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The dielectric constant and the dielectric loss of hydroxyl doped potassium chloride crystals have been explored in the temperature range between 1.5°K and 80°K with frequencies ranging from 105 c. p. s. to 3.3×108 c. p. s. The observed relaxation behavior is discussed in terms of one-phonon processes.

Internal friction measurements on nickel reeds have confirmed the macroeddy‐current limited relaxation behavior predicted by Zener. The macroeddy‐current peak has been observed as a function of frequency, and shown to depend in height and position on the magnetization of the sample. At low frequencies the modulus defect associated with this relaxation causes the ΔE‐effect to exhibit a maximum value at an intermediate magnetization in the vicinity of half the saturation value. As the frequency is raised the maximum disappears and the behavior of the ΔE‐effect reverts to that observed in resonant‐rod experiments. It is emphasized that in this regime, which has frequently been used in the past, the measured ΔE‐effect does not provide an equilibrium characterization of the material.

The current theories of proton relaxation times fall short of explaining satisfactorily the physical and biological mechanisms responsible for the dissimilarities of relaxation behavior in normal and pathological tissues. An alternative approach to understand these mechanisms is needed. This paper advances the possibility that the dissimilarities of relaxation behavior in normal and pathological tissues is due to the consumption of paramagnetic molecular O2 dissolved in cell-associated water.

NMR relaxation time measurements have been made at 20 MHz for proton in polycrystalline hydronium beta″ alumina. Motional narrowing occurs at T > 62;230 K(Ea = 19 kJ mol−1) in the fully hydrated beta″ alumina and the relaxation behavior is compatible with fast proton transport. The protonic motion in the partially dehydrated beta″ alumina has a high activation energy as 24.5 kJ mol−1.

The proton nuclear spin lattice relaxation has been measured in cholesterol and its esters (n‐propionate, n‐decanoate, myristate, and oleate) in the solid, mesophase, and liquid regions using conventional pulsed NMR techniques at a frequency of 30 MHz. All solid phases and the mesophases of all the esters except the oleate exhibited relaxation which could be fit within experimental error with a single exponential. Nonexponential relaxation, which was analyzed assuming two relaxation times, was observed in all liquid phases and throughout the mesophase of the oleate ester. Relaxation in the mesophases of all the esters had very little temperature dependence and this, plus its behavior at the phase transitions, indicated that the relaxation mechanism might be similar to that in nematic liquid crystals. It was not possible to determine the primary source of the nonexponential relaxation behavior but it did not require the presence of an ester group.

Observations of backward stimulated Brillouin scattering (SBS) in glass optical fibers are reported. Threshold for SBS has been achieved with less than 1 W of input power at 5355 A. Relaxation behavior in the SBS signal has also been observed and is attributed to finite‐cell‐length oscillation. Experimental results are compared with theory, and the implied limitation to optical fiber transmission is discussed.

Chemical differences between phosphorus and boron in FeNi-based amorphous structures show up in their structural relaxation behavior as determined by scanning calorimetry and electrical resistometry.

Disseminated osseous tuberculosis is a rare disease. This is a report of two cases of disseminated osseous tuberculosis imaged with MRI at 1.5-T, CT, plain radiography and bone scintigraphy. CT and plain radiography demonstrated either highly destructive or cystic lesions with sclerotic margins. Bone scintigraphy and plain radiography were quite insensitive in detecting areas of involvement compared to MRI. On MRI the abnormal areas had short T-1 relaxation values, which is an atypical appearance for bony infections, and prolonged T-2 relaxation values. The reason for the T-1 relaxation behavior is uncertain. MRI also provided delineation of epidural extent.

The relaxation behavior of glassy Fe-Ni-B alloys has been investigated by microcalorimetric measurements. The reversible relaxation enthalpies show a temperature and concentration dependence. The frequency factor for the relaxation processes obtained by crossover experiments amounts to about 1051 s−1. Activation energies for the relaxation processes obtained from isothermal measurements as well as from measurements with constant heating rate agree very well.

