Determination of blood longitudinal relaxation time (T1) at high magnetic field strengths

In this study, a circulation system was used to measure T(1) values of bovine blood under physiological conditions at field strengths of 4.7, 7 and 9.4 T. Results show that T(1) increases linearly with magnetic field B(0) and can be described with the equation T(1)=129 ms/T B(0)+1167 ms for magnetic field strengths between 1.5 and 9.4 T.     

Segmental relaxation in semicrystalline polymers: A mean-field model for the distribution of relaxation times in confined regimes

The effect of confinement in the segmental relaxation of polymers is considered. On the basis of a thermodynamic model we discuss the emerging relevance of the fast degrees of freedom in stimulating the much slower segmental relaxation, as an effect of the constraints at the walls of the amorphous regions. In the case that confinement is due to the presence of crystalline domains, a quasi-Poissonian distribution of local constraining conditions is derived as a result of thermodynamic equilibrium. This implies that the average free-energy barrier F for conformational rearrangement is of the same order of the dispersion of the barrier heights, ( F) , around F . As an example, we apply the results to the analysis of the -relaxation as observed by dielectric broad-band spectroscopy in semicrystalline poly(ethylene terephthalate) cold-crystallized from either an isotropic or an oriented glass. It is found that in the latter case the regions of cooperative rearrangement are significantly larger than in the former.     

Influence of the moment of inertia of the pendulum on the internal friction (loss tangent) measured by free decay

Summary The internal friction (loss tangent) of solids is normally measured, as a function of temperature, with a torsion pendulum operating in free decay. Curves of the internal friction and the oscillation frequency, against temperature, are obtained at various moments of inertia, to extract the parameters characteristic of the relaxation process (relaxation time and strength). In all these experiments only the temperature is considered as an independent variable and the moment of inertia of the pendulum is mainly used to shift the internal friction peaks in the temperature scale. It is pointed out in the paper that the moment of inertia is also an independent variable which can be used to determine, with high accuracy, if the measured peak is of the Debye type or not. A new torsion pendulum, with continuously variable moment of inertia is presented, which allows measurements of the partial derivative of the internal friction and the oscillation frequency with respect to the moment of inertia, at constant temperature. Finally, some measurements of the Snoek relaxation in Nb-O alloys are presented, to show the applicability of the concepts developed in the paper. The authors of this paper have agreed to not receive the proofs for correction.     

Characterization of energy barrier and particle size distribution of lyophilized ferrofluids by magnetic relaxation measurements

The magnetic properties of a ferrofluid are strongly influenced by its particle size distribution. We analyzed a ferrofluid with an unknown particle size distribution as well as fractionated samples of the original material. The ferrofluid in our investigations consists of a mixture of maghemite and magnetite. We investigated these different samples using temperature-dependent magnetorelaxometry method. The evaluation of the Néel relaxation signal allows us a direct determination of the energy barrier distribution, which is one of the most important parameters of such systems of magnetic nanoparticles. The calculated particle volumes were compared with particle sizes determined by transmission electron microscopy.     

Effect of relaxation rate on population distribution, EIT and refraction in Λ and V systems

In the three-level Λ-type and V-type systems, we find that the same pump-effect parameter R\left(=\dfrac{2|V_{c}|^{2}γ}{(ω_{ac}-ω_{c})^{2}+γ^{2}}\right) determines the population distributions, while the probe field leads to population fluctuations near the absorption peaks. With the increasing of the relaxation rate γ, the population distributions are shifted and their fluctuation amplitudes decrease. At the same time the electromagnetically induced transparency window becomes a broadened absorption peak, and the dispersion at the zero probe detuning changes from positive to negative. Large population fluctuation and non-fluctuation observed in different systems are attributed to the different relaxation rates.     

