Modulational instability of a resonantly polariton condensate in discrete lattices

We study modulational instability of a resonantly polariton condensate in a discrete lattice.Employing a discrete gain-saturation model,we derive the dispersion relation for the modulational instability by means of the linear-stability analysis.Effects of the pumping strength,the nonlinearity,the strength of the detuning,and the coupling strength on the modulation instability are investigated.It is found that the interplay between these parameters will dramatically change the modulational instability condition.We believe that the predicted results in this work can be useful for future possible experiment of exciton-polariton condensate in lattices.

The Asian Option Pricing when Discrete Dividends Follow a Markov-Modulated Model

This paper is concerned with the pricing problem of the discrete arithmetic average Asian call option while the discrete dividends follow geometric Brownian motion. The volatility of the dividends model depends on the Markov-Modulated process. The binomial tree method, in which a more accurate factor has been used, is applied to solve the corresponding pricing problem. Finally, a numerical example with simulations is presented to demonstrate the effectiveness of the proposed method.

Solitary Wave Solutions of Discrete Complex Ginzburg-Landau Equation by Modified Adomian Decomposition Method

在这篇论文，准确、数字的答案为分离复杂 Ginzburg 被计算—有由考虑修改 Adomian 分解方法(mADM ) 的起始的状况的四轮马车方程，它是一个有效方法并且不需要 linearization，弱非线性假设或不安理论。数字答案也与他们的相应分析答案相比。很好的近似与分析答案被完成，这被显示出。最后， modulational 不稳定性被调查，相应条件被给。

Filtered Ring Derived from Discrete Valuation Ring and Its Properties

In this paper we show that if R is a discrete valuation ring, then R is a filtered ring. We prove some properties and relation when R is a discrete valuation ring.

Classification of Multi-User Chirp Modulation Signals Using Wavelet Higher-Order-Statistics Features and Artificial Intelligence Techniques

Higher order statistical features have been recently proved to be very efficient in the classification of wideband communications and radar signals with great accuracy. On the other hand, the denoising properties of the wavelet transform make WT an efficient signal processing tool in noisy environments. A novel technique for the classification of multi-user chirp modulation signals is presented in this paper. A combination of the higher order moments and cumulants of the wavelet coefficients as well as the peaks of the bispectrum and its bi-frequencies are proposed as effective features. Different types of artificial intelligence based classifiers and clustering techniques are used to identify the chirp signals of the different users. In particular, neural networks (NN), maximum likelihood (ML), k-nearest neighbor (KNN) and support vector machine (SVMs) classifiers as well as fuzzy c-means (FCM) and fuzzy k-means (FKM) clustering techniques are tested. The Simulation results show that the proposed technique is able to efficiently classify the different chirp signals in additive white Gaussian noise (AWGN) channels with high accuracy. It is shown that the NN classifier outperforms other classifiers. Also, the simulations prove that the classification based on features extracted from wavelet transform results in more accurate results than that using features directly extracted from the chirp signals, especially at low values of signal-to-noise ratios.

Lifetime estimation of IGBT module using square-wave loss discretization and power cycling test

The insulated gate bipolar transistor(IGBT)module is one of the most age-affected components in the switch power supply, and its reliability prediction is conducive to timely troubleshooting and reduction in safety risks and unnecessary costs. The pulsed current pattern of the accelerator power supply is different from other converter applications;therefore, this study proposed a lifetime estimation method for IGBT modules in pulsed power supplies for accelerator magnets. The proposed methodology was based on junction temperature calculations using square-wave loss discretization and thermal modeling.Comparison results showed that the junction temperature error between the simulation and IR measurements was less than 3%. An AC power cycling test under real pulsed power supply applications was performed via offline wearout monitoring of the tested power IGBT module. After combining the IGBT4 PC curve and fitting the test results,a simple corrected lifetime model was developed to quantitatively evaluate the lifetime of the IGBT module,which can be employed for the accelerator pulsed power supply in engineering. This method can be applied to other IGBT modules and pulsed power supplies.

