Leaderless and leader-following consensus of linear multi-agent systems

This paper studies the consensus problems for multi-agent systems with general linear and nonlinear dynamics. The leaderless and leader-following consensus problems are investigated respectively. Contraction theory is employed to gen- erate some sufficient conditions for testing the agents reaching consensus. Under these conditions and certain assumptions, the trajectories of multi-agent systems in directed topology will converge to each other. Finally, two numerical examples are given to illustrate the effectiveness of the proposed results,

Efficient fast mode decision using mode complexity for multi-view video coding

The variable block-size motion estimation(ME) and disparity estimation(DE) are adopted in multi-view video coding(MVC) to achieve high coding efficiency. However, much higher computational complexity is also introduced in coding system, which hinders practical application of MVC. An efficient fast mode decision method using mode complexity is proposed to reduce the computational complexity. In the proposed method, mode complexity is firstly computed by using the spatial, temporal and inter-view correlation between the current macroblock(MB) and its neighboring MBs. Based on the observation that direct mode is highly possible to be the optimal mode, mode complexity is always checked in advance whether it is below a predefined threshold for providing an efficient early termination opportunity. If this early termination condition is not met, three mode types for the MBs are classified according to the value of mode complexity, i.e., simple mode, medium mode and complex mode, to speed up the encoding process by reducing the number of the variable block modes required to be checked. Furthermore, for simple and medium mode region, the rate distortion(RD) cost of mode 16×16 in the temporal prediction direction is compared with that of the disparity prediction direction, to determine in advance whether the optimal prediction direction is in the temporal prediction direction or not, for skipping unnecessary disparity estimation. Experimental results show that the proposed method is able to significantly reduce the computational load by 78.79% and the total bit rate by 0.07% on average, while only incurring a negligible loss of PSNR(about 0.04 d B on average), compared with the full mode decision(FMD) in the reference software of MVC.

Tunable dual-band terahertz graphene absorber with guided mode resonances

A tunable dual-band terahertz absorber is designed and investigated. The unit cell of the proposed absorber consists of a graphene monolayer on a guided-mode resonant filter. The graphene absorber presents > 40% absorption at two resonance frequencies, which is attributed to the guided mode resonances with different mode numbers. The electric field intensity distribution is analyzed to disclose the physical mechanism of such a dual-band absorption effect. Furthermore,the influence of optical properties of graphene, including Fermi level and relaxation time, on the absorption spectra are investigated. Finally, the influence of geometric parameters on the absorption spectrum is studied, which will provide useful guidance for the fabrication of this absorber. We believe that the results may be useful for developing the next-generation graphene-based optoelectronic devices.

Broadband absorption enhancement with ultrathin MoS2 film in the visible regime

The broadband absorption enhancement effect in ultrathin molybdenum disulfide(Mo S2)films is investigated.It is achieved by inserting the Mo S2 film between a dielectric film and a one-dimensional silver grating backed with a silver mirror.The broadband absorption enhancement in the visible region is achieved,which exhibits large integrated absorption and short-circuit current density for solar energy under normal incidence.The optical properties of the proposed absorber are found to be superior to those of a reference planar structure,which makes the proposed structure advantageous for practical photovoltaic application.Moreover,the integrated absorption and short-circuit current density can be maintained high for a wide range of incident angles.A qualitative understanding of such broadband absorption enhancement effect is examined by illustrating the electromagnetic field distribution at some selected wavelengths.The results pave the way for developing high-performance optoelectronic devices,such as solar cells,photodetectors,and modulators.

