On the measurement of multi-component T2 relaxation in cartilage by MR spectroscopy and imaging

The multicomponent T₂ relaxation in bovine nasal cartilage (BNC) was investigated by nuclear magnetic resonance spectroscopy using the Carr-Purcell-Meiboom-Gill (CPMG) sequence and microscopic magnetic resonance imaging (μMRI) method using a CPMG-SE imaging sequence. All experimental data were analyzed by the non-negative least square (NNLS) procedure. Only one T₂ component was found in BNC by both experimental methods (about 113 and 170 ms before and after being enzymatically digested by trypsin). Several experimental and specimen-related factors were investigated in this study, and it was found that some of them could produce artificial multi-component T₂, including the use of the standard MSME imaging sequence at certain imaging gradients.     

Effect of aggregation on the radiative (T1 → S0) and nonradiative (T1⇝S0 and S1⇝T1) transitions in xanthene dyes

The measurement of triplet decay time (τ_p) and the relative yields of phosphorescence to fluorescence (φ_p/φ_f) have been made in solutions of xanthene dyes. The value of φ_p/φ_f increases while that of τ_p decreases as the concentration of the solution is increased. The rate constants k_p, k_qp and k_is have been estimated. It is found that the values of k_qp and k_is increase while that of k_p remains substantially constant for the entire range of concentration. The deuterium solvent effect is observed in τ_p and φ_p.     

Zeeman effect in complex molecules in solid solutions with laser T1 → S0 excitation. New possibilities for investigation of spin—lattice relaxation

The main peculiarities of Zeeman-effect in phosphorescence spectra of randomly oriented molecular systems under selective T₁→S₀ excitation are investigated. On this basis a new method of measuring triplet state characteristics and spin—lattice relaxation rates in solid solutions is proposed. The results of Zeeman-effect investigations on 5-bromo-acenaphtene in ethanol and butylbromide at magnetic fields 10–50 kG at helium temperatures are given as an example. At low fields the deviation from Boltzmann equilibrium in the spin system of the molecule is observed and the rates of spin—lattice relaxation are determined.     

Simultaneous emissions from T2 and T1 states of naphthalene moiety in a specially designed naphthalene cryptand

We report here the photophysical properties of a naphthalene derivative of a specially designed cryptand system (L). The system exhibits the unusual phenomenon of emission from T₂ and T₁ states of naphthalene which has been attributed to the inherent rigidity of the system. The results obtained have been analysed by comparison with two other model systems where the flexibility of the fluorophore unit with respect to the receptor moiety have been varied.     

Dipolar dielectric relaxation in CeO2-YO1,5 solid solutions

The dielectric properties of yttrium oxide-doped cerium oxide solid solutions have been studied by using a.c. techniques. Frequency and temperature respectively range from 10 to 10⁵ Hz and from 70 to 200°C. Both a complex impedance plot (Z″ vs Z′) and a conductance plot (G at fixed frequency vs inverse of temperature T^?1) are shown to be complementary for an accurate determination of the bulk resistance and of the dielectric loss. For the three investigated concentrations of yttrium oxide (m/% YO_1,5:0.001, 0.01 and 0.1), the activation energies for conduction are equal to 0.86, 0.75 and 0.75 eV, while the activation energy for dipole reorientation is found to be concentration independent (0.75 eV; angular frequency preexponential factor: 6.0 × 10¹², 1.43 × 10¹³ and 3.05 × 10¹³ s^?1). Moreover, the dipolar relaxation rates are found to be of the same order of magnitude as that of the migration rate. Interpretation is given on the basis of Wachtman's model and of previous results obtained by Nowick et al. from ITC (ionic thermo-current) investigations. The observed dielectric peak appears to be due to the redistribution of oxyygen vacancies between charged (Y_Ce-V₀) pairs and fixed charged Y_Ce defects.     

Pressure dependence of the superconducting transition temperature of T5T9 metallic glasses (T5Nb,Ta; T9Rh,Ir)

The pressure dependence of the superconducting transition temperature, T_c, is determined for eight metallic glasses in the series (Nb_1?xTa_x)₅₅T₄₅, where T Rh, Ir. From these data we estimate the Grüneisen parameter, γ_G, and the volume dependence of the electron-phonon coupling constant, λ. Pressure is observed to affect T_c through both γ_G and λ.     

