3,395 research outputs found
Unveiling hidden structures in the Coma cluster
We have assembled a large data-set of 613 galaxy redshifts in the Coma
cluster, the largest presently available for a cluster of galaxies. We have
defined a sample of cluster members complete to b, using a
membership criterion based on the galaxy velocity, when available, or on the
galaxy magnitude and colour, otherwise. Such a data set allows us to define
nearly complete samples within a region of 1~\Mpc\ radius, with a sufficient
number of galaxies per sample to make statistical analyses possible. Using this
sample and the {\em ROSAT} PSPC X--ray image of the cluster, we have
re-analyzed the structure and kinematics of Coma, by applying the wavelet and
adaptive kernel techniques. A striking coincidence of features is found in the
distributions of galaxies and hot intracluster gas. The two central dominant
galaxies, NGC4874 and NGC4889, are surrounded by two galaxy groups, mostly
populated with galaxies brighter than b and well separated in
velocity space. On the contrary, the fainter galaxies tend to form a single
smooth structure with a central peak coinciding in position with a secondary
peak detected in X--rays, and located between the two dominant galaxies; we
suggest to identify this structure with the main body of the Coma cluster. A
continuous velocity gradient is found in the central distribution of these
faint galaxies, a probable signature of tidal interactions rather than
rotation. There is evidence for a bound population of bright galaxies around
other brightest cluster members. Altogether, the Coma cluster structure seems
to be better traced by the faint galaxy population, the bright galaxies being
located in subclusters. We discuss this evidence in terms of an ongoing
accretion of groups onto the cluster.Comment: to appear in A&A, 19 pages, uuencoded gzipped postscript fil
The replacement histone H2A.Z in a hyperacetylated form is a feature of active genes in the chicken
The replacement histone H2A.Z is variously reported
as being linked to gene expression and preventing the
spread of heterochromatin in yeast, or concentrated
at heterochromatin in mammals. To resolve this
apparent dichotomy, affinity-purified antibodies
against the N-terminal region of H2A.Z, in both a triacetylatedandnon-
acetylatedstate, areusedin native
chromatin immmuno-precipitation experiments with
mononucleosomes from three chicken cell types. The
hyperacetylated species concentrates at the 50 end of
active genes, both tissue specific and housekeeping
but is absent from inactive genes, while the
unacetylated form is absent from both active and
inactive genes. A concentration of H2A.Z is also
found at insulators under circumstances implying a
link to barrier activity but not to enhancer blocking.
Although acetylated H2A.Z is widespread throughout
the interphase genome, at mitosis its acetylation is
erased, the unmodified form remaining. Thus,
although H2A.Z may operate as an epigenetic marker
for active genes, its N-terminal acetylation does not
The replacement histone H2A.Z in a hyperacetylated form is a feature of active genes in the chicken
The replacement histone H2A.Z is variously reported
as being linked to gene expression and preventing the
spread of heterochromatin in yeast, or concentrated
at heterochromatin in mammals. To resolve this
apparent dichotomy, affinity-purified antibodies
against the N-terminal region of H2A.Z, in both a triacetylatedandnon-
acetylatedstate, areusedin native
chromatin immmuno-precipitation experiments with
mononucleosomes from three chicken cell types. The
hyperacetylated species concentrates at the 50 end of
active genes, both tissue specific and housekeeping
but is absent from inactive genes, while the
unacetylated form is absent from both active and
inactive genes. A concentration of H2A.Z is also
found at insulators under circumstances implying a
link to barrier activity but not to enhancer blocking.