Quadrupole relaxation enhancement and polarisation transfer in DMSO solution of [Bi(NO3)3(H2O)3]*18-crown-6 in solid state

ABSTRACT

¹H spin-lattice relaxation studies have been performed for pure [Bi(NO₃)₃(H₂O)₃]*18-crown-6 in powder and its solution in dimethyl sulfoxide (DMSO). The experiments have been carried out in the frequency range of 10?kHz–30?MHz and the temperature range of 240–277?K; at 277?K the solution is already frozen. The ¹H relaxation of pure [Bi(NO₃)₃(H₂O)₃]*18-crown-6 has been interpreted in terms of three dynamical processes. Quadrupole Relaxation Enhancement effects have been observed in the frozen DMSO solution of [Bi(NO₃)₃(H₂O)₃]*18-crown-6. The specific mechanisms of the ¹H spin-lattice relaxation enhancement have been discussed distinguishing between effects caused by time independent (residual) and fluctuating ¹H-²⁰⁹Bi dipole-dipole interactions.     

Applications of DNP-NMR for the measurement of heteronuclear T1 relaxation times

Measurement of heteronuclear spin-lattice relaxation times is hampered by both low natural abundance and low detection sensitivity. Combined with typically long relaxation times, this results in extended acquisition times which often renders the experiment impractical. Recently a variant of dynamic nuclear polarisation has been demonstrated in which enhanced nuclear spin polarisation, generated in the cryo-solid state, is transferred to the liquid state for detection. Combining this approach with small flip angle pulse trains, similar to the FLASH-T(1) imaging sequence, allows the rapid determination of spin-lattice relaxation times. In this paper we explore this method and its application to the measurement of T(1) for both carbon-13 and nitrogen-15 at natural abundance. The effects of RF inhomogeneity and the influence of proton decoupling in the context of this experiment are also investigated.     

内耗与力学谱基本原理及其应用

文章对内耗与力学谱的基本原理作了简明介绍,并结合几个具体研究实例评述了内耗技术在凝聚态物理和材料科学研究方面的可能应用,最后指出了该领域今后的主要研究课题是发展新的内耗测量方法和技术以及发现新的内耗谱和建立新的内耗理论.     

On the equivalence of the parallel channel and the correlated cluster relaxation models

The question of the origins of nonexponential relaxation is addressed in terms of the probabilistic approach to relaxation. The interconnection between two differently rooted probabilistic models, i.e., between the parallel channel and the correlated cluster models, is presented. We show that clearly different probabilistic origins yield in both approaches a well-defined class of universally valid two-power-law responses with the stretched-exponential and exponential decay laws as special cases. The equivalence of both models indicates that variations in the local environment of the relaxing configurational units (parallel channel relaxation) can provide a basis for self-similar relaxation dynamics without the need for hierarchically constrained dynamics (correlated clusters relaxation).     

Fluorescence enhancement of samarium complex co-doped with terbium complex in a poly(methyl methacrylate) matrix

The fluorescence property of Sm(DBM)₃phen- (DBM—dibenzoylmethide, phen—1,10-phenanthroline) and Tb(DBM)₃phen-co-doped poly(methyl methacrylate) (PMMA) was investigated. The excitation, emission spectra and fluorescence lifetime of the co-doped samples were examined. In the co-doped samples, the luminescence intensities of Sm³⁺ enhance with an increase of the Tb(DBM)₃phen content and with a decrease of the Sm(DBM)₃phen content. The reason for the fluorescence enhancement effect in the co-doped polymer is the intermolecular energy transfer. To give a vivid picture for this co-doped system, a model for the fluorescence enhancement of Sm(DBM)₃phen- and Tb(DBM)₃phen-co-doped PMMA is presented.     

Nuclear magnetic resonance relaxometry of the normal heart: Relationship between collagen content and relaxation times of the four chambers

The use of nuclear magnetic resonance (NMR) relaxation time measurements for characterization of abnormal cardiac tissue depends upon knowledge of variations of relaxation times of normal myocardium and determinants of these variations. We calculated in vitro NMR T₁ and T₂ relaxation times of canine myocardium from the four cardiac chambers, and determined hydroxyproline concentration (as a measure of collagen) and percent water content of the samples. We found both water content and T₁ relaxation time of the right ventricle to be significantly greater than the left atrium (p < 0.05). T₂ relaxation time of the left ventricle was found to be shorter than each of the other three chambers (p < 0.05). There were significant correlations between the spin-lattice relaxation time and both percent water content (r = 0.58) and hydroxyproline concentration (r = 0.45). A significant correlation was also found between T₂ relaxation time and hydroxyproline concentration (r = 0.49). When T₁ and T₂ were adjusted for water and hydroxyproline content, there was no longer any evidence for significant interchamber differences for either T₁ or T₂. These data suggest that differences in NMR relaxation times exist among the four chambers of the normal canine heart. Furthermore, a major determinant of myocardial spin-lattice relaxation time is tissue water content while both collagen content and percent water content significantly contribute to variability in cardiac chamber T₂ relaxation times.     

