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In this paper, we establish a three-dimensional heat conduction and thermal stress model of a bulk crystal. Based on planar strain assumption of solid-state lasers, we study the thermal conduction and thermal stress of the bulk Ho : CaF2 laser-medium end-pumped by the Gaussian beam. We establish a thermal model of the plate crystal with complex boundary conditions and discuss the effect of pump energy and pump beam waist radius on the thermal performance of Ho : CaF2 crystals in details. Out results show that, as the pump power increases, the thermal effect of Ho :CaF2 crystal increased with the decrease of the pump-spot radius, and the thermal effect of the crystal increases with increase in the pump power. Furthermore, the absolute value of the shear stress of crystals is far smaller than the absolute value of the corresponding normal stress, and the absolute values of the normal stress and shear stress of small size crystals are greater than those of large size crystals. [ABSTRACT FROM AUTHOR]

Rational design of nanostructures with excellent activity and stability for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) to realize efficient hydrogen production is essential for renewable energy development and conversion. Here, we have designed a special pyrolysis reduction method for the synthesis of CoPt3 nanoparticles (NPs) embedded in N‐doped carbon nanospheres (CoPt3@NC). In this process, a facile impregnation combined with pyrolysis reduction strategy is carried out to produce well‐dispersed CoPt3 nanoparticles within the N‐doped carbon, and the resulting CoPt3@NC nanospheres with trace Pt content exhibit superior HER and OER activity to pure Pt@NC, which needs an ultralow overpotential of 65 mV and 360 mV to drive 10 mA/cm2 in 1.0 M KOH, respectively, and also with excellent long‐term durability. The excellent HER and OER activities of CoPt3@NC nanospheres are mainly ascribed to the high surface area, N‐doping, and synergistic effect between catalyst and carrier. This work provides a feasible strategy to design carbon‐based heterostructures with high catalytic activity and stable properties. [ABSTRACT FROM AUTHOR]

Seawater electrolysis could address the water scarcity issue and realize the grid-scale production of carbon-neutral hydrogen, while facing the challenge of high energy consumption and chloride corrosion. Thermodynamically more favorable hydrazine oxidation reaction (HzOR) assisted water electrolysis is efficiency for energy-saving and chlorine-free hydrogen production. Herein, the MoNi alloys supported on MoO2 nanorods with enlarged hollow diameter on Ni foam (MoNi@NF) are synthesized, which is constructed by limiting the outward diffusion of Ni via annealing and thermal reduction of NiMoO4 nanorods. When coupling HzOR and hydrogen evolution reaction (HER) by employing MoNi@NF as both anode and cathode in two-electrode seawater system, a low cell voltage of 0.54 V is required to achieve 1,000 mA·cm−2 and with long-term durability for 100 h to keep above 100 mA·cm−2 and nearly 100% Faradaic efficiency. It can save 2.94 W·h to generate per liter H2 relative to alkaline seawater electrolysis with 37% lower energy equivalent input. [ABSTRACT FROM AUTHOR]

As various small electronics components are being rapidly moved along an assembly line, their leads must be cut and clinched into holes of a circuit board for the next soldering operation. This process must be achieved economically both in time, and in combating wear by preserving the cutting tools' sharpness. The present study investigates the shearing action and subsequent fracture in cutting. Plastic analysis for both cutting and forming (clinching) is presented with the support of measured data obtained on a prototype machine employed in the research. Wear analysis of the cutting surfaces leads to a recognition of the role played by various geometric parameters such as lead shape, cutter and anvil angles, cutter and anvil distance, etc.

Systematic analyses are presented to reveal the mechanism of multi-valued friction behavior in lubricated sliding contacts with time-varying velocities. The analyses are based on the theoretical results generated by a mixed-film friction model developed in this paper for line contacts. The model, which integrates theories of transient elastohydrodynamics and asperity contact mechanics, is validated by comparing its results with published experimental data. The results and the subsequent analyses disclose that strong multi-valued friction behavior can only be generated in the mixed-film lubrication regime with simultaneous presence of significant asperity contacts and hydrodynamic squeeze. Principal factors which influence the magnitude of dynamic friction are investigated in the paper. Being instructive to the design of tribo-contacts in precise-motion control systems, the analyses suggest means to minimize the undesirable multi-valued friction behavior through proper selection of system parameters.

Generation and control of optical signals in a wide wavelength range is of significant importance in optical gates and coherent control. Optical signals of two different wavelengths in the IR regime were generated in atomic Rb vapor using broad bandwidth laser pulses, and competition between the two signals was observed. The effects of pump laser intensity, chirp of laser pulses and Rb number density on the characteristics of the two signals were investigated. The results show that the two signals were generated from two coupled parametric sixwave mixing processes, and the signals vary with pump laser intensity, chirp of pump laser pulses and Rb number density. Moreover, the competition between the two signals was dominantly governed by phase matching conditions closely related to Rb number density. [ABSTRACT FROM AUTHOR]