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The virtual source method (VSM) is well known as a very efficient approach in generating the mode profile of unstable resonators (UR). However, as far as we know, the error of this method has rarely been examined in details. In this paper, we compare the formula in VSM with the uniform asymptotic solution of the Fresnel-Kirchhoff diffraction integral for a two-aperture model. It is shown that, the accuracy of edge wave functions is sensitive to both the equivalent Fresnel number ( N eq ) and the geometrical magnification ( M ) of UR, the error becomes Intolerable when they become very small. A criterion is presented to exam the validity of VSM for specific combination of N eq and M . The origin of the so-called “mask effect” is also discussed, it may be caused by treating all the geometric boundary of EWs emitted from different virtual source as the same. [ABSTRACT FROM AUTHOR]

The effect of functional groups (O, F, or OH) on the hydrogen storage properties of Ti 2 X (X = C or N) monolayer was systematically investigated by first-principles calculations. The results show that the reversible hydrogen storage capacity of Ti 2 X(OH) 2 monolayer is approximately 2.7 wt%, which is larger than that of Ti 2 XO 2 and Ti 2 XF 2 monolayers. The binding energy of the OH group at the F site is stronger than H atom. Thus, H 2 molecules will not be dissociated on Ti 2 X(OH) 2 monolayer. At this time, the loss of 1.8 wt% hydrogen storage capacity is not produced in Ti 2 X(OH) 2 monolayer. Furthermore, the PDOS, the population analysis, and the electron density difference explore that electron transfer appears between Ti and the second layer H 2 molecules on Ti 2 X(OH) 2 monolayer, and a Dewar-Kubas interaction lies between second layer H 2 molecules and Ti 2 X(OH) 2 monolayer. For Ti 2 X(OH) 2 monolayer, the molecular dynamic simulation indicates that the H 2 molecules by Dewar-Kubas interaction sable adsorption at 300 K, and desorption at 400 K. Therefore, Ti 2 X(OH) 2 is appropriate for reversible hydrogen sorbent storage materials under ambient conditions. [Display omitted] • Strong chemical interaction exists between hydrogen atom and bare Ti 2 X. • Reversible hydrogen storage method using functional groups to regulate Ti 2 X. • All hydrogen molecules adsorb on Ti 2 XO 2 and Ti 2 XF 2 are irreversible. • Some hydrogen molecules by Kubas interaction adsorb on Ti 2 X(OH) 2 are reversible. • Total hydrogen storage capacity of Ti 2 X(OH) 2 is 5.3 wt%; Reversible part is 2.7 wt%. [ABSTRACT FROM AUTHOR]

The quest for novel materials exhibiting significant piezoelectricity remains imminent. Herein, the piezoelectricity of Janus Ga 2 XY (X/Y S, Se, Te) monolayers has been investigated by DFT calculation. The results show that in-plane piezoelectric coefficients d 11 of Ga 2 SSe, Ga 2 STe, Ga 2 SeTe are 3.08, 4.76, 3.55 p.m./V, and out-of-plane piezoelectric coefficients d 31 are 0.14, 0.45, 0.33 pm/V. In addition, the vertical mirror asymmetry and different charge distributions lead to large piezoelectric properties of Ga 2 STe. Notably, strain can effectively regulate the piezoelectric properties of Janus Ga 2 XY monolayers. Under tensile strain, the piezoelectric stress coefficients (e 11) of Ga 2 XY increase and the elastic stiffness coefficients (C 11 + C 12 , C 11 – C 12) decrease, resulting in significant piezoelectric coefficients (d 11 and d 31), which can be attributed to an increase in Born effective charge Z x x * and a decrease in the bond force. The results establish a theoretical foundation for the application of novel 2D Janus Ga 2 XY monolayers in piezoelectric devices. Variation of piezoelectric coefficient of Ga 2 XY (X/Y S, Se, Te) under −4%–4% biaxial strain. [Display omitted] • The Janus Ga 2 XY (X/Y S, Se, Te) monolayers exhibit dynamical and thermal stability. • The formation of Janus structures induces piezoelectricity with d 11 (3.08–4.76 pm/V) and d 31 (0.14–0.45 pm/V). • The piezoelectric properties of Janus Ga 2 XY monolayers can be regulated by strain. • Under 4% biaxial tensile strain, Ga 2 STe produces large d 11 (10.65 pm/V) and d 31 (0.52 pm/V). [ABSTRACT FROM AUTHOR]

