Enhancing signal-to-noise ratio and resolution in low-field NMR relaxation measurements using post-acquisition digital filters

The traditional way to enhance signal-to-noise ratio (SNR) of nuclear magnetic resonance (NMR) signals is to increase the number of scans. However, this procedure increases the measuring time that can be prohibitive for some applications. Therefore, we have tested the use of several post-acquisition digital filters to enhance SNR up to one order of magnitude in time domain NMR (TD-NMR) relaxation measurements. The procedures were studied using continuous wave free precession (CWFP-T₁) signals, acquired with very low flip angles that contain six times more noise than the Carr–Purcell–Meiboom–Gill (CPMG) signal of the same sample and experimental time. Linear (LI) and logarithmic (LO) data compression, low-pass infinity impulse response (LP), Savitzky–Golay (SG), and wavelet transform (WA) post-acquisition filters enhanced the SNR of the CWFP-T₁ signals by at least six times. The best filters were LO, SG, and WA that have high enhancement in SNR without significant distortions in the ILT relaxation distribution data. Therefore, it was demonstrated that these post-acquisition digital filters could be a useful way to denoise CWFP-T₁, as well as CPMG noisy signals, and consequently reducing the experimental time. It was also demonstrated that filtered CWFP-T₁ method has the potential to be a rapid and nondestructive method to measure fat content in beef and certainly in other meat samples.     

对超重、失重演示实验的改进

对传统的超重、失重演示实验进行了改进,使弹簧秤的指针能静止在超重(或失重)的位置上,从而能准确地读出读数,提高演示效果.     

A versatile protocol for the preparation of substituted 1- and 2-naphthyl piperazines from aminonaphthols

Aminonaphthols are easily transformed into a variety of 1- and 2-naphthyl piperazines using a sequence of diazotization, iodide substitution and Pd(0) catalyzed coupling reactions.     

西藏区域经济系统的灰色关联分析

区域经济的发展受许多不同因素的影响，本结合西藏社会经济发展的特点，选取了总产值指标、第一产业指标、第二产业指标和第三产业指标等四大类指标体系，采用灰色关联分析法对西藏的区域经济系统进行了简要的分析评价，以研究西藏区域经济的发展状况，从社会经济的角度探讨西藏经济发展落后的原因，以期能为西藏经济发展政策提供参考依据。     

期货经纪公司保证金的一种确定方法

本文基于马尔可夫链在存储论中的应用，结合Ergodic定理，得到确定期货经纪公司保证金的Ergodic模型，即一个双目标规划问题，然后应用乘积最大化准则，将该模型转化为单目标规划问题来求解。该方法考虑期货经纪公司承担的风险和对投资者的吸引程度，为保证金的确定提供新的思路。     

Zn-doping effect on the energy barrier to magnetization reversal in superparamagnetic nickel ferrite nanoparticles

Measurements of ac-susceptibility and dc-magnetization were carried out on samples of Ni_1-xZn_xFe₂O₄ nanoparticles (x=0, 0.25, 0.5, 0.75) with average diameters 〈D〉≈7 nm. Values of the superparamagnetic blocking temperature T̄_B were obtained from the characteristic temperature behavior of the imaginary susceptibility χ_imag. An Arrhenius-type law, which accurately describes the relationship between the observation time τ_obs and the blocking temperature, was used to determine the effective energy barrier to magnetization reversal U_eff. A Zn-content dependence of the energy barrier is observed, where U_eff changes little for 0≤x≤0.25, it peaks at x=0.5, and decreases back upon further Zn-doping. The large increase of U_eff at x=0.5 is attributed to an enhanced magnetic anisotropy induced by the crossover between two spatial arrangements of spins in the A and B sub-lattices of the ferrimagnetic inverse spinel. PACS 75.50.Bb; 75.50.Gg; 75.30.Et     

对光磁共振实验中测量gF值的方法的评述和改进

对文献中测量gF因子的方法进行了评述，阐述了如何基于三角波扫场，用抽运信号确定计算和测量gF的方法。     

Synthesis, Crystal Structure, Fluorescent and Thermal Properties of Sodium Tridecafluorodizirconate Na_5Zr_2F_(13) Compound

1 INTRODUCTION Considerable research effort on the heavy metal fluoride glasses like barium, zirconium fluoride and a series of rare-earth fluorozirconate compounds du- ring the last two decades was initiated by the broad optical transmission window of these glasses and thereby the potential for ultralow-loss optical fi- bers[1~10]. The fluorozirconate of alkali metals was first reported in 1938[11], and most of the sodium and potassium fluorozirconates were reported amongthe 1940s and 19…     

紫外分光光度法测定甲磺酸帕珠沙星原料药含量

采用紫外分光光度法测定了甲磺酸帕珠沙星原料药的含量,并与高效液相色谱法和酸碱滴定法的测定结果进行了比较.该法简便、快速、结果准确.为甲磺酸帕珠沙星在生产过程中的质量控制提供了可靠依据.     

Higher-Order Simple Lie Algebras

It is shown that the non-trivial cocycles on simple Lie algebras may be used to introduce antisymmetric multibrackets which lead to higher-order Lie algebras, the definition of which is given. Their generalised Jacobi identities turn out to be satisfied by the antisymmetric tensors (or higher-order “structure constants”) which characterise the Lie algebra cocycles. This analysis allows us to present a classification of the higher-order simple Lie algebras as well as a constructive procedure for them. Our results are synthesised by the introduction of a single, complete BRST operator associated with each simple algebra. Received: 3 June 1996 / Accepted: 8 November 1996