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Two-dimensional (2D) organic-inorganic hybrid perovskites have attracted growing attention recently due to their naturally formed quantum-well structure, unique photoelectric properties and better environmental stability compared to three-dimensional perovskites. The reduced screening and enhanced Coulomb interaction in 2D perovskites result in the formation of excitonic complexes. While the properties of free excitons have been well investigated, studies on biexcitons remain elusive. Here, we report on the biexcitons in 2D (iso-BA)2PbI4 (BA=C4H9NH3) crystals. The biexciton emission can be observed under a very low excitation power density of 6.4 W/cm2 at 78 K. The biexciton exhibits a large biexciton binding energy of 46 meV due to the large exciton binding energy of (iso-BA)2PbI4. Furthermore, the biexcitons exhibit a favorable polarization orientation, resulting in different anisotropy between biexcitons and excitons. Our findings would motivate more studies on biexcitons in 2D perovskites and pave the way for exploiting the many-body physics for biexciton lasing and optical storage devices. more...

In this study, we concentrate on the seismic signature of subducted sediments and suggest the formation of the L‐discontinuity beneath the ancient craton related to migrated sediment dehydration. We first determined the single‐crystal elasticity of topaz, the product of sediment dehydration, at high pressures and temperatures by Brillouin scattering. Using the derived elastic parameters, we establish the velocity and density profiles of subducted sediments in the upper mantle. According to our modeling results, 8.5–17.5 vol.% sediments intruding into the upper mantle will induce a 2%–4% low‐VS anomaly at 210–260 km. Meanwhile, continuous heating will lead to the dehydration of phengite in sediments. The dehydration of this amount sediments can generate a 3%–6% ISS with negative Clapeyron slopes, satisfying the observed L‐discontinuity in northern Finland and northern America without the anisotropy changes but accompanied by low‐velocity anomalies. Our study thus provides new insights into the origin of the L‐discontinuity. Plain Language Summary: The origin of the global seismic discontinuities in the Earth's mantle has been well understood, but the formation mechanism of some local seismic discontinuities is still vague. Lehmann discontinuity (L‐discontinuity) is one of the regional discontinuities in the upper mantle with a 2%–6% impendence contrast (ISS) and negative Clapeyron slope. However, the deformation mechanism changes of olivine cannot explain the formation of the L‐discontinuity without the anisotropy changes. Here, we emphasize the significance of the migration and dehydration of the subducted sediments in the origin of the L‐discontinuity beneath the ancient craton. We determined the single‐crystal elasticity of topaz, the product of the sediment dehydration, and then investigated the seismic signature of subducted sediments. Our modeling results indicated that ∼17.5 vol.% sediments intruding into the upper mantle would lead to ∼4% low‐VS anomalies at 210–260 km. After the continuous heating, these intruding sediments would dehydrate by the reaction with the negative Clapeyron slopes, thus producing significant ISS. Therefore, the migration and dehydration of the subducted sediments can reasonably interpret the seismic characteristics of the L‐discontinuity beneath the cratonic regions such as northern Finland and northern America. Our results deepen the understanding of the origin of the L‐discontinuity. Key Points: Single‐crystal elasticity of topaz under high pressure and temperature has been investigated by Brillouin scatteringThe obtained elasticity parameters are used to model the density and velocity profiles of the subducted sedimentsWe suggest the formation of the L‐discontinuity beneath the ancient craton related to migrated sediment dehydration [ABSTRACT FROM AUTHOR] more...

