1,572 research outputs found
On the theory of Gordan-Noether on homogeneous forms with zero Hessian (Improved version)
We give a detailed proof for Gordan-Noether's results in "Ueber die
algebraischen Formen, deren Hesse'sche Determinante identisch verschwindet"
published in 1876 in Mathematische Annahlen. C. Lossen has written a paper in a
similar direction as the present paper, but did not provide a proof for every
result. In our paper, every result is proved. Furthermore, our paper is
independent of Lossen's paper and includes a considerable number of new
observations.
An earlier version of this paper has been printed in Proceedings of the
School of Science of Tokai University, Vol.49, Mar. 2014. In this version, a
serious error has been corrected and some new results have been added
On the geometry of C^3/D_27 and del Pezzo surfaces
We clarify some aspects of the geometry of a resolution of the orbifold X =
C3/D_27, the noncompact complex manifold underlying the brane quiver standard
model recently proposed by Verlinde and Wijnholt. We explicitly realize a map
between X and the total space of the canonical bundle over a degree 1 quasi del
Pezzo surface, thus defining a desingularization of X. Our analysis relys
essentially on the relationship existing between the normalizer group of D_27
and the Hessian group and on the study of the behaviour of the Hesse pencil of
plane cubic curves under the quotient.Comment: 23 pages, 5 figures, 2 tables. JHEP style. Added references.
Corrected typos. Revised introduction, results unchanged
Auszug zweier Schreiben des Prof. Hesse an den Herrn Prof. Jacobi und eines Schreibens des Prof. Jacobi an Herrn Prof. Hesse.
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INTEGRAL observations of the black hole candidate H 1743-322 in outburst
INTEGRAL made 3 observations in 2003 April of the black hole candidate H
1743-322 during the rising part, and close to the maximum, of an outburst. H
1743-322 was previously observed in outburst in 1977-1978. The source is
located in a crowded region of the sky (l = 357 deg, b = -2 deg) and at least
18 sources are clearly detected in the field of view of the gamma-ray imager
during a 277 ksec exposure. These are well known persistent X-ray binaries and
3 transient sources in outburst. The combined 5-200 keV JEM-X and SPI spectrum
of H 1743-322 is well fit with an absorbed ((2.5 10E22 atom/cm2) soft (photon
index 2.70 +/- 0.09) power-law model consistent with J 1743-322 being in a
high/soft state.Comment: 5 pages. Figs. 2 and 3 are best viewed in color. To appear in
INTEGRAL special edition of A&A
Equianalytic and equisingular families of curves on surfaces
We consider flat families of reduced curves on a smooth surface S such that
each member C has the same number of singularities of fixed singularity types
and the corresponding (locally closed) subscheme H of the Hilbert scheme of S.
We are mainly concerned with analytic resp. topological singularity types and
give a sufficient condition for the smoothness of H (at C). Our results for
S=P^2 seem to be quite sharp for families of cuves of small degree d.Comment: LaTeX v 2.0
Electron scale structures and magnetic reconnection signatures in the turbulent magnetosheath
Collisionless space plasma turbulence can generate reconnecting thin current
sheets as suggested by recent results of numerical magnetohydrodynamic
simulations. The MMS mission provides the first serious opportunity to check if
small ion-electron-scale reconnection, generated by turbulence, resembles the
reconnection events frequently observed in the magnetotail or at the
magnetopause. Here we investigate field and particle observations obtained by
the MMS fleet in the turbulent terrestrial magnetosheath behind quasi-parallel
bow shock geometry. We observe multiple small-scale current sheets during the
event and present a detailed look of one of the detected structures. The
emergence of thin current sheets can lead to electron scale structures where
ions are demagnetized. Within the selected structure we see signatures of ion
demagnetization, electron jets, electron heating and agyrotropy suggesting that
MMS spacecraft observe reconnection at these scales
First INTEGRAL Observations of Eight Persistent Neutron Star Low Mass X-ray Binaries
Early results from the INTEGRAL Core Program, for a sample of eight
persistently bright neutron star low mass X-ray binaries in the energy range
from 5 keV to 200 keV are presented. It is shown that INTEGRAL efficiently
detects sources and that spectra may be obtained up to several hundreds of keV
by combining data from three of the four INTEGRAL instruments: JEM-X, IBIS and
SPI. For the source GX 17+2 it is shown that the spectrum extends well above
100 keV with a flattening of the spectrum above 30 keV. This might suggest a
non-thermal comptonisation emission, but uncertainties in the current data
reduction and background determination do not allow firm conclusions to be
drawn.Comment: 5 pages, 6 figures, accepted for publication in Astronomy &
Astrophysic
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