2,622 research outputs found
Building up the Stellar Halo of the Galaxy
We study numerical simulations of satellite galaxy disruption in a potential
resembling that of the Milky Way. Our goal is to assess whether a merger origin
for the stellar halo would leave observable fossil structure in the phase-space
distribution of nearby stars. We show how mixing of disrupted satellites can be
quantified using a coarse-grained entropy. Although after 10 Gyr few obvious
asymmetries remain in the distribution of particles in configuration space,
strong correlations are still present in velocity space. We give a simple
analytic description of these effects, based on a linearised treatment in
action-angle variables, which shows how the kinematic and density structure of
the debris stream changes with time. By applying this description we find that
a single satellite of current luminosity 10^8 L_\sun disrupted 10 Gyr ago
from an orbit circulating in the inner halo (mean apocentre kpc)
would contribute about kinematically cold streams with internal
velocity dispersions below 5 km/s to the local stellar halo. If the whole
stellar halo were built by disrupted satellites, it should consist locally of
300 - 500 such streams. Clear detection of all these structures would require a
sample of a few thousand stars with 3-D velocities accurate to better than 5
km/s. Even with velocity errors several times worse than this, the expected
clumpiness should be quite evident. We apply our formalism to a group of stars
detected near the North Galactic Pole, and derive an order of magnitude
estimate for the initial properties of the progenitor system.Comment: 28 pages, 10 figures, minor changes, matches the version to appear in
MNRAS, Vol. 307, p.495-517 (August 1999
The VIMOS VLT Deep Survey: Tracing the galaxy stellar mass assembly history over the last 8Gyr
We selected a mass-limited sample of 4048 objects from the VIMOS VLT Deep
Survey in the redshift interval 0.5<z<1.3. We used the amplitude of the 4000
Balmer break (Dn4000) to separate the galaxy population and the EW[OII]3727
line as proxy for the star formation activity. We discuss to what extent
stellar mass drives galaxy evolution, showing for the first time the interplay
between stellar ages and stellar masses over the past 8Gyr. Low-mass galaxies
have small Dn4000 and at increasing stellar mass, the galaxy distribution moves
to higher Dn4000 values as observed in the local Universe. As cosmic time goes
by, we witness an increasing abundance of massive spectroscopically ET systems
at the expense of the LT systems. This spectral transformation is a process
started at early epochs and continuing efficiently down to the local Universe.
This is confirmed by the evolution of our type-dependent stellar mass function.
The underlying stellar ages of LT galaxies apparently do not show evolution,
likely as a result of a continuous formation of new stars. All star formation
activity indicators consistently point towards a star formation history peaked
in the past for massive galaxies, with little or no residual star formation
taking place in the most recent epochs. The activity and efficiency of forming
stars are mechanisms that depend on stellar mass, and the mass assembly becomes
progressively less efficient in massive systems as time elapses. The concepts
of star formation downsizing and mass assembly downsizing describe a single
scenario that has a top-down evolutionary pattern. The role of (dry) merging
events seems to be only marginal at z<1.3, as our estimated efficiency in
stellar mass assembly can possibly account for the progressive accumulation of
passively evolving galaxies.Comment: Accepted for pubblication in A&A, 14 pages, 5 figure
The physics of dipolar bosonic quantum gases
This article reviews the recent theoretical and experimental advances in the
study of ultracold gases made of bosonic particles interacting via the
long-range, anisotropic dipole-dipole interaction, in addition to the
short-range and isotropic contact interaction usually at work in ultracold
gases. The specific properties emerging from the dipolar interaction are
emphasized, from the mean-field regime valid for dilute Bose-Einstein
condensates, to the strongly correlated regimes reached for dipolar bosons in
optical lattices.Comment: Review article, 71 pages, 35 figures, 350 references. Submitted to
Reports on Progress in Physic
The Pierre Auger Observatory III: Other Astrophysical Observations
Astrophysical observations of ultra-high-energy cosmic rays with the Pierre
Auger ObservatoryComment: Contributions to the 32nd International Cosmic Ray Conference,
Beijing, China, August 201
Regular dorsal dimples and damaged mites of Varroa destructor in some Iranian honey bees (Apis mellifera)
The frequency of damaged Varroadestructor Anderson and Trueman (Mesostigmata: Varroidae) found on the bottom board of hives of the honey bee, Apis mellifera L. (Hymenoptera: Apidae) has been used as an indicator of the degree of tolerance or resistance of honey bee colonies against mites. However, it is not clear that this measure is adequate. These injuries should be separated from regular dorsal dimples that have a developmental origin. To investigate damage to Varroa mites and regular dorsal dimples, 32 honey bee (A. mellifera) colonies were selected from four Iranian provinces: Isfahan, Markazi, Qazvin, and Tehran. These colonies were part of the National Honey bee Breeding Program that resulted in province-specific races. In April, Varroa mites were collected from heavily infested colonies and used to infest the 32 experimental colonies. In August, 20 of these colonies were selected (five colonies from each province). Adult bees from these colonies were placed in cages and after introducing mites, damaged mites were collected from each cage every day. The average percentage of injured mites ranged from 0.6 to 3.0% in four provinces. The results did not show any statistical differences between the colonies within provinces for injuries to mites, but there were some differences among province-specific lines. Two kinds of injuries to the mites were observed: injuries to legs and pedipalps, and injuries to other parts of the body. There were also some regular dorsal dimples on dorsal idiosoma of the mites that were placed in categories separate from mites damaged by bees. This type of classification helps identifying damage to mites and comparing them with developmental origin symptoms, and may provide criteria for selecting bees tolerant or resistant to this mite
State space modelling and data analysis exercises in LISA Pathfinder
LISA Pathfinder is a mission planned by the European Space Agency to test the
key technologies that will allow the detection of gravitational waves in space.