油井样品NMR T2谱的影响因素及T2截止值的确定方法

T₂ 谱是核磁共振（NMR）测、录井技术应用与解释、评价的基础. 岩样T₂ 谱受仪器测量参数、样品性质（岩性、颗粒大小、样品粒度、样品干湿状态、孔隙流体含量及性质、磁化率、润湿性）及地层水矿化度等因素的影响. T₂ 截止值是T₂ 谱中最重要的参数之一,选取的科学性与准确性直接影响到核磁共振测量结果. 通过文献查询,对T2 谱的影响因素及T₂ 截止值的确定方法进行了分析.     

On the relaxation rates determining the NH3 and ND3 inversion spectra

A general approach towards the calculation of relaxation rates in the semiclassical approximation is described and applied to a discussion of the NH₃ and ND₃ inversion spectra.     

MSE-MRI sequence optimisation for measurement of bi- and tri-exponential T2 relaxation in a phantom and fruit

The transverse relaxation signal from vegetal cells can be described by multi-exponential behaviour, reflecting different water compartments. This multi-exponential relaxation is rarely measured by conventional MRI imaging protocols; mono-exponential relaxation times are measured instead, thus limiting information about of the microstructure and water status in vegetal cells. In this study, an optimised multiple spin echo (MSE) MRI sequence was evaluated for assessment of multi-exponential transverse relaxation in fruit tissues. The sequence was designed for the acquisition of a maximum of 512 echoes. Non-selective refocusing RF pulses were used in combination with balanced crusher gradients for elimination of spurious echoes. The study was performed on a bi-compartmental phantom with known T₂ values and on apple and tomato fruit. T₂ decays measured in the phantom and fruit were analysed using bi- and tri-exponential fits, respectively. The MRI results were compared with low field non-spatially resolved NMR measurements performed on the same samples.     

Giant dielectric relaxation in SrTiO3-SrMg1/3Nb2/3O3 and SrTiO3-SrSc1/2Ta1/2O3 solid solutions

Ceramic samples of (1−x)SrTiO₃-xSrMg_1/3Nb_2/3O₃ and (1−x)SrTiO₃-xSrSc_1/2Ta_1/2O₃ were prepared, and their dielectric properties were studied at x=0.005–0.15 and 0.01–0.1, respectively, at frequencies 10 Hz–1 MHz and at temperatures 4.2–350 K. A giant dielectric relaxation was observed in the temperature range 150–300 K, and not so strong but well-developed relaxation was found in the temperature range 20–90 K. The activation energy U and the relaxation time τ₀ were determined to be 0.21–0.3 eV and from 10⁻¹¹ to 10⁻¹² s for the high-temperature relaxation and 0.01–0.02 eV and 10⁻⁸–10⁻¹⁰ s for the low-temperature relaxation, respectively. The additional local charge compensation of the heterovalent impurities Mg²⁺ and Nb⁵⁺ (or Sc³⁺ and Ta⁵⁺) by free charge carriers or the host ion vacancies is suggested to be the underlying physical mechanism of the relaxation phenomena. On the basis of this mechanism, the Maxwell-Wagner model and the model of reorienting dipole centers Mg²⁺ (or Sc³⁺) associated with the oxygen vacancy are proposed to explain the high-temperature relaxation with some arguments in favor of the latter model. The polaron-like model with the Nb⁵⁺-Ti³⁺ center is suggested as the origin of the low-temperature relaxation. The reasons for the absence of ferroelectric phase transitions in the solid solutions under study are also discussed. From Fizika Tverdogo Tela, Vol. 44, No. 11, 2002, pp. 1948–1957. Original English Text Copyright ? 2002 by Lemanov, Sotnikov, Smirnova, Weihnacht. This article was submitted by the authors in English.     

T1 and T2 relaxivities of succimer-coated MFe2O4 (M=Mn, Fe and Co) inverse spinel ferrites for potential use as phase-contrast agents in medical MRI

Superparamagnetic MFe₂³⁺O₄ (M=Mn²⁺, Fe²⁺ and Co²⁺) inverse spinel ferrite (ISF) nanoparticles with narrow size distribution having average diameters of 6-8 nm were synthesized by a diol reduction of organic metals and the surface was modified to be hydrophilic by coating with succimer. Magnetic resonance imaging (MRI) contrast enhancement by dipolar coupling defined interactions between the synthesized ISFs and protons in the bulk water was investigated with initial susceptibility, magnetization and anisotropy of the succimer-coated ISFs. The relaxivity ratios, r₂/r₁, for MnFe₂O₄, Fe₃O₄ and CoFe₂O₄ were measured to be 12.2, 23.1 and 62.3, respectively, which demonstrate the potential usefulness of these magnetic nanoparticles as T₂ contrast agents for MRI.     

