We describe a CADASIL phenotype that is characterized by the absence of focal neurologic symptoms and present the first SPECT study of this disorder.

A combination of a servohydraulic tensile machine and NMR pulse spectrometer is described enabling nuclear-spin relaxation rates to be recorded simultaneously with stress-strain data incorporating tension as well as compression of nonmetallic as well as of metallic samples. The data of the mechanical system are as follows: Maximum load: 5000 N; minimum deformation speed: 10 μm s−1, maximum deformation speed: 3×105 μm s−1; deformation stroke: digitally controlled between 1 and 8×103 μm; bandwidth: dc to 1 kHz; resolution: 2–4 μm; temperature conditions of the sample: from 80 to 570 K. The operation and performance of the system is described by means of experiments observing nuclear-spin relaxation rates which are induced by the movement of dislocations due to the finite deformation rate of the sample.

Résumé. -La résonance magnétique nucléaire est appliquée à l'étude de la variation de la vitesse des dislocations avec la contrainte de compression appliquée dans des cristaux d'halogénures alcalins. T lp a été mesurée en fonction du taux s de la déformation plastique. La route moyenne des dislocations mobiles a été déterminée. Nous indiquons les résultats des expériences sur de différents noyaux, sur de différentes orientations des cristaux et sur des températures différentes.Abstract. -Dislocations moving at various velocities in deforming alkali halide single crystals were studied using the technique of pulsed nuclear magnetic resonance. The spin lattice relaxation rate in the rotating frame is measured as a function of the plastic deformation rate 6. From this the mean free path of mobile dislocations can be determined. The results for different resonant nuclei, different crystal orientations with respect to the crystal axis and different temperatures are presented.

(a), H. SELBACH (a), 0. KANERT (a), A. W. SLEESwYK (b), and G . HUT (b) Wolf's general theory of rotating-frame nuclear spin-lattice relaxation is applied to the effect caused by dislocations moving at an average velocity V. Equations are presented for the dependence of the NMR relaxation rate Rg) on the mean waiting time T of a dislocation before a n obstacle, valid in both the weak-and the strong-collision regions. In the latter the Slichter-Ailion-RowlandFradin theory applies. Nuclear spin relaxation tests on 23NaCl and 23NaF single crystals deformed at constant strain rates E confirm the theory. The experimental data for the predicted maximum in Rg) (reached only for NaCl at k, = 20 s-l) yield directly rm = 2.8 x 8 , the mobile fraction of dislocations em/et = 0.26. The value of r,, together with the mean distance between obstacles of e 2 x 10-4 cm, derived from the slope of the curve in the strong-collision region, leads t o w, = 7.1 cm s-l, corresponding t o a mobile dislocation density em = 1.4 x lo8 cm-2.Ausgehend von der allgemeinen Theorie der Kernspinrelaxation im rotierenden System von Wolf wurde die Relaxation durch Versetzungen untersucht, die sich mit einer mittleren Geschwindigkeit 'i, bewegen. Die hier formulierten Gleichungen beschreiben die Abhiingigkeit der NMRRelasationsrate R g ) von der mittleren Wartezeit T einer Versetzung vor einem Hindernis somohl fur den ,,weak-collision"-als auch fiir den ,,strong-collision"-Bereich, in welchem die SlichterAilion-Rowland-Fradin-Theorie anwendbar ist. Die theoretischen Beziehungen werden bestiitigt durch Kernspinrelaxationszeitmessungen an "NaCl-und WaF-Einkristallen, die mit konstanter Kompressionsrate k plastisch verformt wurden. Aus dem esperirnentellen Wert fur das erwartete Maximum in Rg) (nur erreicht fur NaCl bei: k, = 20 s-l) ergibt sich direkt: t , = 2,8 * sec;Bruchteil der mobilen Versetzungen: em/et FZ 0,26. Zusammen mit eineni mittleren Abstand zwischen den Hindernissen von ca. 2 * cm, der sich aus der Steigung der Kurve irn ,.strongcollision"-Bereich ergibt, erhalt man ; , = 7,l cm sec-', entsprechend einer Dichte der bcweglichen Versetzungen von em = 1,4 * lo8 cm-*.

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