Hadamard技术在不均匀场中获取高分辨核磁共振谱的应用

核磁共振(NMR)谱广泛应用于化学,生物和材料科学等领域。分子间多量子相干技术(iMQCs)可以有效地在不均匀磁场中获得高分辨NMR谱,但是该方法获取高分辨谱通常需要较长的数据采集时间,在很大程度上限制了它的应用。Hadamard技术具有时间短和信噪比高的特点,该技术可以较大地缩短不均匀场下采集高分辨NMR谱的时间,因而扩展并增强iMQCs方法在不均匀场下获取高分辨谱的实用性。总结了近几年Hadamard技术结合iMQCs方法在不均匀磁场中获取高分辨NMR谱的基本原理和应用,并对其优缺点做了详细的分析和讨论。     

A real-time high-resolution technique for angle-of-arrival estimation

A new, fast method for angle-of-arrival estimation comparable in performance to modern eigen-decomposition based techniques is described. This method is well-suited to systolic array implementations. An adjunct to the method is an estimator for determining the most likely number of incident signal components.     

波达方向估计的贝叶斯高分辨方法

根据贝叶斯最大后验估计原理研究了波达方向估计的高分辨方法,在文献基础上对贝叶斯高分辨波达方向估计方法进行了补充和完善。针对两个目标源情况提出了快速算法,有效地减少了运算量,提高了运算速度。与MUSIC法和文献中一次快拍的贝叶斯谱分析法的比较充分体现了该方法性能优越,特别是在低信噪比、少快拍数以及相干源情况下可以得到更为准确、稳定的估计效果。     

A CMOS microcoil-associated preamplifier for NMR spectroscopy

For improving sensitivity of nuclear magnetic resonance (NMR) measurements, an in-field preamplifier in a low-cost CMOS process is presented. It is based on a second-generation positive current conveyor (CCII+), with an impedance-matching output stage. The circuit has been designed with optimization of key performances, such as bandwidth, noise, and offset voltage. There have also been precautions taken against potential effect of strong magnetic field under which the circuit should operate. The designed preamplifier has a voltage gain of 15 dB and a bandwidth of 100 MHz. After fabrication of the circuit, we have carried out testing work, including in-field circuit test and characterization of MOS transistors. Under 2-T magnetic field, there have not been substantial changes in overall circuit performances compared to results obtained by post-layout simulations. For an experiment of NMR measurements with and without in-field preamplifier, the circuit is coupled with a receiver micro-coil. The experiment has been to detect protons at 85.13-MHz resonance frequency under 2-T magnetic field with water sample. The obtained results have shown a 14-dB signal-to-noise ratio improvement when the preamplifier is associated with the receiver coil.     

A self-calibration technique for monolithic high-resolution D/Aconverters

A self-calibration technique based upon charge storage on the gate-source capacitance of CMOS transistors is presented. The technique can produce multiple copies of a reference current. Therefore, it is suitable for the calibration of high-resolution D/A (digital/analog) converters which are based upon equal current sources. As the storage capacitor is internal, no external components are required. A calibrated spare current source is used to allow continuous converter operation. This implies that no special calibration cycles are required. To show the capabilities of the calibration technique, it was implemented in a 16-b D/A converter. Measurement results show a total harmonic distortion of 0.0025% at a power consumption of 20 mW and a minimum supply voltage of 3 V. The design was fabricated in a 1.6-μm double-metal CMOS process without special options     

A high-resolution multi-phase delay-locked loop with offset locking technique

In this work, we propose a new type of high-resolution delay-locked loop (DLL) which achieves the performance of high-resolution output by offset locking techniques without restrictions of intrinsic delay in the delay cell. Compared to traditional multi-phase clock generator, this architecture has the features of small size, low jitters, low-power consumption and high resolution. This DLL has been fabricated in 0.35 μm complementary metal-oxide-semiconductor (CMOS) process. The measured root-mean-square and peak-to-peak jitters are 2.89 ps and 31.1 ps at 250 MHz, respectively. The power dissipation is 68 mW for a supply voltage of 3.3 V. The maximum resolution of this work is 144 p and the intrinsic delay of 0.35 μm CMOS process is 220 ps. Comparing with intrinsic delay, the improvement of maximum resolution is 34.5%.     

