1,913 research outputs found
UCD Candidates in the Hydra Cluster
NGC 3311, the giant cD galaxy in the Hydra cluster (A1060), has one of the
largest globular cluster systems known. We describe new Gemini GMOS (g',i')
photometry of the NGC 3311 field which reveals that the red, metal-rich side of
its globular cluster population extends smoothly upward into the mass range
associated with the new class of Ultra-Compact Dwarfs (UCDs). We identify 29
UCD candidates with estimated masses > 6x10^6 solar masses and discuss their
characteristics. This UCD-like sequence is the most well defined one yet seen,
and reinforces current ideas that the high-mass end of the globular cluster
sequence merges continuously into the UCD sequence, which connects in turn to
the E galaxy structural sequence.Comment: 5 pages, 3 figures. Accepted for publication in ApJ Letter
A model of ant route navigation driven by scene familiarity
In this paper we propose a model of visually guided route navigation in ants that captures the known properties of real behaviour whilst retaining mechanistic simplicity and thus biological plausibility. For an ant, the coupling of movement and viewing direction means that a familiar view specifies a familiar direction of movement. Since the views experienced along a habitual route will be more familiar, route navigation can be re-cast as a search for familiar views. This search can be performed with a simple scanning routine, a behaviour that ants have been observed to perform. We test this proposed route navigation strategy in simulation, by learning a series of routes through visually cluttered environments consisting of objects that are only distinguishable as silhouettes against the sky. In the first instance we determine view familiarity by exhaustive comparison with the set of views experienced during training. In further experiments we train an artificial neural network to perform familiarity discrimination using the training views. Our results indicate that, not only is the approach successful, but also that the routes that are learnt show many of the characteristics of the routes of desert ants. As such, we believe the model represents the only detailed and complete model of insect route guidance to date. What is more, the model provides a general demonstration that visually guided routes can be produced with parsimonious mechanisms that do not specify when or what to learn, nor separate routes into sequences of waypoints
Probability tree algorithm for general diffusion processes
Motivated by path-integral numerical solutions of diffusion processes,
PATHINT, we present a new tree algorithm, PATHTREE, which permits extremely
fast accurate computation of probability distributions of a large class of
general nonlinear diffusion processes
Tsirelson bounds for generalized Clauser-Horne-Shimony-Holt inequalities
Quantum theory imposes a strict limit on the strength of non-local
correlations. It only allows for a violation of the CHSH inequality up to the
value 2 sqrt(2), known as Tsirelson's bound. In this note, we consider
generalized CHSH inequalities based on many measurement settings with two
possible measurement outcomes each. We demonstrate how to prove Tsirelson
bounds for any such generalized CHSH inequality using semidefinite programming.
As an example, we show that for any shared entangled state and observables
X_1,...,X_n and Y_1,...,Y_n with eigenvalues +/- 1 we have | + <X_2
Y_1> + + + ... + - | <= 2 n
cos(pi/(2n)). It is well known that there exist observables such that equality
can be achieved. However, we show that these are indeed optimal. Our approach
can easily be generalized to other inequalities for such observables.Comment: 9 pages, LateX, V2: Updated reference [3]. To appear in Physical
Review
On the connection between Complementarity and Uncertainty Principles in the Mach-Zehnder interferometric setting
We revisit, in the framework of Mach-Zehnder interferometry, the connection
between the complementarity and uncertainty principles of quantum mechanics.
Specifically, we show that, for a pair of suitably chosen observables, the
trade-off relation between the complementary path information and fringe
visibility is equivalent to the uncertainty relation given by Schr\"odinger
and Robertson, and to the one provided by Landau and Pollak as well. We also
employ entropic uncertainty relations (based on R\'enyi entropic measures) and
study their meaning for different values of the entropic parameter. We show
that these different values define regimes which yield qualitatively different
information concerning the system, in agreement with findings of [A. Luis,
Phys. Rev. A 84, 034101 (2011)]. We find that there exists a regime for which
the entropic uncertinty relations can be used as criteria to pinpoint non
trivial states of minimum uncertainty.Comment: 7 pages, 2 figure
The Globular Cluster Systems around NGC 3311 and NGC 3309
We present extensive new photometry in (g',i') of the large globular cluster
(GC) system around NGC 3311, the central cD galaxy in the Hydra cluster. Our
GMOS data cover a 5.5' field of view and reach a limiting magnitude i' = 26,
about 0.5 magnitude fainter than the turnover point of the GC luminosity
function. We find that NGC 3311 has a huge population of ~16, 000 GCs, closely
similar to the prototypical high specific frequency Virgo giant M87. The
color-magnitude distribution shows that the metal-poor blue GC sequence and the
metal-richer red sequence are both present, with nearly equal numbers of
clusters. Bimodal fits to the color distributions confirm that the blue
sequence shows the same trend of progressively increasing metallicity with GC
mass that has previously been found in many other large galaxies; the
correlation we find corresponds to a scaling of GC metallicity with mass of Z ~
M^0.6 . By contrast, the red sequence shows no change of mean metallicity with
mass, but it shows an upward extension to much higher than normal luminosity
into the UCD-like range, strengthening the potential connections between
massive GCs and UCDs. The GC luminosity function, which we measure down to the
turnover point at M_I = -8.4, also has a normal form like those in other giant
ellipticals. Within the Hydra field, another giant elliptical NGC 3309 is
sitting just 100" from the cD NGC 3311. We use our data to solve simultaneously
for the spatial structure and total GC populations of both galaxies at once.
Their specific frequencies are S_N (NGC 3311) = 12.5 +/- 1.5 and S_N (NGC 3309)
= 0.6 +/-0.4. NGC 3311 is completely dominant and entirely comparable with
other cD-type systems such as M87 in Virgo.Comment: 15 pages, 15 figures. Accepted to the Astrophysical Journal. Version
with higher resolution figures is available at
http://www.thewehners.net/astro/papers/wehner_n3311_highres.pd
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