Generation of non-integer high-order harmonics and significant enhancement of harmonic intensity

High-order harmonics from helium atom in the orthogonally two-color(OTC) laser field are investigated by solving the two-dimensional time-dependent Schrodinger equation.Non-integer high-order harmonics are obtained in some ratio of frequencies of two components.Pure odd and even harmonics from atoms could be separated in two components by adjusting the ratio of frequencies in OTC scheme,and the resolution of harmonics is improved at the same time.The physical mechanism is explained by the periodicity of dipole.With the same intensity of the incident laser,the intensity of the high-order harmonics from the OTC field scheme is improved by three orders of magnitude compared to the monochromatic laser field scheme.A theoretical scheme is provided for experimentally achieving improving energy resolution and separation of pure odd and even harmonics in atoms.Also,we provide a means for improving harmonic intensity.

Speech Enhancement Using Cross-Correlation Compensated Multi-Band Wiener Filter Combined with Harmonic Regeneration

The speech signal in general is corrupted by noise and the noise signal does not affect the speech signal uniformly over the entire spectrum. An improved Wiener filtering method is proposed in this paper for reducing background noise from speech signal in colored noise environments. In view of nonlinear variation of human ear sensibility in frequency spectrum, nonlinear multi-band Bark scale frequency spacing approach is used. The cross-correlation between the speech and noise signal is considered in the proposed method to reduce colored noise. To overcome harmonic distortion introduced in enhanced speech, in the proposed method regenerate the suppressed harmonics are regenerated. Objective and subjective tests were carried out to demonstrate improvement in the perceptual quality of speeches by the proposed technique.

Enhancement effect of cumulative second-harmonic generation by closed propagation feature of circumferential guided waves

On the basis of second-order perturbation approximate and modal expansion approach,we investigate the enhancement effect of cumulative second-harmonic generation(SHG)of circumferential guided waves(CGWs)in a circular tube,which is inherently induced by the closed propagation feature of CGWs.An appropriate mode pair of primary-and double-frequency CGWs satisfying the phase velocity matching and nonzero energy flux is selected to ensure that the second harmonic generated by primary CGW propagation can accumulate along the circumference.Using a coherent superposition of multi-waves,a model of unidirectional CGW propagation is established for analyzing the enhancement effect of cumulative SHG of primary CGW mode selected.The theoretical analyses and numerical simulations performed directly demonstrate that the second harmonic generated does have a cumulative effect along the circumferential direction and the closed propagation feature of CGWs does enhance the magnitude of cumulative second harmonic generated.Potential applications of the enhancement effect of cumulative SHG of CGWs are considered and discussed.The theoretical analysis and numerical simulation perspective presented here yield an insight previously unavailable into the physical mechanism of the enhancement effect of cumulative SHG by closed propagation feature of CGWs in a circular tube.

Cascading Enhancement of Reflected Optical Third-Harmonic Imaging in Bio-Tissues

A new nonlinear optical third\|harmonic imaging technology in reflected fashion in bio\|tissues by using cascading effect, a process whereby the second\|order effects combine to contribute to a third\|order nonlinear process, has been analyzed. The performance of the reflected optical third harmonic imaging enhanced by cascading effect in bio\|tissues is analyzed with the semi\|classical theory. The microscopic understanding of the enhancement of cascaded optical third\|harmonic imaging in reflected manner in bio\|tissues has been discussed.Some i deas for further enhancement is given.

SPEECH ENHANCEMENT USING HARMONICS REGENERATION BASED ON MULTIBAND EXCITATION

This paper proposes an algorithm that adopts the harmonic regeneration as post-processing to improve the performance of speech enhancement using traditional Short Time Spectral Amplitude(STSA).The proposed algorithm aims to alleviate the distortion of the high harmonics of enhanced speech via the traditional STSA,and consequently improves the speech quality.We first detect the pitch,or fundamental frequency,of the enhanced speech via the traditional STSA,and then,divide the whole spectrum into multiple sub-bands which center on each harmonic.After that,a series of specially designed windows centered on each harmonic are applied to all the sub-bands,in order to redistribute the energy in the sub-bands.The results of experiment demonstrate that the method has both theo-retical and practical basis.