Multiple-loading relaxation data for annealed 2/sup 1///sub 4/ Cr-1 Mo steel are reported for times to 100 hr and for temperatures in the range 450 to 566/sup 0/C. At 450 and 482/sup 0/C the relaxation strength rises with the plastic flow stress, and recovery phenomena are not very significant in the time span of concern. At 510, 538, and 566/sup 0/C the relaxation behavior during the first loading is unusual in the sense that for a period the relaxation rate is almost independent of stress. This behavior is thought to be associated with a strain-induced aging process, which depletes the proeutectoid ferrite of solid-solution strengtheners. At 510/sup 0/C and above the plastic flow stress partially recovers during the relaxation process. At 566/sup 0/C there is clear recovery in the sense that the relaxation rates after the first loading depend on the current value of stress and not on history. Multiple loading tests at 566/sup 0/C on material in the normalized-and-tempered condition show no unusual behavior.

The 13C spin‐lattice relaxation time T1 has been measured as a function of temperature by the PRFT technique in a sample of carefully dried glycerol. Data were taken between 267 and 339°K and the results fitted to a theoretical description of relaxation involving unlike spins which are undergoing anisotropic reorientation. The best fit gave a ratio of rotational diffusion coefficients of 1:5:200 and an activation energy for molecular reorientation of 2.41±0.05 kcal/mole. The results indicate that it is not necessary to invoke a continuous distribution of correlation times in order to describe the relaxation behavior. A speculative model for rotational and translational motion, consistent with the results of previous studies, is presented.

The experimental values of the exponents γ and τ which characterize the divergence of a mean average mass distribution of clusters at the gelation threshold and the mass distribution of clusters respectively, show that gelation and percolation belong to the same class of universality. The dynamical structure factor, measured on solution of such percolating clusters elaborated near and below the gelation threshold, exhibits relaxation behavior similar to those observed in disordered media near the glass transition.

The relaxation behavior of glassy Fe-Ni-B alloys has been investigated as a function of composition by calorimetric, dilatometric and stress relaxation measurements. All property changes investigated show characteristic extremal values. The results are discussed in terms' of short range order effects, the magnitude of which varies strongly with concentration.

The rheological behavior of five nonmetallic dental materials was studied. Short-term stress relaxation was found to be strongly dependent on time and temperature. Relaxation behavior of the test materials conformed well to simple mathematical models.

It is shown that defects can be identified in liquids, that they are related to atomic diffusion, and a model is described whereby defects give rise to the observed relaxation behavior of viscous liquids. A review is presented of defects in silicate and fluoroberyllate liquids, as studied by computer simulation. It is found that defects have the form of overcoordinated or undercoordinated atoms, and that atomic diffusion occurs only at the site of defects. The manner in which an Ising model can represent the detect structure of viscous liquids to a first approximation is presented. The results of Monte Carlo simulations of a 2-dimensional kinetic Ising model are described. The behavior of this model is qualitatively the same as that of viscous liquids.

Two apparently quite general anelastic effects are associated with the presence of hydrogen in solution in metallic glasses. One of these is a short-range reorientation relaxation of the Snoek type; the other is the long-range Gorsky relaxation. In contrast to the situation for bcc crystalline metals, these relaxations reveal the H-interstitial not only as a dilatation center of normal strength, but also as a strong elastic dipole. Coupled with a relatively low mobility associated with migration energies of 0.25−0.5eV, the H-interstitial in metallic glasses emerges as a quasi-classical defect analogous to the heavier interstitial solutes in bcc metals. Both relaxations exhibit features that reflect the structural disorder of the glassy host. The reorientation relaxation shows considerable dispersion, the Gorsky relaxation reveals non-ideal solution behavior, and both relaxations have activation energies which characteristically decrease with increasing hydrogen concentration. The available experimental results agree well with Kirchheim’s analysis for solution and diffusion in a structurally-disordered host. We point out that an apparent difficulty in explaining the strength of the reorientation relaxation may be related to a need to consider the spatial distribution of disorder, and suggest that packing constraints may lead to a near-degeneracy of neighboring interstitial sites.

