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15 papers · 1 filter
Non-hopfian relatively free groups
S. V. Ivanov, A. M. Storozhev
To solve problems of Gilbert Baumslag and Hanna Neumann, posed in the 1960's, we construct a nontrivial variety of groups all of whose noncyclic free groups are non-hopfian.
Effective collective barrier for magnetic relaxation in frozen ferrofluids
Ruslan Prozorov, Tanya Prozorov, Alexey Snezhko
Magnetic relaxation and frequency response were measured in frozen ferrimagnetic colloids of different concentrations. A crossover from reversible to irreversible behavior is obser…
Imaging and Spectroscopy of the Planetary Nebula NGC 6778
Vicente Maestro, Martin A. Guerrero, Luis F. Miranda
We present narrow-band images and long-slit echelle spectra of the planetary nebula (PN) NGC 6778. The data show this PN as bipolar, with a very prominent low-excitation equatorial…
Multiple Point-Symmetric Ejections in IC 4634
Martin A. Guerrero, Luis F. Miranda, You-Hua Chu
We present a spatio-kinematical study of the planetary nebula (PN) IC 4634 which has experienced several episodes of point-symmetric ejections oriented at different directions. The…
Hot Gas in Planetary Nebulae
Y. -H. Chu, R. A. Gruendl, M. A. Guerrero
Diffuse X-ray emission has been detected in a small number of planetary nebulae (PNe), indicating the existence of shocked fast stellar winds and providing support for the interact…
X-ray Observations of Planetary Nebulae
M. A. Guerrero, Y. -H. Chu, R. A. Gruendl
Planetary nebulae (PNe) are an exciting addition to the zoo of X-ray sources. Recent Chandra and XMM-Newton observations have detected diffuse X-ray emission from shocked fast wind…