An ISGW Filtering Antenna with Spurious Modes and Surface Wave Suppression for Millimeter Wave Communications

In this paper,an integrated substrate gap waveguide(ISGW)filtering antenna is proposed at millimeter wave band,whose surface wave and spurious modes are simultaneously suppressed.A secondorder filtering response is obtained through a coupling feeding scheme using one uniform impedance resonator(UIR)and two stepped-impedance resonators(SIRs).To increase the stopband width of the antenna,the spurious modes are suppressed by selecting the appropriate sizes of the ISGW unit cell.Furthermore,the ISGW is implemented to improve the radiation performance of the antenna by alleviating the propagation of surface wave.And an equivalent circuit is investigated to reveal the working principle of ISGW.To demonstrate this methodology,an ISGW filtering antenna operating at a center frequency of 25 GHz is designed,fabricated,and measured.The results show that the antenna achieves a stopband width of 1.6f0(center frequency),an out-of-band suppression level of 21 dB,and a peak realized gain of 8.5 dBi.

Geometrical Reconstruction and CNC Process of Spurious Tympanic Membrane Based on Reverse Engineering

Perforation of tympanic membrane is one of the main reasons for both deafness and dyssaudia.We could improve and restore audition by restoring or replacing the tympanic membrane.So,whether you can make the spurious tympanic membrane successfully is one of the keys to a successful operation.Utilizing CMM (Coordinate Measuring Machine) measurement equipment, we measured tympanic membrane model precisely and digitally.We also analysed the measured data by point to surface and we have successfully reconstructed the CAD model of the spurious tympanic membrane.Using the model we have got,we schemed out the mold of spurious tympanic membrane.In addition,we utilized MasterCAM compiling CNC (Computerized Numerical Con- trol) code and simulating the course of working.Ultimately,we obtained the mold of spurious tympanic membrane.Our research in this article has great significance to the success of spurious tympanic membrane grafting operation.

Low spurious noise frequency synthesis based on a DDS-driven wideband PLL architecture

An S-band frequency synthesizer for a stepped-frequency radar is presented. This frequen- cy synthesizer is based on a direct digital synthesizer （ DDS ） -driven wideband phase-locked loop （PLL） architecture which can achieve low spurious noise and rapid frequency hopping simultaneous- ly. The mechanism of introducing high level spurs by the images of DDS digital to analog convertor （DAC） output is analyzed. A novel DDS frequency planning method is proposed to ensure low col- ored noise within the entire bandwidth. The designed output frequency range is 3. 765 -4. 085 GHz, and the step size is 5 MHz with frequency agility of less than 1 μs. Measured results demonstrate that the average spurious free dynamic range （SFDR） is about 64 dBc in a 320 MHz bandwidth.

Impact of symmetrized and Burt—Foreman Hamiltonians on spurious solutions and energy levels of InAs/GaAs quantum dots

We present a systematic investigation of calculating quantum dots （QDs） energy levels using finite element method in the frame of eight-band k · p method. Numerical results including piezoelectricity, electron and hole levels, as well as wave functions are achieved. In the calculation of energy levels, we do observe spurious solutions （SSs） no matter Burt Foreman or symmetrized Hamiltonians are used. Different theories are used to analyse the SSs, we find that the ellipticity theory can give a better explanation for the origin of SSs and symmetrized Hamiltonian is easier to lead to SSs. The energy levels simulated with the two Hamiltonians are compared to each other after eliminating SSs, different Hamiltonians cause a larger difference on electron energy levels than that on hole energy levels and this difference decreases with the increase of QD size.

DDFS spurious signals due to amplitude quantization in absence of phase-accumulator truncation

Spurious signals in direct digital frequency synthesizers （DDFSs） are partly caused by amplitude quantization and phase truncation, which affect their application to many wireless telecommunication systems. These signals are deterministic and periodic in the time domain, so they appear as line spectra in the frequency domain. Two types of spurious signals due to amplitude quantization are exactly formulated and compared in the time and frequency domains respectively. Then the frequency spectra and power levels of the spurious signals due to amplitude quantization in the absence of phase-accumulator truncation are emphatically analyzed, and the effects of the DDFS parameter variations on the spurious signals are thoroughly studied by computer simulation. And several important conclusions are derived which can provide theoretical support for parameter choice and spurious performance evaluation in the application of DDFSs.

