Effects of spot size on the operation mode of Ga As photoconductive semiconductor switch employing extrinsic photoconductivity

To guide the illuminating design to improve the on-state performances of gallium arsenide(GaAs)photoconductive semiconductor switch(PCSS),the effect of spot size on the operation mode of GaAsPCSS based on a semi-insulating wafer with a thickness of 1 mm,triggered by a 1064-nm extrinsic laser beam with the rectangular spot,has been investigated experimentally.It is found that the variation of the spot size in length and width can act on the different parts of the output waveform integrating the characteristics of the linear and nonlinear modes,and then significantly boosts the PCSS toward different operation modes.On this basis,a two-channel model containing the active and passive parts is introduced to interpret the relevant influencing mechanisms.Results indicate that the increased spot length can peak the amplitude of static domains in the active part to enhance the development of the nonlinear switching,while the extended spot width can change the distribution of photogenerated carriers on both parts to facilitate the linear switching and weaken the nonlinear switching,which have been proved by comparing the domain evolutions under different spot sizes.

Study of ultra-wideband radar signals-generated technology using two-channel signal generator

Synthesis of ultra-wideband （UWB） linear frequency modulation radar signals is a very important technology for microwave imaging, target identification and detection of low radar-cross-section （RCS） targets. A new method of UWB radar signals generation with two-channel signal generator is presented. The realization structure is given; the principle and errors of signal synthesis are analyzed. At the same time, an automatic .adjustment measure of signal phase is proposed because of phase discontinuity of waveform in this method. The simulation experiment and analysis results indicate that radar signals with large instantaneous bandwidth can be generated by means of this method on the condition that the high-speed digital devices are limited.

Random-injection-based two-channel chaos with enhanced bandwidth and suppressed time-delay signature by mutually coupled lasers: Proposal and numerical analysis

Simultaneous bandwidth(BW) enhancement and time-delay signature(TDS) suppression of chaotic lasing over a wide range of parameters by mutually coupled semiconductor lasers(MCSLs) with random optical injection are proposed and numerically investigated. The influences of system parameters on TDS suppression(characterized by autocorrelation function(ACF) and permutation entropy(PE) around characteristic time) and chaos BW are investigated. The results show that, with the increasing bias current, the ranges of parameters(detuning and injection strength) for the larger BW(> 20 GHz) are broadened considerably, while the parameter range for optimized TDS(< 0.1) is not shrunk obviously.Under optimized parameters, the system can simultaneously achieve two chaos outputs with enhanced BW(> 20 GHz)and perfect TDS suppression. In addition, the system can generate two-channel high-speed truly physical random number sequences at 200 Gbits/s for each channel.

An Ocular Artifacts Removal Method Based on Canonical Correlation Analysis and Two-Channel EEG Recordings

In order to more effectively apply an artifact removal melhod in an online brain-computer interface （BCI） system, a new method based on canonical correlation analysis （CCA） and two-channel eleetroeneephalography （EEG） recordings to quickly remove ocular artifacts （OA） is proposed in this paper. Considering both the formation of EEG signals contaminated by OA and the spread of OA, vertical electrooculo~＇aphy （VEOG） was appropriately introduced in CCA, and the blind source separation （BSS~ method based on CCA was used in a new way during the OA removal process. Both experimental and comparison with ICA and SOBI results show that the new method with simple calculation and fast processing speed can effectively separate and remove OA using only two-channel EEG recordings, with retaining useful EEG signals. Hence, this method used in an online BCI system will be more effective.

An improved form of the ELMS algorithm

ELMS algorithm is the first two-channel adaptive filtering algorithm that takes into account the cross-correlation between the two input signals. The algorithm does not preprocess input signals, so it does not degrade the quality of the speech. However, a lot of computer simulation results show that ELMS algorithm has a bad performance. The ELMS algorithm is analyzed firstly, then a new algorithm is presented by modifying the block matrix used in ELMS algorithm to approximate input signals self-correlation matrix. The computer simulation results indicate that the improved algorithm has a better behavior than the ELMS algorithm.

Non-universal Fermi polaron in quasi two-dimensional quantum gases

We consider an impurity problem in a quasi-two-dimensional Fermi gas, where a spin-down impurity is immersed in a Fermi sea of N spin-up atoms. Using a variational approach and an effective two-channel model, we obtain the energy for a wide range of interaction strength and for various different mass ratios between the impurity and the background fermion in the context of heteronuclear mixture. We demonstrate that in a quasi-two-dimensional Fermi gas there exists a transition of the ground state from polaron in the weakly interacting region to molecule in the strongly interacting region.The critical interaction strength of the polaron–molecule transition is non-universal and depends on the particle density of the background Fermi sea. We also investigate the excited repulsive polaron state, and find similar non-universal behavior.