Side-chain interactions in racemic mixtures of α-helical polypeptides were investigated by means of dielectric measurements in relation to the regular stacks of phenyl groups in the racemic mixture of poly (γ-benzyl glutamate) (PBG). The samples used in this work were poly(β-phenethyl aspartate) (PPA), poly(γ-phenethyl glutamate) (PPG), and poly[γ-(3-phenylpropyl) glutamate] (PPPG). A dielectric dispersion due to the side-chain motion was observed around room temperature for all the samples. For PPA and PPPG, the dispersion shifted to lower frequencies by racemization, and the relaxation strength decreased in a similar manner as PBG. The racemic mixture of PPPG showed a thermally reversible transition at about 80°C, which was attributed to the breakdown and the formation of stacks of phenyl groups. Racemization had no effect for PPG. The conformational change from the right-handed α-helix to the left-handed π-helix which occured at 140°C in the L isomer of PPA was not observed in the racemic mixture.

The introduction of STEAM (stimulated echo acquisition mode) magnetic resonance (MR) sequences provides access to a variety of MR parameters. T1-weighted and calculated T1 proton MR images of the head of healthy volunteers and a patient with an astrocytoma are presented. MR examinations were performed with a 2.0-T whole-body system. The STEAM T1 method can be used to characterize multiexponential relaxation behavior, to evaluate T1 relaxation times, and to improve the T1 contrast within MR images. Both the measuring time and the spatial resolution are the same as for a conventional image.

The relaxation of a perturbed chemical system to its stable states provides a means for characterizing the essential dynamic features of the system. These features are contained in the phase portrait, a plot of the concentration of one variable species as a function of another variable species for a variety of initial conditions. A particular steady state may be characterized as a stable node or a stable focus according to the appearance of the relaxation trajectories around that state. In addition, basins of attraction in multistable systems may be determined as well as the separatrix partitioning these basins. The nature of the unstable steady state may be determined from relaxation experiments in systems that can be accurately described in terms of one or two variable species. This paper reports on measurements and modelling of the relaxation behavior of the bistable iodate-arsenous acid system. The stable and unstable steady states are characterized and the separatrix is located in the phase plane. In addition, the special case of relaxation to the critical point is investigated. A more detailed account of this study will be forthcoming [1,2].

This exploratory project illustrates, in contrast to earlier opinions, that psychotic children can be taught muscular relaxation through carefully structured training in physical relaxation. The learned relaxation behavior was apparently antagonistic to and effected a significant decrement in the generalized response of high anxiety which had previously led to aggressive outbursts. As a result of the exploratory project it was hypothesized that although systematic desensitization may be necessary for modifying specific patterns such as phobias, the generalized excitement response of psychotic and other severely disturbed children may be effectively and parsimoniously modified simply through general training in muscular relaxation.

The format of this year's chapter is essentially the same as last year's. In addition to major sections on conduction and breakdown, sections on the following topics are included: technology, fluid motion, electrostatics, and dielectric phenomena. The selection of subject matter in the dielectric phenomena section is based upon its direct or indirect connection with conduction or breakdown. Although the connection may seem obscure in some cases, those concerned will recognize the articles of interest to them. Relaxation behavior is generally excluded from this section, but subjects like opalescence and secondary electron emission are included, in addition to the obviously-important subject of electric field distribution.

4-Perfluoroalkylsulfonyl (RfSO2)-substituted azo nonlinear optical chromophores (NLOphores) showed enhanced second-order nonlinear coefficients (d33) and improved relaxation behavior compared with the corresponding nitro compound (Disperse Red 1 (DR 1)) in both doped poly(methylmethacrylate) (PMMA) and pendanted methylmethacrylate (MMA) copolymer.

In recent years, 1H MRS has been used in a number of studies to measure the lactate content of brain, and it is generally assumed that the methyl resonance at 1.3 ppm reflects the total amount of lactate present in the tissue. However, reduced NMR visibility of lactate has recently been reported for blood, heart and skeletal muscle as well as for bacteria. We have assessed the NMR visibility of lactate in cultures of human and rat brain cells, comparing the concentrations measured by NMR and by biochemical methods. Contributions of fatty acids have been eliminated using their different relaxation behavior. We found approximately 30% of the lactate to be undetectable by NMR in the studied cell cultures. While the mechanism partially masking lactate in 1H spectra is not yet understood, the potential invisibility of some pools of lactate to NMR may greatly affect the interpretation of brain spectra.

