Active Fault Isolation for Multimode Fault Systems Based on a Set Separation Indicator.

This paper considers the active fault isolation problem for a class of uncertain multimode fault systems with a high-dimensional state-space model. It has been observed that the existing approaches in the literature based on a steady-state active fault isolation method are often accompanied by a large delay in making the correct isolation decision. To reduce such fault isolation latency significantly, this paper proposes a fast online active fault isolation method based on the construction of residual transient-state reachable set and transient-state separating hyperplane. The novelty and benefit of this strategy lies in the embedding of a new component called the set separation indicator, which is designed offline to distinguish the residual transient-state reachable sets of different system configurations at any given moment. Based on the results delivered by the set separation indicator, one can determine the specific moments at which the deterministic isolation is to be implemented during online diagnostics. Meanwhile, some alternative constant inputs can also be evaluated for isolation effects to determine better auxiliary excitation signals with smaller amplitudes and more differentiated separating hyperplanes. The validity of these results is verified by both a numerical comparison and an FPGA-in-loop experiment.

Constrained Active Fault Tolerant Control Based on Active Fault Diagnosis and Interpolation Optimization.

A new active fault tolerant control scheme based on active fault diagnosis is proposed to address the component/actuator faults for systems with state and input constraints. Firstly, the active fault diagnosis is composed of diagnostic observers, constant auxiliary signals, and separation hyperplanes, all of which are designed offline. In online applications, only a single diagnostic observer is activated to achieve fault detection and isolation. Compared with the traditional multi-observer parallel diagnosis methods, such a design is beneficial to improve the diagnostic efficiency. Secondly, the active fault tolerant control is composed of outer fault tolerant control, inner fault tolerant control and a linear-programming-based interpolation control algorithm. The inner fault tolerant control is determined offline and satisfies the prescribed optimal control performance requirement. The outer fault tolerant control is used to enlarge the feasible region, and it needs to be determined online together with the interpolation optimization. In online applications, the updated state estimates trigger the adjustment of the interpolation algorithm, which in turn enables control reconfiguration by implicitly optimizing the dynamic convex combination of outer fault tolerant control and inner fault tolerant control. This control scheme contributes to further reducing the computational effort of traditional constrained predictive fault tolerant control methods. In addition, each pair of inner fault tolerant control and diagnostic observer is designed integratedly to suppress the robust interaction influences between estimation error and control error. The soft constraint method is further integrated to handle some cases that lead to constraint violations. The effectiveness of these designs is finally validated by a case study of a wastewater treatment plant model.

Passively Q-switched and mode-locked erbium-doped fiber lasers based on tellurene nanosheets as saturable absorber.

Various two-dimensional (2D) materials show unique optical properties and excellent performance in acting as saturable absorber (SA) for demonstrating all-fiber ultra-fast lasers. Tellurene, as a new-fashioned few-layer 2D monoelemental material, was designed as an excellent saturable absorber to achieve Q-switched and mode-locked operations within erbium-doped fiber (EDF) lasers in our experiment. High-quality tellurene-based SA with a modulation depth of 0.97% was obtained by blending few-layer tellurene nanosheet solution prepared by liquid phase exfoliation method and the polyvinyl alcohol (PVA) solution. Inserting the SA into the EDF laser cavity by sandwiching the tellurene-PVA film between two fiber ferrules, either the passively Q-switched or the passively mode-locked operations can be obtained. The repetition rate varies from 15.92 to 47.61 kHz, and the pulse duration decreases from 8.915 to 5.196 µs in the passively Q-switched operation. To the best of our knowledge, this is the first demonstration focusing on the modulation application of tellurene in designing Q-switched pulsed laser operations. Additionally, mode-locked operations were also achieved by adjusting the polarization state. The obtained results fully indicate that tellurene can be developed as an efficient SA for pulsed fiber lasers.

Observation of spin-glass like behavior in the layered oxyselenides La2O3(Mn1-x Co x )2Se2.

We have synthesized a new series of layered oxyselenides La2O3(Mn1-x Co x )2Se2 through a solid state reaction method. Their structure and physical properties were studied through powder X-ray diffraction, electric transport measurements, absorption spectroscopy, bulk magnetization and specific heat experiments. These compounds crystallize in layered structures with the space group I4/mmm. All the samples present semiconducting or insulating behavior with the activation energy ranging from 0.134 eV to 0.400 eV. The ferromagnetic (FM) component is induced as Co enters the lattice, and the FM component raises to its maximum when x is 0.6. The competing of FM and antiferromagnetic (AFM) components led to the emergence of a spin-glass like behavior in the intermediate alloys.

Broadband nonlinear absorption properties of two-dimensional hexagonal tellurene nanosheets.

Two dimensional (2D) Group-VI Te, tellurene, was successfully exfoliated using a liquid phase exfoliation (LPE) method. The prepared tellurene nanosheets possessed a thickness of 4.3-4.6 nm and the lateral dimension ranged from hundreds of nanometers to several microns. The broadband nonlinear absorption properties were explored for the first time (as we know) using a z-scan method with the laser photon energy in the range of 0.73-2.76 eV, corresponding to the near-infrared-visible waveband. Tellurene nanosheets exhibited excellent broadband saturated absorption and optical limiting behaviors. The low saturable intensity and the large modulation depth for saturated absorption with low energy photon excitation highlight the superiority of the infrared band as a saturable absorber. In addition, with large energy excitation, tellurene manifested an apparent two photon absorption behavior in the visible band, thus it can be used as an optical limiting material. By adopting the mode-locking technique, this high-quality saturable absorber can be applied in all-solid-state or fiber lasers to generate ultra-short and ultra-high peak power laser pulses. Meanwhile, tellurene as an optical limiting material can protect the sensitive optical devices and human eyes. So, our work not only demonstrates that tellurene is a promising broadband nonlinear optical material, but also implies its application prospects in optics.