Walsh Hadamard Transform Based Transceiver Design for SC-FDMA with Discrete Wavelet Transform

This article proposes a new transceiver design for Single carrier frequency division multiple access(SCFDMA)system based on discrete wavelet transform(DWT). SCFDMA offers almost same structure as Orthogonal frequency division multiple access(OFDMA)with extra advantage of low Peak to Average Power Ratio(PAPR). Moreover,this article also suggests the application of Walsh Hadamard transform(WHT)for linear precoding(LP)to improve the PAPR performance of the system. Supremacy of the proposed transceiver over conventional Fast Fourier transform(FFT)based SCFDMA is shown through simulated results in terms of PAPR,spectral efficiency(SE)and bit error rate(BER).

New bounds on the mutual information for discrete constellations and application to wireless channel estimation

The lack of closed-form expressions of the mutual information for discrete constellations has limited its uses for analyzing reliable communication over wireless fading channels.In order to address this issue,this paper proposes analytically-tractable lower bounds on the mutual information based on Arithmetic-Mean-Geometric-Mean(AMGM)inequality.The new bounds can apply to a wide range of discrete constellations and reveal some insights into the rate behavior at moderate to high Signal-to-Noise Ratio(SNR)values.The usability of the bounds is further demonstrated to approximate the optimum pilot overhead in stationary fading channels.

Generalized Parseval’s Theorem on Fractional Fourier Transform for Discrete Signals and Filtering of LFM Signals

This paper investigates the generalized Parseval’s theorem of fractional Fourier transform (FRFT) for concentrated data. Also, in the framework of multiple FRFT domains, Parseval’s theorem reduces to an inequality with lower and upper bounds associated with FRFT parameters, named as generalized Parseval’s theorem by us. These results theoretically provide potential valuable applications in filtering, and examples of filtering for LFM signals in FRFT domains are demonstrated to support the derived conclusions.

Comparison of performance between bipolar and unipolar double-frequency sinusoidal pulse width modulation in a digitally controlled H-bridge inverter system

By deriving the discrete-time models of a digitally controlled H-bridge inverter system modulated by bipolar sinusoidal pulse width modulation(BSPWM) and unipolar double-frequency sinusoidal pulse width modulation(UDFSPWM) respectively,the performances of the two modulation strategies are analyzed in detail.The circuit parameters,used in this paper,are fixed.When the systems,modulated by BSPWM and UDFSPWM,have the same switching frequency,the stability boundaries of the two systems are the same.However,when the equivalent switching frequencies of the two systems are the same,the BSPWM modulated system is more stable than the UDFSPWM modulated system.In addition,a convenient method of establishing the discrete-time model of piecewise smooth system is presented.Finally,the analytical results are confirmed by circuit simulations and experimental measurements.

基于线性调频连续波的合作式通信辐射源测距

针对加速运动目标参数估计中,离散多项式变换方法无法进行非整数估计的问题,本文提出基于瑞夫算法的离散多项式变换法和基于Chirp-Z变换的离散多项式变换法2种新型离散多项式变换算法,对加速运动目标速度和加速度进行估计,并对2种算法的估计误差和计算量进行了分析比较。结果表明:2种算法在信噪比-20 dB时均方误差开始接近克拉美罗界。基于瑞夫算法的离散多项式变换法与3次迭代基于Chirp-Z变换的离散多项式变换法均可在较低信噪比下可实现任意频率的有效估计且性能接近,二者均可实现低信噪比下速度、加速度的有效估计,但基于瑞夫算法的离散多项式变换法计算量远小于3次迭代基于Chirp-Z变换的离散多项式变换法。

基于硬件同步的四态离散调制连续变量量子密钥分发

在连续变量量子密钥分发系统中,同步技术是确保通信双方时钟和数据一致的关键技术.本文通过巧妙设计发送端和接收端仪器的硬件时序,采用时域差拍探测方式和峰值采集技术,实验实现了可硬件同步的四态离散调制连续变量量子密钥分发.通信双方在设计好的硬件同步时序下可实现时钟的恢复和数据的自动对齐,无需借助软件算法实现数据的对齐.本文采用了加拿大滑铁卢大学Norbert Lütkenhaus研究组提出的针对连续变量离散调制协议的安全密钥速率计算方法.该方法需计算出接收端所测各种平移热态的一阶矩和二阶(非中心)矩,以此为约束条件结合凸优化算法可计算出安全密钥速率.计算过程中无需假设信道为线性信道,无需额外噪声的估算.密钥分发系统重复频率为10 MHz,传输距离为25 km,平均安全密钥比特率为24 kbit/s.本文提出的硬件同步方法无需过采样和软件帧同步,减小了系统的复杂度和计算量,在一定程度上降低了系统所需的成本、功耗和体积,有效地增强了连续变量量子密钥分发的实用性.

