多频探头结合法对颈部动脉的检测

目的讨论利用不同频率的多探头结合法对颈部动脉的检测的应用价值。方法用传统高频线阵探头检测法对50名对照组病例进行检测,用多频率探头结合法对另外50名观察组病例进行检测,其结果做统计学处理。结果二种方法对比中对颈总动脉检测的阳性例数及阳性率无明显差异,P>0.05,对颈内动脉、椎动脉、锁骨下动脉检测中阳性例数及阳性率有明显差异,P<0.01。结论不同频率多探头结合法对颈部动脉疾病的诊断有极大的应用价值。

时尚与宽频同行——Vifa HD3000放大器、幻影一号扬声器系统

数月前，一件在业界甚为轰动的事是丹麦(Vifa)与日本先锋(Pioneer)“联合打造宽频影音新标准”的战略合作，它的实质是以先锋久负盛名的碟机与威发新设计的宽频音响结合，共同倡导DVD Audio、SACD的宽频格式，并将其器材普及化，让一种全新的影音标准，令传统的频率响应上限为20000Hz。

射频消融结合臭氧术联合中药治疗腰椎间盘突出症

射频消融结合臭氧术联合中药治疗腰椎间盘突出症(LDH)。方法 取我院(2021年1月至2022年12月)患者(114例),随机分为3组(38例/组)。分三组比较。结果 结束后即刻、疗程结束后1周、1、3、6、12个月VAS评分比较均有差异性,ODS评分比较均降低(P<0.05)。结论 对LDH患者使用射频消融结合臭氧术联合中药治疗能够显著改善患者的各项指标,降低其术后并发症发生率。

基于索引调制OTFS系统的应用

正交时频空(Orthogonal Time Frequency Space,OTFS)调制技术和索引调制(Index Modulation,IM)技术适用于高移动性场景,具有高频谱效率等优势,在图像传输领域应用前景广泛。然而,结合索引调制的正交时频空(Orthogonal Time Frequency Space with Index Modulation,OTFS-IM)调制技术的算法实现复杂度较高。对此,在广义近似消息传递(Generalized Approximate Message Passing,GAMP)的基础上改进,提出一种基于概率排序的阻尼广义消息传递算法。实验结果表明,在图像传输应用中,与传统的最小均方误差结合最大似然方案(Minimum Mean Squared Error with Maximum Likelihood,MMSEML)相比,所提的算法具有更低的复杂度,性能也优于传统的MMSE-ML传输方案。

Sound absorption performance of various nickel foam-base multi-layer structures in range of low frequency

Commercial3D reticular nickel foam and its composite structure were investigated on the sound absorption at200-2000Hz.The absorption performance of foam plates1?5layers(1-layer thickness:2.3mm;porosity:89%;average pore-diameter:0.57mm)was found to be poor,and could be improved by adding backed cavum or front perforated thin sheet.The absorption coefficient could reach about0.4at1000-1600Hz for the composite structure of5-layer foam with a backed5mm-thick cavum,and even0.68at about1000Hz for that of2-layer foam with the same cavum and a perforated plate closely in front of the foam.

取消省界收费站带来的风险及应对方案探析

通过对取消省界收费站形成全国一张网后高速公路运营潜在的风险和问题的思考,从现阶段可行的技术方案出发,结合未来高速公路收费模式及运营模式的发展,提出射频与视频结合、北斗定位技术融合、差异化收费、集中监控系统建设及全国信用体系建设等几个方面的应对方案。

Sound absorption of several various nickel foam multilayer structures at aural frequencies sensitive for human ears

Using the three-dimensional reticular nickel foam as experimental material, the sound absorption performance was investigated for several various multilayer structures in the frequency range of 2000-4000 Hz, which is aurally sensitive for human ears. The results showed that the 7.5 mm-thick foam sample, which was formed by piling of 5-layer foam plate（thickness： 1.5 mm; porosity： 96%; average pore-diameter： 0.65 mm） could exhibit an excellent sound absorption effect at 4000 Hz, with the absorption coefficient about 0.8. Constituting alternate air gap with the total thickness of about 18.5 mm can greatly improve the absorption performance at relatively low frequencies of 2000-3150 Hz, with the absorption coefficient up to about 0.5 or more. In addition, the research showed that alternate piling up the perforated plate inside the foam plates can also achieve a quite good effect of sound absorption at relatively low frequencies.

Structures and Stability of Metal Amidoboranes (MAB): Density Functional Calculations

Molecule geometry structures, frequencies, and energetic stabilities of ammonia borane （AB, NH3BH3 ） and metal amidoboranes （MAB, MNH2BH3）, formed by substituting H atom in AB with one of main group metal atoms, have been investigated by density-functional theory and optimized at the B3LYP levels with 6-311G＋＋ （3dr, 3pd） basic set. Their structural parameters and infrared spectrum characteristic peaks have been predicted, which should be the criterion of a successfully synthesized material. Several parameters such as binding energies, vibrational frequencies, and the energy gaps between the HOMO and the LUMO have been adopted to characterize and evaluate their structure stabilities. It is also found that the binding energies and HOMO-LUMO energy gaps of the MAB obviously change with the substitution of the atoms. MgAB has the lowest binding energy and is easier to decompose than any other substitutional structures under same conditions, while CaAB has the highest chemical activity.

Radiofrequency ablation of the connections between two atriums in dogs

Objective:To observetheelectrophysiologicalchangesafterblockageof theconnectionsbetweentwo atriumsin dogs.Methods :Theatrialeffectiverefractoryperiods,itsdispersionsandtheconductivetimesbetween atriumsweremeasuredandcomparedbeforeandaftertheinteratrialblockagein tendogs.Results:The atrial effectiverefractoryperiodsand its dispersionsnonsignificantlychanged,but its conductivetimessignificantly prolonged(P<0.01),P wavedurationin electrocardiogramalsoprolonged(P<0.05).Conclusion:Atrialactivation patterncouldbecomechangeby theblockageof theconnectionsof atriumsand theprolongedP wave duration mightbe regardedas a surrogateto indicatesuccessfulblockage.