Theoretical study of stereodynamics for the N+H2/D2/T2 reactions

The effects of isotopic variants on stereodynamic properties for the title reactions have been investigated using a quasi-classical trajectory method based on the first excited state NH2（I^2A＇） potential energy surface [Li Y Q and Varandas A J C 2010 J. Phys. Chem. A 114 9644]. The forward–backward symmetry scattering of the differential cross section can be observed, which demonstrates that all these reactions follow the insertion mechanism. Three angle distribution functions P（θr）, P（φr）, and P（θr, φr） with different collision energies and target molecules H2/D2/T2 are calculated. It is shown that the product rotational angular momentum is not only aligned, but also oriented along the direction perpendicular to the scattering plane. The title reaction is mainly governed by the ＂in-plane＂ mechanism through the calculated distribution function P（θr, φr）. The observable influences on the rotational polarization of the product by the isotopic substitution of H/D/T can be demonstrated.     

Phantom and in vivo study of the look–locher T1 mapping method

This paper describes and tests the LL-EPI method for obtaining quantitative T₁ estimates in a few seconds thereby allowing dynamic T₁ studies. It is shown that the method works even when there is an inflow into the imaged volume, e.g., in a vessel. No calibration is needed. The method has been tested in a phantom study with several different scan parameter set-ups, with and without inflow. The method shows robustness and individual scan parameters and inflow rates do not influence the ability to calculate the Gd-DTPA concentration. Linearity prevail between the measured 1/T₁ and the Gd-DTPA concentration in the range 150 < T₁ < 2500 ms. In a dynamic Gd-DTPA phantom study, it was shown that the dynamic LL-EPI T₁ mapping technique was three times more sensitive than the signal from a T^*₂-weighted EPI sequence. In an in vivo study, dynamic T₁ mapping of the Gd-DTPA uptake in a meningioma was performed. Inspection of the uptake curves indicates that the method is feasible in clinical perfusion studies.     

Excitation and ionization accompanying the beta decay of T2

The probabilities for shake-up and shake-off excitation accompanying the beta decay of molecular tritium have been computed. The shake-off channels account for 15% of the excitation probability. Roughly 2/3 of the shake-off intensity is concentrated in a band of resonances occuring about 20 eV above threshold.     

对多孔介质NMR实验弛豫时间分布的实现

报道了人工岩石样品--多孔介质的NMR实验的弛豫时间T₁的测量数据及其处理分析方法. 文中采用Levenberg-Marquardt(L-M)拟合技术, 对实验数据利用3种不同的模型进行拟合：单指数,双指数和多指数模型拟合,特别是多指数拟合的弛豫时间τ -分布曲线. 各种方法利用价值函数χ²进行对比, 与实验结果进行了比较.     

不同能量的氦原子与同位素分子H2(D2，T2)碰撞分波截面的理论计算

用Tang-Toennies势模型和密耦近似方法计算了不同能量下惰性气体原子He与H₂及其同位素D₂,T₂替代碰撞体系的振转激发碰撞截面. 通过分析He-H₂(D₂,T₂)各碰撞体系分波截面的差异,总结出在H₂分子的对称同位素替代情形下He-H₂(D₂,T₂)碰撞体系分波截面随量子数和体系 关键词： 散射截面 密耦方法 同位素     

Estimation of T1 for Co2+ ions from the temperature variation of the ESR linewidths for VO2+ in Cs2Co(SeO4)2·6H2O single crystals

The electron spin resonance of VO²⁺ is studied in single crystals of Cs₂M″ (SeO₄)₂·6H₂O (M″ = Zn, Co) from 290 to 77 K at ～ 9.45 GHz. The line broadening of VO²⁺ spectra on cooling the Cs₂Co(SeO₄)₂·6H₂O crystal is explained on the basis of host spin-lattice relaxation narrowing. T₁ for Co²⁺ is estimated to be ≈ 1.7 × 10^?12 sec. at 290 K.     

不同能量的氦原子与同位素分子H2(D2，T2)碰撞分波截面的理论计算

用Tang-Toennies势模型和密耦近似方法计算了不同能量下惰性气体原子He与H₂及其同位素D₂，T₂替代碰撞体系的振转激发碰撞截面. 通过分析He-H₂(D₂，T₂)各碰撞体系分波截面的差异，总结出在H₂分子的对称同位素替代情形下He-H₂(D₂，T₂)碰撞体系分波截面随量子数和体系