Study on the Perturbation Characteristics of Two-Channel Laser Propagation in Atmospheric Turbulence

In order to study the influence factors of acquisition detection target information by lidar and understand the influence degree of each factor, the two-channel phase perturbation model and the two-channel eikonal variance model are derived in detail by using the geometrical optics method in this paper, and each factor is discussed in detail. The results show that the transmission distance is the main factor to affect the two-channel perturbation. With the increase of the transmission distance, the disturbing degree will gradually weaken. With the increase of transverse coordinates,the disturbing of two channels will also be weakened. In order to further weaken the disturbing degree, the feature dimension should be far larger than the wavelength, but far less than the transmission distance.

Wavelet Packets Analysis Based on IIR Two-channel Bi-orthogonal Filter Banks

A framework of IIR two-channel bi-orthogonal filter banks is presented. The design of the analysis/synthesis systems reduces to the design of a single transfer function. The wavelet bases corresponding to the IIR maximally flat filters are generated. Use the wavelet bases in wavelet packets analysis, take information entropy function as information cost function, adjust the best bases dynamically, and the section of signal's spectramfits its characteristics well. A lot of audio signals are processed. Compared to that of the wavelet transform and the wavelet packet transform using the Daubechies' wavelet which has the same order with our IIR wavelet, the properties of our system are better

All-optical two-channel polarization-multiplexing format conversion from QPSK to BPSK signals in a silicon waveguide

All-optical two-channel format conversion is proposed and experimentally demonstrated from a 40 Gbit/s polarization multiplexing(Pol-MUX) non-return-to-zero quadrature phase-shift keying(QPSK) signal to Pol-MUX binary phase-shift keying(BPSK) signals by using phase-doubled four-wave mixing effects with two polarization-angled pumps in a silicon waveguide. The eye diagrams and constellation diagrams of the original QPSK sequences and the converted BPSK sequences of each channel are clearly observed on the two polarization states. Moreover,the bit error rates(BERs) of the two converted idlers are measured. The power penalties of all these converted BPSK sequences on both X and Y polarization states are less than 3.4 dB at a BER of 3.8 × 10^(-3).

Vertical integration of self-rolled-up microtube and silicon waveguides: a two-channel optical add–drop multiplexer

A novel design of a two-channel optical add-drop multiplexer based on a self-rolled-up microtube （SRM） is presented. This design consists of an SRM that has a parabolic lobe-like pattern along the tube＇s axial direction, as well as straight silicon waveguides and a 180° waveguide bend. The vertical configuration of the SRM and waveguides is analyzed by the coupled mode theory for achieving the optinmm gap. In the critical coupling regime, when the device serves as an optical demultiplexer, the minimum insertion loss is 1.94 dB, and the maximunl channel crosstalk is -6.036 dB. Also, as an optical multiplexer, the maximum crosstalk becomes -11.9 dB.

THE INFLUENCE OF DIFFERENT DESIGN PARAMETERS AND WORKING CONDITIONS ON CHARACTERISTICS OF HEAT METERS

In this article, the UDF technology in Fluent software is used to simulate three-dimensional flow fields and to obtain various flow parameters. The standard k -ε model and the RNG k -ε model are both used to calculate the inner flow field of the basal meter, and a comparison of the calculated results between two models shows that RNG k - ε model is more effective for calculations of the inner flow of rotary wing mechanism. The influence of tip clearance on the characteristics of the basal meter is studied. The influence of the bottom ribs on the heat meter is evaluated by the numerical simulation method. This article also simulates the flow of disturbance located at the inlet of the basal meter, and shows that a swirl located at the front of the basal meter can affect the stability of the heat meter.

A noise cross PSD estimator for dual-microphone speech enhancement based on minimum statistics

Some two-microphone noise reduction techniques that work in the frequency domain exploit coherence function between two noisy signals. They have shown good results when noise signals on two sensors are uncorrelated, but their per-formance decreases with correlated noises. Coherence based methods can be improved when the cross power spectral density (CPSD) of correlated noise signals is available. In this paper, we propose a new method for estimation of the CPSD of the noise, which is based on the minimum tracking technique. Despite the fact that the proposed estimator does not need to implement a voice activity detector (VAD), its performance is comparable to a CPSD estimator that uses an ideal VAD.

Electrochemical quartz crystal microbalance study on the two-electrode-system cyclic voltammetric behavior of Prussian blue films

A two-channel electrochemical quartz crystal microbalance (EQCM) was used to investigate the cyclic voltammetric behavior of two Prussian blue (PB) film-modified Au electrodes in a two-electrode con-figuration in aqueous solution. The redox peaks observed in the two-electrode cyclic voltammogram (CV) are assigned to the intrinsic redox transitions among the Everitt's salt, PB, and Prussian yellow for the film itself, the redox process of the Au substrate and the redox process of small-quantity ferri-/ferrocyanide impurities entrapped in the PB film, as also supported by ultraviolet-visible (UV-Vis) spectroelectrochemical data. The profile of the two-electrode solid-state CV for the PB powder sand-wiched between two gold-coated indium-tin oxide (ITO) electrodes is similar to that for two PB-modified Au electrodes in aqueous solution, implying similar origins for the corresponding redox peaks. The two-channel EQCM method is expected to become a highly effective technique for the studies of the two-electrode electrochemical behaviors of many other species/materials.