在抑制强溶剂峰的条件下测量T_1值

当所测样品含有强溶剂信号时,由于主要谱线的动态范围受到严重限制,用常规的方法例如IR方法)测量T_1其精度将受到很大影响,而现有的脉冲抑制溶剂峰技术在用于T_1测量时都有一定的困难.本文提出了一种新的改进型IR方法,通过两次结果相加实现溶剂信号抑制后测量T_1,从而解决了上述困难.文中给出了该方法的理论说明,计算和主要实验结果,且与常规反转恢复法(IR)所获得的结果作了比较.     

气垫导轨上的磁阻尼效应实验

为了克服摩擦力对运动磁体与非磁性导体相互作用产生的磁阻尼效应的影响,在铝合金气垫导轨上进行磁阻尼效应实验,推导了相互作用过程中各物理量间的解析关系,并运用自己开发的专用实验设备,获得了与理论推导一致的实验结果.     

A new sequence for the MQMAS/HETCOR experiment

Two-dimensional (2D) multiple quantum MAS (magic angle spinning) spectroscopy has been combined with cross-polarisation to obtain a heteronuclear correlation spectrum between a quadrupolar spin-3/2 and a spin-1/2 nucleus. The advantage over the conventional correlation experiment is the increased resolution obtained in the multiple quantum dimension. Pure absorption 2D spectra can be obtained by implementing a zero quantum filter between the evolution of multiple quanta and the subsequent cross-polarisation step. The current experiment shows a considerable improvement in sensitivity compared to a previously introduced sequence.     

新型钕铁硼电磁阻尼演示仪

利用稀土永磁材料钕铁硼（Ｎｄ－Ｆｅ－Ｂ）设计制作出一种新型电关演示仪,可演示阻尼振动的三种状态（欠阻尼状态、临界阻尼状态、过阻尼状态）,配合投影仪使用,演示效果显著。     

Minimization of sound radiation from baffled beams through optimization of partial constrained layer damping treatment

An optimization study is presented with aim to minimize the sound power radiated by a simply supported, baffled beam with constrained layer damping (CLD) treatment. The governing equation of motion for the calculation of time-harmonic response of a partially CLD covered beam is derived first on the basis of energy approach. Assumed-modes method is used to solve the equation with obtained frequency response functions at different beam locations, which are further used for the calculation of its radiated sound power into half free-space by using Rayleigh’s integral. The optimization problem is then formulated to minimize the sound power radiated by the beam over a frequency range of interest covering multiple resonant modes. A genetic algorithm-based penalty function method is employed to search for the optimum of location/length of the CLD patch and the shear modulus of viscoelastic layer. Optimal results show that for a simply supported beam with a transverse force applied at its central location, it is not necessary to fully cover the structure using CLD patch in order to achieve the largest reduction in the sound power radiated by the beam over a frequency range. With inclusion of the amount of damping material to be minimized, the optimal CLD coverage length is only one-fourth of the base beam’s. Moreover, the optima of three design variables, the CLD coverage length, location on the beam and the shear modulus of viscoelastic layer, are highly relevant to each other.     

A system for low field imaging of laser-polarized noble gas

We describe a device for performing MRI with laser-polarized noble gas at low magnetic fields (<50 G). The system is robust, portable, inexpensive, and provides gas-phase imaging resolution comparable to that of high field clinical instruments. At 20.6 G, we have imaged laser-polarized (3)He (Larmor frequency of 67 kHz) in both sealed glass cells and excised rat lungs, using approximately 0.1 G/cm gradients to achieve approximately 1 mm(2) resolution. In addition, we measured (3)He T(2)(*) times greater than 100 ms in excised rat lungs, which is roughly 20 times longer than typical values observed at high ( approximately 2 T) fields. We include a discussion of the practical considerations for working at low magnetic fields and conclude with evidence of radiation damping in this system.     