基于改进Faster R-CNN的隧道衬砌中离散实体目标自动检测研究

隧道衬砌中离散实体目标的检测精度和时效性直接关乎隧道的运营安全,采用图像视觉技术进行图像自动解译可极大提升检测效率和结果的准确性,因此基于离散实体目标的雷达图像数据构建自定义雷达数据集合,并提出一套改进的Faster R-CNN算法对隧道衬砌中的离散实体目标进行自动检测。该算法首先对现有Faster R-CNN网络的特征提取模块进行改进,提出一套全新的轻量化特征提取网络ResNet_FMBConv对雷达图像特征进行深度挖掘;基于ResNet_FMBConv网络改进现有特征金字塔(FPN)结构,实现对多尺寸下目标的精准辨识。其次,基于实测和仿真的雷达图像数据构建离散实体目标的自定义雷达数据集合,通过几何变换方法对雷达图像进行数据增强后用于算法验证。结果表明,改进算法在IOU=0.50∶0.95情况下的检测精确率、召回率、F 1分数和FPS分别为45.1%、54.0%、49.1%和21.65 fps。在保证召回率基本持平的情况下,同比YOLOv3_spp、SSD、Retinanet和Faster R-CNN等目标检测算法的精确率和F 1分数分别提升2%~9%和1%~6%。同时,试验结果表明改进后的特征提取网络ResNet_FMBConv也优于现有Resnet-50、VGG16、Efficientnet_b0和Mobilenetv3等目标分类网络。

面向6G的高速太赫兹无线通信系统与关键技术验证

太赫兹通信以其可提供更高速、更大容量和更安全的数据传输的独特优势,在未来6G中成为重要的关键技术之一。基于固态电子的太赫兹通信系统存在带宽受限、频谱响应不平坦等问题,需要先进的信号形式结合灵活高效的处理方法来提升系统性能。搭建了基于固态电子的G波段太赫兹无线通信系统,通过采用比特-功率加载的离散多音(Bit and Power Loading-Discrete Multitone, BPL-DM)调制技术,实现了对系统频谱资源的有效利用;通过对通信速率的灵活调整、自适应削波和基于三阶多项式的后均衡技术,解决了峰值功率约束带来的挑战,提升了整体传输性能,实现了在195 GHz中心频率下,单通道130 Gbit/s的通信线路速率。基于以上技术,为进一步提升系统容量,搭建了4×4的多输入多输出(Multiple-Input Multiple-Output, MIMO)太赫兹通信系统,总线路速率超过399 Gbit/s。

高频纳秒脉冲调制器的分立磁耦合驱动器设计

随着高压纳秒固态脉冲发生器在生物、工业和环境等领域的应用日益广泛和深入,脉冲波形、电压幅值、脉冲持续时间、脉冲重复频率等参数已成为特定脉冲功率应用所需的基本可控变量。为了进一步减小电源的体积、降低成本,提出一款以正极性Marx为主电路、多个脉冲变压器为核心驱动器、具有纳秒级前沿高重复频率的高压纳秒脉冲调制器。提出的驱动器结构紧凑,无需提供多路隔离供电的驱动电源,可以在高重复频率下实现两个金属氧化物半导体场效应晶体管(MOSFETs)的栅极电压快速同步上升和下降,获得百纳秒以内、幅值可控的栅极驱动电压。不仅最大脉宽不受磁芯饱和的限制,而且负偏置电压使开关管可控关断,同时在一定程度上避免了电流流过MOSFET米勒电容而引起的寄生导通,提高了电路工作的可靠性。此外,研究了不同匝数和磁芯材料对驱动波形的影响。搭建了一台14级脉冲调制器样机,测试结果表明,基于该驱动器下的调制器输出电压和脉宽都连续可调,具有改变脉冲轮廓的能力,最大输出电压可达5.5 kV,脉宽调节范围为100 ns~50 ms,最小上升时间约18 ns,重复频率为100 kHz。

