2,115 research outputs found
Wandering globular clusters: the first dwarf galaxies in the universe?
In the last decade we witness an advent of new types of dwarf stellar systems
in cluding ultra-compact dwarfs, ultra-faint dwarf spheroidals, and exotic
globular clusters, breaking the old simple paradigm for dwarf galaxies and
globular clusters. These objects become more intriguing, and understanding of
these new findings be comes more challenging. Recently we discovered a new type
of large scale structure in the Virgo cluster of galaxies: it is composed of
globular clusters. Globular clusters in Virgo are found wandering between
galaxies (intracluster globular clusters) as well as in galaxies. These
intracluster globular clusters fill a significant fraction in the area of the
Virgo cluster and they are dominated by blue globular clusters. These
intracluster globular clusters may be closely related with the first dwarf
galaxies in the universe.Comment: 6 pages, 3 figures, Conference Proceedings: "A Universe of Dwarf
Galaxies", 14-18 June 2010, Lyon, Franc
UBV stellar photometry of bright stars in GC M5. I. UV colour-magnitude and colour-colour diagrams and some peculiarities in the HB stellar distribution
We present stellar photometry in the UBV passbands for the globular cluster
M5 = NGC5904. The observations, short-exposured photographic plates and CCD
frames, were obtained in the RC-focus of the 2m telescope of the Natl. Astron.
Obs. 'Rozhen'. All stars in an annulus with radius 1 < r < 5.5 arcmin were
measured. We show that the UV CMDs describe different evolutionary stages in a
better manner than the 'classical' (V, B-V) diagram. We use HB stars, with
known spectroscopic Teff, to check the validity of the colour zero-point. A
review of all known UV-bright star candidates in M5 is made and some of their
parameters are catalogued. Six new stars of this kind are suspected on the
basis of their position on the CMD. New assessment of the cluster reddening and
metallicity is done using the (U-B, B-V) diagram. We find [Fe/H]= -1.38, which
confirms the Zinn & West (1984) value contrasting with recent spectroscopic
estimates. In an effort to clarify the question of the gap in the BHB stellar
distribution and to investigate some other peculiarities, we use the relatively
long-base colour index U-V. A comparison of the unreddened (V, U-V)
distribution of HB stars with a canonical ZAHB model (Dorman et al. 1993)
reveals that the hottest stars rise above the model line. We find this similar
to the 'u-jump' found in the Stroemgren photometry (Grundahl et al. 1998,
1999). (U-B)o indeces of 18 BHB stars with (B-V)o in [-0.02, 0.18] were used to
estimate their ultraviolet deficiency. It is shown that low gravity log g < 2
Kurucz's atmospheric models fit well the observed distribution of these stars
along the two-colour diagram.Comment: 9 pages, 7 EPS figures. MNRAS accepte
Condensation in nongeneric trees
We study nongeneric planar trees and prove the existence of a Gibbs measure
on infinite trees obtained as a weak limit of the finite volume measures. It is
shown that in the infinite volume limit there arises exactly one vertex of
infinite degree and the rest of the tree is distributed like a subcritical
Galton-Watson tree with mean offspring probability . We calculate the rate
of divergence of the degree of the highest order vertex of finite trees in the
thermodynamic limit and show it goes like where is the size of the
tree. These trees have infinite spectral dimension with probability one but the
spectral dimension calculated from the ensemble average of the generating
function for return probabilities is given by if the weight
of a vertex of degree is asymptotic to .Comment: 57 pages, 14 figures. Minor change
Search for Invisible Decays of and in and
Using a data sample of decays collected with the BES
II detector at the BEPC, searches for invisible decays of and
in to and are performed.
