Southwest University

About: Southwest University is a education organization based out in Chongqing, China. It is known for research contribution in the topics: Gene & Population. The organization has 29772 authors who have published 27755 publications receiving 409441 citations. The organization is also known as: Southwest University in Chongqing & SWU.

Primordial black holes and secondary gravitational waves from natural inflation

Abstract: The possibility that in the mass range around ${10}^{\ensuremath{-}12}\text{ }\text{ }{M}_{\ensuremath{\bigodot}}$ most of dark matter is constituted of primordial black holes (PBHs) is a very interesting topic. To produce PBHs with this mass, the primordial scalar power spectrum needs to be enhanced to the order of 0.01 at the scale $k\ensuremath{\sim}{10}^{12}\text{ }\text{ }{\mathrm{Mpc}}^{\ensuremath{-}1}$. The enhanced power spectrum also produces large secondary gravitational waves at the mHz band. A phenomenological delta function power spectrum is usually used to discuss the production of PBHs and secondary gravitational waves. Based on $k$ and $G$ inflations, we propose a new mechanism to enhance the power spectrum at small scales by introducing a noncanonical kinetic term $[1\ensuremath{-}2G(\ensuremath{\phi})]X$ with the function $\ensuremath{-}G(\ensuremath{\phi})$ having a peak. Away from the peak, $G(\ensuremath{\phi})$ is negligible and we recover the usual slow-roll inflation which is constrained by the cosmic microwave background anisotropy observations. Around the peak, the slow-roll inflation transiently turns to ultra slow-roll inflation. The enhancement of the power spectrum can be obtained with generic potentials, and there is no need to fine tune the parameters in $G(\ensuremath{\phi})$ to several significant digits. The energy spectrum ${\mathrm{\ensuremath{\Omega}}}_{\mathrm{GW}}(f)$ of secondary gravitational waves produced by the model have the characteristic power law behavior ${\mathrm{\ensuremath{\Omega}}}_{\mathrm{GW}}(f)\ensuremath{\sim}{f}^{n}$ and is testable by pulsar timing array and space based gravitational wave detectors.

Strong Electronic Interaction Enhanced Electrocatalysis of Metal Sulfide Clusters Embedded Metal-Organic Framework Ultrathin Nanosheets toward Highly Efficient Overall Water Splitting.

Abstract: Unique metal sulfide (MS) clusters embedded ultrathin nanosheets of Fe/Ni metal-organic framework (MOF) are grown on nickel foam (NiFe-MS/MOF@NF) as a highly efficient bifunctional electrocatalyst for overall water splitting. It exhibits remarkable catalytic activity and stability toward both the oxygen evolution reaction (OER, ƞ = 230 mV at 50 mA cm-2) and hydrogen evolution reaction (HER, ƞ = 156 mV at 50 mA cm-2) in alkaline media, and bi-functionally catalyzes overall alkaline water splitting at a current density of 50 mA cm-2 by 1.74 V cell voltage without iR compensation. The enhancement mechanism is ascribed to the impregnated metal sulfide clusters in the nanosheets, which not only promote the formation of ultrathin nanosheet to greatly enlarge the reaction surface area while offering high electric conductivity, but more importantly, efficiently modulate the electronic structure of the catalytically active atom sites to an electron-rich state via strong electronic interaction and strengthen the adsorption of oxygenate intermediate to facilitate fast electrochemical reactions. This work reports a highly efficient HER/OER bifunctional electrocatalyst and may shed light on the rational design and synthesis of uniquely structured MOF-derived catalysts.