Although acetylated H2A.Z is widespread throughout
the interphase genome, at mitosis its acetylation is
erased, the unmodified form remaining. Thus,
although H2A.Z may operate as an epigenetic marker
for active genes, its N-terminal acetylation does not
Innovative Configuration for a Far Infrared Space Interferometer
In the last ten years many proposals and studies have been advanced for a far-IR kilometer baseline interferometer. This paper shows the results of FISICA (Far Infrared Space Interferometer Critical Assessment), an FP7 program of the European Community. In particular, we focus on an innovative strategy to cover the plane of observation with a minimal propellant consumption. Results of some numerical simulations, carried out for a three-booms configuration, are provided
Size of Outbreaks Near the Epidemic Threshold
The spread of infectious diseases near the epidemic threshold is
investigated. Scaling laws for the size and the duration of outbreaks
originating from a single infected individual in a large susceptible population
are obtained. The maximal size of an outbreak n_* scales as N^{2/3} with N the
population size. This scaling law implies that the average outbreak size
scales as N^{1/3}. Moreover, the maximal and the average duration of an
outbreak grow as t_* ~ N^{1/3} and ~ ln N, respectively.Comment: 4 pages, 5 figure
Circuits in random graphs: from local trees to global loops
We compute the number of circuits and of loops with multiple crossings in
random regular graphs. We discuss the importance of this issue for the validity
of the cavity approach. On the one side we obtain analytic results for the
infinite volume limit in agreement with existing exact results. On the other
side we implement a counting algorithm, enumerate circuits at finite N and draw
some general conclusions about the finite N behavior of the circuits.Comment: submitted to JSTA
γδ TCRs Function as Innate-like Receptors in the Bovine γδ T Cell Response against Leptospira
The Cretaceous-Palaeogene (K/P) boundary in the Aïn Settara section (Kalaat Senan, Central Tunisia): lithological, micropalaeontological and geochemical evidence
The Cretaceous-Palaeogene (K/P) boundary, until recently known as the "Cretaceous-Tertiary" or K/T boundary, is well exposed at Aïn Settara in the Kalaat Senan area (Central Tunisia), 50 km south of the El Kef section. Micropalaeontological and geochemical studies led to the identification of six main features tentatively named "events", which characterise the K/P boundary interval, and of which at least two (B and C) have global significance. The lowermost event A located at about 14 cm below the base of the Dark Boundary Clay is marked by a sudden increase in tiny bioturbations, by small nodules and a few macrofossils, a 50% drop in calcareous nannofossil abundance and an increase in Scytinascias (organic linings of foraminifera). It is thought to witness a slowdown in sedimentation. Event B is characterised by a burrowed surface, separating the ca 60-cm thick Dark Boundary Clay from the underlying Aïn Settara marls. It indicates an episode of nondeposition, just before a major change in lithology from marls to clays, corresponding to a major flooding. No substantial palaeontological changes have been recorded in relation to this event. Event C is characterised by maximum concentrations of Ir and Ni-rich spinels, which have been observed in platy nodules, similar to the level at El Kef (K/P boundary sensu ODIN, 1992). It coincides with a major extinction in planktonic foraminiferal species (71%) and a 60% drop in nannofossil abundance. The change in lithology (occurrence of small ripples and channel-like structures) recorded at event D, a few cm up-section, might be related to a locally recorded storm activity. Events E and F, which are situated higher up in the Dark Boundary Clay, are mainly determined by palaeontological changes (palynomorphs and nannofossils), probably resulting from small sea-level variations. The coincidence of the cosmic markers with the major biotic changes at event C pleads for the asteroid impact hypothesis. Their disjunction from the base of the Dark Boundary Clay shows that the change of lithology usually used to determine the K-P boundary is distinct from the major extinction (in the planktonic realm), classically referred to this boundary and linked to the presence of cosmic markers. These results argue the need for the revaluation of the K-P boundary GSSP at El Kef. It is suggested to redefine the K-P boundary at the level of coincidence of the major biotic changes and the cosmic markers
Solar-like oscillations in a massive star
Seismology of stars provides insight into the physical mechanisms taking
place in their interior, with modes of oscillation probing different layers.
Low-amplitude acoustic oscillations excited by turbulent convection were
detected four decades ago in the Sun and more recently in low-mass
main-sequence stars. Using data gathered by the Convection Rotation and
Planetary Transits mission, we report here on the detection of solar-like
oscillations in a massive star, V1449 Aql, which is a known large-amplitude (b
Cephei) pulsator.Comment: Published in Sience, 19 June 2009, vol. 324, p. 154
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