MR digital subtraction angiography with asymmetric echo acquisition and complex subtraction: improved lumen and stenosis visualization

The use of complex subtraction in dynamic thick slab 2D MR digital subtraction angiography (MR-DSA) has been shown to eliminate partial volume effects, which are present if vessels cover a small fraction of the 2D slab. However, spin dephasing still results in a poor visualization of areas with complex flow. In this paper, it is shown that this can be overcome by using asymmetric echo (ASE) acquisition combined with complex subtraction. It is proven that an ASE acquisition does not destroy information necessary for complex subtraction if the subtraction is performed in k-space. As a consequence, the subtraction reconstruction is as reliable as the magnitude reconstruction of a single ASE data set. Experiments with ASE and complex subtraction show that flow voids near stenoses disappear, that the signal-to-noise ratio is improved and that temporal resolution is increased.     

QCD One-Loop Effective Coupling Constant and Quark Mass Given in a Mass-Dependent Renormalization

The QCD one-loop renormalization is restudied in a mass-dependent subtraction scheme in which the quark mass is not set to vanish and the renormalization point is chosen to be an arbitrary time-like momentum. The correctness of the subtraction is ensured by the Ward identities which are respected in all the processes of subtraction.By considering the mass effect, the effective coupling constant and the effective quark masses derived by solving the renormalization group equations are given in improved expressions which are different from the previous results.     

QCD One-Loop Effective Coupling Constant and Quark Mass Given in a Mass-Dependent Renormalization

The QCD one-loop renormalization is restudied in a mass-dependent subtraction scheme in which the quark mass is not set to vanish and the renormalization point is chosen to be an arbitrary time-like momentum. The correctness of the subtraction is ensured by the Ward identities which are respected in all the processes of subtraction.By considering the mass effect, the effective coupling constant and the effective quark masses derived by solving the renormalization group equations are given in improved expressions which are different from the previous results.PACS numbers: 11.10.Gh, 11.10.Hi, 12.38.-t, 12.38.Bx     

Performance Improvement of Atmospheric Continuous-Variable Quantum Key Distribution with Untrusted Source

Atmospheric continuous-variable quantum key distribution (ACVQKD) has been proven to be secure theoretically with the assumption that the signal source is well protected by the sender so that it cannot be compromised. However, this assumption is quite unpractical in realistic quantum communication system. In this work, we investigate a practical situation in which the signal source is no longer protected by the legitimate parts, but is exposed to the untrusted atmospheric channel. We show that the performance of ACVQKD is reduced by removing the assumption, especially when putting the untrusted source at the middle of the channel. To improve the performance of the ACVQKD with the untrusted source, a non-Gaussian operation, called photon subtraction, is subsequently introduced. Numerical analysis shows that the performance of ACVQKD with an untrusted source can be improved by properly adopting the photon subtraction operation. Moreover, a special situation where the untrusted source is located in the middle of the atmospheric channel is also considered. Under direct reconciliation, we find that its performance can be significantly improved when the photon subtraction operation is manipulated by the sender.     

Performance improvement of spectral amplitude coding-optical code division multiple access systems using NAND detection with enhanced double weight code

The bit-error rate (BER) performance of the spectral amplitude coding-optical code division multiple access (SACOCDMA) system has been investigated by using NAND subtraction detection technique with enhanced double weight (EDW) code. The EDW code is the enhanced version of double weight (DW) code family where the code weight is any odd number and greater than one with ideal cross-correlation. In order to evaluate the performance of the system, we used mathematical analysis extensively along with the simulation experiment. The evaluation results obtained using the NAND subtraction detection technique was compared with those obtained using the complementary detection technique for the same number of active users. The comparison results revealed that the BER performance of the system using NAND subtraction detection technique has greatly been improved as compared to the complementary technique.     

Speech dereverberation method based on spectral subtraction and spectral line enhancement

Speech signals recorded with a distant microphone usually are interfered by the spatial reverberation in the room, which severely degrades the clarity and intelligibility of speech. A speech dereverberation method based on spectral subtraction and spectral line enhancement is proposed in this paper. Following the generalized statistical reverberation model, the power spectrum of late reverberation is estimated and removed from the reverberation speech by the spectral subtraction method. Then, according to the human auditory model, a spectral line enhancement technique based on adaptive post-filtering is adopted to further eliminate the reverberant components between adjacent speech formants. The proposed method can effectively suppress the spatial reverberation and improve the auditory perception of speech. The subjective and objective evaluation results reveal that the perceptual quality of speech is greatly improved by the proposed method.     

Contrast and sensitivity of the vibration fringes in time-averaged electronic speckle-pattern interferometry: effect of variations of force level

The time averaged frame subtraction technique is improved by subtracting two Bessel fringe patterns at two different force levels. The technique enables significant enhancement of fringe contrast and increased measurement sensitivity. The contrast and sensitivity of the fringes obtained at different force ratios are investigated. Both theoretical and experimental results are presented.     

