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Abstract The indirect‐to‐direct band‐gap transition in transition metal dichalcogenides (TMDCs) from bulk to monolayer, accompanying with other unique properties of two‐dimensional materials, has endowed them great potential in optoelectronic devices. The easy transferability and feasible epitaxial growth pave a promising way to further tune the optical properties by constructing van der Waals heterostructures. Here, we performed a systematic high‐throughput first‐principles study of electronic structure and optical properties of the layer‐by‐layer stacking TMDCs heterostructing superlattices, with the configuration space of [(MX2)n(M′X′2)10−n] (M/M′ = Cr, Mo, W; X/X′ = S, Se, Te; n = 0‐10). Our calculations involving long‐range dispersive interaction show that the indirect‐to‐direct band‐gap transition or even semiconductor‐to‐metal transition can be realized by changing component compositions of superlattices. Further analysis indicates that the indirect‐to‐direct band‐gap transition can be ascribed to the in‐plane strain induced by lattice mismatch. The semiconductor‐to‐metal transition may be attributed to the band offset among different components that is modified by the in‐plane strain. The superlattices with direct band‐gap show quite weak band‐gap optical transition because of the spacial separation of the electronic states involved. In general, the layers stacking‐order of superlattices results in a small up to 0.2 eV band gap fluctuation because of the built‐in potential. Our results provide useful guidance for engineering band structure and optical properties in TMDCs heterostructing superlattices.

In this paper, a new robust adaptive control method has been proposed for nonlinear systems with uncertainties. This method combines the advantages of self-tuning control and sliding mode control. A simple parameterization model is first derived based on a linear dynamic model and unmodeled dynamics. Based on a modified sliding surface, the design procedure is based on the indirect adaptive control concept. This controller consists of four parts: 1) the system parameters estimation; 2) the unmodeled dynamics estimation; 3) the weighting polynomials updating; and 4) the control law calculation. The key merits of this controller are as follows: 1) the controller is applicable to non-minimum phase and open-loop unstable systems; 2) the estimation of the unmodeled dynamics is introduced as a feedback compensation control to improve the response; and 3) the strict stability condition is eliminated and a desirable performance is ensured during a wide operation region. Moreover, the control problem of a shape memory alloy actuator system is considered. In the literature, the mechanism model-based controllers have been extensively reported to address this issue. As an alternative, we describe this plant as a gray-box model. The adaptation algorithm and the control law have been implemented through the Beckhoff controller. The experimental results have demonstrated that the proposed controller has wider applicability than some existing methods.

Objective To explore the techniques and curative effect of microsurgical procedures assisted by minimal exposure tubular retractor system (METRx) in the treatment of lumbar disc herniation (LDH). Methods A total of 51 LDH patients, including 24 patients with L4-5 herniation and 27 patients with L5-S1 herniation, underwent discectomy assisted by METRx system. The operation time, intraoperative blood loss, postoperative complications and hospital stay were recorded. Visual Analogue Scale (VAS) and Oswestry Disability Index (ODI) were used to evaluate the degree of low back pain before operation, one week, 3 months after operation, and in the last follow-up. Lumbar MRI was used to evaluate the decompression of spinal canal. Results The success rate of operations in 51 cases was 98.04% (50/51). The average operation time was 125 min, the average intraoperative blood loss was 50 ml, the mean hospital stay was 5 d, all patients were followed up for 6-48 months (average 24 months). Compared with preoperation, both VAS and ODI scores decreased significantly one week after operation (P = 0.036, 0.029), 3 months after operation (P = 0.018, 0.023) and in the last follow-up (P = 0.007, 0.013). The improvement rate of ODI was 35.37% in the last follow-up. No infection, postoperative cerebrospinal fluid (CSF) fistula, neurological defects or incision infection was found. One patient presented acute abdominalgia on the 2nd day after operation, and was diagnosed as annexitis. One patient showed nerve root irritation symptoms after operation caused by thick nerve root during the surgery. They were cured after symptomatic treatment. Conclusions Microsurgical procedures for treating LDH assisted by METRx system can effectively relieve nerve root compression, protect the dural sac and nerve roots, and reduce surgical complications. DOI: 10.3969/j.issn.1672-6731.2016.04.008