Asymmetric Shell Research Articles

Asymmetric Coordination Regulating D‐Orbital Spin‐Electron Filling in Single‐Atom Iron Catalyst for Efficient Oxygen Reduction

AbstractThe single‐atom Fe−N−C catalyst has shown great promise for the oxygen reduction reaction (ORR), yet the intrinsic activity is not satisfactory. There is a pressing need to gain a deeper understanding of the charge configuration of the Fe−N−C catalyst and to develop rational modulation strategies. Herein, we have prepared a single‐atom Fe catalyst with the co‐coordination of N and O (denoted as Fe−N/O−C) and adjacent defect, proposing a strategy to optimize the d‐orbital spin‐electron filling of Fe sites by fine‐tuning the first coordination shell. The Fe−N/O−C exhibits significantly better ORR activity compared to its Fe−N−C counterpart and commercial Pt/C, with a much more positive half‐wave potential (0.927 V) and higher kinetic current density. Moreover, using the Fe−N/O−C catalyst, the Zn‐air battery and proton exchange membrane fuel cell achieve peak power densities of up to 490 and 1179 mW cm−2, respectively. Theoretical studies and in situ electrochemical Raman spectroscopy reveal that Fe−N/O−C undergoes charge redistribution and negative shifting of the d‐band center compared to Fe−N−C, thus optimizing the adsorption free energy of ORR intermediates. This work demonstrates the feasibility of introducing an asymmetric first coordination shell for single‐atom catalysts and provides a new optimization direction for their practical application.

Stability of asymmetric Schwarzschild–Rindler–de Sitter thin shell wormhole

The paper examines the dynamics of asymmetric thin shell wormholes that connect two distinct spacetimes using the cut and paste technique. The focus is on analyzing the linear stability of these wormholes by considering radial perturbations and utilizing the modified generalized Chaplygin gas equation of state. The specific case of an asymmetric wormhole connecting Schwarzschild–Rindler spacetime to Schwarzschild–Rindler–de Sitter space–time is analyzed using this formalism. Our investigation uncovers the existence of both stable and unstable regions, which are contingent upon the appropriate selection of various parameters within the metric spacetime and equation of state. Additionally, we determine that stability regions exist as a consequence of the square speed of sound. By increasing the value of the cosmological constant, the stability region is expanded. Furthermore, the stability regions are augmented by the influence of Rindler parameters, while the stability regions are also affected by adjustments in the equation of state parameters, leading to their enlargement.

Asymmetric Coordination Regulating D-Orbital Spin-Electron Filling in Single-Atom Iron Catalyst for Efficient Oxygen Reduction.

The single-atom Fe-N-C catalyst has shown great promise for the oxygen reduction reaction (ORR), yet the intrinsic activity is not satisfactory. There is a pressing need to gain a deeper understanding of the charge configuration of the Fe-N-C catalyst and to develop rational modulation strategies. Herein, we have prepared a single-atom Fe catalyst with the co-coordination of N and O (denoted as Fe-N/O-C) and adjacent defect, proposing a strategy to optimize the d-orbital spin-electron filling of Fe sites by fine-tuning the first coordination shell. The Fe-N/O-C exhibits significantly better ORR activity compared to its Fe-N-C counterpart and commercial Pt/C, with a much more positive half-wave potential (0.927 V) and higher kinetic current density. Moreover, using the Fe-N/O-C catalyst, the Zn-air battery and proton exchange membrane fuel cell achieve peak power densities of up to 490 and 1179 mW cm-2, respectively. Theoretical studies and in situ electrochemical Raman spectroscopy reveal that Fe-N/O-C undergoes charge redistribution and negative shifting of the d-band center compared to Fe-N-C, thus optimizing the adsorption free energy of ORR intermediates. This work demonstrates the feasibility of introducing an asymmetric first coordination shell for single-atom catalysts and provides a new optimization direction for their practical application.