Novel analysis method for the spurious spectrum of direct digitalfrequency synthesizer in the presence of phase truncation

Based on the analysis of the spurious introduced by phase accumulation truncation which was made by Nicholas, a new simplified algorithm for spurious spectrum in the presence of phase truncation is presented by using the mapping mathematics and number theoretic method, it is possible to precisely analyze the spurious location and the spurious amplitude introduced by phase truncation in practical applications by computer.

A NOVEL IMAGING METHOD IN STEPPED FREQUENCY RADAR WITHOUT SPURIOUS PEAKS

Stepped frequency signal is often used to synthesize high-resolution range profile,but redundant high-resolution range profile exists before synthesis. Two methods have been given to extract target from overlapped high-resolution range profile and analyzed to show how spurious peaks appear. This paper provides a reverse-count algorithm to resolve the problem of spurious peaks for moving target. This proposed method selects the peak with maximum amplitude as the extracted target and gets its position by using the number of samples prceding before the present sample position and the number of high-resolution range cell of the target. This proposed method is compared with the already given method and the result shows the ability of the proposed method to remove spurious peaks, it provides the foundation for high-resolution range profile.

Unbalanced Regressions and Spurious Inference

Spurious regression has been extensively studied in time series econometrics since Granger and Newbold’s seminal paper. Recently, it has been advanced that this phenomenon is due to a mistreatment of short-range autocorrelation in the residuals of the regression when at least one of the variables in a bivariate regression is stationary. HAC errors, feasible GLS and Cochrane-Orcutt-type procedures are then proposed to draw correct inference. Such a proposal should be cautiously considered, since nonsense inference might also be due to deterministic trend mechanisms, structural breaks, and long range dependence. In these cases, standard autocorrelation correction procedures would not solve the problem of spurious regression. We aim to make the later argument clear.

Mitigating Spurious Correlations for Self-supervised Recommendation

Recent years have witnessed the great success of self-supervised learning(SSL)in recommendation systems.However,SSL recommender models are likely to suffer from spurious correlations,leading to poor generalization.To mitigate spurious correlations,existing work usually pursues ID-based SSL recommendation or utilizes feature engineering to identify spurious features.Nevertheless,ID-based SSL approaches sacrifice the positive impact of invariant features,while feature engineering methods require high-cost human labeling.To address the problems,we aim to automatically mitigate the effect of spurious correlations.This objective requires to 1)automatically mask spurious features without supervision,and 2)block the negative effect transmission from spurious features to other features during SSL.To handle the two challenges,we propose an invariant feature learning framework,which first divides user-item interactions into multiple environments with distribution shifts and then learns a feature mask mechanism to capture invariant features across environments.Based on the mask mechanism,we can remove the spurious features for robust predictions and block the negative effect transmission via mask-guided feature augmentation.Extensive experiments on two datasets demonstrate the effectiveness of the proposed framework in mitigating spurious correlations and improving the generalization abilities of SSL models.

Spurious Thermoluminescence Characteristics of the Ediacaran Doushantuo Formation(ca. 635–551 Ma) and Its Implications for Marine Dissolved Organic Carbon Reservoir

