173 citations
- University of Illinois Urbana-ChampaignUS13 papers
- Texas A&M UniversityUS10 papers
- Fermi National Accelerator LaboratoryUS9 papers
- Michigan State UniversityUS9 papers
- University of FloridaUS9 papers
- University of PennsylvaniaUS9 papers
- University of RochesterUS9 papers
- Argonne National LaboratoryUS8 papers
- Baylor UniversityUS8 papers
- Brandeis UniversityUS8 papers
- Carnegie Mellon UniversityUS8 papers
- Centre National de la Recherche ScientifiqueFR8 papers
7 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.
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…
Formation of Supermassive Black Holes: Simulations in General Relativity
Stuart L. Shapiro
There is compelling evidence that supermassive black holes exist. Yet the origin of these objects, or their seeds, is still unknown. We discuss several plausible scenarios for form…