Contrast-enhanced harmonic endoscopic ultrasonography for assessment of lymph node metastases in pancreatobiliary carcinoma

AIM: To assess the usefulness of contrast-enhanced harmonic endoscopic ultrasonography (CH-EUS) for lymph node metastasis in pancreatobiliary carcinoma.METHODS: All patients suspected of pancreatobiliary carcinoma with visible lymph nodes after standard EUS between June, 2009 and January, 2012 were enrolled. In the primary analysis, patients with successful EUS-fine needle aspiration (FNA) were included. The lymph nodes were assessed by several standard EUS variables (short and long axis lengths, shape, edge characteristic and echogenicity), color Doppler EUS variable [central intranodal blood vessel (CIV) presence] and CH-EUS variable (heterogeneous/homogeneous enhancement patterns). The diagnostic accuracy relative to EUS-FNA was calculated. In the second analysis, N-stage diagnostic accuracy of CH-EUS was compared with EUS-FNA in patients who underwent surgical resection.RESULTS: One hundred and nine patients (143 lymph nodes) fulfilled the criteria. The short axis cut-off ≥ 13 mm predicted malignancy with a sensitivity and specificity of 72% and 85%, respectively. These values were 72% and 63% for the long axis cut-off ≥ 20 mm, 62% and 75% for the round shape variable, 81% and 30% for the sharp edge variable, 66% and 61% for the hypoechogenicity variable, 70% and 72% for the CIV-absent variable, and 83% and 91% for the heterogeneous CH-EUS-enhancement variable, respectively. CH-EUS was more accurate than standard and color Doppler EUS, except the short axis cut-off. Notably, three patients excluded because of EUS-FNA failure were correctly N-staged by CH-EUS.CONCLUSION: CH-EUS complements standard and color Doppler EUS and EUS-FNA for assessment of lymph node metastases.

Refinement of Enhanced Speech Using Hybrid-Median Filter and Harmonic Regeneration Approach

This study proposes a post-processor to improve the harmonic structure of a vowel in an enhanced speech, enabling the speech quality to be improved. Initially, a speech enhancement algorithm is employed to reduce the background noise for a noisy speech. Hence the enhanced speech is post-processed by a hybrid-median filter to reduce the musical effect of residual noise. Since the harmonic spectra are impacted by background noise and a speech enhancement process, the quality of a vowel is deteriorated. A harmonic regenerated method is developed to improve the quality of post-processed speech. Experimental results show that the proposed method can improve the quality of post-processed speech by adequately regenerating harmonic spectra.

Evaluation of quantitative contrast harmonic imaging to assess malignancy of liver tumors:A prospective controlled two-center study

AIM: To establish the extent to which contrast enhancement with SonoVue in combination with quantitative evaluation of contrast-medium dynamics facilitates the detection of hepatic tumors. METHODS: One hundred patients with histologically confirmed malignant or benign hepatic tumor (maximum size 5 cm) were analyzed. Contrast-enhanced ultrasound (bolus injection 2.5 mL SonoVue) was carried out with intermittent breath-holding technique using a multifrequency transducer (2.5-4 MHz). Native vascularization was analyzed with power Doppler. The contrast-enhanced dynamic ultrasound investigation was carried out with contrast harmonic imaging in true detection mode during the arterial,portal venous and late phases. Mechanical index was set at 0.15. Perfusion analysis was performed by post-processing of the raw data time intensity curve (TIC) analysis. The cut-off of the gray value differences between tumor and normal liver tissue was established using Receiver Operating Characteristic (ROC) analysis 64-line multi-slice computed tomography served as reference method in all cases. Magnetic resonance tomography was used additionally in 19 cases. RESULTS: One hundred patients with 59 malignant (43 colon,5 breast,2 endocrine metastases,7 hepatocellular carcinomas and 2 kidney cancers) and 41 benign (15 hemangiomas,7 focal nodular hyperplasias,5 complicated cysts,2 abscesses and 12 circumscribed fatty changes) tumors were included. The late venous phase proved to be the most sensitive for classification of the tumor type. Fifty-eight of the 59 malignant tumors were classified as true positive,and one as false negative. This resulted in a sensitivity of 98.3%. Of the 41 benign tumors,37 were classified as true negative and 4 as false negative,which corresponds to a specificity of 90.2%. Altogether,95.0% of the diagnoses were classified as correct on the basis of the histological classification. No investigator-dependency (P = 0.23) was noted. CONCLUSION: The results show the possibility of accurate prediction of malignancy of hepatic tumors with a positive prognostic value of 93.5% using advanced contrast-enhanced ultrasound. Contrast enhancement with SonoVue in combination with quantitative evaluation of contrast-medium dynamics is a valuable tool to discriminate hepatic tumors.