Origin of extrinsic chirality in metasurfaces and nanoholes fabricated by nanosphere lithography

Nanosphere lithography is a cost- and time-efficient tool for the fabrication of various nanostructured materials. Multiple steps of metal layer deposition at different oblique angles were shown to produce complex asymmetric and chiral shapes. Here, we investigate samples in which polystyrene nanospheres are covered by Ag or combination of Ag and Au at a single step (under 45°). In this way, we obtain metasurfaces with asymmetric shells, with a nanohole array formed due to the shadowing effect. We investigate chiro-optical properties of four samples by exciting them in the 700-1000 nm range, at angles of incidence from -45° to +45°; we report on dissymmetry in the total extinction between left and right circularly polarized excitation gext, which follows the rules of extrinsic chirality. We then resolve the transmission of Ag metasurface in terms of hyperspectral Stokes parameters, and we connect the S3 parameter with gext. Finally, we characterize nanohole arrays obtained from the same samples when the nanospheres are removed; we further perform electromagnetic simulations to gain insight into the “egg” shaped nanohole.

Dual-propelled polydopamine@SiO2@Pt micromotor with asymmetrical yolk-mesoporous shell for the enhanced catalytic reduction

Micro/nanomotors exhibit unique self-propulsion capabilities at the micro/nanoscale, offering significant potential as nanocatalysts in the field of catalysis by enhancing the contact probability between catalytic active sites and reactant molecules. Herein, a dual-propelled polydopamine (PDA)@SiO2@Pt micromotor with asymmetric yolk-mesoporous shell nanostructure is developed to enhance the catalytic reduction performance. The synthesis of PDA@SiO2@Pt micromotor involves a two-step process. First, the mesoporous silica is grown on the surface of the thermally swelled PDA sphere through heterogeneous interface self-assembly. Subsequently, the Pt nanoparticles (Pt NPs) are selectively loaded onto the PDA yolk. The asymmetric PDA yolk demonstrates outstanding photothermal conversion abilities, generating local thermal gradients under near-infrared (NIR) light irradiation, which propels the micromotor through thermophoresis. Simultaneously, the Pt NPs on PDA yolk catalyze the decomposition of H2O2 decomposition, generating O2 gradient that drives the micromotor through self-diffusiophoresis. The motion behavior of PDA@SiO2@Pt micromotor can be controlled through adjusting the NIR light illumination power density or varying concentration of H2O2. Moreover, the mesostructured architecture of PDA@SiO2@Pt micromotor can be employed to achieve the efficient catalytic reduction, achieving up to 93 % conversion of methylene blue (MB) within 5 min due to the combined effects of photothermal and particle motion properties induced by NIR light. The PDA@SiO2@Pt micromotor exhibits immense potential for future applications in complex catalytic systems using multi-driven micro/nanomotors.

Extrinsic chirality tailors Stokes parameters in simple asymmetric metasurfaces.

Metasurfaces tailor electromagnetic confinement at the nanoscale and can be appropriately designed for polarization-dependent light-matter interactions. Adding the asymmetry degree to the desing allows for circular polarizations of opposite handedness to be differently absorbed or emitted, which is of interest in fields spanning from chiral sensing to flat optics. Here, we show that simple, low-cost asymmetric metasurfaces can control Stokes parameters in the transmitted far-field. With only 50 nm of asymmetric plasmonic shells on self-assembled polystyrene nanospheres, our metasurfaces allow for great spectral and incident angle tunability. We first investigated broadband extrinsic chirality in metasurfaces with asymmetric plasmonic semishells; we found high extinction circular dichroism (CD) in the near-infrared range. We then excited it with linear polarization and performed hyperspectral Stokes polarimetry on the transmitted field. We showed that the S3 parameter follows the behavior of CD in extinction, and that the output field position on the Poincaré sphere can be widely controlled by using the incidence angle and wavelength. Furthermore, simulations agreed well with the experiments and showed how the near-field chiro-optical response influences the extrinsic chiral behavior in absorption and the polarization state of the transmitted field.

