5,559 research outputs found
Deep hypothermic circulatory arrest for the surgical treatment of complicated adult coarctation
Faint X-ray Sources in the Globular Cluster Terzan 5
We report our analysis of a Chandra X-ray observation of the rich globular
cluster Terzan 5, in which we detect 50 sources to a limiting 1.0-6 keV X-ray
luminosity of 3*10^{31} ergs/s within the half-mass radius of the cluster.
Thirty-three of these have L_X>10^{32} ergs/s, the largest number yet seen in
any globular cluster. In addition to the quiescent low-mass X-ray binary (LMXB,
identified by Wijnands et al.), another 12 relatively soft sources may be
quiescent LMXBs. We compare the X-ray colors of the harder sources in Terzan 5
to the Galactic Center sources studied by Muno and collaborators, and find the
Galactic Center sources to have harder X-ray colors, indicating a possible
difference in the populations. We cannot clearly identify a metallicity
dependence in the production of low-luminosity X-ray binaries in Galactic
globular clusters, but a metallicity dependence of the form suggested by Jordan
et al. for extragalactic LMXBs is consistent with our data.Comment: 15 pages, 10 figures (3 color). Resubmitted to ApJ after
incorporating referee comments. v2: Added references to introductio
Domino tilings and the six-vertex model at its free fermion point
At the free-fermion point, the six-vertex model with domain wall boundary
conditions (DWBC) can be related to the Aztec diamond, a domino tiling problem.
We study the mapping on the level of complete statistics for general domains
and boundary conditions. This is obtained by associating to both models a set
of non-intersecting lines in the Lindstroem-Gessel-Viennot (LGV) scheme. One of
the consequence for DWBC is that the boundaries of the ordered phases are
described by the Airy process in the thermodynamic limit.Comment: 14 pages, 8 figure
Doping Dependence of Polaron Hopping Energies in La(1-x)Ca(x)MnO(3) (0<= x<= 0.15)
Measurements of the low-frequency (f<= 100 kHz) permittivity at T<= 160 K and
dc resistivity (T<= 430 K) are reported for La(1-x)Ca(x)MnO(3) (0<= x<= 0.15).
Static dielectric constants are determined from the low-T limiting behavior of
the permittivity. The estimated polarizability for bound holes ~ 10^{-22}
cm^{-3} implies a radius comparable to the interatomic spacing, consistent with
the small polaron picture established from prior transport studies near room
temperature and above on nearby compositions. Relaxation peaks in the
dielectric loss associated with charge-carrier hopping yield activation
energies in good agreement with low-T hopping energies determined from
variable-range hopping fits of the dc resistivity. The doping dependence of
these energies suggests that the orthorhombic, canted antiferromagnetic ground
state tends toward an insulator-metal transition that is not realized due to
the formation of the ferromagnetic insulating state near Mn(4+) concentration ~
0.13.Comment: PRB in press, 5 pages, 6 figure
Chandra X-ray Sources in the Collapsed-Core Globular Cluster M30 (NGC 7099)
We report the detection of six discrete, low-luminosity (Lx < 10^33 erg/s)
X-ray sources, located within 12 arcsec of the center of the collapsed-core
globular cluster M30 (NGC 7099), and a total of 13 sources within the half-mass
radius, from a 50 ksec Chandra ACIS-S exposure. Three sources lie within the
very small upper limit of 1.9 arcsec on the core radius. The brightest of the
three core sources has a luminosity of Lx (0.5-6 keV) = 6x10^32 erg/s and a
blackbody-like soft X-ray spectrum, which are both consistent with it being a
quiescent low-mass X-ray binary (qLMXB). We have identified optical
counterparts to four of the six central sources and a number of the outlying
sources, using deep Hubble Space Telescope and ground-based imaging. While the
two proposed counterparts that lie within the core may represent chance
superpositions, the two identified central sources that lie outside of the core
have X-ray and optical properties consistent with being CVs. Two additional
sources outside of the core have possible active binary counterparts. We
discuss the X-ray source population of M30 in light of its collapsed-core
status.Comment: 18 pages, 13 figures (8 color), resubmitted to ApJ after
incorporating referee comment
Constraints and Period Relations in Bosonic Strings at Genus-g
We examine some of the implications of implementing the usual boundary
conditions on the closed bosonic string in the hamiltonian framework. Using the
KN formalism, it is shown that at the quantum level, the resulting constraints
lead to relations among the periods of the basis 1-forms. These are compared
with those of Riemanns' which arise from a different consideration.Comment: 16 pages, (Plain Tex), NUS/HEP/9320
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