Femtosecond enhancement cavity with kilowatt average power

Femtosecond enhancement cavity(fsEC) has been proved to be a powerful tool in a diverse range of applications.Here, we report the recent progresses in building an fsEC on kilowatt level average power, with the aim of realization of intracavity high harmonic generation(HHG) and extension of the wavelength of femtosecond optical frequency comb from infrared(IR) to extreme ultraviolet(XUV). Upon mode-matching optimization and cavity length locking, an intracavity average power of 6.08 kW is reached and the corresponding buildup is 225. After introducing noble gas of Xe into the focus region, clear sign of plasma has been observed. The generated HHG is also coupled out by a sapphire plate placed at Brewster's angle for the fundamental laser. Our work paves the way for the realization of an XUV comb.

Efficiency enhancement of a two-beam free-electron laser using a nonlinearly tapered wiggler

A nonlinear and non-averaged model of a two-beam free-electron laser （FEL） wiggler that is tapered nonlinearly in the absence of slippage is presented. The two beams are assumed to have different energies, and the fundamental resonance of the higher energy beam is at the third harmonic of the lower energy beam. By using Maxwell＇s equations and the full Lorentz force equation of motion for the electron beams, coupled differential equations are derived and solved numerically by the fourth-order Runge-Kutta method. The amplitude of the wiggler field is assumed to decrease nonlinearly when the saturation of the third harmonic occurs. By simulation, the optimum starting point of the tapering and the slopes for reducing the wiggler amplitude are found. This technique can be applied to substantially improve the efficiency of the two-beam FEL in the XUV and X-ray regions. The effect of tapering on the dynamical stability of the fast electron beam is also studied.

High-order harmonic generation of Li^+ with combined infrared and extreme ultraviolet fields

We investigate high-order harmonic generation （HHG） ofLi＋ ion driven by an intense infrared （IR） laser field in corn-bination with a weak XUV pulse. To achieve this, we first construct an accurate single-active electron angular-momentumdependent model potential of Li＋ ion, by which the accurate singlet energy levels of Li＋ for the ground state and excited states with higher quantum numbers can be obtained. Then, we solve numerically the three dimensional time-dependent Schr/Sdinger equation of Li＋ ion by means of the generalized pseudospectral method to obtain HHG. Our results show that the strength of assisted XUV is not amplified during the harmonic generation process, but the yield of HHG power spectrum in the whole plateau has a significant enhancement. Furthermore, the optimal phase delay between the IR and XUV pulses allows the production of ultrabroadband supercontinuum spectra. By superposing some harmonics, a strong new single 27-attosecond ultrashort pulse can be obtained.

具有谐波抑制功能的多极化微带天线阵设计

本文提出了一种基于切换馈电网络的极化可重构微带天线阵。阵列单元采用正方形辐射贴片,利用微带线缝隙耦合进行馈电,通过在馈电结构中心加载短路柱,可获得宽带性能的同时,有效抑制偶次谐波。综合采用串联组阵和并联组阵技术,优化设计了一款2×2的天线阵列,将阵列端口分别与微带分支线耦合器及微带混合环相连,最终实现了水平和垂直线极化,左旋和右旋圆极化四种模式的切换。实验结果表明,所提出的天线在ISM频段2.4~2.5 GHz频率范围内获得了良好的匹配和多极化特性。该天线阵设计简单、易于操作,可潜在应用于无线通信系统中天线极化分集的场合。

超声内镜在胃肠道间质瘤诊断中的应用进展

胃肠道间质瘤(gastrointestinal stromal tumor,GIST)是具有恶性潜能的间质瘤,不同恶性风险的GIST选择不同的治疗策略,如监测随访、内镜治疗、手术切除或/和药物治疗。因此,GIST的早期诊断以及风险评估对选择合适的治疗方案十分重要。目前,随着内镜技术的广泛应用,超声内镜(endoscopic ultrasound,EUS)、超声内镜弹性成像(endoscopic elastic imaging,EUS-EG)、超声内镜谐波增强(contrast-enhanced harmonic endoscopic ultrasound,CH-EUS)、超声内镜引导下细针抽吸/活检(endoscopic ultrasound-guided fine-needle aspiration/biopsy,EUS-FNA/EUS-FNB)被应用于GIST的诊断以及风险评估。本文主要对以上检查方式在GIST中的应用进行阐述。

