Output-based disturbance rejection control for non-linear uncertain systems with unknown frequency disturbances using an observer backstepping approach

This study is concerned with the output feedback control design for a class of non-linear uncertain systems subject to multiple sources of disturbances including model uncertainties, unknown constant disturbances, harmonic disturbances with unknown frequency and amplitude. The total disturbances and uncertainties are delicately represented by a compact exogenous model first. By incorporating the adaptive internal model principle, a set of dynamic estimators are developed for both state and disturbance observations. By means of observer backstepping technique, a composite output feedback controller is constructed based on the disturbance and state estimations. The stability of the closedloop system is rigorously established based on Lyapunov stability criterion. A missile roll stabilisation example is finally investigated to validate the effectiveness of the proposed control approach

Finishing the euchromatic sequence of the human genome

The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers ∼99% of the euchromatic genome and is accurate to an error rate of ∼1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead

New approach to second-order sliding mode control design

The second-order sliding mode control generates important properties for closed-loop systems, such as robustness, disturbance rejection and finite-time convergence. In this study, it is shown that the adding a power technique plus the nested saturation method will bring in a new second-order sliding mode control scheme for non-linear systems with relative degree two. Based on this, a second-order sliding mode controller is constructed by imposing a natural assumption on the sliding mode dynamics, that is, the uncertainty of the sliding mode dynamics can be bounded by a known function instead of a constant. Under the proposed sliding mode controller, it is proved that the closed-loop system is not only globally convergent, but also locally finite-time stable, which implies the global finite-time stability. Finally, the effectiveness of the proposed method is verified by a numerical example

Nonsmooth stabilization of a class of nonlinear cascaded systems

A global nonsmooth stabilization scheme is presented for a class of nonlinear cascaded systems with uncontrollable linearization. A stepwise constructive control methodology is proposed for the driving subsystem by using the adding a power integrator technique. Under suitable conditions and based on homogeneous properties, it is proved that the stabilization of the driving subsystem implies the stabilization of the overall cascaded system. Due to the versatility of the adding a power integrator technique and homogeneous properties, the proposed controller not only can be used to stabilize the cascaded system asymptotically, but also is able to lead to an interesting result of finite-time stabilization under appropriate conditions

Effect of Mesa Size on Thermal Characteristics of Vertical-cavity Surface-emitting Lasers

The effect of mesa size on the thermal characteristics of etched mesa vertical-cavity surfaceemitting lasers(VCSELs) is studied. The numerical results show that the mesa size of the top mirror strongly influences the temperature distribution inside the etched mesa VCSEL. Under a certain driving voltage, with decreasing mesa size, the location of the maximal temperature moves towards the p-contact metal, the temperature in the core region of the active layer rises greatly, and the thermal characteristics of the etched mesa VCSELs will deteriorate

Crystal structure and microwave dielectric properties of Li-modified BaSi2O5 ceramics

Ba1-xLixSi2O5-x/2 (x = 0–0.5) ceramics were prepared by solid-state reaction method. The occupation tendency of Li+ was well explained based on First-principle calculation and unit cell volume changes. Li+ non-equivalent substitution for Ba2+ considerably reduced the sintering temperature to 975 °C, in comparison with 1225 °C for pure BaSi2O5. Single phase solid solution with orthorhombic structure was observed with x = 0–0.1. Nevertheless, trace amounts of unexpected secondary phases Li2Si2O5 and SiO2 were detected for higher Li-containing samples. Notably, the Q×f significantly enhanced up to 58.16% from 16,134 GHz (x = 0) to 25,518 GHz (x = 0.01), which predominantly depended on the structural characteristics, such as packing fraction and bond covalence. Increase x from 0 to 0.5 led to the reduction of dielectric constant εr from 7.11 to 5.95. The resonant frequency temperature coefficient τf was directly dominated by oxygen bond valence (VO), rather than VBa and VSi. Ba0.99Li0.01Si2O4.995 ceramic sintered at 1050 °C for 4 h exhibited a high Q×f value of 25,518 GHz, and the εr and τf values were 6.94 and −29.46 ppm/°C, respectively