Origin and evolution of circular waves and spirals in Dictyostelium discoideum territories.

Randomly distributed Dictyostelium discoideum cells form cooperative territories by signaling to each other with cAMP. Cells initiate the process by sending out pulsatile signals, which propagate as waves. With time, circular and spiral patterns form. We show that by adding spatial and temporal noise to the levels of an important regulator of external cAMP levels, the cAMP phosphodiesterase inhibitor, we can explain the natural progression of the system from randomly firing cells to circular waves whose symmetries break to form double- and single- or multi-armed spirals. When phosphodiesterase inhibitor is increased with time, mimicking experimental data, the wavelength of the spirals shortens, and a proportion of them evolve into pairs of connected spirals. We compare these results to recent experiments, finding that the temporal and spatial correspondence between experiment and model is very close.

Magnetars: Properties, Origin and Evolution

Magnetars are neutron stars in which a strong magnetic field is the main energy source. About two dozens of magnetars, plus several candidates, are currently known in our Galaxy and in the Magellanic Clouds. They appear as highly variable X-ray sources and, in some cases, also as radio and/or optical pulsars. Their spin periods (2–12 s) and spin-down rates (∼10−13–10−10 s s−1) indicate external dipole fields of ∼1013−15 G, and there is evidence that even stronger magnetic fields are present inside the star and in non-dipolar magnetospheric components. Here we review the observed properties of the persistent emission from magnetars, discuss the main models proposed to explain the origin of their magnetic field and present recent developments in the study of their evolution and connection with other classes of neutron stars.

The problems of the origin and structure of chondrules in stony meteorites / Sharat Kumar Roy --

v.10:no.31(1957)

The psychological origin and the nature of religion /

"Magic and religion": p. 48-79.

Corporations; a study of the origin and development of great business combinations and of their relation to the authority of the state.

Mode of access: Internet.

The number concept : its origin and development /

Includes bibliographical references and indexes.

The origin and development of early Christian church architecture.

Bibliography: p. 143-147.

The Federal reserve act, its origin and problems,

Mode of access: Internet.

English tragicomedy : its origin and history.

"A list of English tragicomedies": p. 207-228.

The flag of the United States of America, depicting its early origin and progressive development,

Mode of access: Internet.