谐波结构相位估计联合幅度补偿的语音增强方法

传统语音增强方法,通常只对含噪语音信号的幅度进行增强处理,忽略了相位信息。相位谱在语音的可懂度和感知质量方面也具有积极影响。为了解决传统语音增强方法对相位处理的不足以及在语音增强过程中普遍存在的可理解性较低的问题,提出一种谐波结构相位估计联合幅度补偿的语音增强方法,该方法强调谐波结构的相位估计恢复浊音信息,并针对由浊音相位估计后清音特征被背景噪声破坏引起的语音信息丢失问题,提出一种平滑背景噪声策略来抑制噪声的影响。此外,还利用谐波比分离谐波结构和清音特征,基于谐波判决来判断是否应该平滑背景噪声,为避免不可靠的判决导致清音特征损失,在谐波判决的基础上还增加了清音特征信息的利用。实验结果表明,该方法在白噪声环境下的信噪比(signal to noise ratio,SNR)、语音质量感知评估(perceptual evaluation of speech quality,PESQ)和短时客观可懂度(short-time objective intelligibility,STOI)分别提升了12.02 dB,1.03和0.07,进一步证实该方法可以有效减少语音失真,提高噪声环境下语音信号质量和可懂度。

抑制电网背景谐波的变流器导纳重塑方法

电网电压中的背景谐波作用在并网变流器上产生谐波电流,而并网变流器的频率耦合特性还会映射出新的谐波电流成分。为抑制电网背景谐波对并网电流的影响,文中提出改善并网电流质量的导纳重塑方法。首先,为了消除变流器的频率耦合特性,减少并网电流谐波成分,构造出内、外环导纳重塑因子的一般形式,将并网变流器重塑为dq坐标系下的对称系统;然后,从减少谐波含量出发,对导纳重塑因子进行合适选择,通过降低变流器导纳值来改善并网电流质量,实现消除变流器频率耦合特性的同时抑制电网背景谐波的目的;此外,变流器序导纳模值减小,使得其与电网阻抗构成的回路比曲线更难在幅相平面包围(-1,0)点,有益于并网系统的稳定。仿真和实验均验证了所提导纳重塑方法的可行性和有效性。

多功能并网逆变器的预测-等效滑模控制策略

为满足分布式发电系统中新能源消纳和电能质量治理的需求,对多功能并网逆变器(multifunctional grid-tied inverter,MTGTI)兼具电能质量治理功能的关键技术进行研究,针对传统控制方案中补偿电流检测方法精度不高、控制跟踪效果较差的问题,提出一种基于改进型滑模的整体控制方案。首先,将平均值算法引入基于FBD(Fryze-Buchholz-Depenbrock)功率理论的谐波及无功检测方法,提高了补偿电流检测的精度及响应速度,从而提升指令电流的准确度。然后,在滑模控制(sliding mode control,SMC)的基础上结合模型预测控制(mode predictive control,MPC),提出预测-等效滑模控制策略,进一步提高了多功能并网逆变器对复杂指令电流的高精度快速跟踪的控制性能。最后,基于MATLAB/Simulink仿真平台,在并网、负载不平衡、负载突变等不同状态下,验证所提整体控制方案的可行性及有效性。

基于内卷特征提取和前景细节增强的图像协调化方法

在编辑合成图像时,前景区域与背景区域由于分属不同来源,外观通常存在较大差异,不能呈现真实的视觉效果。图像协调化主要消除合成图像的不真实感,通过将背景域的外观信息迁移到前景域中,使人眼尽可能少地感受差异。现有方法在将背景信息进行转移时,能触及到的背景范围有限,信息提取不充分使得图像协调效果不佳。同时,前景细节丢失会影响图像协调的整体效果。基于以上问题,提出内卷特征提取和前景细节增强模块,进行图像协调。在iHarmony4数据集上试验结果表明,该方法能生成细节更充分、真实感更强的图像效果。