Reputation-Based Hierarchically Cooperative Spectrum Sensing Scheme in Cognitive Radio Networks

Cooperative spectrum sensing in cog- nitive radio is investigated to improve the det- ection performance of Primary User （PU）. Meanwhile, cluster-based hierarchical coop- eration is introduced for reducing the overhead as well as maintaining a certain level of sens- ing performance. However, in existing hierar- chically cooperative spectrum sensing algo- rithms, the robustness problem of the system is seldom considered. In this paper, we pro- pose a reputation-based hierarchically coop- erative spectrum sensing scheme in Cognitive Radio Networks （CRNs）. Before spectrum sensing, clusters are grouped based on the location correlation coefficients of Secondary Users （SUs）. In the proposed scheme, there are two levels of cooperation, the first one is performed within a cluster and the second one is carried out among clusters. With the reputa- tion mechanism and modified MAJORITY rule in the second level cooperation, the pro- posed scheme can not only relieve the influ- ence of the shadowing, but also eliminate the impact of the PU emulation attack on a rela- tively large scale. Simulation results show that, in the scenarios with deep-shadowing or mul- tiple attacked SUs, our proposed scheme ach- ieves a better tradeoff between the system robustness and the energy saving compared with those conventionally cooperative sensing schemes.

点阵绝对相位彩色多频光栅傅里叶变换轮廓术

提出一种将三角法测距与多频光栅相结合的方法,充分利用数字投影的RGB通道,将多频光栅与点阵同时投影在物体表面,综合控制受高度调制的相位信息的提取,最终获取物体的三维形貌。仿真结果显示,在高度跳变使高频光栅位移达102量级个周期时,可以准确还原原始形貌。通过实验验证,本方法能够同时复原169mm的陡峭高度跳变以及3mm的微小细节,提高了传统双频光栅的性能,具有处理较大截断面和保证细节部分的测量能力,较好地改善了傅里叶变换轮廓术(FTP)的应用性能。

外激作用下自激热声系统的非线性动力学响应

在高温高压燃烧实验台上,以频率ff为78~716Hz,幅值A为0.026~0.629的外激信号激励有自激响应的同心分层旋流部分预混预蒸发火焰热声系统,研究其非线性动力学响应。结果表明:系统的自激频率fn为366.85Hz;当外激频率和自激频率的比值为1.022,幅值A为0.629时,火焰主要被外激频率其谐波控制,其状态轨迹密集在很窄的封闭带中;当外激频率和自激频率的比值与A在其他的范围时,火焰不仅在ff和fn处响应,还在谐频、结合频和分频处响应。说明当外激幅值足够大并且外激频率靠近自激频率时,火焰发生锁相;当火焰未锁相时,出现了谐频、结合频以及分频的非线性响应,火焰准周期振荡。受迫范德波尔振荡器模型能够预测锁相、奇数谐频以及结合频2fn±ff。

Compressed sensing-based structured joint channel estimation in a multi-user massive MIMO system

Acquisition of accurate channel state information （CSI） at transmitters results in a huge pilot overhead in massive multiple input multiple output （MIMO） systems due to the large number of antennas in the base station （BS）. To reduce the overwhelming pilot overhead in such systems, a structured joint channel estimation scheme employing compressed sensing （CS） theory is proposed. Specifically, the channel sparsity in the angular domain due to the practical scattering environment is analyzed, where common sparsity and individual sparsity structures among geographically neighboring users exist in multi-user massive MIMO systems. Then, by equipping each user with multiple antennas, the pilot overhead can be alleviated in the framework of CS and the channel estimation quality can be improved. Moreover, a structured joint matching pursuit （SJMP） algorithm at the BS is proposed to jointly estimate the channel of users with reduced pilot overhead. Furthermore, the probability upper bound of common support recovery and the upper bound of channel estimation quality using the proposed SJMP algorithm are derived. Simulation results demonstrate that the proposed SJMP algorithm can achieve a higher system performance than those of existing algorithms in terms of pilot overhead and achievable rate.

Magnetoelectric cylindrical layered composite structure with multi-resonance frequencies

A combined ME composite structure is made of several cylindrical layered composites in series or parallel connection.Due to the cylindrical structure,the combined structure does not need more space.The characteristics of multi-resonance frequencies have been studied.Each resonance frequency of the structure can be adjusted by changing the cylinder diameter of the corresponding cylindrical layered composites.The number of resonance frequencies increases as the number of cylindrical layered composites increases.The multi-resonance frequencies behavior makes these cylindrical layered composite structures suitable for applications in multifuctional devices with multi-frequencies operation.

Vortices in a Rotating Spin-Orbit-Coupled Bose–Einstein Condensate under Extreme Elongation in a Harmonic Plus Quartic Trap

We consider the ground-state properties of a rotating spin-orbit-coupled Bose–Einstein condensate under extreme elongation in a harmonic plus quartic potential. The effects of spin-orbit coupling and rotation on the groundstate vortex structures are investigated. In the absence of spin-orbit coupling, new nucleated vortices gradually form vortex lines and annular vortex structures with the increase of the rotation frequency. In the presence of spin-orbit coupling, part of the vortices arrange in a line and form a stable vortex chain, and the remanent vortices coexist in pairs aside such vortex chain. More specially, the remanent vortices of each component repel each other and form vortex pair for isotropic spin-orbit coupling, while attract each other and locate in the same positions for anisotropic spin-orbit coupling.