The instrument on-board, the LISA Technology package, will undergo an
exhaustive campaign of calibrations and noise characterisation campaigns in
order to fully describe the noise model. Data analysis plays an important role
in the mission and for that reason the data analysis team has been developing a
toolbox which contains all the functionalities required during operations. In
this contribution we give an overview of recent activities, focusing on the
improvements in the modelling of the instrument and in the data analysis
campaigns performed both with real and simulated data.Comment: Plenary talk presented at the 9th International LISA Symposium, 21-25
May 2012, Pari
Quantum entanglement and disentanglement of multi-atom systems
We present a review of recent research on quantum entanglement, with special
emphasis on entanglement between single atoms, processing of an encoded
entanglement and its temporary evolution. Analysis based on the density matrix
formalism are described. We give a simple description of the entangling
procedure and explore the role of the environment in creation of entanglement
and in disentanglement of atomic systems. A particular process we will focus on
is spontaneous emission, usually recognized as an irreversible loss of
information and entanglement encoded in the internal states of the system. We
illustrate some certain circumstances where this irreversible process can in
fact induce entanglement between separated systems. We also show how
spontaneous emission reveals a competition between the Bell states of a two
qubit system that leads to the recently discovered "sudden" features in the
temporal evolution of entanglement. An another problem illustrated in details
is a deterministic preparation of atoms and atomic ensembles in long-lived
stationary squeezed states and entangled cluster states. We then determine how
to trigger the evolution of the stable entanglement and also address the issue
of a steered evolution of entanglement between desired pairs of qubits that can
be achieved simply by varying the parameters of a given system.Comment: Review articl
Measurements of branching fraction ratios and CP-asymmetries in suppressed B^- -> D(-> K^+ pi^-)K^- and B^- -> D(-> K^+ pi^-)pi^- decays
We report the first reconstruction in hadron collisions of the suppressed
decays B^- -> D(-> K^+ pi^-)K^- and B^- -> D(-> K^+ pi^-)pi^-, sensitive to the
CKM phase gamma, using data from 7 fb^-1 of integrated luminosity collected by
the CDF II detector at the Tevatron collider. We reconstruct a signal for the
B^- -> D(-> K^+ pi^-)K^- suppressed mode with a significance of 3.2 standard
deviations, and measure the ratios of the suppressed to favored branching
fractions R(K) = [22.0 \pm 8.6(stat)\pm 2.6(syst)]\times 10^-3, R^+(K) =
[42.6\pm 13.7(stat)\pm 2.8(syst)]\times 10^-3, R^-(K)= [3.8\pm 10.3(stat)\pm
2.7(syst]\times 10^-3, as well as the direct CP-violating asymmetry A(K) =
-0.82\pm 0.44(stat)\pm 0.09(syst) of this mode. Corresponding quantities for
B^- -> D(-> K^+ pi^-)pi^- decay are also reported.Comment: 8 pages, 1 figure, accepted by Phys.Rev.D Rapid Communications for
Publicatio
Measurement of branching ratio and Bs0 lifetime in the decay Bs0 -> J/psi f0(980) at CDF
We present a study of Bs0 decays to the CP-odd final state J/psi f0(980) with
J/psi -> mu+ mu- and f0(980) -> pi+ pi-. Using ppbar collision data with an
integrated luminosity of 3.8/fb collected by the CDF II detector at the
Tevatron we measure a Bs0 lifetime of tau(Bs0 -> J/psi f0(980)) = 1.70
-0.11+0.12(stat) +-0.03(syst) ps. This is the first measurement of the Bs0
lifetime in a decay to a CP eigenstate and corresponds in the standard model to
the lifetime of the heavy Bs0 eigenstate. We also measure the product of
branching fractions of Bs0 -> J/psi f0(980) and f0(980) -> pi+ pi- relative to
the product of branching fractions of Bs0 -> J/psi phi and phi -> K+ K- to be
R_f0/phi = 0.257 +_0.020(stat) +-0.014(syst), which is the most precise
determination of this quantity to date.Comment: accepted by Phys. Rev.
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