频谱受限下容量优化的多标签并发反射通信系统

无源反射通信技术因其微瓦级别的功耗,使得物联网设备易于部署且免维护.多标签并发反射通信技术使反射标签无需实现冲突避免等复杂协议,从而在降低设备功耗的同时提升系统的吞吐量和规模.然而,反射标签可用的频谱资源有限,导致多标签并发面临相互干扰和频谱利用效率低的问题.为此,提出了CamScatter,一个容量优化的多标签并发反射通信系统,设计了针对有限频谱资源进行最优化信道划分和高效分配的策略,避免标签之间的干扰,显著提升系统的容量.在预处理阶段,提出了带宽最大化的信道划分算法,为系统通信提供频谱上互不干扰且带宽利用率高的信道划分方案.在初始化阶段,提出了高效信道分配和最优化速率分配方案,根据系统中所有标签的信噪比,为标签分配最合适的信道和速率,以解决标签能量差异造成的信号干扰,提升系统吞吐量.在运行阶段,系统利用边带聚合和匹配滤波技术增强待解调标签信号的强度,减轻其他标签的信号干扰.系统可以利用的带宽范围为142.4~773.5 kHz,由于谐波干扰限制,理论上最大频谱利用率为81.1%,避免干扰的情况下最大系统容量为2925 kbps.仿真实验表明,算法可以实现78.6%的频谱利用率,最大系统容量可达1914 kbps.实际部署实验验证,本系统最高支持305 kbps的系统吞吐量,最多可支持30个标签的并发通信,有效解决了标签之间的相互干扰问题.

超声内镜弹性成像技术联合谐波造影增强超声内镜在胰腺占位性病变中的诊断价值

目的研究胰腺占位性病变检查中超声内镜弹性成像技术(EUS-EG)与谐波造影增强超声内镜(CEH-EUS)联合诊断的价值。方法以回顾性分析为法,观察对象为2022年1月至2023年6月华北医疗健康集团峰峰总医院收治的80例胰腺占位性病变患者,参考不同检查方式分为单一组(仅接受EUS-EG检查,n=80)与联合组(EUS-EG联合CEH-EUS检查,n=80)。比较两组患者的疾病检出率、误诊率、准确度、特异度及敏感度,并比较胰腺良性、恶性病变超声造影时相,观察CEH-EUS、EUS-EG影像学特点。结果以病理学检查结果为诊断金标准,80例胰腺占位性病变患者均行手术切除处理,病理学检验显示44例为良性病变,36例为恶性病变。两组患者疾病检出率差异无统计学意义(P>0.05);联合组疾病误诊率(5.00%)明显低于单一组(30.00%),差异有统计学意义(P<0.05)。联合组诊断准确性、敏感度分别为95.00%、97.36%,均明显高于单一组(70.00%、67.85%),差异均有统计学意义(P<0.05);两组诊断特异度比较,差异无统计学意义(P>0.05)。良性病变的超声造影时相早增晚退、同增同退率分别为22.72%、54.54%,均明显高于恶性病变(0、0),晚增早退率为13.63%,低于恶性病变(55.56%),差异均有统计学意义(P<0.05)。结论EUS-EG与CEH-EUS联合诊断胰腺占位性病变的准确性和敏感度均高于单纯EUS-EG检测,可有效减少误诊。

基于增强型谐波游标效应的光纤温度传感器

提出一种基于增强型谐波游标效应增敏的光纤温度传感器,该传感器由光纤萨格奈克干涉计(Sagnac Interferometer,SI)和法布里-珀罗干涉计(Fabry-Perot Interferometer,FPI)级联构成。通过控制FPI的自由光谱范围为SI的自由光谱范围的整数倍且两者具有相反的温度响应,实现增强型谐波游标效应。实验结果表明,增强型谐波游标效应和增强型普通游标效应具有几乎相同的温度灵敏度,分别为单个FPI和SI灵敏度的28.7倍和16.9倍,增强型谐波游标放大倍率分别为普通谐波游标放大倍率的3.4倍和1.8倍,但增强型谐波游标效应对应的熊猫光纤长度失谐量明显大于增强型普通游标效应,且阶数越高对应的失谐量越大,因此,增强型谐波游标放大倍率更容易控制和实现。该传感器在获取高灵敏度的同时,稳定性能好、制备成本低,具有非常好的应用前景。