The Ediacaran Doushantuo Formation（ca. 635–551 Ma） deposited immediately after the last Neoproterozoic glaciations and recorded the most prominent negative excursions of carbonate carbon isotopic composition（δ^（13）C（carb））. These excursions have been interpreted as a result of widespread remineralization of a large dissolved organic carbon（DOC） reservoir in the Ediacaran deep oceans. However, there is no direct evidence so far found in rocks for the proposed DOC reservoir, which devalues such an interpretation. Here, we conducted a detailed study on the glow-curves characteristics and signal origins of spurious thermoluminescence（TL） of the Doushantuo Formation at Jiulongwan in Yangtze Gorges area, South China, through sequential tests under CO2, N2 and air. Spurious TL intensities for test samples before and after removing soluble organic matter via accelerated solvent extraction（ASE） are nearly identical. Further, significant positive correlation between the spurious TL intensity and total inorganic carbon（TIC） content（R^2=0.7） indicate that the Doushantuo spurious TL with the characteristic peak at 393.5 °C from the sequential test is chemiluminescence（CL） which is derived from the oxidation of a type of non-volatile organic matter strongly associated with carbonate mineral lattice（termed as “X-OM”）. A most likely explanation is that the X-OM is a type of dissolved organic matter which co-precipitated with carbonate minerals into sediments in the Ediacaran Doushantuo Ocean. Furthermore, a significant exponential negative correlation（R^2=0.55） is observed between the CL data and the isotopic difference between carbonate and coexisting bulk organic matter（i.e., Δ^（13）C（carb-org）, a proxy for remineralization degree of DOC reservoir in proposed DOC hypothesis）, suggesting that the X-OM was derived from the oxidation of the DOC reservoir in the Ediacaran Ocean. We thus propose that the X-OM and its CL detected in our study may have recorded the evolution of the possible DOC reservoir in the Ediacaran Doushantuo Ocean. If this is correct, the stratigraphic variations of the CL intensity in the Doushantuo Formation at Jiulongwan support the pulsed oxidation of the DOC reservoir in the Ediacaran Ocean. Our findings indicate that the CL derived from the oxidation of non-volatile organic matter which is strongly associated with carbonate mineral lattices in rocks may provide a feasible approach for probing the evolution of DOC reservoir in the ancient oceans, thus likely provide direct geological evidence for the development of oceanic DOC reservoir in geological times.

SPURIOUS NUMERICAL SOLUTIONS OF DELAY DIFFERENTIAL EQUATIONS

This paper deals with the relationship between asymptotic behavior of the numerical solution and that of the true solution itself for fixed step-sizes. The numerical solution is viewed as a dynamical system in which the step-size acts as a parameter. We present a unified approach to look for bifurcations from the steady solutions into spurious solutions as step-size varies.

Spurious-mode vibrations caused by alternating current poling and their solution process for Pb(Mg_(1/3)Nb_(2/3))O_(3)-PbTiO_(3) single crystals

The effects of alternating current poling(ACP)at 80℃on electrical properties of[001]-oriented 0.72 Pb(Mg_(1/3)Nb_(2/3))O_(3)-0.28PbTiO_(3)(PMN-28PT)single crystals(SCs)have been investigated.The square-wave ACP SCs poled at high voltage(HV,5 kV_(rms)/cm)occasionally showed large fluctuations and low opposite values of piezoelectric coefficient(d_(33)=±1370 pC/N)in one plate.This revealed spuriousmode vibrations(SMV)of impedance spectrum.However,after depolarizing and repolarizing the sample with a sine-wave ACP at low voltage(LV,3.5 kV_(rms)/cm),the d_(33) enhanced to be 1720 pC/N(+26%)and did not exhibit large fluctuation or opposite values in one plate any more.The impedance spectrum became clean and the abnormal SMV disappeared.We proposed four possible mechanisms of the SMV,and speculate that the main cause maybe by macro-scale sub-domain structure and/or phase change in the main domain structure and/or phase in the SC plate due to the specific poling conditions not eternal mechanical damage of PMN-PT SCs.This study will be useful to realize a high d_(33) and improve other properties of PMN-PT ACP SC ultrasonic transducers without any SMV for high-frequency medical imaging equipment.

Spurious Solutions in the Multiband Effective Mass Theory Applied to Low Dimensional Nanostructures

In this paper we analyze a long standing problem of the appearance of spurious,non-physical solutions arising in the application of the effective mass theory to low dimensional nanostructures.The theory results in a system of coupled eigenvalue PDEs that is usually supplemented by interface boundary conditions that can be derived from a variational formulation of the problem.We analyze such a system for the envelope functions and show that a failure to restrict their Fourier expansion coeffi-cients to small k components would lead to the appearance of non-physical solutions.We survey the existing methodologies to eliminate this difficulty and propose a simple and effective solution.This solution is demonstrated on an example of a two-band model for both bulk materials and low-dimensional nanostructures.Finally,based on the above requirement of small k,we derive a model for nanostructures with cylindrical symmetry and apply the developed model to the analysis of quantum dots using an eight-band model.

