Experimental Study of High-Strength Steel Fiber Lightweight Aggregate Concrete on Mechanical Properties and Toughness Index

In this paper, three different kinds of steel fibers, being micro (M), end-hooked (H), and corrugated (C), commonly used in engineering applications, are added to high-strength lightweight aggregate concrete (HLAC) to study the effects of steel fiber and volume content ratio of fiber on the compressive, splitting tensile, and flexural strength of HLAC. The range of steel fiber volume content fraction studied is 0.5% to 2.0%. The research shows that different types of steel fiber have different effects on the mechanical properties and toughness of HLAC. M steel fibers have the best reinforcing performance on the mechanical properties. The study also shows that the toughness of M steel fibers is the best with the same fiber content. The toughening effect of H and C steel fibers can only reach 2/3 and 1/2 of M steel fibers, respectively. At the end of this paper, the unified strength formula and toughness index of these three kinds of high-strength steel fiber lightweight aggregate concrete (HSLAC) with different fiber contents are given to provide a reference for engineering practice and design

NPC Three-Level Inverter Open-Circuit Fault Diagnosis Based on Adaptive Electrical Period Partition and Random Forest

Fault detection can increase the reliability and efficiency of power electronic converters employed in power systems. Among the converters in the power system, a Neutral Point Clamped (NPC) three-level inverter is most commonly used to drive electric motors. In this paper, a new approach for open-circuit fault detection and location of the NPC three-level inverter for a shifting process using a constant voltage-to-frequency ratio is proposed. In order to diagnose open-circuit fault in as short a time as possible, an adaptive electrical period partition (AEPP) algorithm is proposed to pick single electrical periods from real-time three-phase current signals. The Maximal Overlap Discrete Wavelet Transformation (MODWT) and Park’s Vector Modulus (PVM) are used for feature analysis and normalization of electrical period signals. The statistical characteristics of the electrical period signals are extracted, and a random forest model is constructed to realize the state classification. Compared with the traditional fault diagnosis method, the proposed algorithm finds fault locations quickly and accurately. The effectiveness and accuracy of the proposed algorithm are verified by experiments

A Novel Three-Level Voltage Source Converter for AC–DC–AC Conversion

This paper presents a novel three-level voltage source converter for AC–DC–AC conversion. The proposed converter based on H-bridge structure is studied in detail. The control method with traditional double-closed-loop control strategy and voltage balancing algorithm is applied to the rectifier side. Correspondingly, a simplified modulation algorithm is applied to the inverter side, and the voltage balancing of inverter side is realized through the optimal selection of switching combination. Then, the application of the proposed topology is assessed in general and ideal operation conditions. Furthermore, the proposed topology with a variable voltage variable frequency (VVVF) is verified in experimental conditions. The performance of the proposed converter and control strategy is evaluated by experimental and simulation results

Dexmedetomidine for prevention of postoperative delirium in older adults undergoing oesophagectomy with total intravenous anaesthesia: A double-blind, randomised clinical trial.

BackgroundDexmedetomidine is known to be a sedative. Recent studies suggest that administration of dexmedetomidine can prevent postoperative delirium (POD) which has been confirmed as a common complication after major surgery. However, its effects in patients undergoing oesophagectomy are scarce.ObjectiveTo investigate the efficacy and safety of dexmedetomidine in reducing POD in elderly patients after transthoracic oesophagectomy with total intravenous anaesthesia (TIVA).DesignA randomised, double-blind, placebo-controlled trial.SettingSingle-centre, tertiary care hospital, November 2016 to September 2018.PatientsEligible patients (n = 177) undergoing transthoracic oesophagectomy were randomly assigned to receive total intravenous anaesthesia (TIVA, n = 87) or dexmedetomidine with TIVA (DEX-TIVA, n = 90).InterventionsPatients receiving DEX-TIVA received a loading dose of dexmedetomidine (0.4 μg kg-1), over 15 min, followed by a continuous infusion at a rate of 0.1 μg kg-1 h-1 until 1 h before the end of surgery. Patients receiving TIVA received physiological saline with a similar infusion rate protocol.Outcome measuresThe primary outcome was the incidence of POD. The secondary endpoints were the incidence of emergence agitation, serum interleukin-6 (IL-6) levels and haemodynamic profile.ResultsAll randomised patients were included with planned intention-to-treat analyses for POD. Delirium occurred in 15 (16.7%) of 90 cases given dexmedetomidine, and in 32 (36.8%) of 87 cases given saline (P = 0.0036). The DEX-TIVA group showed less frequent emergence agitation than the TIVA group (22.1 vs. 48.0%, P = 0.0058). The incremental change in surgery-induced IL-6 levels was greater in the TIVA group than DEX-TIVA group (P < 0.0001).ConclusionAdding peri-operative dexmedetomidine to a total intravenous anaesthetic safely reduces POD and emergence agitation in elderly patients undergoing open transthoracic oesophagectomy. These benefits were associated with a postoperative reduction in circulating levels of the pro-inflammatory cytokine IL-6 and stabilisation of the haemodynamic profile.Trial registrationChinese Clinical Trials Register Identifier: ChiCTR-IPR-17010881