25,022 research outputs found
Chemical abundances in LMC stellar populations. II. The bar sample
This paper compares the chemical evolution of the Large Magellanic Cloud
(LMC) to that of the Milky Way (MW) and investigates the relation between the
bar and the inner disc of the LMC in the context of the formation of the bar.
We obtained high-resolution and mid signal-to-noise ratio spectra with
FLAMES/GIRAFFE at ESO/VLT and performed a detailed chemical analysis of 106 and
58 LMC field red giant stars (mostly older than 1 Gyr), located in the bar and
the disc of the LMC respectively. We measured elemental abundances for O, Mg,
Si, Ca, Ti, Na, Sc, V, Cr, Co, Ni, Cu, Y, Zr, Ba, La and Eu. We find that the
{\alpha}-element ratios [Mg/Fe] and [O/Fe] are lower in the LMC than in the MW
while the LMC has similar [Si/Fe], [Ca/Fe], and [Ti/Fe] to the MW. As for the
heavy elements, [Ba,La/Eu] exhibit a strong increase with increasing
metallicity starting from [Fe/H]=-0.8 dex, and the LMC has lower [Y+Zr/Ba+La]
ratios than the MW. Cu is almost constant over all metallicities and about 0.5
dex lower in the LMC than in the MW. The LMC bar and inner disc exhibit
differences in their [{\alpha}/Fe] (slightly larger scatter for the bar in the
metallicity range [-1,-0.5]), their Eu (the bar trend is above the disc trend
for [Fe/H] > -0.5 dex), their Y and Zr, their Na and their V (offset between
bar and disc distributions). Our results show that the chemical history of the
LMC experienced a strong contribution from type Ia supernovae as well as a
strong s-process enrichment from metal-poor AGB winds. Massive stars made a
smaller contribution to the chemical enrichment compared to the MW. The
observed differences between the bar and the disc speak in favour of an episode
of enhanced star formation a few Gyr ago, occurring in the central parts of the
LMC and leading to the formation of the bar. This is in agreement with recently
derived star formation histories.Comment: 22 pages, 20 figures; Accepted for publication in A&
Majorana spinors and extended Lorentz symmetry in four-dimensional theory
An extended local Lorentz symmetry in four-dimensional (4D) theory is
considered. A source of this symmetry is a group of general linear
transformations of four-component Majorana spinors GL(4,M) which is isomorphic
to GL(4,R) and is the covering of an extended Lorentz group in a 6D Minkowski
space M(3,3) including superluminal and scaling transformations. Physical
space-time is assumed to be a 4D pseudo-Riemannian manifold. To connect the
extended Lorentz symmetry in the M(3,3) space with the physical space-time, a
fiber bundle over the 4D manifold is introduced with M(3,3) as a typical fiber.
The action is constructed which is invariant with respect to both general 4D
coordinate and local GL(4,M) spinor transformations. The components of the
metric on the 6D fiber are expressed in terms of the 4D pseudo-Riemannian
metric and two extra complex fields: 4D vector and scalar ones. These extra
fields describe in the general case massive particles interacting with an extra
U(1) gauge field and weakly interacting with ordinary particles, i.e.
