Based on the geometry of the codimension-2 surface in general spherically symmetric spacetime, we give a quasi-local definition of a photon sphere as well as a photon surface. This new definition is ...the generalization of the one provided by Claudel, Virbhadra, and Ellis but without referencing any umbilical hypersurface in the spacetime. The new definition effectively excludes the photon surface in spacetime without gravity. The application of the definition to the Lemaître–Tolman–Bondi (LTB) model of gravitational collapse reduces to a second order differential equation problem. We find that the energy balance on the boundary of the dust ball can provide one of the appropriate boundary conditions to this equation. Based on this crucial investigation, we find an analytic photon surface solution in the Oppenheimer–Snyder (OS) model and reasonable numerical solutions for the marginally bounded collapse in the LTB model. Interestingly, in the OS model, we find that the time difference between the occurrence of the photon surface and the event horizon is mainly determined by the total mass of the system but not the size or the strength of the gravitational field of the system.
A
bstract
We study the
P
−
V
criticality and phase transition in the extended phase space of charged Gauss-Bonnet black holes in anti-de Sitter space, where the cosmological constant appears as a ...dynamical pressure of the system and its conjugate quantity is the thermodynamic volume of the black holes. The black holes can have a Ricci flat (
k
= 0), spherical (
k
= 1), or hyperbolic (
k
= −1) horizon. We find that for the Ricci flat and hyperbolic Gauss-Bonnet black holes, no
P
−
V
criticality and phase transition appear, while for the black holes with a spherical horizon, even when the charge of the black hole is absent, the
P
−
V
criticality and the small black hole/large black hole phase transition will appear, but it happens only in
d
= 5 dimensions; when the charge does not vanish, the
P
−
V
criticality and the small black hole/large phase transition always appear in
d
= 5 dimensions; in the case of
d
≥ 6, to have the
P
−
V
criticality and the small black hole/large black hole phase transition, there exists an upper bound for the parameter
, where
is the Gauss-Bonnet coefficient and
Q
is the charge of the black hole. We calculate the critical exponents at the critical point and find that for all cases, they are the same as those in the van der Waals liquid-gas system.
•Core scientific challenges in electrocatalytic water splitting were discussed.•Prussian blue analogues (PBAs) as electrocatalysts for water splitting.•PBA derived nanomaterials as electrocatalysts ...for water splitting.•Perspectives for PBA-based water-splitting electrocatalysts were put forward.
The electrocatalytic water splitting is considered as a prospect meaning to address the urgent energy and environmental problems. However, the electrocatalytic water splitting is greatly limited by the high overpotentials of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Especially, OER involves a complex multistep proton-coupled electron transfer process, which demands a high overpotential to accelerate this sluggish oxygen evolution kinetics. The high overpotentials for OER significantly decrease the efficiency of the overall water splitting. The OER half reaction has thus become the bottleneck of electrocatalytic overall water splitting. It is vital to synthesize highly active electrocatalysts to reduce the activation energy of the reaction and accelerate the generation of H2 and O2, thereby improving the efficiency of the overall water splitting. Prussian blue analogues (PBAs) are representative cyanide-based coordination polymer materials. PBAs possess open framework structures, large specific surface areas, adjustable metal active sites and uniform catalytic centers, showing promising application in electrocatalytic water splitting. Besides, benefiting from the unique structural features of PBAs, their derived electrocatalysts also have large specific surface areas and uniform active sites. Moreover, PBAs can serve as carbon and nitrogen sources. The doped N can regulate the electronic structure of surface active sites, enhancing the intrinsic activity of electrocatalysts. Therefore, the PBA-derived electrocatalysts also exhibit good catalytic performance for water splitting. In this review, we not only summarize the most recent advances on PBAs and their derivatives as electrocatalysts for water splitting, but also conclude the core scientific challenges faced in water splitting. Finally, we provide perspectives for the future research in this field, including catalyst design, catalytic system establishment and so on.
State‐of‐the‐art proton exchange membranes (PEMs) often suffer from significantly reduced conductivity under low relative humidity, hampering their efficient application in fuel cells. Covalent ...organic frameworks (COFs) with pre‐designable and well‐defined structures hold promise to cope with the above challenge. However, fabricating defect‐free, robust COF membranes proves an extremely difficult task due to the poor processability of COF materials. Herein, a bottom‐up approach is developed to synthesize intrinsic proton‐conducting COF (IPC‐COF) nanosheets (NUS‐9) in aqueous solutions via diffusion and solvent co‐mediated modulation, enabling a controlled nucleation and in‐plane‐dominated IPC‐COF growth. These nanosheets allow the facile fabrication of IPC‐COF membranes. IPC‐COF membranes with crystalline, rigid ion nanochannels exhibit a weakly humidity‐dependent conductivity over a wide range of humidity (30–98%), 1–2 orders of magnitude higher than that of benchmark PEMs, and a prominent fuel cell performance of 0.93 W cm−2 at 35% RH and 80 °C arising from superior water retention and Grotthuss mechanism‐dominated proton conduction.
A bottom‐up approach based on the diffusion and solvent co‐mediated growth of covalent organic frameworks (COFs) is proposed to synthesize nanosheets of a highly crystalline, intrinsically proton‐conducting COF (IPC‐COF) in aqueous solution. The high‐quality IPC‐COF nanosheets allow the fabrication of defect‐free and robust IPC‐COF membranes that exhibit a weakly humidity‐dependent proton conduction and a prominent fuel‐cell performance.