In this study, we have determined the single‐crystal elasticity of clinohumite [Mg8.85Ti0.19Si3.93O16(OH1.11F0.89)] using Brillouin measurement up to 21 GPa at 300 K and 1 bar at 750 K, respectively. The elasticity of clinohumite was determined to be KS0 = 126.2(3) GPa, G0 = 79.7(2) GPa with pressure derivatives KS′ = 4.2(1), G′ = 1.3(1), pressure derivatives ∂KS/∂T = −0.024(1) GPa/K, and ∂G/∂T = −0.011(1) GPa/K). We comprehensively examined the effects of varying H2O, fluorine content and thermal states, on the velocity and density structures of the subducted harzburgite layer. Assuming a typical H2O content of 2 wt.% within harzburgite, our modeling has shown that hydrous harzburgite with clinohumite as the decomposition product of serpentine along a hot slab geotherm even has the VP and VS 0.4–0.8(6)% greater than it dry counterpart at 250–380 km depth. Yet in the top transition zone, the addition of H2O and F can effectively lower the sound velocities and density. The F‐bearing hydrous harzburgite has the VP and VS 1.1(5)–1.3(3)% lower than its dry counterpart, and only 0.6(5)% and 2.3(5)% greater than the pyrolitic mantle. Along cold slab geotherm, phase A will replace clinohumite as the dominant hydrous phase in the harzburgite, the VP and VS are 4.8(5)–5.3(3)% and 5.9(5)–6.0(3)% greater than the pyrolitic mantle in the upper mantle. In the top transition zone, the difference is approximately 3% in VP and 5% in VS. Our results provide crucial experimental evidence for future assessments of the seismic signals of subducted slabs with different hydrous minerals and thermal states. Plain Language Summary: Subducted slab plays a crucial role in connecting the Earth's surface to the interior. Transportation of H2O and other important volatiles to the Earth's mantle via subducted slab can greatly influence a series of physical properties of mantle minerals. Clinohumite is one of the most important H2O and fluorine (F) carriers in the subducted slab. Here, we determined the single‐crystal elasticity of F‐bearing clinohumite at high pressures and temperatures. The obtained elasticity data were applied to model the velocity profiles of the hydrous harzburgite. Our results show that the addition of H2O and F can enhance the velocity difference between harzburgite and pyrolitic mantle at 250–380 km depth along the hot slab geotherm, and VP and VS of harzburgite with 2 wt.% H2O and clinohumite as the H2O‐bearing phase are 0.4–0.8(6)% greater than those of dry harzburgite. In the transition zone depth, addition of H2O and Fe lowers the sound velocities of harzburgite. Hydrous harzburgite has a lower VP and VS than its corresponding dry phase. These new velocity constraints can help us better understand the circulation of H2O and F within Earth's interior and identify the detected seismic observations of subducted slabs with different compositions and thermal states. Key Points: Single‐crystal elasticity of F‐bearing clinohumite was determined to 21 GPa and 750 K and shows strong dependence with F contentThe obtained results were used to model the velocity profiles of the hydrous harzburgite layer considering the thermal state and compositionH2O and F in clinohumite have significant influence on the velocity profile of subduction slab [ABSTRACT FROM AUTHOR] more...

In order to obtain the influence on unloading of bank slope during the process of valley down-cutting, this paper takes the bank slope at the lower dam site of a hydropower station as the research object, and analyzes the stress field characteristics, displacement field and plastic zone evolution characteristics during the process of valley down-cutting by establishing the corresponding three-dimensional model for numerical simulation. The results show that during the process of valley down-cutting,in the horizontal direction, the stress inside the slope is greater than that of the free face of the slope with the same elevation; the displacement perpendicular to the channel increases gradually; the unloading depth continuously extends to the inside of the slope; and the existence of the ductile shear zone has a greater impact on the unloading of the rock mass. more...

The high rock slope on the right bank of a hydropower station on Lancang river, which isto be built, is excavated for nearly 400 m.According to the on-site geological survey, the rockmass of the slope is hard and brittle dacite with strong unloading, and small and medium-sizedfaults developed in the slope.In addition, there are two ductile shear zones that dipping towardto the inside slope in the right bank slope,and mylonization occurs in the shear zone, which leadsto the very complex geological conditions and rock mass structure of the right bank slope. Inorder to study the mechanism and rule of deformation response of high rock slope excavation underthis condition, this paper selects the right-bank dam axis slope of hydropower station as theresearch object, and simulates the excavation process of the slope by the UDEC (universal distinctelement code). The results show that:(1) The excavation results in large deformation of theshallow rock mass in the ductile shear zone, which affects the stability of the slope; (2) Thedeformation caused by excavation is mainly controlled by the unloading fissure and overflowsurface that dipping toward to the outside slope, and the geological-mechanical deformation andfailure mode is mainly slipping and fracturing; (3) The slope mainly occurs lateral displacementafter excavation, and its cumulative displacement mode is transmission to high elevation andaccumulation at the trailing edge; (4) The slope excavation and the resulting deformation energyare kept in sync, and finally affected by the elastic recovery lag of rock mass, and the residualdeformation is small near the end of excavation. more...

Rock creep has a great influence on the stability of rock engineering, and water contentis an important factor affecting the properties of rock creep, but a large number of existing rockcreep models do not consider the effect of water content. Based on the Burgers model and theprinciple of damage mechanics, this paper proposes an improved Burgers model by introducing thecreep experience element which takes into account the water content, verifies the rationality ofthe proposed model by experimental data, carries out the secondary development of the proposedmodel by FLAC3D software, and analyzes the deformation trend of the Laoqingshan tunnel (as anexample) based on the proposed model. The results show that the larger the water content is, thesmaller the displacement of the crown after support and the tunnel floor occur. more...

In order to study the mechanical properties of dacite under the unloading condition, thispaper selects the dacite in the lower dam of a hydropower station in southwest China as the researchobject, obtains the stress-strain curve under the unloading condition by triaxial unloading test ofthe sample at natural state, and analyzes and discusses the deformation and strengthcharacteristics of the dacite under the unloading condition.The test results show that under theunloading condition, the lateral dilatancy of dacite appears; under the same confining pressure,the confining pressure difference and elastic modulus of the dacite decrease with the increase ofthe unloading rate, which can provide a reference for the engineering practice with dacite. more...

