NiMo alloys are efficient electrocatalysts in alkaline water electrolyzer for the hydrogen evolution reaction (HER). Metals are usually considered to be stable during the cathodic process. However, ...the actual behaviors of Mo in the NiMo alloys are unexplored. Here, we present the instability of Mo in the Ni4Mo alloy as a highly efficient HER electrocatalyst in an alkaline medium. Mo in Ni4Mo is oxidized and dissolved in the form of MoO42− first. The dissolved MoO42− will re‐adsorb on the electrode surface and polymerize. Theoretical calculations indicate that the adsorption of the dimer Mo2O72− can promote the HER activity of metal Ni. The addition of MoO42− to the electrolyte can not only repair the durability of Ni4Mo alloy, but also facilitate the HER activity of pure metal of Ni, Fe, and Co. Our findings provide insight into the structural transformation mechanism and performance‐enhanced origin of cathodic materials under the reaction conditions.
NiMo alloys, as one of the most efficient electrocatalysts in the alkaline electrolyzer, are unstable during the alkaline hydrogen evolution. An in situ transformation including oxidative dissolution of Mo in the form of MoO42−, the re‐adsorption of MoO42−, the polymerization of MoO42− to Mo2O72−, and the activity promotion by the Mo2O72− is presented.
Abstract The analysis of gamma-ray burst (GRB) spectra often relies on empirical models lacking a distinct physical explanation. Previous attempts to couple physical models with observed data focus ...on individual burst studies, fitting models to segmented spectra with independent physical parameters. However, these approaches typically neglect to explain the time evolution of observed spectra. In this study, we propose a novel approach by incorporating the synchrotron radiation model to provide a self-consistent explanation for a selection of single-pulse GRBs. Our study comprehensively tests the synchrotron model under a unified physical condition, such as a single injection event of electrons. By tracing the evolution of cooling electrons in a decaying magnetic field, our model predicts time-dependent observed spectra that align well with the data. Using a single set of physical parameters, our model successfully fits all time-resolved spectra within each burst. Our model suggests that the rising phase of the GRB light curve results from the increasing number of radiating electrons, while the declining phase is attributed to the curvature effect, electron cooling, and the decaying magnetic field. Our model provides a straightforward interpretation of the peak energy’s evolution, linked to the decline of the magnetic field and electron cooling due to the expansion of the GRB emission region. Our findings strongly support the notion that spectral and temporal evolution in GRB pulses originates from the expansion of the GRB emission region, with an initial radius of approximately 10 15 cm, and synchrotron radiation as the underlying emission mechanism.
Abstract The Type II gamma-ray burst (GRB) 200826A challenges collapsar models by questioning how they can generate a genuinely short-duration event. The other Type I GRB 211211A confused us with a ...kilonova signature observed in the afterglow of a long burst. Here, we propose a comprehensive model in which both bursts are the results of the collapse of Thorne–Żytkow–like objects (TZlOs). The TZlO consists of a central neutron star (NS), with a dense white dwarf (WD) material envelope, which is formed as the aftermath of a WD-NS coalescence. We find that the characteristics of the resultant GRBs depend on whether the TZlO collapses immediately following the WD-NS merger or not. Additionally, the observational properties of the consequent GRBs manifest variations contingent upon whether the collapse of the TZlO results in a magnetar or a black hole. We also show that our model is consistent with the observations of GRB 211211A and GRB 200826A. Specifically, the optical excess in GRB 211211A can be attributed to an engine-fed kilonova, while the supernova bump in GRB 200826A is likely due to the collision between the ejecta and the disk wind shell.