possessing properties of invisible (dark) matter.Comment: 24 page
Resonant optical electron transfer in one-dimensional multiwell structures
We consider coherent single-electron dynamics in the one-dimensional
nanostructure under resonant electromagnetic pulse. The structure is composed
of two deep quantum wells positioned at the edges of structure and separated by
a sequence of shallow internal wells. We show that complete electron transfer
between the states localized in the edge wells through one of excited
delocalized states can take place at discrete set of times provided that the
pulse frequency matches one of resonant transition frequencies. The transfer
time varies from several tens to several hundreds of picoseconds and depends on
the structure and pulse parameters. The results obtained in this paper can be
applied to the developments of the quantum networks used in quantum
communications and/or quantum information processing.Comment: 25 pages,16 figure
Measuring the temperature dependence of individual two-level systems by direct coherent control
We demonstrate a new method to directly manipulate the state of individual
two-level systems (TLS) in phase qubits. It allows one to characterize the
coherence properties of TLS using standard microwave pulse sequences, while the
qubit is used only for state readout. We apply this method to measure the
temperature dependence of TLS coherence for the first time. The energy
relaxation time is found to decrease quadratically with temperature for
the two TLS studied in this work, while their dephasing time measured in Ramsey
and spin-echo experiments is found to be limited at all temperatures.Comment: 4 pages, 5 figure
Emission of charged particles from excited compound nuclei
The formation of excited compound nucleus (CN) and its statistical decay is
investigated within the dinuclear system (DNS) model.The initial DNS is formed
in the entrance channel when the projectile is captured by a target, and then
the evolution of DNS in mass asymmetry coordinate leads to formation of the hot
CN. The emission barriers for complex fragments were calculated within the DNS
model by using the double folding procedure for the interaction potential. It
is shown that cross sections for complex fragment emission become larger when
excited CN is more neutron deficient. This approach gives also an opportunity
to calculate the new neutron deficient isotopes production cross sections and
can be applied to describe the hot fission of heavy systems.The model was
tested by comparison of calculated results with experimental dat
Entangling microscopic defects via a macroscopic quantum shuttle
In the microscopic world, multipartite entanglement has been achieved with
various types of nanometer sized two-level systems such as trapped ions, atoms
and photons. On the macroscopic scale ranging from micrometers to millimeters,
recent experiments have demonstrated bipartite and tripartite entanglement for
electronic quantum circuits with superconducting Josephson junctions. It
remains challenging to bridge these largely different length scales by
constructing hybrid quantum systems. Doing this may allow for manipulating the
entanglement of individual microscopic objects separated by macroscopically
large distances in a quantum circuit. Here we report on the experimental
demonstration of induced coherent interaction between two intrinsic two-level
states (TLSs) formed by atomic-scale defects in a solid via a superconducting
phase qubit. The tunable superconducting circuit serves as a shuttle
communicating quantum information between the two microscopic TLSs. We present
a detailed comparison between experiment and theory and find excellent
agreement over a wide range of parameters. We then use the theoretical model to
study the creation and movement of entanglement between the three components of
the quantum system.Comment: 11 pages, 5 figure
Quantitative evaluation of defect-models in superconducting phase qubits
We use high-precision spectroscopy and detailed theoretical modelling to
determine the form of the coupling between a superconducting phase qubit and a
two-level defect. Fitting the experimental data with our theoretical model
allows us to determine all relevant system parameters. A strong qubit-defect
coupling is observed, with a nearly vanishing longitudinal component. Using
these estimates, we quantitatively compare several existing theoretical models
for the microscopic origin of two-level defects.Comment: 3 pages, 2 figures. Supplementary material, lclimits_supp.pd
Rare earth spin ensemble magnetically coupled to a superconducting resonator
Interfacing superconducting quantum processors, working in the GHz frequency
range, with optical quantum networks and atomic qubits is a challenging task
for the implementation of distributed quantum information processing as well as
for quantum communication. Using spin ensembles of rare earth ions provide an
excellent opportunity to bridge microwave and optical domains at the quantum
level. In this letter, we demonstrate magnetic coupling of Er spins
doped in YSiO crystal to a high-Q coplanar superconducting
resonator.Comment: 5 pages, 3 figure
Is BMI alone a sufficient outcome to evaluate interventions for child obesity?
BACKGROUND: BMI is often used to evaluate the effectiveness of childhood obesity interventions, but such interventions may have additional benefits independent of effects on adiposity. We investigated whether benefits to health outcomes following the Mind, Exercise, Nutrition…Do It! (MEND) childhood obesity intervention were independent of or associated with changes in zBMI.
METHODS: A total of 79 obese children were measured at baseline; 71 and 42 participants were followed-up at 6 and 12 months respectively, and split into four groups depending on magnitude of change in zBMI. Differences between groups for waist circumference, cardiovascular fitness, physical and sedentary activities, and self-esteem were investigated.
RESULTS: Apart from waist circumference and its z-score, there were no differences or trends across zBMI subgroups for any outcome. Independent of the degree of zBMI change, benefits in several parameters were observed in children participating in this obesity intervention.
CONCLUSION: We concluded that isolating a single parameter like zBMI change and neglecting other important outcomes is restrictive and may undermine the evaluation of childhood obesity intervention effectiveness
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