Damage of topaz and other minerals in the electron microscope

Summary Hydroxyl bearing topaz suffers beam-damage in the electron microscope. Irradiation by the beam rapidly produces contrast from strain fields around small needle-shaped pores about 2–5 nm wide and 30–120 nm long, produced by the loss of hydrogen as water and/or hydrogen fluoride. In the majority of cases the damage ceases after a short period of time, and the topaz electron diffraction pattern remains apparently unchanged. In a few cases complete breakdown of the topaz occurs to produce mullite and/or fine-grained -alumina, the latter usually being sputtered onto the carbon support film. The different degrees of breakdown which are found in the electron beam are similar to reactions which occur on heating in air. Although the main factor which determines the degree of beam-induced damage which occurs is believed to be temperature, the heating effect of the beam is alone unlikely to cause the reactions. The lowering of reaction temperature is attributed to mechanically induced enhancement of diffusion in the electron beam and to the weakening of chemical bonds by ionisation effects. The strain fields found in topaz were also produced in samples of humite and apatite observed in the electron microscope, and the formation of fine-grained metal oxides was found in several silicates and phosphates.

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Zerstörung von Topas und anderen Mineralen im Elektronenmikroskop

Zusammenfassung Hydroxil-hältige Topase unterliegen im Elektronenmikroskop einer Zerstörung durch den Elektronenstrahl. Durch die Bestrahlung entstehen rasch Kontraste von gestörten Bereichen rund um kleine nadelförmige Poren von etwa 2–5 nm Durchmesser und 30–120 nm Länge, die durch den Verlust von Wasserstoff als Wasser und/oder Hydrogenfluorid verursacht werden. Meist hört die Zerstörung nach kurzer Zeit auf und das Elektronen-Beugungsbild des Topases bleibt anscheinend unverändert. In wenigen Fällen kommt es zu einem kompletten Zusammenbruch des Topases und es entsteht Mullit und/oder feinkörniges -Al₂O₃. Die unterschiedlichen Grade des Zusammenbruchs, die im Elektronenstrahl beobachtet werden, sind Reaktionen ähnlich, die beim Erhitzen in Luft auftreten. Obwohl als Hauptfaktor, der den Grad der Strahlinduzierten Zerstörung bestimmt, die Temperatur angenommen werden kann, ist es unwahrscheinlich, daß der Hitzeeffekt des Strahls allein die Reaktionen verursacht. Die Erniedrigung der Reaktionstemperatur wird der mechanisch bedingten Erhöhung der Durchdringungsfähigkeit des Elektronenstrahls und der Schwächung der chemischen Bindung durch Ionisierungseffekte zugeschrieben. Die im Elektronenmikroskop in Topas gefundenen gestörten Bereiche wurden auch in Proben von Humit und Apatit beobachtet; in verschiedenen Silikaten und Phosphaten wurde die Bildung feinkörniger Metalloxide gefunden.

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With 3 Figures

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Dedicated to Professor Dr.Josef Zemann on the occasion of his 6oth birthday.     

New data on the „Indosinian“ Orogeny from Central Thailand

The main aspects of the geosynclinal and orogenic evolution of the Petchabun foldbelt in Central Thailand are described. This area was previously thought to be deformed by the Indosinian (Triassic) orogeny. The new data show that the main orogenic event in Thailand can be dated: Post Lower Permian — Pre Uppermost Permian. Evidence is given that Paleotethys closed on Thai territory during this orogenic event. The known Upper Triassic deformations in Northern Thailand are supposed to be strictly intracontinental and therefore of minor importance.

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Zusammenfassung Die Grundzüge der geosynklinalen und orogenen Entwicklung des Faltengürtels von Petchabun werden beschrieben. Bisher wurde angenommen, daß dieses Gebiet während der Indosinischen Orogenese (Trias) deformiert wurde. Die neuen Daten belegen, daß die bedeutendste Orogenese in Thailand nach dem Unter Perm einsetzte (West-Thailand) und vor dem höchsten Perm abgeschlossen war (Petchabun). Die sog. Paleotethys wurde während dieser Orogenese hier geschlossen. Die bekannten obertriadischen Deformationen sind dagegen rein intrakontinental und somit von untergeordneter Bedeutung.