泰勒级数的DDS设计与FPGA实现

为了提高直接数字频率合成输出信号的动态范围,提出了一种在不增加直接数字频率合成中的累加器的位数的基础上,利用泰勒级数法较少数字频率合成的相位抖动的方法。并且对一个具有32位累加器的直接数字频率合成,输出一定频率范围的信号进行了仿真。仿真结果表明,基于泰勒级数的直接数字频率合成具有较好的动态范围,比一般的方法提高了12 dB。该方法对直接数字频率合成设计者有着重要的参考价值。

DDS频率合成器杂散的分析与仿真

在理论分析的基础上,利用MATLAB中DSPBuilder建立DDS系统,通过实验对DDS的输出进行了时、频域仿真,通过定义输出信噪比,对不同参数设置对系统输出频谱的影响进行了比较,从而为实际系统参数选择提供了指导。

DDS频率合成器杂散的PLL抑制

DDS频率合成器由于其固有的数字特征,使得输出信号中存在大量的杂散,杂散的抑制一般通过输出端的低通或带通滤波器来进行,但效果较差。PLL具有良好的窄带和跟踪特性,文中提出了基于PLL的窄带滤波器杂散抑制方法。利用ALTERA公司Dspbuilder工具箱实现的DDS进行仿真,通过输出信噪比的比较,验证了该法的正确性。

An Algorithm for Ship Wake Detection from the SAR Images Using the Radon Transform and Morphological Image Processing

Using the Radon transform and morphological image processing, an algorithm for ship's wake detection in the SAR (synthetic aperture radar) image is developed. Being manipulated in the Radon space to invert the gray-level and binary images, the linear texture of ship wake in oceanic clutter can be well detected. It has been applied to the automatic detection of a moving ship from the SEASAT SAR image. The results show that this algorithm is well robust in a strong noisy background and is not very sensitive to the threshold parameter and the working window size.

基于PLL的直接数字频率合成器研究

介绍了锁相环(PLL)和直接数字频率合成器(DDS)的基本原理,分析了二者的优缺点,以此为基础,提出了基于锁相环加直接频率合成技术的频率合成器实现方式,同时介绍了DDS芯片AD9850,给出了技术方案,讨论了部分电路设计,并对信号杂散进行了分析。

Solution to the Dirac equation using the finite difference method

In this study,single-particle energy was examined using the finite difference method by taking 208Pb as an example.If the first derivative term in the spherical Dirac equation is discretized using a three-point formula,a one-to-one correspondence occurs between the physical and spurious states.Although these energies are exactly the same,the wave functions of the spurious states exhibit a much faster staggering than those of the physical states.Such spurious states can be eliminated when applying the finite difference method by introducing an extra Wilson term into the Hamiltonian.Furthermore,it was also found that the number of spurious states can be reduced if we improve the accuracy of the numerical differential formula.The Dirac equation is then solved in a momentum space in which there is no differential operator,and we found that the spurious states can be completely avoided in the momentum space,even without an extra Wilson term.

∑-Δ调制器MASH模型的结构寄生研究

∑-Δ调制小数分频频率合成器利用噪声成型技术,将量化噪声的频谱搬移到频率高端,借助锁相环路的低通特性对这种高频噪声进行抑制,不但实现了锁相环输出频率的精细步进,而且解决了小数分频存在的尾数调制问题。然而,作为有限状态机,特定输入情形下会形成特有的杂散谱,即∑-Δ调制器的结构寄生。介绍了∑-Δ调制器MASH模型的结构寄生,详细推导了1阶、2阶和3阶MASH模型的输出序列长度关系式,揭示了序列长度与输入数值和累加器初始值密切关系,获得了避免极短序列长度的有效方法,有效消除了结构寄生,为高性能∑-Δ调制小数分频频率合成器的设计提供了理论依据。分析方法也适合其它新型调制器结构寄生的分析,具有重要意义。