Core genes of biomineralization and cis-regulatory long non-coding RNA regulate shell growth in bivalves

IntroductionBivalve molluscs are abundant in marine and freshwater systems and contribute essential ecosystem services. They are characterized by an exuberant diversity of biomineralized shells and typically have two symmetric valves (a.k.a shells), but oysters (Ostreidae), some clams (Anomiidae and Chamidae) and scallops (Pectinida) have two asymmetrical valves. Predicting and modelling the likely consequences of ocean acidification on bivalve survival, biodiversity and aquaculture makes understanding shell biomineralization and its regulation a priority. ObjectivesThis study aimed to a) exploit the atypical asymmetric shell growth of some bivalves and through comparative analysis of the genome and transcriptome pinpoint candidate biomineralization-related genes and regulatory long non-coding RNAs (LncRNAs) and b) demonstrate their roles in regulating shell biomineralization/growth. MethodsMeta-analysis of genomes, de novo generated mantle transcriptomes or transcriptomes and proteomes from public databases for six asymmetric to symmetric bivalve species was used to identify biomineralization-related genes. Bioinformatics filtering uncovered genes and regulatory modules characteristic of bivalves with asymmetric shells and identified candidate biomineralization-related genes and lncRNAs with a biased expression in asymmetric valves. A shell regrowth model in oyster and gene silencing experiments, were used to characterize candidate gene function. ResultsShell matrix genes with asymmetric expression in the mantle of the two valves were identified and unique cis-regulatory lncRNA modules characterized in Ostreidae. LncRNAs that regulate the expression of the tissue inhibitor of metalloproteinases gene family (TIMPDR) and of the shell matrix protein domain family (SMPDR) were identified. In vitro and in vivo silencing experiments revealed the candidate genes and lncRNA were associated with divergent shell growth rates and modified the microstructure of calcium carbonate (CaCO3) crystals. ConclusionLncRNAs are putative regulatory factors of the bivalve biomineralization toolbox. In the Ostreidae family of bivalves biomineralization-related genes are cis-regulated by lncRNA and modify the planar growth rate and spatial orientation of crystals in the shell.

Core/shell bimagnetic microwires with asymmetric shell: MOKE and FMR behavior

A new type of multilayered microwires with a partially covering shell and bimagnetic character is here introduced. A precursor Pyrex-coated Fe-based microwire was fabricated by quenching and drawing technique, and subsequently an outer magnetic shell was deposited by magnetron sputtering covering only partly the precursor microwire (contrary to previously reported fully covered wires). Particularly, an amorphous magnetically soft core (Fe77.5B15Si7.5) was selected in this study and a polycrystalline shell (FeNi soft or Co hard) covered only half of microwire along the axis. After performing a geometry and surface roughness characterization, their surface azimuthal static magnetic profile was determined by magneto-optic Kerr-magnetometer, MOKE. In addition, the ferromagnetic resonance, FMR, response was experimentally studied by Network Analyzer up to 16 GHz frequency where the contributions of internal core and partly covering shell are analyzed and compared with fully covered microwires. The magnetoelastic behavior of such asymmetric bimagnetic microwires open up new perspectives to employ such materials for sensing and biomedical tweezer applications.

Evolution of Tb-shell homogeneity in Nd-Fe-B sintered magnets by long-term Tb grain boundary diffusion

Grain boundary diffusion process has been applied to effectively facilitate the coercivity enhancement of Nd-Fe-B magnets by the formation of core-shell structure with less heavy rare earth consumption. However, the excessively thick Tb-rich shells and asymmetric shells formed near the shallow diffused surface, not only have minor contribution to the coercivity enhancement but consume more Tb resources. In this work, the influences of diffusion time on coercivity changes and the evolution of asymmetric to symmetric Tb-rich shell have been investigated for the Tb-diffused Nd-Fe-B magnets. With prolonging the diffusion time at 890 ℃, the coercivity rapidly increases from 17.66 kOe to 24.41 kOe when the diffusion time is less than 18 h and keeps nearly unchanged after a longer diffusion time due to the trade-off effect of Tb-rich shell homogeneity and grain growth. Besides, magnetic domain structure and its dynamic evolution of different core-shell structures in Nd-Fe-B magnet further illustrate the positive effects of homogeneous symmetric Tb-rich shell on coercivity enhancement, which is directly observed by in-situ Lorentz TEM and magneto-optical Kerr microscope, and further proved by micromagnetic simulation. This work thus provides a new insight for tuning the Tb-rich shell distribution in the Nd-Fe-B sintered magnets with high performance by grain boundary diffusion.