Metastabilities in the electrical characteristics of CIGS devices are commonly observed phenomena originating from persistent changes of shallow and deep levels distributions within the absorber. We examine characteristic changes induced by voltage bias and light together with their relaxation behavior and interpret them as the consequences of a negative-U type of centers predicted by theoretical calculations of Lany and Zunger. It is shown how the properties of these centers justify a model of p+ layer explaining specific features of light and dark current-voltage characteristics. The discussion showing the impact of various charge distributions on carrier transport is presented. The arguments are provided, that centers responsible for metastable effects are also to blame for majority of photovoltaic losses exhibited in various devices.

The coupling between Librational motions and rotational isomeric jumps in polymers is investigated. Librations originate from bond stretching, bond angle distortion, and small-amplitude fluctuations in the bond dihedral angles. Molecular dynamics trajectories for a polymer chain of 100 bonds in vacuo are used for assessing the contribution of librations to the dynamic behavior of chains. Each trajectory is resolved into two sets of components, low and high frequency, representing bond rotameric transitions and librations, respectively. Librational motions are observed to be strongly correlated with the rotational jumps of bonds between isomeric states. In fact, the passage from an isomeric state to another is accompanied by an enhancement in librational motions. Examination of the contribution of Librations to the local relaxation behavior of polymers indicates that librations affect the mechanism of motion via two opposing effects. On the one hand, they provide an additional degree of freedom which causes a faster relaxation of the conformational correlation functions associated with the bond dihedral angles. On the other hand, the orientational correlation functions associated with the spatial reorientation of backbone bonds exhibit a slower time decay due to the compensating effect of librational motions. In fact, librational motions are not random but highly directed such that they collectively preserve local chain direction and help in accommodating the local reorientations induced by isomeric jumps, which would otherwise result in larger displacements of chain segments. Finally, it is shown that replacing the librations of a trajectory with random, uncorrelated fluctuations leads to an overestimation of the relaxation rate of configurational correlations.

Time dependent behavior of thin nylon films is investigated by depth sensing nanoindentation. Different loading rates and holding times are applied in single indentation procedures to study the relaxation behavior of nylon resulting in a characteristic nonlinear displacement – time dependence. Several load – time functions of multi-cycling indentation are developed, such as constant load repetition and incremental load increase mode sometimes containing holding segments. Hysteresis loops in multi-cycling nanoindentation quantify the visco-elastic energy of nylon films. The loading rate does not change the loop size if the maximum and minimum load of the cycle are the same. The unloading process has to be sufficiently large to allow the performance of the visco-elastic relaxation of the material.

The dielectric properties, dielectric relaxation behavior, electric conduction and kinetic characteristics of fluorine-containing polysiloxane-imide were investigated. The fluorine-containing polyimide [6FDA + p-PDA] has a low dielectric constant of 3.04, compared to normal polyimides such as Upilex-S [BPDA + p-PDA] with a dielectric constant of 3.47, due to the addition of perfluoroalkyl groups into the polymer backbone, while fluorine-containing polysiloxane-imide (6FDA + siloxane) has the lowest dielectric constant of 2.43, which is less than 2.5. The introduction of siloxane groups on the fluoric polyimides provides the possibility of obtaining high-performance polyimides with ultralow dielectric constants. The dielectric relaxation spectra suggest that the fluorine-containing polysiloxane-imide (6FDA + siloxane) has a phase separation structure. As frequency increases, the a relaxation strengths decrease and the;3 relaxation strengths hardly change. The conduction study indicates that the / peak corresponds to the /3 dipolar relaxation whereas the a one is due to the conductive effects in the bulk and the a dipolar relaxation. The activation energy of the a transition decreases with increasing frequency, while the activation energy of the /3 transition does not vary with frequency

We have investigated the 1H and 19F spin-spin relaxation behavior in the melts and swollen gels of cross-linked polyfluoroalkyl acrylates PFA-nR where n is the number of CF2 groups in the side chain (n = 2, 3, 4). It was found that in the strands the anisotropic motion of the main chain units and the side groups lead to the non-zero degree of averaging of magnetic dipole-dipole interactions (Q). Q of side groups was estimated to depend on the degree of cross-linking Q ≈ blx, where x is the number of persistent lengths in the strand, b was found to decrease with increasing n. In opposite to PFA-3F and PFA-2H networks, the dangling ends in PFA-4R network were shown to influence the relaxation behavior, indicating the growth of motional anisotropy of dangling ends with chain diameter.

