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The thermal stability of metastable ReB2‐type transition metal diborides (TMB2), which are considered as new type of superhard material, is of vital importance to obtain bulk samples. In the present work, thermal stability of four kinds of ReB2‐type TMB2 powders, ReB2, OsB2, Os1–xRexB2, and Os1‐xWxB2, were synthesized with varied transition metal (TM)‐to‐B molar ratio by mechanochemical methods and the subsequent annealing was compared. The as‐synthesized powders were then consolidated using a pressureless sintering technique. The results showed that the B content required to obtain the pure hexagonal ReB2‐type Os1–x(TM)xB2 phase varied, which indicated different thermal stabilities, such as OsB2 < Os0.1W0.1B2 < Os0.9Re0.1B2 < Os0.8W0.2B2 < ReB2 < Os0.6W0.4B2 and Os0.5W0.5B2. Among them, Os0.6W0.4B2 and Os0.5W0.5B2 were found to be relatively thermally stable and could be synthesized with a stoichiometric molar ratio of (Os + W):B = 1:2. It was also found that the thermal stability of TMB2 with a hexagonal ReB2 structure could be mainly governed by the length of lattice constant c. The results have guiding significance for the design and preparation of new type of TM borides. In addition, the hardness of TMB2 can be increased by tailoring the B content in the raw materials more precisely. [ABSTRACT FROM AUTHOR]

The phase composition, microstructure, and mechanical properties of the WB2–B4C composites fabricated by a combination of boro/carbothermal reduction and spark plasma sintering (SPS) method with WO3, B4C, and graphite as raw materials were investigated in this study. The experimental results showed that the relative density of the as‐sintered WB2–B4C composites was ∼93.1% and ∼99.5%, respectively, after being SPS sintered at 1600°C under the applied load of 30 MPa for 10 min. Scanning electron microscope analysis showed that a network structure with WB2 grains surrounded by B4C grains was observed after sintering. Analyses of high‐resolution TEM showed semi‐coherent interface and lattice distortion transition region between WB2 and B4C grains. The Vickers hardness of WB2–B4C composite increased to 22.3 ± 0.9 GPa at 9.8 N owing to the fully dense, solid solution of C, and three‐dimensional network structure. Moreover, the fracture toughness and flexural strength of WB2–B4C composite reach 6.04 ± 0.81 MPa m1/2 and 750 ± 80 MPa, respectively, which could be attributed to the semi‐coherent interface between WB2 and B4C grains. [ABSTRACT FROM AUTHOR]

This paper proposes two effective numerical methods to solve the optimal problem of contrast enhancement for the coherent and incoherent cases, respectively. For the coherent case, the objective function of the optimal problem is transformed into a bilinear form. Then a numerical method is presented by using the idea of the Sequential Unconstrained Minimization Technique (SUMT). For the incoherent case, a cross-iterative method is proposed for solving the optimal problem of contrast enhancement, based on the formula of the optimal contrast polarization state in the matched-polarized channel. Both the proposed methods are convergent and straightforward for programming. In addition, the proposed methods can be used for the bistatic radar case because in this paper, it is unnecessary to restrict the symmetry of the scattering matrix and the Kennaugh matrix. For showing the effectiveness of the proposed methods, we give three examples. The results of the calculation are completely identical with other papers', showing the validity of the proposed methods. In these three examples, if the receiving polarization state is independent of the transmitting's, the power ratios may be much larger than those in the cases of the co-polarized, the cross-polarized, and the matched-polarized channels, showing the importance of the considered models. In addition, the computation costs are estimated by these illustrative examples, illustrating that the proposed methods are very effective. Index Terms--Polarimetric contrast, polarization, radar polarimetry, scattering matrix.

The co-cavity two-section (CCTS) bistable semiconductor laser with DH and MQW structures has been investigated experimentally and theoretically in this laboratory. Many attractive functions, such as optical bistable switching, optical memory effect, high stability of single longitudinal mode emission spectrum in steady on state, high gain optical amplification, mode conversion effect on injecting signal light, long delay and abnormal relaxation oscillation, ultrafast light pulse generation are investigated in the device. As a high speed, single wavelength, novel laser light source, a monolithic MQW CCTS bistable laser with MQW EA modulator has been fabricated. [ABSTRACT FROM AUTHOR]

GaAs/GaAlAs MQW reflection modulators and SEED have been investigated. The analysis is emphasized on the combined behaviors of quantum confined Stark effect (QCSE), distributed Bragg reflector (DBR), and different asymmetric Fabry-Perot cavities (ASFP). Experimental results include the fabrication and characterization of a modulator array with a contrast ratio of about 10 dB and S-SEED array with optical switch energy less than 10 /(µ)2. An application of a modulator array in microoptical interconnection module is also demonstrated. [ABSTRACT FROM AUTHOR]