Asymmetry-driven reconfigurability of magnetic vortices in hemispherical shells

Inhomogeneous magnetic configurations like vortices attract tremendous appeal as an emerging candidate in understanding nanoscale spin behaviours and utilizing their spin configurations for advanced technological applications. For vortex-driven practical applications, independent control and manipulation of both the circularity and polarity of the magnetic vortex is a prerequisite. In this study, we have shown that both the circularity and polarity of the magnetic vortex in an asymmetric hemispherical shell can be controlled by changing a single parameter - the direction of the in-plane external magnetic field. Furthermore, our results demonstrate the influence of geometrical asymmetry on the characteristics of magnetic vortices in ferromagnetic permalloy shells. These findings are expected to be helpful while designing vortex-based advanced technologies.

Dynamics of Asymmetric Three-Layer Hemispherical Shells with a Discrete-Inhomogeneous Filler Under Pulsed Loads

Dynamics of Asymmetric Three-Layer Hemispherical Shells with a Discrete-Inhomogeneous Filler Under Pulsed Loads

Dynamics of Asymmetric Three-Layer Spherical Shells with a Discretely Inhomogeneous Core Under Nonstationary Loading*

Dynamics of Asymmetric Three-Layer Spherical Shells with a Discretely Inhomogeneous Core Under Nonstationary Loading*

Complex Phase Behavior in Binary Blends of AB Diblock Copolymer and ABC Triblock Terpolymer

Blending block polymers with different block compositions provides an opportunity to create nanostructures that are not accessible from neat block copolymer melts. In this study, we investigate the equilibrium phase behavior in binary blends composed of an AB diblock copolymer and an ABC triblock terpolymer, using self-consistent field theory (SCFT). Blending these simple linear block polymers results in complex phase behaviors, including unusual core–shell network phases with asymmetric core and shell volume fractions and a new cylinder-in-O70 hybrid network phase. The phase diagrams with respect to segregation strength and blend composition reveal an unexpected morphological richness, including 15 ordered phases, illustrating the potential inherent in blending these relatively simple components.

Evidence for past interaction with an asymmetric circumstellar shell in the young SNR Cassiopeia A

Context. Observations of the supernova remnant (SNR) Cassiopeia A (Cas A) show significant asymmetries in the reverse shock that cannot be explained by models describing a remnant expanding through a spherically symmetric wind of the progenitor star. Aims. We investigate whether a past interaction of Cas A with a massive asymmetric shell of the circumstellar medium can account for the observed asymmetries of the reverse shock. Methods. We performed three-dimensional (3D) (magneto)-hydrodynamic simulations that describe the remnant evolution from the SN explosion to its interaction with a massive circumstellar shell. The initial conditions (soon after the shock breakout at the stellar surface) are provided by a 3D neutrino-driven SN model whose morphology closely resembles Cas A and the SNR simulations cover ≈2000 yr of evolution. We explored the parameter space of the shell, searching for a set of parameters able to produce an inward-moving reverse shock in the western hemisphere of the remnant at the age of ≈350 yr, analogous to that observed in Cas A. Results. The interaction of the remnant with the shell can produce asymmetries resembling those observed in the reverse shock if the shell was asymmetric with the densest portion in the (blueshifted) nearside to the northwest (NW). According to our favorite model, the shell was thin (thickness σ ≈ 0.02 pc) with a radius rsh ≈ 1.5 pc from the center of the explosion. The reverse shock shows the following asymmetries at the age of Cas A: (i) it moves inward in the observer frame in the NW region, while it moves outward in most other regions; (ii) the geometric center of the reverse shock is offset to the NW by ≈0.1 pc from the geometric center of the forward shock; and (iii) the reverse shock in the NW region has enhanced nonthermal emission because, there, the ejecta enter the reverse shock with a higher relative velocity (between 4000 and 7000 km s−1) than in other regions (below 2000 km s−1). Conclusions. The large-scale asymmetries observed in the reverse shock of Cas A can be interpreted as signatures of the interaction of the remnant with an asymmetric dense circumstellar shell that occurred between ≈180 and ≈240 yr after the SN event. We suggest that the shell was, most likely, the result of a massive eruption from the progenitor star that occurred between 104 and 105 yr prior to core-collapse. We estimate a total mass of the shell of the order of 2 M⊙.

