91 research outputs found
X-ray Sources and their Optical Counterparts in the Globular Cluster M4
We report on the Chandra X-ray Observatory ACIS-S3 imaging observation of the
Galactic globular cluster M4 (NGC 6121). We detect 12 X-ray sources inside the
core and 19 more within the cluster half-mass radius. The limiting luminosity
of this observation is Lx~10e29 erg/sec for sources associated with the
cluster, the deepest X-ray observation of a globular cluster to date. We
identify 6 X-ray sources with known objects and use ROSAT observations to show
that the brightest X-ray source is variable. Archival data from the Hubble
Space Telescope allow us to identify optical counterparts to 16 X-ray sources.
Based on the X-ray and optical properties of the identifications and the
information from the literature, we classify two (possibly three) sources as
cataclysmic variables, one X-ray source as a millisecond pulsar and 12 sources
as chromospherically active binaries. Comparison of M4 with 47 Tuc and NGC 6397
suggests a scaling of the number of active binaries in these clusters with the
cluster (core) mass.Comment: 11 pages, 6 figures, accepted for publication in ApJ. Figure 1 and 5
are of reduced qualit
Dilogarithm Identities in Conformal Field Theory and Group Homology
Recently, Rogers' dilogarithm identities have attracted much attention in the
setting of conformal field theory as well as lattice model calculations. One of
the connecting threads is an identity of Richmond-Szekeres that appeared in the
computation of central charges in conformal field theory. We show that the
Richmond-Szekeres identity and its extension by Kirillov-Reshetikhin can be
interpreted as a lift of a generator of the third integral homology of a finite
cyclic subgroup sitting inside the projective special linear group of all real matrices viewed as a {\it discrete} group. This connection
allows us to clarify a few of the assertions and conjectures stated in the work
of Nahm-Recknagel-Terhoven concerning the role of algebraic -theory and
Thurston's program on hyperbolic 3-manifolds. Specifically, it is not related
to hyperbolic 3-manifolds as suggested but is more appropriately related to the
group manifold of the universal covering group of the projective special linear
group of all real matrices viewed as a topological group. This
also resolves the weaker version of the conjecture as formulated by Kirillov.
We end with the summary of a number of open conjectures on the mathematical
side.Comment: 20 pages, 2 figures not include
Fermionic Quasi-Particle Representations for Characters of {(G^{(1)})_1 \times (G^{(1)})_1 \o (G^{(1)})_2}
We present fermionic quasi-particle sum representations for some of the
characters (or branching functions) of ~{(G^{(1)})_1 \times (G^{(1)})_1 \o
(G^{(1)})_2} ~for all simply-laced Lie algebras . For given the
characters are written as the partition function of a set of rank~ types of
massless quasi-particles in certain charge sectors, with nontrivial lower
bounds on the one-particle momenta. We discuss the non-uniqueness of the
representations for the identity character of the critical Ising model, which
arises in both the and cases.Comment: 14/9 pages in harvmac, ITP-SB-92-64/RU-92-51. References adde
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Block regional off-resonance correction (BRORC): A fast and effective deblurring method for spiral imaging
Altered expression of nerve growth factor in the skin of transgenic mice leads to changes in response to mechanical stimuli
It has recently become clear that the neurotrophic factor, nerve growth factor, interacts specifically with nociceptive sensory neurons during development and maturity. Indeed, it may serve as a critical link between inflammation and the hyperalgesia that ensues in adult animals. Nerve growth factor is normally expressed in limiting amounts in target tissues of sensory and postganglionic sympathetic neurons. In the present study we have altered the basal level of nerve growth factor expression in the skin by producing transgenic mice that express a fusion gene construct containing either a sense or antisense nerve growth factor complementary DNA linked to the K14 keratin promoter. The K14-nerve growth factor transgene (sense or antisense) is abundantly expressed in skin from approximately embryonic day 15 and is then constitutively expressed throughout the life of the animal. In light of the fact that systemic administration of nerve growth factor to neonatal or adult rats leads to hyperalgesia, we have asked whether mice expressing the sense K14-nerve growth factor transgene exhibit similar sensory abnormalities and whether mice expressing the antisense nerve growth factor complementary DNA were hypoalgesic. Here we show that mice over-expressing nerve growth factor in skin display a profound hyperalgesia to noxious mechanical stimulation. Additionally, K14-nerve growth factor antisense mice displayed a profound hypoalgesia to the same stimuli
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Determining and Optimizing the Precision of Quantitative Measurements of Perfusion from Dynamic Contrast Enhanced MRI
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