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Résumé Les traits principaux du développement géosynclinal et orogénique de la ceinture plissée du Petchabun (Thailande) sont décrits. Jusqu'à présent on pensait que cette région avait été déformée pendant l'orogenèse «Indosinienne» (Trias). Les données nouvelles indiquent que l'orogenèse la plus importante a commencée après le Permien inférieur (dans l'Ouest de la Thailande) et qu'elle s'est terminée avant le Permien supérieur (région de Petchabun). Ici, la soi-disant «Paléotéthys» s'est fermée au cours de cette orogenèse. Les déformations bien connues du Trias supérieur sont exclusivement intracontinentales et n'ont ainsi qu'une signification subordonnée.

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Petchabun. , (). , ( ) (Petchabun). . . .

     

ENSO cycle in a coupled ocean-atmosphere model and its negative feedback mechanism

Summary A coupled ocean-atmosphere anomaly model has been developed for simulating ENSO cycle and its mechanism-study in this paper. After a long model run, the coupled model is successful in demonstrating ENSO-like irregular interannual variability and corresponding horizontal spatial structures. Based on the simulated results, the dynamics and the thermodynamics of the model ENSO cycle have been investigated, and in particular the negative feedback mechanisms that act to oppose instability of air-sea interaction, inducing termination of warm and cold events, have been examined. A detailed analysis of the oceanic wave dynamical properties and heat budget of the SST changes in a representative cycle suggest that the negative feedback mechanism to check the unstable growth of a warm event obviously differs from that of a cold event. The mechanism that induces decay and termination of a cold event is closely related to the negative, delayed feedback effect produced by the oceanic dynamical wave reflection at the western boundary. However, independent of the wave reflection effect, the negative feedback mechanism by which the coupled system returns from a warm event is associated with a slowly eastward-propagating coupling mode. Accompanied with the strong unstable development of the equatorial positive SST anomaly, the anomalous upwelling of cold water generated off the equator and the nonlinear anomalous meridional advection generated in the equator west of instability area jointly restrain the instability and finally plunge the system from a mature warm phase into a weak cold phase. A comparison between the results from the present model and the previous works is also discussed in this paper.With 16 Figures     

Numerical integration of a linear barotropic model using three methods of treating meteorological and gravitational modes separately

Summary The analytical solution of a linear barotropic model is derived, including details of the quasi-geostrophic initialization procedure. The prognostic equations are integrated using three different methods of treating the meteorological and gravitational modes separately. These are a semi-Eulerian, semi-implicit (EI) technique, a semi-Lagrangian, semi-implicit (LI) procedure, and a split-explicit (SE) method. The stability criteria and phase speeds are derived for each of the three techniques.The following theoretical conclusions are derived. Of course, in actual numerical integrations particularly those using more complex models, the results are not so unequivocal.The stability of the EI procedure is governed by the CFL criterion for the meteorological mode. Gravity waves have no effect on the timestep but move more slowly than the analytical waves. The LI method is unconditionally stable with respect to both meteorological and gravitational modes. There is thus no timestep restriction. However, the gravity waves have the same reduced phase speed as in the EI technique. The SE procedure has CFL timestep criteria for both the meteorological and gravitational calculations. However, its gravity wave phase speeds are relatively accurate. Moreover, it is the only one of the three methods that handles the nearly-compensating pressure gradient and Coriolis forces together. From the point of computational efficiency, the LI technique is probably the best.     

Geomorphology and the location of nuclear power plant sites: the Czechoslovakian experience

The need for secure sites for such sensitive installations as nuclear power plants and radioactive waste storage has brought increasing significance to the study of the geodynamic processes of the Earth's crust. Among other Earth sciences, geomorphology in Czechoslovakia is also participating in the study of both planning and operating nuclear power station sites. The experience of Czech geomorphologists has shown that the geomorphological information is necessary part of the accurate prediction of events and time which can endanger the security of nuclear power plants, radioactive waste storages, pipelines and other large installations. Geomorphological mapping and morphostructural analysis are important tools for such studies.     

Social network interactions among mentally ill persons in community housing: research issues and agenda

This paper discusses social network interactions among individuals who have been hospitalized with mental illness and who currently reside in different types of community housing programmes. First, a conceptualisation of social networks that focuses on network interactions, both supportive and non-supportive, between network interactions may be more important influences on successful or unsuccessful adaptation of current and former psychiatric patients to community life than the structural dimensions of social networks more commonly analysed in the literature. The design of a current longitudinal study of social network interactions is presented. The results of two pilot studies that examine social network interactions is presented. The results of two pilot studies that examine social network interactions with data from several community housing programmes in southern Ontario, Canada are reviewed and an agenda is stated for further data collection and analysis.