Nitrogen reduction reactions (NRRs) under mild conditions retain an enormous challenge in effective N 2 activation on metal-based catalysts. Here, by spin-polarized DFT calculations, we systematically investigated the potential of single transition-metal atoms (Sc to Zn, Nb to Cd, W, Pt and Au) supported on the experimentally available WS 2 nanosheets with sulfur vacancies as catalysts for N 2 fixation and conversion. The results confirm that the WS 2 nanosheet with sulfur vacancies is a good platform for anchoring single transition-metal atoms. Based on proposed several criteria, it is found that the single Ni atoms anchored to sulfur vacancies possess outstanding catalytic activity of NRR. Here, the Ni-WS 2 nanosheet acts as likely Lewis-acid system and accepts electrons from the N 2 *, which causes the weakening of N–N bond. Reaction energy diagrams of the NRRs show that the whole NRRs on Ni-WS 2 surface prefer to occur along the alternating associative pathway, and form the ammonia without the requirement of energy input. Overall, our results reveal that the Ni-WS 2 system is a quite promising single-atom catalyst with less energy-consuming and good stability for NRRs. These findings could motivate more experimental and theoretical researches to further explore the potential of single transition-metal atoms anchored to two-dimensional substrate materials for NRRs. Unlabelled Image • WS 2 nanosheet with S-vacancies is potential substrate for anchoring single TM atoms. • Single Ni atom anchored to the S-vacancy possesses outstanding NRR catalytic activity. • Stability of reaction intermediate relates to the charge difference between two nitrogen atoms. • NRR on Ni-WS 2 surface prefers to occur along the alternating associative pathway. • Ammonia can form on the Ni atom without the requirement of energy input. [ABSTRACT FROM AUTHOR]

The BaTiO 3 (BTO) / CoFe 2 O 4 (CFO) / BaTiO 3 (BTO) laminated ceramic composites were prepared via spark plasma sintering (SPS). The ceramic composites were highly dense with clear boundaries between the three layers. The short time and low temperature required for densification during the SPS process diminish the possibility for unwanted reactions to occur. The BTO/CFO/BTO laminated ceramic composites exhibit excellent ME properties including: (1) maximal ME voltage coefficient as high as ~ 1.0 V/Oe cm; (2) obvious AC magnetic field frequency response and sensitivity from 10 2 to 10 7 Hz; (3) perfect ME anisotropy matches well with the theoretical fitting curve; (4) giant transverse ME voltage coefficient as large as ~ 4.1 V/Oe cm at resonance frequency of ~ 10 5 Hz. It is possible to fabricate several kinds of ME function devices with the BTO/CFO/BTO laminated ceramics prepared in this work. [ABSTRACT FROM AUTHOR]

Abstract: The properties of an all-optical 2R regenerator based on cascaded four-wave mixing (FWM) in a highly nonlinear fiber (HNLF) are investigated. The regeneration is based on the nonlinear cascaded FWM transfer function and a study of the system's static behavior reveals the operating conditions, under which the transfer function approaches most the ideal, step-like discrimination characteristic function. Numerical simulations for the regenerated temporal satellite wave with different signal and pump powers are investigated, and the optimal transfer function based on different fiber lengths and different injected wavelengths are also demonstrated. [Copyright &y& Elsevier]

Potassium-ion energy-storage devices have established themselves as the most important candidates for next-generation energy-storage devices in the coming future. Recently, inorganic electrode materials have riveted ever-increasing interest due to large theoretical capacity, rich sources, low price and environmental friendly advantages. However, the electrode materials of potassium-containing devices have been suffering low theoretical capacity, poor rate performance and short lifespan due to integration effects of seriously electrochemical pulverization and slow kinetics. In this timely review, we will focus on the latest progress of potassium ion energy storage devices based on beyond-carbon materials, referring to the synthesis of materials and the construction of microstructure, material component-oriented electrochemical performance, energy storage mechanism discussion, newfangled device assembly and key components. The key materials and novel theories are reviewed, and some personal viewpoints have been proposed, targeting providing some inductive opinions. Potassium-ion energy-storage devices have established themselves as one of the most important candidates for next-generation energy-storage devices in the coming future. In this timely review, we will focus on the latest progress of key materials and novel theories in potassium-containing devices. And some personal viewpoints have been proposed, targeting providing some inductive opinions. [Display omitted] • The beyond-carbon anode materials for potassium ion batteries were systematically analyzed and summarized. • Other components of potassium ion batteries, such as cathode, electrolyte and binder, were also studied. • The development bottleneck of potassium ion battery was analyzed and some countermeasures were put forward. • It provides comprehensive and reliable information and enlightening opinions for the researchers of new energy devices. [ABSTRACT FROM AUTHOR]