1,790 research outputs found
The Peculiar Rotation Curve of NGC 157
We present the results of a new HI, optical, and H-alpha interferometric
study of the nearby spiral galaxy NGC 157. Our combined C- and D-array
observations with the VLA show a large-scale, ring-like structure in the
neutral hydrogen underlying the optical disk, together with an extended, low
surface density component going out to nearly twice the Holmberg radius.
Beginning just inside the edge of the star-forming disk, the line of nodes in
the gas disk commences a 60 degree warp, while at the same time, the rotation
velocity drops by almost half its peak value of 200 km/s, before leveling off
again in the outer parts. While a flat rotation curve in NGC 157 cannot be
ruled out, supportive evidence for an abrupt decline comes from the ionised gas
kinematics, the optical surface photometry, and the global HI profile. A
standard `maximum-disk' mass model predicts comparable amounts of dark and
luminous matter within NGC 157. Alternatively, a model employing a disk
truncated at 2 disk scale lengths could equally well account for the unusual
form of the rotation curve in NGC 157.Comment: 26 pages, 15 figures, LaTeX, uses mn-1.4.sty. Accepted for
publication in MNRA
Spectropolarimetry of the Type IIb Supernova 2001ig
We present spectropolarimetric observations of the Type IIb SN 2001ig in NGC
7424; conducted with the ESO VLT FORS1 on 2001 Dec 16, 2002 Jan 3 and 2002 Aug
16 or 13, 31 and 256 days post-explosion. These observations are at three
different stages of the SN evolution: (1) The hydrogen-rich photospheric phase,
(2) the Type II to Type Ib transitional phase and (3) the nebular phase. At
each of these stages, the observations show remarkably different polarization
properties as a function of wavelength. We show that the degree of interstellar
polarization is 0.17%. The low intrinsic polarization (~0.2%) at the first
epoch is consistent with an almost spherical (<10% deviation from spherical
symmetry) hydrogen dominated ejecta. Similar to SN 1987A and to Type IIP SNe, a
sharp increase in the degree of the polarization (~1%) is observed when the
outer hydrogen layer becomes optically thin by day 31; only at this epoch is
the polarization well described by a ``dominant axis.'' The polarization angle
of the data shows a rotation through ~40 degrees between the first and second
epochs, indicating that the asymmetries of the first epoch were not directly
coupled with those observed at the second epoch. For the most polarized lines,
we observe wavelength-dependent loop structures in addition to the dominant
axis on the Q-U plane. We show that the polarization properties of Type IIb SNe
are roughly similar to one another, but with significant differences arising
due to line blending effects especially with the high velocities observed for
SN 2001ig. This suggests that the geometry of SN 2001ig is related to SN 1993J
and that these events may have arisen from a similar binary progenitor system.Comment: 42 pages, 12 figures (figs. 11 and 12 are both composed of four
subpanels, figs. 6,7,8,11 and 12 are in color, fig. 1 is low res and a high
res version is available at http://www.as.utexas.edu/~jrm/), ApJ Accepte
Generalized Grassmannian Coherent States For Pseudo-Hermitian Level Systems
The purpose of this paper is to generalize fermionic coherent states for
two-level systems described by pseudo-Hermitian Hamiltonian \cite{Trifonov}, to
n-level systems. Central to this task is the expression of the coherent states
in terms of generalized Grassmann variables. These kind of Grassmann coherent
states satisfy bi-overcompleteness condition instead of over-completeness one,
as it is reasonably expected because of the biorthonormality of the system.