Plasmonic Hot-Electron-Painted Au@Pt Nanoparticles as Efficient Electrocatalysts for Detection of H2O2.

Plasmon-driven catalysis of metal nanostructures has garnered wide interest. Here, a photogenerated plasmonic hot-electron painting strategy was reported to form Au@Pt composite nanoparticles (Au@Pt NPs) with high catalytic reactivity without using reducing agents. Au nanoparticles, including Au nanospheres (Au NSs), Au nanorods (Au NRs), and Au nanobipyramids (Au NBPs), generated hot electrons under localized surface plasmon resonance (LSPR) excitation, which made the platinum precursor reduced as a consequence that Pt(0) atoms were painted on the surface of Au NPs to form an asymmetric Pt shell outside the plasmonic Au core. Compared with bare Au NPs, Au@Pt NPs exhibited significantly enhanced electrocatalytic activity toward reduction of H2O2 due to the bimetallic synergistic effect and great dispersion of Au@Pt NP-modified indium tin oxide (Au@Pt NPs/ITO). It exhibited a linear detection of H2O2 in a wide concentration range from 0.5 to 1000 μM with a low detection limit of 0.11 μM (S/N = 3). Therefore, the plasmonic hot-electron-painted Au@Pt NPs represent a novel and simple method for the design of advanced noble asymmetric metal nanomaterials.

Water Defect Stabilizes the Bi3+ Lone-Pair Electronic State Leading to an Unusual Aqueous Hydration Structure.

The aqueous hydration structure of the Bi3+ ion is probed using a combination of extended X-ray absorption fine structure (EXAFS) spectroscopy and density functional theory (DFT) simulations of ion-water clusters and condensed-phase solutions. Anomalous features in the EXAFS spectra are found to be associated with a highly asymmetric first-solvent water shell. The aqueous chemistry and structure of the Bi3+ ion are dramatically controlled by the water stabilization of a lone-pair electronic state involving the mixed 6s and 6p orbitals. This leads to a distinct multimodal distribution of water molecules in the first shell that are separated by about 0.2 Å. The lone-pair structure is stabilized by a collective response of multiple waters that are localized near the lone-pair anti-bonding site. The findings indicate that the lone-pair stereochemistry of aqueous Bi3+ ions plays a major role in the binding of water and ligands in aqueous solutions.

The recurrent nova U Scorpii from the 2010.1 to 2022.4 eruptions; the missed eruption of 2016.78 ± 0.10 and the critical complex period changes

ABSTRACT U Sco is a recurrent nova with 11 observed eruptions, most recently in 2010.1 and 2022.4. I report on my program (running since 1989) of measuring eclipse times and brightnesses of U Sco in quiescence, from 2010 to 2022. The orbital period suddenly increased by +22.4 ± 1.0 parts-per-million across the 2010.1 eruption. This period change is greater than the near-zero period change (+3.9 ± 6.1 parts-per-million) across the 1999.2 eruption. This period change cannot come from any of the usual mechanisms, whereas the one remaining possibility is that the period changes are dominated by the little-known mechanism of the nova ejecting asymmetric shells. From 2010.1 to 2016.78, the O − C curve showed a steady period change that was large, with $\dot{P}$ = (−21.0 ± 3.2) × 10−9. This is greatly higher than the steady period changes in the two previous inter-eruption intervals (−3.2 ± 1.9 and −1.1 ± 1.1 × 10−9). This large, variable, and negative $\dot{P}$ apparently comes from magnetic braking of the companion star’s rotation. Starting in 2016.9 ± 0.6, the O − C curve showed a strong kink that is a unique characteristic of the sudden period change (+35.4 ± 7.1 parts-per-million) across a nova event. The brightness in quiescence after 2010.4 shows that the white dwarf accreted the trigger mass for the next nova event in the year 2017.1 ± 0.6. Photometric records show the only possible time for the eruption to peak (such that its total duration of 60 d was undetectable by any observation) is during a 75-d interval inside the 2016 solar gap, thus constraining the missed eruption to 2016.78 ± 0.10.

