Hypoxia as a negative reinforcing stimulus in the squirrel monkey

Summary Squirrel monkeys learned to avoid hypoxia by pressing a bar. Each bar-press replaced the noxious gas mixture with normal air for 3 sec. The data further indicated that O₂ itself has no positive reinforcing effect.     

Experimental brain tumours in dogs

Zusammenfassung Durch wiederholte i.v. Injektionen von gelöstem Methylnitrosoharnstoff werden bei 4 Hunden intrazerebrale Geschwülste induziert. Damit ist der Beweis erbracht, dass dieser Stoff nicht nur bei Nagetieren, sondern auch bei grösseren Säugetieren Geschwülste des Zentralnervensystems verursachen kann.     

Effect of hydrocortisone on the ultrastructure of the small,granule-containing cells in the superior cervical ganglion of the newborn rat

Zusammenfassung Hydrocortison-Injektionen führen bei neugeborenen Ratten zu einer Vermehrung der kleinen granulahaltigen Zellen im Ganglion cervicale craniale und zu einer Vermehrung der granulären Vesikeln im Zytoplasma dieser Zellen.

---

---

University of Melbourne Senior Research Fellow September 1971–August 1972. Present address: Department of Anatomy, University of Helsinki, Siltavuorenpenger, Helsinki, Finland 00170.

---

In receipt of a grant from the National Health and Medical Research Council of Australia.

---

Sunshine Foundation and Rowden White Overseas Research Fellow September 1971–August 1972. Present address: Department of Anatomy, University of Helsinki, Siltavuorenpenger, Helsinki, Finland 00170.     

Localization of acetylcholinesterase activity in myotendinous and myomyous junctions of the striated skeletal muscles of the rat

Zusammenfassung Mit licht- und elektronenmikroskopischen Methoden wird demonstriert, dass die quergestreiften Muskelfasern sich ohne kollagenes Bindegewebe an andere Muskelfasern anschliessen können. An den gegenüber liegenden Sarcoplasmamembranen konnte Azetylcholinesterase nachgewiesen werden.     

The effect of vitamin B12 on the coenzyme a content of normal strains ofescherichia coli

Zusammenfassung Auf vitaminfreien Nährböden wurdenEscherichia-Coli-Stämme kultiviert, die bei Zusatz von Vitamin B₁₂ einen deutlichen Rückgang der Abgabe von Pantothensäure in das Nährmedium zeigten.Die Bestimmung des Coenzym-A-Gehaltes der Bakterien ist mittels der Methode vonKaplan undLipmann durchgeführt worden. Es ergab sich, dass keine grösseren Schwankungen des Coenzym-A-Gehaltes der Bakterien vorkamen, obgleich der Gehalt an freier Pantothensäure in der Nährflüssigkeit deutlich abnahm.

---

---

This work has been aided by grants from Emil Aaltonen Foundation and Sigrid Juselius Stiftelse.     

Aktivitätsuntersuchungen bei Fransenfledermäusen (Myotis nattereri,Kuhl 1818)

Summary Field experiments on the diurnal activity of Natterer's bat (Myotis nattereri, Kuhl 1818) are described. The diurnal activity pattern follows the course of the light intensity with a phase difference. This phase difference and certain details of the activity pattern are subject to seasonal changes and are influenced by the ambient temperature.     

Collapse and revival of the matter wave field of a Bose-Einstein condensate

A Bose-Einstein condensate represents the most 'classical' form of a matter wave, just as an optical laser emits the most classical form of an electromagnetic wave. Nevertheless, the matter wave field has a quantized structure owing to the granularity of the discrete underlying atoms. Although such a field is usually assumed to be intrinsically stable (apart from incoherent loss processes), this is no longer true when the condensate is in a coherent superposition of different atom number states. For example, in a Bose-Einstein condensate confined by a three-dimensional optical lattice, each potential well can be prepared in a coherent superposition of different atom number states, with constant relative phases between neighbouring lattice sites. It is then natural to ask how the individual matter wave fields and their relative phases evolve. Here we use such a set-up to investigate these questions experimentally, observing that the matter wave field of the Bose-Einstein condensate undergoes a periodic series of collapses and revivals; this behaviour is directly demonstrated in the dynamical evolution of the multiple matter wave interference pattern. We attribute the oscillations to the quantized structure of the matter wave field and the collisions between individual atoms.     

Cavity solitons as pixels in semiconductor microcavities

Cavity solitons are localized intensity peaks that can form in a homogeneous background of radiation. They are generated by shining laser pulses into optical cavities that contain a nonlinear medium driven by a coherent field (holding beam). The ability to switch cavity solitons on and off and to control their location and motion by applying laser pulses makes them interesting as potential 'pixels' for reconfigurable arrays or all-optical processing units. Theoretical work on cavity solitons has stimulated a variety of experiments in macroscopic cavities and in systems with optical feedback. But for practical devices, it is desirable to generate cavity solitons in semiconductor structures, which would allow fast response and miniaturization. The existence of cavity solitons in semiconductor microcavities has been predicted theoretically, and precursors of cavity solitons have been observed, but clear experimental realization has been hindered by boundary-dependence of the resulting optical patterns-cavity solitons should be self-confined. Here we demonstrate the generation of cavity solitons in vertical cavity semiconductor microresonators that are electrically pumped above transparency but slightly below lasing threshold. We show that the generated optical spots can be written, erased and manipulated as objects independent of each other and of the boundary. Numerical simulations allow for a clearer interpretation of experimental results.