bunched electron beam is significantly amplified by the coherent radiation emitted in the self-modulator. Consequently, a coherent signal at ultra-high harmonics of the seed is achieved, and this signal is further amplified in the subsequent radiator through the fresh bunch and superradiant processes. Based on the parameters of the Shanghai soft X-ray FEL facility, three-dimensional simulations have been performed. The simulation results demonstrate that an electron beam with a laser-induced energy modulation as small as 2.3 times the slice energy spread can generate ultrashort coherent radiation pulses of around 2 GW within the water window spectral range. Moreover, the experimental results demonstrate that self-enhanced coherent energy modulation enables the production of coherent signals up to the 15th harmonic of a 266-nm seed laser. These findings indicate that the proposed scheme promises to generate ultrashort and coherent soft X-ray pulses at MHz repetition rates.