The temperature and frequency dependent dielectric relaxation behavior of a liquid crystalline (S)-(+)-1-methylheptyl 4-[2-(4-alkoxyphenyl) thiophene-5-carbonylthiooxy] benzoate system is reported. Interesting successive antiferroelectric-ferroelectric-antiferroelectric (AF-FE-AF) phase transitions are observed in this system resembling the successive phase transitions observed in crystalline Rochelle salt. The smectic-${C}^{*}$ $(\mathrm{Sm}{C}^{*})$ to AF1 phase transition (around 103.0 \ifmmode^\circ\else\textdegree\fi{}C) is first order in nature, predicted from the use of Orihara and Ishibashi theory. It is also found that a contribution of the ferroelectric $\mathrm{Sm}{C}^{*}$ phase ordering penetrates even in the antiferroelectric AF1 $(\mathrm{Sm}{C}_{A}^{*})$ and AF2 $(\mathrm{Sm}{C}_{A}^{*})$ phases very close to the $\mathrm{Sm}{C}^{*}\ensuremath{-}\mathrm{AF}1$ and $\mathrm{Sm}{C}^{*}\ensuremath{-}\mathrm{AF}2$ phase boundaries (critical regions). It is suggested that this type of mixing of AF and FE phases might cause surface induced ferroelectric- or ferroelectric-type ordering near the AF-FE phase transitions. A soft mode with Debye-type dispersion was observed in the $\mathrm{Sm}A$ phase. The thermal behaviors of dielectric dispersion, absorption, and dielectric strength in different phases are also reported and discussed.

The transition features from the resting to the time-ordered states of squid giant axons were studied experimentally in detail by observing membrane potential changes induced by weak current pulses. The observed features near the transition point are that (1) a critical slowing-down was observed in the relaxation behavior, (2) the subthreshold oscillation frequency remained invariant before and after the transition point, and (3) the transition was of a discontinuous type. These experimental results could be satisfactorily simulated by numerical calculation on the basis of an electric circuit model proposed by FitzHugh and by Nagumo et al.

The static and dynamic properties of a model polymre chain immersed in a solvent are studied by computer molecuar dynamics techniques. The effect of the attractive part of the Lennard‐Jones potential, on the dynamic properties of polymeric chains is studied. Autocorrelation functions are calculated.(AIP)

The results of dielectric constant and loss measurements over a frequency range 1 MHz–140 GHz are reported for n‐hexanol and 2‐methyl‐3‐heptanol, each at several concentrations, in n‐heptane solution at 25°C.

Compressive deformation studies on BaTiO3 single crystals show that the crystals deform easily at room temperature because of the movement of twin boundaries which are the 90° domain walls. In the twin‐deformation region, the crystals exhibit time‐dependent deformation, which could be observed as stress relaxation. Some features of this deformation and relaxation behavior are reported.

The low field relaxation time for various states of the 165 Ho 2+ , a coupled nuclear-electronic system, is observed to depend exponentially on temperature down to 0.15°K.

Compared to standard Verneuil ruby, Czochralski ruby shows a rather high inversion ratio when used as a microwave maser material in the 4-GHz range. This is in good agreement with the more pure spin-lattice relaxation behavior which was observed when testing this material.

These investigations are directed at identifying the microscopic polymer characteristics which determine the properties and relaxation behavior of amorphous polymers. In addition to the molecular structure, the number of holes (free volume) and the fraction of flexed bonds (i. e., gauche states) can be used as a starting point for the specification of the states of the glass. In addition, the effect of pressure is used to influence the number of holes and the fraction of flexed bonds frozen in the glass. Fourier transform infrared spectroscopy (FTIR) has been used to follow the trans to gauche populations as a function of temperature and pressure.