The supersymmetric Adler-Bardeen theorem and regularization by dimensional reduction

We examine the subtraction scheme dependence of the anomaly of the supersymmetric, gauge singlet axial current in pure and coupled supersymmetric Yang-Mills theories. Preserving supersymmetry and gauge invariance explicitly by using supersymmetric background field theory and dimensional reduction, we show that only the one-loop value of the axial anomaly is subtraction scheme independent, and that one can always define a subtraction scheme in which the Adler-Bardeen theorem is satisfied to all orders in perturbation theory. In general this subtraction scheme may be non-minimal, but in both the pure and the coupled theories, the Adler-Bardeen theorem is satisfied to two loops in minimal subtraction.     

基于B样条的TERS形貌成像背景扣除方法

在针尖增强拉曼光谱(TERS)形貌成像过程中，由于针尖与扫描台无法绝对平行、样品电子密度骤变处针尖快速升降以及扫描控制系统响应时间特性差等综合原因的影响，往往使形貌图中带有倾斜或边界面卷曲的成像背景。成像背景对样品形貌的识别和分析带来十分不利的影响，而背景扣除就是解决该问题的重要手段，也是形貌成像预处理的重要组成部分。背景扣除的原理一般是通过拟合背景的方法来扣除成像中的背景。传统的背景扣除方法是利用多项式拟合的方法对成像进行逐行的基线校正，但是该方法在处理形貌成像时常常会由于过拟合而造成样品形貌的失真，同时容易在图片上留下明显的线条纹理。针对传统方法的缺点，本文提出采用B样条曲面拟合方法，直接对样品形貌图进行曲面背景拟合，发挥B样条低阶光滑的优点，能够有效克服传统方法的缺陷。在实验中，同时利用传统方法和该方法对金单晶和合成金片的形貌图进行背景扣除，实验结果表明，两种方法都能够扣除样品形貌图中的成像背景，但与传统方法相比，所提出的方法不会造成样品形貌的失真，且不会留下线条纹理，获得了更加良好的背景扣除效果，为进一步分析样品形貌特征提供了更准确可靠的信息，是一种更加有效的TERS形貌成像背景扣除算法。     

低信噪比下的语音增强处理

本文介绍了一种基于功率谱减的方法来增强带有白噪声的语音信号。过量功率谱减是语音增强的一个有效的方法，其处理后产生的纯音噪声采用中心限幅的方法可以很好地得到抑制。     

Contrast-enhanced MR angiography with frequency-dependent mask subtraction

One of the main challenges for high-resolution contrast-enhanced magnetic resonance angiography (CE-MRA) is the limited signal-to-noise ratio (SNR). In conventional CE-MRA, spoiled gradient-recalled echo sequence is typically used to acquire raw data before and after contrast material injection, followed by mask subtraction to improve vessel contrast at the cost of increased image noise. We reported here on a frequency-dependent mask subtraction technique where only low spatial frequency data were subject to mask subtraction to improve image contrast and reduce motion artifact while high spatial frequency data were not subtracted to preserve image noise level. The feasibility of this technique was demonstrated through phantom, animal, and human volunteer studies. The lowest half, quarter, 1/8 and 1/16 of all spatial frequencies were subject to mask subtraction, respectively. These partial subtraction techniques were compared with conventional mask subtraction in terms of SNR and artifact power. An SNR gain up to 37% was achieved without significant artifact power increase for quarter-subtraction where only the central one quarter k-space data were subject to mask subtraction.     

Resolution enhancement by subtraction of confocal signals taken at different pinhole sizes

Subtractive imaging in confocal fluorescence light microscopy is based on the subtraction of a suitably weighted widefield image from a confocal image. An approximation to a widefield image can be obtained by detection with an opened confocal pinhole. The subtraction of images enhances the resolution in-plane as well as along the optic axis. Due to the linearity of the approach, the effect of subtractive imaging in Fourier-space corresponds to a reduction of low spatial frequency contributions leading to a relative enhancement of the high frequencies. Along the direction of the optic axis this also results in an improved sectioning. Image processing can achieve a similar effect. However, a 3D volume dataset must be acquired and processed, yielding a result essentially identical to subtractive imaging but superior in signal-to-noise ratio. The latter can be increased further with the technique of weighted averaging in Fourier-space. A comparison of 2D and 3D experimental data analysed with subtractive imaging, the equivalent Fourier-space processing of the confocal data only, and Fourier-space weighted averaging is presented.     

Renormalization using the background-field method

Renormalization using the background-field method is examined in detail. The subtraction mechanism of subdivergences is described with reference to multi-loop diagrams and one- and two-loop counter-term formulae are explicitly given. The original one-loop counter-term formula of 't Hooft is thereby improved. The present method of renormalization is far easier to manage than the usual one owing to the fact that only gauge-invariant quantities are to be considered when worked in an appropriate gauge. Gravity and Yang-Mills theories are studied as examples.     