Recently, the emergence of photoactive metal–organic frameworks (MOFs) has given great prospects for their applications as photocatalytic materials in visible‐light‐driven hydrogen evolution. Herein, ...a highly photoactive visible‐light‐driven material for H2 evolution was prepared by introducing methylthio terephthalate into a MOF lattice via solvent‐assisted ligand‐exchange method. Accordingly, a first methylthio‐functionalized porous MOF decorated with Pt co‐catalyst for efficient photocatalytic H2 evolution was achieved, which exhibited a high quantum yield (8.90 %) at 420 nm by use sacrificial triethanolamine. This hybrid material exhibited perfect H2 production rate as high as 3814.0 μmol g−1 h−1, which even is one order of magnitude higher than that of the state‐of‐the‐art Pt/MOF photocatalyst derived from aminoterephthalate.
The in visible MOF: A high performance for visible‐light‐driven H2‐evolution is obtained with a new methylthio‐functionalized metal–organic framework (MOF) photocatalyst that is rationally designed and facilely prepared. This approach opens up a new way to achieve photocatalysis based on MOF materials with high quantum efficiency value (up to 8.9 %) and excellent photoactivity.
Hydrogen‐bonded organic frameworks (HOFs) are a class of crystalline framework materials assembled by hydrogen bonds. HOFs have the advantages of high crystallinity, mild reaction conditions, good ...solution processability, and reproducibility. Coupled with the reversibility and flexibility of hydrogen bonds, HOFs can be assembled into a wide diversity of crystalline structures. Since the bonding energy of hydrogen bonds is lower than that of ligand and covalent bonds, the framework of HOFs is prone to collapse after desolventisation and the stability is not high, which limits the development and application of HOFs. In recent years, numerous stable and functional HOFs have been developed by π–π stacking, highly interpenetrated networks, charge‐assisted, ligand‐bond‐assisted, molecular weaving, and covalent cross‐linking. Charge‐assisted ionic HOFs introduce electrostatic attraction into HOFs to improve stability while enriching structural diversity and functionality. In this paper, we review the development, the principles of rational design and assembly of charge‐assisted ionic HOFs, and introduces the different building block construction modes of charge‐assisted ionic HOFs. Highlight the applications of charge‐assisted ionic HOFs in gas adsorption and separation, proton conduction, biological applications, etc., and prospects for the diverse design of charge‐assisted ionic HOFs structures and multifunctional applications.
Strategies for the construction of charge‐assisted ionic hydrogen‐bonded organic frameworks (HOFs) as well as recent advances form the focus of this review. The applications of these charge‐assisted ionic hydrogen‐bonded organic frameworks in gas adsorption and separation, proton conduction, and biological applications are highlighted, as well as prospects for future developments in this field.
Perovskite solar cells (PSCs) have been brought into sharp focus in the photovoltaic field due to their excellent performance in recent years. The power conversion efficiency (PCE) has reached to be ...25.2% in state-of-the-art PSCs due to the outstanding intrinsic properties of perovskite materials as well as progressive optimization of each functional layer, especially the active layer and hole transporting layer (HTL). In this review, we mainly discuss various hole transporting materials (HTMs) consisting of HTL in PSCs. The progress in PSCs is firstly introduced, then the roles of HTL playing in photovoltaic performance improvement of PSCs are emphasized. Finally, we generally categorize HTMs into organic and inorganic groups and demonstrate both their advantages and disadvantages. Specially, we introduce several typical organic HTMs such as P3HT, PTTA, PEDOT:PSS, spiro-OMeTAD, and inorganic HTMs such as copper-based materials (CuO
x
, CuSCN, CuI, etc.), nickel-based materials (NiO
x
), and two-dimensional layered materials (MoS
2
, WS
2
, etc.). On basis of reviewing the reported HTMs in recent years, we expect to provide some enlightenment for design and application of novel HTMs that can be used to further promote PSCs performance.
Using the characteristics of grey forecasting, which requires a small amount of sample data and a simple modeling process, to predict the main macroeconomic indicators in the early stage, combined ...with the filtering decomposition method and the production function method, establishes a short-term high-precision combination forecasting algorithm for macroeconomics based on the grey model. The algorithm uses the improved HP filter method in the HP filter method to study whether the potential economic growth rate can be more accurately measured, and the production function method is used to calculate the potential economic growth rate. First, the two methods are used to calculate the potential economic growth rate. The accuracy of this method finally established a combined model based on the two models for short-term forecasting. Under the premise of considering economic factors, the input data is preprocessed, and the high-precision combined forecast is used to finally obtain the macroeconomic forecast results. The calculation examples in the paper show that the method is feasible and effective.
The mechanisms of lung injury in acute respiratory distress syndrome (ARDS) are not well understood.Piezo1 was recently identified as a mechanotransduction protein. The present study found the ...expression of Piezo1 in type II pneumocytes and investigated its role in mediating ARDS-related lung injury.
Sprague-Dawley rats were used to establish an ARDS model, the expression of Piezo1,lung injuries, apoptosis as well as calcium influx were assessed.
Piezo1 was expressed in type II pneumocytes as shown by immunofluorescence staining and expression was increased in the ARDS model. Knockdown of Piezo1 reduced apoptosis which was related to the elevation of Bcl-2.Calcium influx played a vital role in Piezo1-induced apoptosis.
Piezo1 was expressed in type II pneumocytes. Mechanical stretch of alveoli during ARDS induced activation of the Piezo1 channel,which resulted in calcium influx. The increased intracellular Ca2+ induced the apoptosis of type II pneumocytes, which may be related to the Bcl-2 pathway.
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