A longitudinally detected high-field ESR spectrometer for the measurement of spin-lattice relaxation times

We describe a high-field longitudinally detected electron spin resonance (LOD-ESR) spectrometer operating at 35 and 75 GHz. The lack of resonant microwave circuits facilitates operation at different microwave frequencies without changing the probehead. A very low noise radio frequency detection compensates partially the resulting low sensitivity. The major elements of the LOD-ESR spectrometer are commercially available and may be adapted to usual high frequency spectrometers. The instrument allows field and frequency dependent spin lattice relaxation time (T1) studies. T1 in the range of 2-80 ns can be determined from the phase sensitively detected LOD-ESR spectra. We demonstrate the performance of the apparatus by the measurement of T1 in the normal state of RbC60, an electrically conducting alkaline fulleride polymer.     

Saturation absorption studies of intersubband relaxation rates in a p-GaAs/AlGaAs QW using a free electron laser

We present saturation absorption studies of the HH1→LH1 intersubband transition in a 70 Å p-type GaAs/AlGaAs multi-quantum well. The subband separation in this sample, with strongly non-parabolic bands, varies from 26 meV at k=0 to 16 meV at the Fermi wave vector. The absorption behaviour of this transition is studied over a range of four orders of magnitude of intensity of incident THz radiation. The results are analysed within the contexts of a simple two-level model and an instantaneous thermalization model. The results indicate that the lifetime obtained with these models is limited by the pulsewidth, i.e. is greater than 1.7 ps. This places a lower limit on the energy relaxation time for transitions below the LO-phonon energy.     

弛豫过程对能级AC Zeeman(Stark)移动的影响

以衰减的Bloch方程理论为基础计算了二能级原子能级ACZeeman(Stark)移动,结果表明纵向和横向弛豫过程均会对原子能级移动产生影响,随纵向和横向弛豫率的增加,能级移动呈现出不同的变化趋势。两种弛豫相对强弱的不同也会直接影响能级移动的色散性和饱和性。     

Proton magnetic relaxation in (TMA)2HgBr4 and (TMA)2HgI4

Internal motions of the protonic groups have been studied in polycrystalline [(CH₃)₄N]₂HgBr₄ and [(CH₃)₄N]₂HgI₄ from the temperature dependence of proton spin relaxation time (T ₁) and the data analysed according to the spin lattice relaxation model due to Albert and coworkers. The temperature dependence ofT ₁ in the above compounds is compared with that in (TMA)₂HgCl₄ and (TMA)₂ZnCl₄.     

Comparison of a fractal analysis and debye relaxation for the structural relaxation in amorphous metals

Abstract

Magnetic After-Effect isotherms have been measured on a metallic glass pre-annealed for different times. The results have been analyzed simultaneously by Debye relaxation functions leading to spectra of activation enthalpies and by extended exponential functions leading to a unique effective activation enthalpy. The thermodynamic activation parameters issued from both analyses compare well. The average values of the enthalpy spectra determined by assuming Debye relaxations are equal to the effective enthalpies resulting from the non-Debye relaxation.

Magnetische Nachwirkungs-Isothermen wurden an amorphen Legierungen gemessen, die mit verschiedenen Anlasszeiten vorbehandelt wurden. Die Ergebnisse wurden sowohl unter der Annahme von Debye-Relaxationsprozessen analysiert, die mit Aktivierungsspektren beschrieben wurden, als auch mit gestreckten Exponentialfunktionen, die zu einer einheitlichen effektiven Aktivierungsenthalpie führt. Die thermodynamischen Parameter von beiden Analysen sind gut vergleichbar. Die Mittelwerte der Aktivierungsenthalpie-Spektren, welche sich bei Zugrundelegung der Debye-Relaxationsprozesse ergeben, entsprechen den effektiven Enthalpien, die sich bei Anwendung der gestreckten Exponentialfunktionen ergeben.