脉冲抑制强溶剂信号的组合滤波方法

本文提出了一种组合法的建议,并将其应用于众多的脉冲抑制强溶剂信号方法之中,从而拓宽了现有脉冲抑制强溶剂信号方法的应用面,提高了检测效益。文中提出了四种可行的组合滤波脉冲序列,并以WEFT与1-3-3-1之组合为例,给出了具体说明和实验结果。     

High-resolution NMR spectra in inhomogeneous and unstable fields via the three-pulse method

In modern solution nuclear magnetic resonance (NMR), the spectral resolution is mainly dependent on the spatial homogeneity and temporal stability of the magnetic field. The spectral linewidths are usually proportional to the overall field homogeneity and the stability experienced by the sample. Many high-resolution NMR methods have been developed, but few are applicable in inhomogeneous and unstable fields. In this paper, a high-resolution three-pulse method based on intermolecular zero-quantum coherences (iZQCs) is proposed. Since this method is insensitive to field inhomogeneity and instability, spectral information such as the chemical shift can be retained in the resulting spectra. In comparison with the CPMG-HOMOGENIZED method, the new method provides almost pure solvent–solute iZQC signals.     

包含辐射阻尼效应的束流纵向微波不稳定性研究

 包含束团辐射阻尼效应的Fokker-Planck方程是比较完备地描述粒子运动状态的束团分布方程。在Fokker-Planck方程的基础上采用微扰展开方法对纵向微波不稳定性的发生机制及过程进行了分析，并且根据计算结果，研究了辐射阻尼效应对纵向微波不稳定性的影响。在计算中包含了静态的势阱畸变效应。计算结果表明，包含辐射阻尼效应的纵向微波不稳定性阈值高于没有辐射阻尼效应的不稳定性阈值。     

一种手持便携式核磁共振样品管高压清洗器的设计与实现

在液体核磁共振（NMR）实验使用的耗材中,NMR样品管用量非常大,通常需经清洗后回收利用.NMR样品管的清洗效率及清洗后的洁净程度直接影响到NMR实验的进程,清洗过程中产生的废液也将对环境产生影响.本文首先介绍了一款自主设计的手持便携式NMR样品管高压清洗器,并对该装置的结构和功能做了详细的说明.然后,对曾装存过不同溶剂和溶液的NMR样品管,分别利用该装置和商用NMR样品管清洗装置进行清洗,并比较了清洗效率和效果.最后,对利用此高压清洗器清洗NMR样品管时,NMR样品管的损伤程度进行了评估.结果证实,对于没有样品严重附着管壁的NMR样品管,本文设计的装置清洗效果良好、效率高;并且清洗过程中不使用有毒的有机溶剂,非常环保;而且对NMR样品管损伤较小.     

探讨黑洞Hawking辐射的新方法——量子统计法

将黑洞看作由裸黑洞和二维热力学面(黑洞的视界)组成的正则系综,利用量子统计方法给出黑洞Hawking 辐射的能量谱.找到黑洞辐射温度与熵的关系. 关键词： Hawking辐射 正则系统 量子统计     

基于核磁共振的子空间量子过程重构

基于三核自旋量子系统实现了内嵌两量子位子空间量子过程重构.通过输入完备态集合对执行的量子过程进行了表征.由于量子过程内嵌于子空间,使得重构实验所需输入次数及时间显著减少,同时实验尽量避免使用时间较长的J偶合演化,有效控制了系统的退相干。     

Dynamical beats of forward-scattered resonant synchrotron radiation as a nuclear polariton effect

The decay of the nuclear exciton (immobile collective excitation), created by a pulse of synchrotron radiation, is analyzed. It is shown that in the later phases of the decay, the exciton becomes localized at the sample’s frontal surface. Inside the sample, the secondary gamma-quanta, emitted by the contracting exciton, are converted into polaritons (mobile nuclear excitations) characterized by different frequencies and equal group velocities. On the sample’s back surface, the polariton interference causes a beating structure of the transmitted radiation, observed in experiments.     

A new method of creating minibeam patterns for synchrotron radiation therapy: a feasibility study

Several synchrotrons around the world are currently developing innovative radiotherapy techniques with the aim of palliating and possibly curing human brain tumors. Amongst them, microbeam radiation therapy (MRT) and, more recently, minibeam radiation therapy (MBRT) have shown promising results. In MBRT the beam thickness ranges from 500 to 700 µm with a separation between two adjacent minibeams of the same value, whilst in MRT the thickness is of the order of 25–50 µm with a distance between adjacent microbeams of the order of 200 µm. An original method has been developed and tested at the ESRF ID17 biomedical beamline to produce the minibeam patterns. It utilizes a specially developed high‐energy white‐beam chopper whose action is synchronized with the vertical motion of the target moving at constant speed. Each opening of the chopper generates a horizontal beam print. The method described here has the advantage of being simple and reliable, and it allows for an easy control of the patient safety in future clinical trials. To study the feasibility of the method, dosimetric measurements have been performed using Gafchromic HD‐810 films and compared with Monte Carlo simulations. The results of this comparison are discussed.     