Dendritic spine development is crucial for the establishment of excitatory synaptic connectivity and functional neural circuits. Alterations in spine morphology and density have been associated with ...multiple neurological disorders. Autism candidate gene disconnected-interacting protein homolog 2 A (DIP2A) is known to be involved in acetylated coenzyme A (Ac-CoA) synthesis and is primarily expressed in the brain regions with abundant pyramidal neurons. However, the role of DIP2A in the brain remains largely unknown. In this study, we found that deletion of Dip2a in mice induced defects in spine morphogenesis along with thin postsynaptic density (PSD), and reduced synaptic transmission of pyramidal neurons. We further identified that DIP2A interacted with cortactin, an activity-dependent spine remodeling protein. The binding activity of DIP2A-PXXP motifs (P, proline; X, any residue) with the cortactin-Src homology 3 (SH3) domain was critical for maintaining the level of acetylated cortactin. Furthermore, Dip2a knockout (KO) mice exhibited autism-like behaviors, including excessive repetitive behaviors and defects in social novelty. Importantly, acetylation mimetic cortactin restored the impaired synaptic transmission and ameliorated repetitive behaviors in these mice. Altogether, our findings establish an initial link between DIP2A gene variations in autism spectrum disorder (ASD) and highlight the contribution of synaptic protein acetylation to synaptic processing.
The ant colony optimization (ACO) algorithm is a type of classical swarm intelligence algorithm that is especially suitable for combinatorial optimization problems. To further improve the convergence ...speed without affecting the solution quality, in this paper, a novel strengthened pheromone update mechanism is designed that strengthens the pheromone on the edges, which had never been done before, utilizing dynamic information to perform path optimization. In addition, to enhance the global search capability, a novel pheromone-smoothing mechanism is designed to reinitialize the pheromone matrix when the ACO algorithm's search process approaches a defined stagnation state. The improved algorithm is analyzed and tested on a set of benchmark test cases. The experimental results show that the improved ant colony optimization algorithm performs better than compared algorithms in terms of both the diversity of the solutions obtained and convergence speed.
The development of electrocatalysts to generate hydrogen, with good activity and stability, is a great challenge in the fields of chemistry and energy. Here we demonstrate a “hitting three birds ...with one stone” method to synthesize less toxic metallic WO2–carbon mesoporous nanowires with high concentration of oxygen vacancies (OVs) via calcination of inorganic/organic WO3–ethylenediamine hybrid precursors. The products exhibit excellent performance for H2 generation: the onset overpotential is only 35 mV, the required overpotentials for 10 and 20 mA/cm2 are 58 and 78 mV, the Tafel slope is 46 mV/decade, the exchange current density is 0.64 mA/cm2, and the stability is over 10 h. Further studies, in combination with density functional theory, demonstrate that the unusual electronic structure and the large amount of active sites, generated by the high concentration of OVs, as well as the closely attached carbon materials, were key factors for excellent performance. Our results experimentally and theoretically establish metallic transition metal oxides (TMOs) as intriguing novel electrocatalysts for H2 generation. Such TMOs with OVs might be promising candidates for other energy storage and conversion applications.
In coordination chemistry, catalytically active metal complexes in a zero‐ or low‐valent state often adopt four‐coordinate square‐planar or tetrahedral geometry. By applying this principle, we have ...developed a stable Pt1 single‐atom catalyst with a high Pt loading (close to 1 wt %) on phosphomolybdic acid(PMA)‐modified active carbon. This was achieved by anchoring Pt on the four‐fold hollow sites on PMA. Each Pt atom is stabilized by four oxygen atoms in a distorted square‐planar geometry, with Pt slightly protruding from the oxygen planar surface. Pt is positively charged, absorbs hydrogen easily, and exhibits excellent performance in the hydrogenation of nitrobenzene and cyclohexanone. It is likely that the system described here can be extended to a number of stable SACs with superior catalytic activities.
An atomically dispersed Pt1 catalyst has been developed with a high catalyst loading where each Pt atom is anchored on supported phosphomolybdic acid with distorted square‐planar coordination geometry. The catalyst is highly active for nitrobenzene and cyclohexanone hydrogenation.
