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51.
Zhihua Liu ;Yajing Li 《Discrete and continuous dynamical systems》2024,29(6):2633-2649
A diffusive age-structured predator-prey model with Ivlev-type functional response is considered. Taking advantage of the Hopf bifurcation theorem for non-densely defined cauchy problem and the persistence of nondegenerate Hopf bifurcation for singularly perturbed second order equation, we prove the existence of periodic wave train solutions of our model. Finally, numerical simulations are carried out as supporting evidences of our analytical results. 相似文献
52.
材料超声回波衰减是评价材料均匀一致性的常用方法, 针对具有复杂结构的航空发动机盘件难以进行材料底面超声回波衰减评价的问题, 本文提出了利用超声背散射波信号直接预测底面回波衰减的方法。采用10MHz聚焦探头进行超声背散射波数据的采集, 利用深度学习技术构建和训练模型,建立了基于深度学习的材料底面回波衰减预测方法, 同时讨论了采用不同信号形式的超声波信号分类识别模型的准确率差异。研究发现：基于深度学习技术可实现通过超声背散射波预测材料的底面回波衰减, 预测结果和实际底面回波衰减试验结果具有良好的一致性。 相似文献
53.
传统多波束测深仪姿态校正处理效率较低,并且校正质量受姿态设备精度影响较大。在平坦海底条件下,测底数据的一些数学拟合特征可较好地反演姿态,为此提出基于多波束测底数据特征进行姿态拟合并校正的方法。本文首先对姿态对测深的影响进行理论分析和仿真分析,得到“横滚和升沉的影响较大、俯仰的影响较小”的结论。其次提出基于测底数据进行姿态补偿的方法,并对实测海底数据进行姿态拟合并校正,校正后海深分布集中度提高。分析表明提出的方法在多波束测深仪姿态校正技术领域有较好的应用价值。 相似文献
54.
基于激光不同波段的探测传输特点,通过分析典型微小摄像头的回波传输特性,提出了一种针对多波长激光特征检测微小摄像头的研究方案。利用几何光学和波动光学理论,分析微小摄像头结构及其反射光谱特征,计算并仿真了一定探测距离下的回波光场,在此基础上搭建多波长激光检测系统。实验结果表明,在一定的景深范围内,具有红外截止滤光片的微小摄像头对可见光的回波光斑衍射环特征明显、条纹对比度高且可探测距离远;近红外波段的目标回波功率低、后向散射干扰严重,可探测距离近;短波红外波段几乎不受红外截止滤光片影响,且1550 nm处于人眼安全波段。实验结果与数值分析、理论仿真结果一致,验证了短波红外激光用于探测微小摄像头的可行性。 相似文献
55.
After passing some results of fuzzy synthesis of heat exchanger networks in review the application of this approach to the synthesis of distillation trains for the separation of multicomponent mixtures is demonstrated. The available heuristic rules are transformed into fuzzy implications dependent on different criteria and that competing rule, which is to be applied, is selected by the fuzzy algorithm.The theoretically possible amount of heat recovery within the networks generated in this way is estimated by a graphical method and included in the final cost evaluation. Regarding operating parameters like column pressure and reflux ratio, according to the mathematical effort at least qualitative statements can be made in result of the estimation of possible heat recovery.As already in the case of heat exchanger networks a following learning algorithm can serve to overcome the disadvantages of this sequential approach, representing at the same time the first step of a further evolutionary improvement of the initial distillation train. 相似文献
56.
Fast imaging using the STimulated Echo Acquisition Mode (STEAM) sequence can produce cine images of the heart with black-blood contrast. Nevertheless, correction of deformation-related artifacts is required in order to maintain myocardial signal throughout the cardiac cycle. Recent work by our group has eliminated this artifact by combining two STEAM sequences acquired with two different demodulation gradients. Unfortunately, these two STEAM sequences were acquired on two separate breath-holds; thus, scan time doubled. In this work, we present a technique to reduce the total scan time by one half, without sacrificing image quality. The technique is based on interleaving two demodulations within one acquisition in order to obtain quality cine images of the heart in a single breath-hold. The technique was tested on animal models and human subjects, and the impact of interleaved acquisition on image quality was studied using quantitative and qualitative measures. 相似文献
57.
In active sonar operation,the presence of background reverberation and the low signal-to-noise ratio hinder the detection of targets.This paper investigates the application of single-channel monostatic iterative time reversal to mitigate the difficulties by exploiting the resonances of the target.Theoretical analysis indicates that the iterative process will adaptively lead echoes to converge to a narrowband signal corresponding to a scattering object’s dominant resonance mode,thus optimising the return level.The experiments in detection of targets in free field and near a planar interface have been performed.The results illustrate the feasibility of the method. 相似文献
58.
Starting from the extended nonlinear Schr?dinger equation inwhich the self-steepening effect is included, the evolution and thesplitting processes of continuous optical wave whose amplitude isperturbed into time related ultra-short optical pulse trains in anoptical fibre are numerically simulated by adopting the split-stepFourier algorithm. The results show that the self-steepening effectcan cause the characteristic of the pulse trains to vary with time,which is different from the self-steepening-free case where thegenerated pulse trains consist of single pulses which are identicalin width, intensity, and interval, namely when pulses move a certaindistance, they turn into the pulse trains within a certain timerange. Moreover, each single pulse may split into severalsub-pulses. And as time goes on, the number of the sub-pulses willdecrease gradually and the pulse width and the pulse intensity willchange too. With the increase of the self-steepening parameter, thedistance needed to generate time-dependent pulse trains willshorten. In addition, for a large self-steepening parameter and atthe distance where more sub-pulses appear, the correspondingfrequency spectra of pulse trains are also wider. 相似文献
59.
60.
扩频雷达探测一阶海洋回波 总被引：1，自引：1，他引：0
利用扩频通信良好的抗干扰性和低功率谱密度下工作的特点,本文把扩频技术引入高频海洋探测雷达来探测海洋一阶回波,研究结果表明,该技术对回波质量无不良影响,同时可降低雷达发射功率,增加雷达探测距离． 相似文献