On universality of concurrent expressions with synchronization primitives

AbstractConcurrent expressions are a class of extended regular expressions with a shuffle operator (‖) and its closure (). The class of concurrent expressions with synchronization primitives, called synchronized concurrent expressions, is introduced as an extended model of Shaw's flow expressions. This paper discusses some formal properties of synchronized concurrent expressions from a formal language theoretic point of view. It is shown that synchronized concurrent expressions with three signal/wait operations are universal in the sense that they can simulate any semaphore controlled concurrent expressions and they can describe the class of recursively enumerable sets. Some results on semaphore controlled regular expressions are also included to give a taste of more positive results

Anomalous Hall effect in field-effect structures of (Ga,Mn)As

The anomalous Hall effect in metal-insulator-semiconductor structures having thin (Ga,Mn)As layers as a channel has been studied in a wide range of Mn and hole densities changed by the gate electric field. Strong and unanticipated temperature dependence, including a change of sign, of the anomalous Hall conductance $\sigma_{xy}$ has been found in samples with the highest Curie temperatures. For more disordered channels, the scaling relation between $\sigma_{xy}$ and $\sigma_{xx}$, similar to the one observed previously for thicker samples, is recovered.Comment: 5 pages, 5 figure

Grain size effect on the low-temperature oxidation of titanomagnetite

The low-temperature oxidation process in titanomagnetite has been investigated. Using samples with controlled grain sizes, it has been shown that there is a critical grain size in the oxidation behaviour of titanomagnetites; smaller grains undergo low-temperature oxidation, while larger ones separate to Fe-rich titanomagnetite and Ti-rich hemo-ilmenite (high-temperature oxidation). The difference between the results of similar experiments by Ozima and Sakamoto (1971) and by Readman and O'Reilly (1972) can be explained in terms of differences in partide sizes of titanomagnetites. Comparable results were obtained from natural subaerial and submarine basalts; when they are heated to temperatures between 150° C and 375° C, oxidation proceeds in submarine basalts, but it does not in subaerially erupted basalts and a high-temperature oxidation process occurs. This fact indicates that the grain size of the magnetic minerals is one of the most important controlling factors in low-temperature oxidation of titanomagnetites.           ARK: https://n2t.net/ark:/88439/y041502 Permalink: https://geophysicsjournal.com/article/266 &nbsp