In order to study the effects of water on the deformation and strength of the altered rock during unloading, this paper obtains the micro-structure and mineral distribution of the altered rock at the right dam abutment of a hydropower station in southwest China by SEM (scanning electron microscope), then analyzes and discusses the influences of water in different stress paths on the stress-strain curves, deformation characteristics and strength characteristics of altered rock through triaxial loading and unloading tests of rock samples under natural state and saturated state. The results indicate that: compared with loading test, the cohesive force of rock sample increased and its angle of internal friction decreased under unloading test; based on triaxial loading and unloading tests, the strength of altered rock under saturated state is lower than that under natural state; the strength of altered rock decreases obviously after being exposed to water. more...

Two-dimensional (2D) organic-inorganic hybrid perovskites have attracted growing attention recently due to their naturally formed quantum-well structure, unique photoelectric properties and better environmental stability compared to three-dimensional perovskites. The reduced screening and enhanced Coulomb interaction in 2D perovskites result in the formation of excitonic complexes. While the properties of free excitons have been well investigated, studies on biexcitons remain elusive. Here, we report on the biexcitons in 2D (iso-BA)2PbI4 (BA=C4H9NH3) crystals. The biexciton emission can be observed under a very low excitation power density of 6.4 W/cm2 at 78 K. The biexciton exhibits a large biexciton binding energy of 46 meV due to the large exciton binding energy of (iso-BA)2PbI4. Furthermore, the biexcitons exhibit a favorable polarization orientation, resulting in different anisotropy between biexcitons and excitons. Our findings would motivate more studies on biexcitons in 2D perovskites and pave the way for exploiting the many-body physics for biexciton lasing and optical storage devices. [ABSTRACT FROM AUTHOR] more...

Abstract: The implementation of Computing-intensive tasks which based on reconfigurable computing technology can provide hardwire efficiency and software flexibility. This paper presents a method Based on universal HMI (hardware module interface) design for encryption applications. It can give an effective way to control the status of the user module, independent of the lower level implementation. The validation and performance analysis are also demonstrated by the AES and DES encryption on Xilinx Virtex-2 FPGA. [Copyright &y& Elsevier] more...

The incorporation of chloride (Cl) into methylammonium lead iodide (MAPbI3) perovskites has attracted much attention because of the significantly improved performance of the MAPbI3‐based optoelectronic devices with a negligible small amount of Cl incorporation. It is expected that the Cl incorporation in 2D perovskites with layered nature would be much more efficient and thus can greatly alter the morphology, optical properties, phase transition, and charge transport; however, studies on those aspects in 2D perovskites remain elusive up to date. Here, a one‐pot solution method to synthesize the Cl‐doped lead‐free 2D perovskite (BA)2SnI4 with various Cl incorporation concentrations is reported and how the Cl incorporation affects the morphology change, photoluminescence, phase transition, and charge transport is investigated. The Cl element is successfully incorporated into the crystal lattice in the solution‐processed perovskite materials, confirmed by X‐ray photoelectron spectroscopy and energy dispersive X‐ray spectroscopy measurements. The temperature‐dependent photoluminescence studies indicate that the emission properties and phase transition behavior in (BA)2SnI4−xClx can be tuned by varying the Cl incorporation concentration. Electrical measurement suggests that the charge transport behavior can also be greatly altered by the Cl doping concentration and the electrical conductivity can be significantly improved under a higher Cl incorporation concentration. A one‐pot solution method to synthesize lead‐free 2D perovskite (BA)2SnI4−xClx crystals with various Cl incorporation concentrations is reported. The Cl element is successfully incorporated into the crystal lattice. The Cl incorporation greatly alters the morphology, optical properties, phase transition temperature, and charge transport behavior of the as‐synthesized crystals. [ABSTRACT FROM AUTHOR] more...

All‐inorganic lead halide perovskites have been extensively studied in the past several years due to their superior stability against moisture, oxygen, light, and heat compared with their organic–inorganic counterparts. CsPbBr3 with suitable band gap and ultrahigh photoluminescence quantum yield is a promising candidate for pure green emitter in the backlighting display to fill the so‐called "green gap." Here, vapor‐phase growth of CsPbBr3 microspheres is reported for highly efficient pure green light emission. The as‐synthesized microspheres exhibit a stronger photoluminescence (PL) intensity with a photoluminescence quantum yield of 75% resulting from the lower energy of longitudinal optical phonons revealed by temperature dependent PL studies. Importantly, with the diameter increasing from 2 to 50 µm the PL peak positions of the microspheres can be readily tuned from 527 to 539 nm, well filling the so‐called "green gap." The red‐shift with increasing diameter can be ascribed to the reabsorption process during the photon propagation inside the microspheres. The studies provide a route to improve the photoluminescence quantum yield in all‐inorganic lead halide perovskites, but also suggest an alternative approach to achieve the pure green emission for the backlighting display. Vapor‐phase growth of CsPbBr3 microspheres for highly efficient pure green light emission is reported. The as‐synthesized microspheres exhibit a stronger photoluminescence (PL) intensity resulting from the lower energy of longitudinal optical phonons. By tuning the diameter of the microsphere, the PL peak positions can be tuned from 527 to 539 nm, well filling the "green gap." [ABSTRACT FROM AUTHOR] more...