A high-resolution technique for ultrasound harmonic imaging using sparse representations in Gabor frames

Over the last few decades there were dramatic improvements in ultrasound imaging quality with the utilization of harmonic frequencies induced by both tissue and echo-contrast agents. The advantages of harmonic imaging cause rapid penetration of this modality to diverse clinical uses, among which myocardial perfusion determination seems to be the most important application. In order to effectively employ the information, comprised in the higher harmonics of the received signals, this information should be properly extracted. A commonly used method of harmonics separation is linear filtering. One of its main shortcomings is the inverse relationship between the detectability of the contrast agent and the axial resolution. In this paper, a novel, nonlinear technique is proposed for separating the harmonic components, contained in the received radio-frequency images. It is demonstrated that the harmonic separation can be efficiently performed by means of convex optimization. It performs the separation without affecting the image resolution. The procedure is based on the concepts of sparse signal representation in overcomplete signal bases. A special type of the sparse signal representation, that is especially suitable for the problem at hand, is explicitly described. The ability of the novel technique to acquire "un-masked," second (or higher) harmonic images is demonstrated in series of computer and phantom experiments.     

Measuring molecular flows with high-resolution stimulated Raman spectroscopy

We propose using high-resolution stimulated Raman spectroscopy to directly measure high-speed molecular flow velocities in wind tunnels and in combustive chambers. Our feasibility study indicates that flow speeds from Mach 0.04 up may be measured with the proposed method using available laser systems. It is pointed out that the success of the proposed technique will make possible the potential of measuring all interesting flow parameters, i.e., species concentration, temperature, and velocity, in a time of less than 1 μs at a repetition rate of 10⁴/s using a single experimental arrangement.     

基于减采样技术的快速高分辨数字全息重建算法

为了缓和传统数字全息重建算法在分辨率和计算量之间的相互制约关系,基于欠采样数字解调理论,通过对恢复后的物波场先进行空域或频域减采样,滤除物波中的冗余信息,然后通过补零算法提高有用信息的重建分辨率,从而实现高分辨数字全息的快速重建。分别给出了减采样菲涅尔重建（FR）算法和减采样角谱重建（AS）算法的最大允许采样间隔,推导...     

Data-based matrix decomposition technique for high-resolution array processing of coherent signals

A new data-based matrix decomposition (DMD) method for high-resolution array processing is presented. It is shown here that the DMD method is independent of the coherency between signals of arrival, so it can be used for the high resolution of uncorrelated signals as well as coherent signals. The results of simulation support the theoretical predictions.     

A technique for aging the phosphor of high-resolution cathode-ray tubes with particular application to P-16

An accelerated aging technique--restricted to P-16 phosphor--that measures a cathode-ray tube screen degradation with use is described. A small area of the screen is aged at high excitation densities and the light output from this area is plotted as a function of deposited charge per unit area. A pre-aged part of the screen is used as a reference level for measuring these light output levels. Measurements made to determine phosphor aging with cathode-ray tube operating modes are described. Aging is found invariant with spot focus, beam voltage, beam current, power density per unit area, and sweep speed over normal operating ranges. Deposited charge per unit area is confirmed as the dominant stress factor. Under restricted operating conditions, the data is reproducible within ±4 percent at the 95 percent confidence level. Aging rates accelerated by a factor of more than a thousand as compared to normal usage have been obtained.     

A pipelined architecture for the multidimensional DFT

This paper presents an efficient pipelined architecture for the N ^m-point m-dimensional discrete Fourier transform (DFT). By using a two-level index mapping scheme that is different from the conventional decimation-in-time (DIT) or decimation-infrequency (DIF) algorithms, the conventional pipelined architecture for the one-dimensional (1-D) fast Fourier transform (FFT) can be efficiently used for the computation of higher dimensional DFTs. Compared with systolic architectures, the proposed scheme is area-efficient since the computational elements (CEs) use the minimum number of multipliers, and the number of CEs increases only linearly with respect to the dimension m. It can be easily extended to the N^m-point m-dimensional DFT with large m and/or N, and it is more flexible since the throughput can be easily varied to accommodate various area/throughput requirements     

A series representation for multidimensional Rayleigh distributions

The Rayleigh distribution is of paramount importance in signal processing and many other areas, yet an expression for random variables of arbitrary dimensions has remained elusive. In this note, we generalise the results of Beard and Tekinay for quadrivariate random variables to cases of unconstrained order and provide a simple algorithm for evaluation. The assumptions of cross‐correlation between in‐phase and quadrature, as well as nonsingularity of the covariance matrix, are retained throughout our computations.     