Fragments dispersion characteristics of the casing with the mismatched shell under internal explosive loading

The shell of the conventional casings filled with explosives is often in a good matching state with the charged explosive, but the conventional casings cannot meet the needs of the design of innovative warheads. To further improve the control capability for fragment dispersion characteristics of fragment warheads, the concept of the casing with the mismatched shell is proposed and studied in this paper. This kind of casing is composed of a cylindrical explosive and an asymmetric shell. A typical casing with the mismatched shell is designed, and the fragment dispersion characteristics of the casing are experimentally obtained using X-ray radiography technology and witness target test technology. It is found that the flying direction of fragments from the casing is consistent with the normal direction of the shell, and the fragment dispersion density in a direction is significantly improved. The particular fragment dispersion characteristic of the casing is verified, and the effects of eccentric initiation and shell strength on the fragment dispersion characteristics of the casing are analyzed by numerical simulation. The numerical results show that the shell strength has little effect on the special fragment dispersion characteristics of this kind of charged casing. By controlling the position of the initiation point, the fragments in a specific direction can be concentrated to achieve the fragment directional killing. The findings herein could serve as a solid foundation for the engineering design of innovative fragment warheads and could also be a reference for the hazard assessment of Improvise Explosive Devices (IEDs).

The prochloraz chronic exposure to Daphnia magna derived in biochemical alterations of F0 generation daphnids and malformed F1 progeny

In the present study, D. magna individuals were exposed to several sublethal prochloraz concentrations (87, 130, 170, 230 and 380 μg/L) for 21 days according to; the previous acute toxicity results. The fungicide effects on reproduction, survival, individual size, and growth population rate were evaluated after an exposure of 21 days, and no changes were observed compared to the control group. On the other hand, F1 generation neonates were collected and their external morphology evaluated; to estimate if the fungicide concentrations used induced effects during oogenesis and; embryogenesis processes. Neonates from parents which were previously exposed to 170 μg/L and higher concentrations were malformed since 16-d of exposure onward. All animals presented the same malformation: asymmetrical shell morphology and separated valves that did not cover the complete animal body regardless of the; concentration. The biochemical parameters tested in the broodstock were cholesterol, triglycerides, glucose and LDH activity. At the end of the chronic exposure experiment, cholesterol and triglycerides remained unaltered while glucose and the LDH enzyme levels increased significantly. The results of the present work showed a direct effect of; prochloraz on D. magna individual growth, along with mobilization of some; biochemical intermediate metabolism. A daphnid stress response as a result of the fungicide presence in the medium could be an explanation for the metabolic disorders. On the other hand, the F1 malformed neonates found in the present study suggested an effect of prochloraz among different daphnid generations and more studies would be necessary in this field.

First record of the brachiopod Erymnaria in the Chruteren Member (Euthal Formation) from a new Palaeogene site in the Br\xfclisau Schuppenzone of northeastern Switzerland (Canton St. Gallen) with remarks on shell asymmetry

A small, smooth-shelled rhynchonellid brachiopod, Erymnaria Cooper, 1959 was discovered in a previously unknown locality in the so-called Brülisau Schuppenzone (imbricate zone) of the South Helvetic region of northeastern Switzerland. It is the first record of this genus in this region and in Switzerland in general. It is comparable to the type species of Erymnaria, E. polymorpha (Massalongo, 1850). Its specific identity is currently undetermined, and the species is referred to Erymnaria sp. 1. The main characteristic of Erymnaria sp.1 is its asymmetric shell. This prompted a comparison of E. sp. 1 with other known asymmetric brachiopods. Questions of asymmetry and variability within the same genus and with brachiopods in general are discussed. Another, larger brachiopod species found at the new site is tentatively named Erymnaria? sp. 2. The site can be assigned to the Chruteren Member (Euthal Formation) of Early Ypresian age, dated by large Foraminifera. Thus, the previous distribution area of the Chruteren Member can be extended.