Des isothermes de trainage magnétique ont été réalisées sur des echantillons de verres métalliques ayant subi des traitements thermiques de différentes durées. Les résultats ont été simultanément analysés par des processus de relaxation de Debye engendrant des distributions d'enthalpies d'activation, et par des exponentielles etirées possédant des enthalpies effectives. Les paramètres thermodynamiques issus des deux analyses sont cohérents et comparables. Les valeurs moyennes des distributions d'enthalpies résultant de la relaxation de Debye sont identiques aux enthalpies effectives qui découlent des exponentielles etirées.     

可激发气体分子声弛豫过程振动模式能量转移速率计算

研究可激发气体中振动模式能量转移速率和声弛豫过程形成的关系,将单一气体Tanczos弛豫方程理论[J.Chem.Phys.25,439(1956)]扩展应用于混合气体中振动模式的振动-振动(V-V)和振动-平动(V-T)能量转移速率的计算。在室温下CO₂,CH₄,CL₂,N₂和O₂组成的多种混合气体中,振动模式能量转移速率的计算结果表明:对于多个振动模式所形成的声复合弛豫过程,各振动模式的声激发能可由V-V能量转移相互耦合后传递给具有最快V-T转移速率的最低振动频率振动模式,再通过该振动模式的V-T转移退激发形成主弛豫过程。这种选择最快转移路径的声激发量弛豫方式,造成了大多数可激发气体中声弛豫吸收谱的实测数据只存在一个吸收峰的现象。从而提供了一个可通过计算微观振动能量转移速率分析混合气体声弛豫过程形成机理的理论模型。     

Special features of the EPR spectroscopy of a system of centers with different relaxation times

We found that the interaction of paramagnetic centers that have different relaxation times differs fundamentally from the interaction of centers having close relaxation times. Simulation showed that in this case there is an anomalous redistribution of the spectral-line intensity from the center to the wings with a virtually preserved distance between extremal points (super-Lorentzian shape of the line), which leads to underestimation of the total intensity recorded. The results obtained make it possible to explain a number of aspects of the radiospectroscopy of carbon materials of practical importance such as the nature of the generally accepted maximum on the curve for the dependence of the total intensity of an EPR signal on the temperature of the heat treatment of organic compounds and the degree of metamorphism of natural coals, the specific features of the effect of oxygen molecules and paramagnetic ions of metals on the EPR spectra of carbon materials, etc. Belarusian State University, 4, F. Skorina Ave., Minsk, 220080 Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 2, pp. 224–229, March–April, 1998.     

Dielectric relaxation of poly(ethylenglycol)- b-poly(propylenglycol)-b-poly(ethylenglycol) copolymers above the glass transition temperature

The complex dielectric permittivity has been measured for three poly(ethylenglycol)-b-poly(propylenglycol)-b-poly(ethylenglycol) copolymers with different content of poly(ethylenglycol) (15%, 33% and 80%), and increasing degree of crystallinity (0%, 10% and 20%, respectively). Only the non-crystalline sample shows the normal mode relaxation together with the segmental (α-relaxation) and the Johari-Goldstein (β-relaxation) modes. The crystalline samples show also polarization contributions due to the existence of interfaces between the crystallites and the amorphous phase. The relaxation times of the (α and normal modes can be described by a VFT equation with the same value of T₀. There is a slowing-down of the segmental mode due to the presence of crystallites. The temperature dependence of the α and β relaxations in the copolymers is very similar to that found in pure PPG, while there are significant differences in the case of the normal mode of the non-crystalline sample. The size of the cooperatively rearranging regions CRR, and the width of the glass transition region increase slightly with the degree of crystallinity. The temperature dependence of the size of CRRs is compatible with the prediction of fluctuation theory. No systematic effect of the degree of crystallinity on the β-relaxation has been found. Near T _g the β-relaxation time is close to the primitive time of the coupling model. Received: 31 May 2000