L.A. Thomas

Bio: L.A. Thomas is an academic researcher from General Electric. The author has contributed to research in topic(s): Quartz & Crystal twinning. The author has an hindex of 1, co-authored 1 publication(s) receiving 37 citation(s).

The control and elimination of electrical (Dauphiné) twinning in quartz

Abstract: Quartz for telecommunication purposes has to be of the highest crystalline quality. A considerable proportion of raw material is rejected on account of electrical twinning. The war-time need for economy of quartz led to an investigation of means of removing this defect. The paper surveys the experimental methods used in exploring the possibilities of untwinning quartz. The basis of these methods is a heat treatment of the quartz plate while subjected to a system of stresses applied to the plate by temperature gradients, pure bending, longitudinal compression or torque. The effect of crystallographic orientation is discussed, and the new physical phenomenon of “piezocrescence” is defined.The paper also describes the practical application of the untwinning techniques to quartz-crystal plates, with particular reference to the requirements of telecommunication. It is shown that the method employing heat treatment with an applied torque may be successfully applied to many important types of quartz crystals including the BT and AT cuts. The proportion of success and the occurrence of quartz showing anomalous behaviour are discussed.

Models of aftershock occurrence

Abstract: Summary. The Omori formula for aftershock activity can be shown to be a consequence of each of two models of a complex earthquake. In the first case. aftershocks are assumed to be caused by subsequent slip on asperities of a fault which are locked during the fracture in the main shock. In the second, aftershocks are caused by catastrophic coalescence of nearby small fractures with the fracture surface of the main shock. Hence, the first source model describes aftershock activity in the interior of a main-shock rupture zone, while the second describes aftershock activity near the outer boundary of a main-shock rupture zone. Stress corrosion cracking is assumed to be the physical cause of the quasistatic growth of the main fracture zone at the expense of the area of the locked patches in the first model and is also the cause of the growth of the small satellite fractures in the second.