Flexibility and thermal dynamic stability increase of dsDNA induced by Ru(bpy)2dppz2+ based on AFM and HRM technique.

Ru(bpy)2dppz2+ has been widely used as a probe for exploring the structure of double-stranded DNA (dsDNA). The flexibility change of DNA helix is important in many of its biological functions but not well understood. Here, flexibility change of dsDNA helix caused by intercalation with Ru(bpy)2dppz2+ was investigated using the atomic force microscopy. At first, the interactions between ruthenium complex and dsDNA helix were characterized and the binding site size (p = 2.87 bp) and binding constant (Ka = 5.9 * 107 M-1) were determined by the relative extension of DNA helix using the equation of McGhee and von Hippel. By measuring intercalator-induced DNA elongation and the mean square of end-to-end distance at different molar ratios of Ru(bpy)2dppz2+ to dsDNA, the changes of persistence length under different ruthenium concentrations were determined by the worm-like chain model. We found that the persistence length of dsDNA decreased with increasing Ru(bpy)2dppz2+ concentration, demonstrating that the flexibility of dsDNA obviously enhanced due to the intercalation. Especially, the persistence length changed greatly from 54 to 34 nm on changing the molar ratio of ruthenium to dsDNA from 0 to 0.2. We speculated that the intercalation of dsDNA with Ru(bpy)2dppz2+ resulted in local deformation or bending of the DNA duplex. In addition, the thermal dynamic stability of DNA helix was measured with high resolution melting method which revealed the increase in thermal dynamic stability of DNA helix due to the ruthenium intercalation.

Nonlinear absorption properties of silicene nanosheets.

As the cousins of graphene, i.e. same group IVA element, the nonlinear absorption (NLA) properties of silicene nanosheets were rarely studied. In this paper, we successfully exfoliated the two-dimensional silicene nanosheets from bulk silicon crystal using liquid phase exfoliation method. The NLA properties of silicene nanosheets were systemically investigated for the first time, as we have known. Silicene performed exciting saturable absorption and two photon absorption (2PA) behavior. The lower saturable intensity and larger 2PA coefficient at 532 nm excitation indicates that silicene has potential application in ultrafast lasers and optical limiting devices, especially in visible waveband.

83.4 W, 17.69 kHz spectral bandwidth, continuous-wave, beam densely folded Innoslab amplifier.

Combined with the advantages of the narrow bandwidth of a non-planar ring oscillator seed laser and the structure of a direct pumped Innoslab amplifier, a high-efficiency and high-power continuous-wave (CW) single-frequency laser was obtained by densely folding the seed laser beam in an Innoslab amplifier with a wedged multi-folded configuration. A maximum output power of 83.4 W of a single-frequency amplifier with a bandwidth of 17.69 kHz was obtained under a pump power of 234 W, corresponding to an optical-to-optical conversion efficiency of 33.2%. The beam quality factor M2 at the maximum output power in horizontal and vertical directions was measured to be 1.15 and 1.24, respectively. The long-term power instability in 2 h was less than 1.63%.

High power single-frequency Innoslab amplifier.

A laser diode array (LDA) end-pumped continuous-wave single-frequency Innoslab amplifier has been demonstrated. The Gaussian ray bundle method was used to model the light propagation in the Innoslab amplifier for the first time to the best of our knowledge. With discrete reflectors, the maximum output of 60 W with a linewidth of 44 MHz was achieved under the pump power of 245 W, corresponding to the optical-optical efficiency of 24.5%. The beam quality factor M2 at the output power of 51 W in the horizontal and vertical direction was measured to be 1.4 and 1.3, respectively. The long-term power instability in 2 h was less than 0.25%.

Passively Q-switched mode-locking of Tm:YAP laser based on Cr:ZnS saturable absorber.

Using a Cr:ZnS wafer as the saturable absorber, diode-pumped passively Q-switched mode-locking of a Tm:YAP laser at 1976 nm has been realized for the first time, to the best of our knowledge, and nearly 100% modulation depth of Q-switched mode-locking was achieved. The width of the mode-locked pulse was estimated to be about 980 ps with a repetition rate of 350 MHz within a roughly 300-ns-long Q-switched pulse envelope. A maximum output power of 940 mW was obtained, corresponding to the Q-switched pulse energy of 0.55 mJ. The emission wavelength evolution between the continuous-wave and Q-switched mode-locked operations was presented and discussed. The experimental results indicate that the Cr:ZnS absorber is a promising saturable absorber for passively Q-switched mode-locking operation around 2 µm.

Continuous transform of transverse modes and transitional status analysis in solid-state laser.

With the agility of cavity control in solid-state-laser, we report abundant experimental phenomena of relatively complete Laguerre-Gaussian (LG) transverse multimodes transformation process including both stable and transitional status in a diode pumped Nd:YVO4 microcavity laser. Cavity structure, absorber, pump power, etc, synthetically have been found to contribute such abundant generation of patterns.