Choosing an appropriate Grassmann weight function resolution of identity is
examined. Moreover Grassmannian coherent and squeezed states of deformed group
for three level pseudo-Hermitian system are presented.Comment: 17 page
Recommended from our members
Precision nomenclature for the new genomics
The confluence of two scientific disciplines may lead to nomenclature conflicts that require new terms while respecting historical definitions. This is the situation with the current state of cytology and genomics, which offer examples of distinct nomenclature and vocabularies that require reconciliation. In this article, we propose the new terms C-scaffold (for chromosome-scale assemblies of sequenced DNA fragments, commonly named scaffolds) and scaffotype (the resulting collection of C-scaffolds that represent an organism\u27s genome). This nomenclature avoids conflict with the historical definitions of the terms chromosome (a microscopic body made of DNA and protein) and karyotype (the collection of images of all chromosomes of an organism or species). As large-scale sequencing projects progress, adoption of this nomenclature will assist end users to properly classify genome assemblies, thus facilitating genomic analysis
Haematological and Biochemical Values or the Blood and Blood Serum of Captive Northern White Rhinoceroses (Ceratotherium simum cottoni)
Chimerism studies in HLA-identical nonmyeloablative hematopoietic stem cell transplantation point to the donor CD8+ T-cell count on day +14 as a predictor of acute graft-versus-host disease
AbstractChimerism analysis of hematopoietic cells has emerged as an essential tool in nonmyeloablative hematopoietic stem cell transplantation. We have investigated the development of donor chimerism in granulocytes and CD4+ and CD8+ T cells in blood and bone marrow of 24 patients with hematologic malignancies who received HLA-identical sibling peripheral blood stem cell grafts after conditioning with fludarabine and 2 Gy of total body irradiation. The T-cell chimerism of blood and bone marrow was tightly correlated. Complete donor chimerism was reached earlier in the granulocytes than in the T cells. Mixed T-cell chimerism was common at the time of onset of acute graft-versus-host disease (aGVHD), and both CD4+ and CD8+ donor T-cell chimerism increased with the occurrence of aGVHD grades II to IV (P = .0002 and P = .019, respectively). The rate of disappearance of recipient CD8+ T cells was faster in patients with aGVHD grades II to IV than in patients without clinically significant aGVHD (P = .016). This observation indicates a role of graft-versus-lymphohematopoietic tissue reactions in creating complete donor T-cell chimerism. A donor CD8+ T-cell count above the median on day +14 increased the risk of subsequent development of aGVHD grades II to IV (P = .003)
The Free Energy of High Temperature QED to Order From Effective Field Theory
Massless quantum electrodynamics is studied at high temperature and zero
chemical potential. We compute the Debye screening mass to order and
the free energy to order } by an effective field theory approach,
recently developed by Braaten and Nieto. Our results are in agreement with
calculations done in resummed perturbation theory. This method makes it
possible to separate contributions to the free energy from different momentum
scales (order and ) and provides an economical alternative to
computations in the full theory which involves the dressing of internal
propagators.Comment: 10 pages Latex, 6 figure
Involvement of Mhc Loci in immune responses that are not Ir-gene-controlled
Twenty-nine randomly chosen, soluble antigens, many of them highly complex, were used to immunize mice of two strains, C3H and B10.RIII. Lymphnode cells from the immunized mice were restimulated in vitro with the priming antigens and the proliferative response of the cells was determined. Both strains were responders to 28 of 29 antigens. Eight antigens were then used to immunize 11 congenic strains carrying different H-2 haplotypes, and the T-cell proliferative responses of these strains were determined. Again, all the strains responded to seven of the eight antigens. These experiments were then repeated, but this time -antibodies specific for the A (AA) or E (EE) molecules were added to the culture to block the in vitro responsiveness. In all but one of the responses, inhibition with both A-specific and E-specific antibodies was observed. The response to one antigen (Blastoinyces) was exceptional in that some strains were nonresponders to this antigen. Furthermore, the response in the responder strains was blocked with A-specific, but not with E-specific, antibodies. The study demonstrates that responses to antigens not controlled by Irr genes nevertheless require participation of class II Mhc molecules. In contrast to Ir gene-controlled responses involving either the A- or the E-molecule controlling loci (but never both), the responses not Ir-controlled involve participation of both A- and E-controlling loci. The lack of Ir-gene control is probably the result of complexity of the responses to multiple determinants. There is thus no principal difference between responses controlled and those not controlled by Ir genes: both types involve the recognition of the antigen, in the context of Mhc molecules
- …