The signals, which are reconstructed in final states, are used
to tag the and decays. No signals are found for the
invisible decays of either or , and upper limits at the 90%
confidence level are determined to be for the ratio
and for . These are the first
searches for and decays into invisible final states.Comment: 5 pages, 4 figures; Added references, Corrected typo
Observation of Two New N* Peaks in J/psi -> and Decays
The system in decays of is limited to be
isospin 1/2 by isospin conservation. This provides a big advantage in studying
compared with and experiments which mix
isospin 1/2 and 3/2 for the system. Using 58 million decays
collected with the Beijing Electron Positron Collider, more than 100 thousand
events are obtained. Besides two well known
peaks at 1500 MeV and 1670 MeV, there are two new, clear peaks in
the invariant mass spectrum around 1360 MeV and 2030 MeV. They are the
first direct observation of the peak and a long-sought "missing"
peak above 2 GeV in the invariant mass spectrum. A simple
Breit-Wigner fit gives the mass and width for the peak as MeV and MeV, and for the new peak above 2 GeV
as MeV and MeV, respectively
The influence of gene expression time delays on Gierer-Meinhardt pattern formation systems
There are numerous examples of morphogen gradients controlling long range signalling in developmental and cellular systems. The prospect of two such interacting morphogens instigating long range self-organisation in biological systems via a Turing bifurcation has been explored, postulated, or implicated in the context of numerous developmental processes. However, modelling investigations of cellular systems typically neglect the influence of gene expression on such dynamics, even though transcription and translation are observed to be important in morphogenetic systems. In particular, the influence of gene expression on a large class of Turing bifurcation models, namely those with pure kinetics such as the Gierer–Meinhardt system, is unexplored. Our investigations demonstrate that the behaviour of the Gierer–Meinhardt model profoundly changes on the inclusion of gene expression dynamics and is sensitive to the sub-cellular details of gene expression. Features such as concentration blow up, morphogen oscillations and radical sensitivities to the duration of gene expression are observed and, at best, severely restrict the possible parameter spaces for feasible biological behaviour. These results also indicate that the behaviour of Turing pattern formation systems on the inclusion of gene expression time delays may provide a means of distinguishing between possible forms of interaction kinetics. Finally, this study also emphasises that sub-cellular and gene expression dynamics should not be simply neglected in models of long range biological pattern formation via morphogens
Influence of history on saccade countermanding performance in humans and macaque monkeys
AbstractThe stop-signal or countermanding task probes the ability to control action by requiring subjects to withhold a planned movement in response to an infrequent stop signal which they do with variable success depending on the delay of the stop signal. We investigated whether performance of humans and macaque monkeys in a saccade countermanding task was influenced by stimulus and performance history. In spite of idiosyncrasies across subjects several trends were evident in both humans and monkeys. Response time decreased after successive trials with no stop signal. Response time increased after successive trials with a stop signal. However, post-error slowing was not observed. Increased response time was observed mainly or only after cancelled (signal inhibit) trials and not after noncancelled (signal respond) trials. These global trends were based on rapid adjustments of response time in response to momentary fluctuations in the fraction of stop signal trials. The effects of trial sequence on the probability of responding were weaker and more idiosyncratic across subjects when stop signal fraction was fixed. However, both response time and probability of responding were influenced strongly by variations in the fraction of stop signal trials. These results indicate that the race model of countermanding performance requires extension to account for these sequential dependencies and provide a basis for physiological studies of executive control of countermanding saccade performance
Novel universality class of absorbing transitions with continuously varying critical exponents
The well-established universality classes of absorbing critical phenomena are
directed percolation (DP) and directed Ising (DI) classes. Recently, the pair
contact process with diffusion (PCPD) has been investigated extensively and
claimed to exhibit a new type of critical phenomena distinct from both DP and
DI classes. Noticing that the PCPD possesses a long-term memory effect, we
introduce a generalized version of the PCPD (GPCPD) with a parameter
controlling the memory effect. The GPCPD connects the DP fixed point to the
PCPD point continuously. Monte Carlo simulations show that the GPCPD displays
novel type critical phenomena which are characterized by continuously varying
critical exponents. The same critical behaviors are also observed in models
where two species of particles are coupled cyclically. We suggest that the
long-term memory may serve as a marginal perturbation to the ordinary DP fixed
point.Comment: 13 pages + 10 figures (Full paper version
Systematics of pion emission in heavy ion collisions in the 1A GeV regime
Using the large acceptance apparatus FOPI, we study pion emission in the
reactions (energies in GeV/nucleon are given in parentheses): 40Ca+40Ca (0.4,
0.6, 0.8, 1.0, 1.5, 1.93), 96Ru+96Ru (0.4, 1.0, 1.5), 96Zr+96Zr (0.4, 1.0,
1.5), 197Au+197Au (0.4, 0.6, 0.8, 1.0, 1.2, 1.5). The observables include
longitudinal and transverse rapidity distributions and stopping, polar
anisotropies, pion multiplicities, transverse momentum spectra, ratios for
positively and negatively charged pions of average transverse momenta and of
yields, directed flow, elliptic flow. The data are compared to earlier data
where possible and to transport model simulations.Comment: 56 pages,42 figures; to be published in Nuclear Physics
Partial wave analysis of J/\psi \to \gamma \phi \phi
Using events collected in the BESII detector, the
radiative decay is
studied. The invariant mass distribution exhibits a near-threshold
enhancement that peaks around 2.24 GeV/.
A partial wave analysis shows that the structure is dominated by a
state () with a mass of
GeV/ and a width of GeV/. The
product branching fraction is: .Comment: 11 pages, 4 figures. corrected proof for journa
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