Integrating microfabricated fluidic systems and NMR spectroscopy

The philosophy of miniature total analysis systems (mu-TAS) hinges on the integration of multiple chemical processing steps and the means of analyzing their results on the same miniaturized system. We have constructed chip-based capillary electrophoresis (CE) devices equipped with an integrated planar radio-frequency detector coil used for nuclear magnetic resonance spectroscopy (NMR). Separations were accomplished in the devices, but satisfactory NMR spectra could only be obtained from samples of high concentration. The relative sensitivity is explained and the scaling law dichotomy of CE and NMR explored.     

A unified framework for peak detection and alignment: application to HR-MAS 2D NMR spectroscopy

In this paper, we propose a new scheme to detect and align simultaneously peaks that correspond to different metabolites within a biopsy. The proposed peak detection and alignment scheme is based on the use of evidence theory, which is well suited to model uncertainty and imprecision characterizing the 2D NMR HR-MAS spectra. Consequently, we propose the coupling use of Bayesian and fuzzy set theories to model and quantify the imprecision degree, which is then exploited to define the mass function. We particularly show that our new mass function definition and the use of evidence theory for peak detection and alignment achieve consistently high performance compared to a Bayesian scheme on both synthetic and real spectra. The high quality of peak alignment precision reached by the use of evidence theory allows us to efficiently detect reliable biomarkers, which is an essential step for a better therapeutic and human complement system management in case of multiple sclerosis disease, cancer, etc.     

Admittance spectroscopy: A powerful characterization technique for semiconductor crystals—Application to ZnTe

The admittance spectroscopy technique is shown to be a very convenient tool for analyzing majority carrier traps: energy level, capture cross section and concentrations are easily obtained without complicated mathematical treatment. The series resistance in the material underlying the Schottky or pn junction is also detected when the free carriers are freezing out. It allows to get the shallowest level energy and its compensation ratio. The method has been applied to ZnTe material analysis and the effect on the admittance of six different acceptors is demonstrated. When comparing the electrically determined ionization energy of a given impurity with its optical value the former appears as systematically lower but most of the difference can be ascribed to Poole Frenkel or impurity concentration effects.     

应用光电流光谱法测定氖原子的高分辨光谱

应用光电流光谱技术,测量了氖原子跃迁2P_4→4S_1和2P_3→4S_1的精细结构,首次认定了氖原子谱线5919.037埃为2P_7→4d_3跃迁。获得的光谱谱线轮廓具有典型的对称性线型,测得的谱线半宽度为3.2千兆赫。     

A compatible high-resolution TV system for cablecasting

Cablecasting offers the possibility of a new and improved system of color television. New technology for wide bandwidth, for large displays, and better signal transmission systems make it desirable to improve on the National Television System Committee (NTSC) system which has served so well for over-the-air transmissions. In this paper, a system is suggested with which a subscriber owning a present TV receiver Will continue to get the same picture quality as he does now. New receivers can be designed to provide substantially improved resolution and better color reception. The system uses two adjacent 6-MHz channels for each one now used. The upper channel is standard NTSC, while the lower channel is filled with a lower sideband that permits a 7-MHz video response, Present receivers use the upper channel, while new receivers will use signals from both channels.     

一种低失调CMOS比较器设计

本文在研究各种比较器失调消除技术基础上,提出了一种用于ADC电路的高速高精度比较器失调消除技术.该比较器由主动复位和共模箝位的预放大器和输出锁存器构成,通过负反馈自适应调整比较器输入失调电压,降低了开关电容沟道电荷注入和时钟馈通对比较器精度的影响.仿真结果表明,在Chartered 0.35μm COMS工艺下,电源电压3.3V,调整后的比较器失调误差为34μV,比较速率100MHz.     

A multidimensional phase-locked loop for blind multiuser detection

This paper concerns the problem of blind multiuser detection, a special case of the blind source separation problem in which the source signals have finite alphabets. Specifically, we address the problem of identifying and resolving the n/spl times/n unitary matrix ambiguity U that results from whitening the receiver observations, where n is the number of sources. We propose the multidimensional phase-locked loop (MPLL) as a generalization of a scalar decision-directed PLL to vector-valued signals. The MPLL adapts an estimate of U according to the recursion U/spl circ//sub k+1/=U/spl circ//sub k/R/sub k/, where R/sub k/ is an n-dimensional Householder-like rotation depending on only the kth receiver observation. The O(n/sup 2/) complexity of an efficient implementation of the algorithm is extremely low. Nevertheless, simulation results demonstrate good convergence properties and superior steady-state performance when compared with prior techniques. The algorithm is also able to accommodate large alphabets and shaped alphabets.