近红外无创生化检测中不同光程的光谱校正模型研究

近红外无创生化检测中采用不同血流容积光谱相减的方法理论上能够消除人体组织产生的强背景干扰,但人体光谱相减后得到的血液光谱的光程是未知的,这给校正模型的建立带来了困难。通过设计模拟实验并采用正交信号校正的方法对光程信息进行校正,提高不同光程的光谱建立校正模型的预测精度。分别建立了光程校正前后的模型,模型的交叉验证标准偏差从90.17mg.dL-1下降到31.62mg.dL-1,相关系数从0.978 7提高到0.996 8。实验结果表明,采用正交信号校正的方法能够有效抑制光程信息的干扰,提高模型的预测精度,这为不同血流容积光谱相减法的实际应用提供了基础。     

基于ERB尺度划分的多子带语声信号抗噪谱减算法

为了研究心理声学在语声增强方面的应用,本文提出了一种基于等效矩阵带宽(ERB)尺度划分的多子带语声信号抗噪谱减算法。此算法根据ERB尺度将带噪信号的频谱划分成多个子带,然后再根据每个子带的分段信噪比以及心理声学掩蔽原则分别计算每个子带的谱减参数,最后在每个子带中分别进行谱减算法处理。实验结果表明,应用新算法所获得的语声增强结果在信噪比、IS失真以及PESQ方面均优于之前提出的多子带语声信号抗噪谱减算法。     

Generalization of the momentum-space subtraction procedure for renormalized perturbation theory

The momentum-space subtraction procedure for defining renormalized Feynman integrals is modified to allow for subtraction operators more general than the usual Taylor operators. The added generality permits one to assign subtraction degree less than four to some terms of the unperturbed Lagrangian.     

Seeing jets in heavy-ion collisions

In these proceedings, we briefly review how jets can be reconstructed in heavy-ion collisions. The main point we address is the subtraction of the large contamination from the underlying event background. We first present the main ingredients needed to define the jets and perform the background subtraction and then discuss the efficiency of the subtraction for different jet algorithms and background-estimation methods.     

航空变焦距镜头被动消热设计

为减小温度对航空变焦距镜头成像质量的影响,设计了一种基于差动原理的被动消热结构。通过NXNastran有限元分析软件对变焦镜头在高温和低温两种工况下进行了热分析,利用消热原理及分析数据对变焦镜头4个组件进行了消热设计。对消热设计前、后的变焦镜头进行了消热结构耦合分析,分析结果表明变焦镜头经过消热设计后最大热变形量减小了0.03mm。利用泽尼克系数作为数据接口,将获得的热结构分析结果作为光学分析软件Code V输入,仿真出了消热设计前、后变焦镜头在+55℃时的光学传递函数曲线。和镜头设计传递函数值相比,消热设计前镜头在78lp/mm处传递函数值减小约0.2,传递函数值下降了50%,而消热设计后镜头传递函数值基本保持不变。仿真结果证实了消热设计的有效性。最后通过实验验证了仿真结果的正确性。     

Four-State Continuous-Variable Quantum Key Distribution with Photon Subtraction

Four-state continuous-variable quantum key distribution (CVQKD) is one of the discretely modulated CVQKD which generates four nonorthogonal coherent states and exploits the sign of the measured quadrature of each state to encode information rather than uses the quadrature \(\hat {x}\) or \(\hat {p}\) itself. It has been proven that four-state CVQKD is more suitable than Gaussian modulated CVQKD in terms of transmission distance. In this paper, we propose an improved four-state CVQKD using an non-Gaussian operation, photon subtraction. A suitable photon-subtraction operation can be exploited to improve the maximal transmission of CVQKD in point-to-point quantum communication since it provides a method to enhance the performance of entanglement-based (EB) CVQKD. Photon subtraction not only can lengthen the maximal transmission distance by increasing the signal-to-noise rate but also can be easily implemented with existing technologies. Security analysis shows that the proposed scheme can lengthen the maximum transmission distance. Furthermore, by taking finite-size effect into account we obtain a tighter bound of the secure distance, which is more practical than that obtained in the asymptotic limit.     

Dual plane in-line digital holographic microscopy

We report a dual plane in-line digital holographic microscopy technique that exploits the method of subtraction of average intensity of the entire hologram to suppress the zero-order diffracted wave. Two interferograms are recorded at different planes to eliminate the conjugate image. The experimental results demonstrate successful reconstruction of phase objects as well as of amplitude objects. The two interferograms can be recorded simultaneously, using two CCD or CMOS sensors, in order to increase the acquisition rate. This enhanced acquisition rate, together with the improved reconstruction capability of the proposed method, may find applications in biomedical research for visualization of rapid dynamic processes at the cellular level.