Residual field suppression for magnetocardiography measurement inside a thin magnetically shielded room using bi-planar coil

For a magnetocardiography(MCG)system inside a magnetically shielded room(MSR),the residual field should be further suppressed to obtain high-quality MCG signals.In this paper,a compensation system has been developed based on the bi-planar coil and the proportional-integral-derivative(PID)controller.The bi-planar coil,derived from the target-field theory and the Tikhonov regularization method,is utilized to generate magnetic field with high uniformity in the predefined target region.And the PID controller is introduced to provide dynamic compensation current for the coil,according to the residual field change monitored by a reference SQUID magnetometer.The measurement results show that the noise suppression ratio(NSR)can reach above 20 dB in the low-frequency range from 0.1 Hz to 50 Hz.The DC component and the fluctuation of the residual field in time-domain can be respectively suppressed to 0 p T and 4 p T,indicating that this proposed compensation method is useful for the MCG measurement.

Comparision between Ga- and N-polarity InGaN solar cells with gradient-In-composition intrinsic layers

Performances of Ga-and N-polarity solar cells(SCs) adopting gradient-In-composition intrinsic layer(IL) are compared.It is found the gradient ILs can greatly weaken the negative influence from the polarization effects for the Gapolarity case,and the highest conversion efficiency(η) of 2.18%can be obtained in the structure with a linear increase of In composition in the IL from bottom to top.This is mainly attributed to the adsorptions of more photons caused by the higher In composition in the IL closer to the p-GaN window layer.In contrast,for the N-polarity case,the SC structure with an InGaN IL adopting fixed In composition prevails over the ones adopting the gradient-In-composition IL,where the highest η of 9.28%can be obtained at x of 0.62.N-polarity SC structures are proven to have greater potential preparations in high-efficient InGaN SCs.

Non-fragile switching tracking control for a flexible air-breathing hypersonic vehicle based on polytopic LPV model

This article proposes a linear parameter varying （LPV） switching tracking control scheme for a flexible air-breathing hypersonic vehicle （FAHV）. First, a polytopic LPV model is constructed to represent the complex nonlinear longitudinal model of the FAHV by using Jacobian linearization and tensor-product （T-P） model transformation approach. Second, for less conservative controller design purpose, the flight envelope is divided into four sub-regions and a non-fragile LPV controller is designed for each parameter sub-region. These non-fragile LPV controllers are then switched in order to guarantee the closed-loop FAHV system to be asymptotically stable and satisfy a specified performance criterion. The desired non-fragile LPV switching controller is found by solving a convex constraint problem which can be efficiently solved using available linear matrix inequality （LMI） techniques, and robust stability analysis of the closed-loop FAHV system is verified based on multiple Lypapunov functions （MLFs）. Finally, numerical simulations have demonstrated the effectiveness of the proposed approach.

A terawatt Nd:glass chirped pulse amplification laser system seeded by two order optical parametric amplification

We present the performance of a high-power Nd:glass laser system,which produces a 1.1 J,250 fs,7.3 nm broadband laser pulse based on the combination of optical parametric amplification(OPA) and chirped pulse amplification(CPA).The two-stage OPA provides broadband seed pulses for the three-stage Nd:glass amplifiers based on the technology of CPA.Compared to the conventional oscillator seed source,the most important advantage of such a seed source supplied by the two-stage OPA is that it possesses the capacities of broad bandwidth and high energy.

SCHMM-based Compensation for the Random Delays in Networked Control Systems

In order to compensate the network-induced random delays in networked control systems（NCSs）, the semi-continuous hidden Markov model（SCHMM） is introduced in this paper to model the controller-to-actuator（CA） delay in the forward network channel. The expectation maximization algorithm is used to obtain the optimal estimation of the model s parameters, and the Viterbi algorithm is used to predict the CA delay in the current sampling period. Thus, the predicted CA delay and the measured sensor-tocontroller（SC） delay in the current sampling period are used to design an optimal controller. Under this controller, the exponentially mean square stability of the NCS is guaranteed, and the SC and CA delays are compensated. Finally, the effectiveness of the method proposed in this paper is demonstrated by a simulation example. Moreover, a comparative example is also given to illustrate the superiority of the SCHMM-based optimal controller over the discrete hidden Markov model（DHMM）-based optimal controller.