基于功率控制环扰动的DC-DC变换器能量信息一体化研究

针对实现DC-DC变换器之间的信息交互较为复杂的问题,提出了一种基于功率控制环扰动实现其能量信息一体化的方法。通过在DC-DC变换器的传统功率控制环中叠加二进制频移键控(binary frequency shift keying,2FSK)信号作为扰动,将数据信息叠加到传统脉冲宽度调制(pulse-width modulation,PWM)信号中,使得该PWM信号同时包含数据信息,实现能量信息一体化。首先,给出基于2FSK的功率/数据双载波调制以及实时的滑动离散傅里叶变换(sliding discrete Fourier transform,SDFT)解调方案。然后,通过对Buck变换器的能量信息一体化模型进行小信号建模与分析可知,降低输入阻抗可提升通信的信噪比。最后搭建一个由两个Buck变换器并联的实验装置进行验证。实验结果表明在稳态和负载突变的工况下均可实现3 kb/s的稳定通信,验证了所提方法的可行性。该方法使得DC-DC变换器能同时进行功率变换和数据传输,提升数字化和智能化水平。

扦样机混样模块的有限元分析

中国作为粮食大国,历来重视粮食储存安全问题。目前,国内粮库一般使用扦样机对仓内粮食进行抽样检测,但是准确率较低。因此,高质量的扦样设备更能保证粮食检测结果的准确性。以电机驱动的扦样机的混样模块为研究课题,主要研究任务是对该混样模块进行有限元分析,主要研究任务有以下几个部分:使用EDEM离散元软件,确定工作过程中各部件的受力大小;将混样模块的模型导入进有限元分析软件中,对其进行前处理;分析该模块的受力情况,并提取其中最容易断裂的搅拌叶片进行更精细的有限元分析。

基于离散模块梁单元理论的超大型浮体在非稳态载荷下的水弹性响应

使用离散模块梁单元(Discrete-Module-Beam,DMB)理论计算超大型浮体在非稳态载荷下的水弹性,包括位移响应和结构力响应。使用三维势流理论进行水动力分析,并基于Cummins方程将DMB方法扩展至时域;使用子梁法进行位移响应还原。在求解结构力响应时,结构被视作无支持、两端自由的无质量梁,将其所受外载荷按沿结构纵向分布是否已知划分为2类。对于已知分布的外载荷,直接对其进行积分即可获得结构力分布;对于未知分布的外载荷,使用改进后的三次曲线插值法求解结构力分布。计算定点货物移动和飞机降落工况下的水弹性响应。采用DMB方法可准确计算结构位移响应,也可给出非稳态加载过程中初始阶段的弯矩分布,并体现由集中力作用引起的弯矩突变。

A novel DPSS filter optimization scheme to reduce the intrinsic interference of FBMC-QAM systems

In order to reduce the intrinsic interference of the filter bank multicarrier-quadrature amplitude modulation(FBMC-QAM)system,a novel filter optimization scheme based on discrete prolate spheroidal sequences(DPSS)is proposed.Firstly,a prototype filter function based on DPSS is designed,since the eigenvalue can be used as an indicator of the energy concentration of DPSS,so a threshold is set,and the sequence with the most concentrated energy is selected under the threshold,that is,the sequence with the eigenvalue higher than the threshold,and the prototype filter function is rewritten as a weighted sum function of multiple eigenvectors.Under the energy constraints of the filter,the relationship between the eigenvectors and the intrinsic interference function is established,and the function problem is transformed into an optimization problem for the weighted coefficients.Through the interior point method,the most suitable weight is found to obtain the minimum intrinsic interference result.Theoretical analysis and simulation results show that compared with the prototype filters such as Type1 and CaseC,the DPSS filter applying the proposed optimization algorithm can effectively suppress the intrinsic interference of the system and obtain a better bit error rate(BER)performance.