Abstract One of the difficulties in nailing down the physical mechanism of gamma-ray bursts (GRBs) comes from the fact that there has been no clear observational evidence on how far from the central ...engine the prompt gamma rays of GRBs are emitted. Here we present a simple study addressing this question by making use of the “high-latitude emission” (HLE). We show that our detailed numerical modeling exhibits a clear signature of HLE in the decaying phase of “broad pulses” of GRBs. We show that the HLE can emerge as a prominent spectral break in F ν spectra and dominate the peak of ν F ν spectra even while the “line-of-sight emission” (LoSE) is still ongoing. This finding provides a new view of HLE emergence since it has been believed so far that the HLE can show up and dominate the spectra only after the LoSE is turned off. We remark, however, that this “HLE break” can be hidden in some broad pulses, depending on the proximity between the peak energies of the LoSE and the HLE. Therefore, this new picture of HLE emergence explains both the detection and nondetection of HLE signature in observations of broad pulses. Also, we present three examples of Fermi Gamma-ray Burst Monitor GRBs with broad pulses that exhibit the HLE signature. We show that their gamma-ray-emitting region should be located at ∼10 16 cm from the central engine, which places a constraint on the GRB models.
Abstract Magnetar giant flares (MGFs), originating from noncatastrophic magnetars, share noteworthy similarities with some short gamma-ray bursts (GRBs). However, understanding their detailed origin ...and radiation mechanisms remains challenging due to limited observations. The discovery of MGF GRB 231115A, the second extragalactic MGF located in the Cigar galaxy at a luminosity distance of ∼3.5 Mpc, offers yet another significant opportunity for gaining insights into the aforementioned topics. This Letter explores its temporal properties and conducts a comprehensive analysis of both the time-integrated and time-resolved spectra through empirical and physical model fitting. Our results reveal certain properties of GRB 231115A that bear resemblances to GRB 200415A. We employ a Comptonized fireball bubble model, in which the Compton cloud, formed by the magnetar wind with high density e ± , undergoes Compton scattering and inverse Compton scattering, resulting in reshaped thermal spectra from the expanding fireball at the photosphere radius. This leads to dynamic shifts in dominant emission features over time. Our model successfully fits the observed data, providing a constrained physical picture, such as a trapped fireball with a radius of ∼1.95 × 10 5 cm and a high local magnetic field of 2.5 × 10 16 G. The derived peak energy and isotropic energy of the event further confirm the burst’s MGF origin and its contribution to the MGF-GRB sample. We also discuss prospects for further gravitational wave detection associated with MGFs, given their high-event-rate density (∼8 × 10 5 Gpc −3 yr −1 ) and ultrahigh local magnetic field.
The presence of labile bulky insulating hydrocarbon ligands in halide perovskite nanocrystals (NCs) passivates surface traps but concurrently makes charge transport difficult in optoelectronic ...devices. Early efforts routinely rely on the replacement of long-chain ligands with short-chain cousins, leading to notable changes in NC’s sizes and photophysical properties and thus making it hard to obtain devices with nearly designed emissions. Here we report a general solution-phase ligand-exchange strategy to produce organic-ligand-lacking halide perovskite NCs with high photoluminescence (PL) quantum yields and good stability in ambient air. We demonstrate that the ligand exchange can be achieved by a well-controlled mild reaction of thionyl halide with the carboxylic and amine groups on the NC’s surface, resulting in nearly dry NCs with well-passivated surfaces and almost unaltered emission characteristics. Consequently, we achieve exceptionally high-performance blue perovskite NC light-emitting diodes (LEDs) with an external quantum efficiency of up to 1.35% and an extremely narrow full width at half-maximum of 14.6 nm. Our work provides a systematic framework for preparing high-quality organic-ligand-lacking perovskite NC inks that can be directly cast as films featuring effective charge transport, thereby providing the foundation for further development of a wide range of efficient perovskite optoelectronic devices.
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