The rapid and automatic combination of proton MRSI data using multi-channel coils without water suppression

The use of multi-channel coils can efficiently increase the signal-to-noise ratio (SNR) of magnetic resonance spectroscopy data if the signals from multiple channels are optimally combined. Combining multi-channel signals requires proper alignment of the phases of the signals from each of the elements of the coil and then accurately weighting the summation of those signals. We present a procedure for acquiring proton magnetic resonance spectroscopic imaging (MRSI) data using an eight-channel coil without water suppression and a rapid and robust method that uses unsuppressed water signal as a reference both for aligning the phases and for weighting the summation of signals that originate in the multiple coil elements. We use both computer simulation and in vivo proton MRSI data to demonstrate the advantages of our method for optimizing the SNR of the combined signal compared with the SNRs of signals that were acquired either using a standard volume head coil or using an eight-channel coil with a metabolite signal as the reference for combination.     

A real-time infrared radiation imaging simulation method of aircraft skin with aerodynamic heating effect

Real-time infrared radiation simulation technology can provide effective support for rapid design and evaluation of a system which integrates infrared imaging technology. Considering the aerodynamic heating effect, this paper presents a real-time infrared radiation characteristic simulation method of aircraft skin based on the panel element method, which can help to assess the infrared radiation impacts of different environment factors and materials. A 3-D model of an aircraft was established and its surface was divided into different parts and panel element meshes to attach material properties. For each mesh, its heat exchange equation is solved so as to obtain the whole skin’s temperature and infrared radiation distribution. The simulation results reveal the influence of different factors on the skin surface radiation, including environmental radiation, aerodynamic heating and material properties. And the credibility and efficiency of the proposed aerodynamic heating simulation method were confirmed by comparing to the CFD simulation results.     

A method of suppression of diffraction oscillations near the diffraction reflection region

Light propagation through the layer of a chiral photonic crystal with graded parameters of modulation is considered in the case of oblique incidence. The problem is solved by the Ambartsumian’s layer addition method. It is shown that under certain conditions it is possible to suppress the diffraction oscillations near the diffraction reflection region.     

利用相位步进脉冲消除探头13C NMR背景信号

由静态探头线圈外有机材料产生的¹³C NMR背景信号强度大,化学位移范围广（δ_C 20~250）,此背景信号在交叉极化实验中还可被增强,并随着样品信号的累积而累积,严重影响谱图分析.将相位步进脉冲引入交叉极化实验（称为PIPCP）中可以有效去除经交叉极化增强的¹³C NMR背景信号,但样品信号不受影响.这是由于经过相位步进脉冲后,线圈外相位严重畸变,而且线圈外锁定场强度急剧降低,来自探头材料的¹³C NMR背景信号无法有效地进行交叉极化.而对于被测样品甘氨酸来说,由于I核和S核之间强烈的偶极耦合作用,所加相位步进脉冲对锁定场强度的影响只有1.4%.     

PSSS50-b-PNIPAM300嵌段共聚物在二元溶剂中自组装的NMR研究

本文结合核磁共振（NMR）、动态光散射（DLS）和透射电子显微镜（TEM）等表征方法,对自主合成的聚阴离子型温敏嵌段共聚物—聚（苯乙烯磺酸钠）-b-聚（N-异丙基丙烯酰胺）（PSSS₅₀-b-PNIPAM₃₀₀）在纯水、水/甲醇以及水/丙酮三种溶剂中的温度响应性和自组装行为进行了系统研究.结果发现PNIPAM链段在水/丙酮以及水/甲醇二元溶剂中的临界溶解温度（LCST）比在纯水溶液中略低,而在水/丙酮体系中的塌缩程度却明显低于纯水和水/甲醇体系.同时,PSSS₅₀-b-PNIPAM₃₀₀在不同溶剂体系中的聚集形貌也存在显著差异,表明加入有机溶剂小分子可以有效地调控温敏嵌段共聚物在水溶液中的自组装过程和聚集形貌.