36,386 research outputs found
Loading of a Bose-Einstein condensate in the boson-accumulation regime
We study the optical loading of a trapped Bose-Einstein condensate by
spontaneous emission of atoms in excited electronic state in the
Boson-Accumulation Regime. We generalize the previous simplified analysis of
ref. [Phys. Rev. A 53, 2466 (1996)], to a 3D case in which more than one trap
level of the excited state trap is considered. By solving the corresponding
quantum many-body master equation, we demonstrate that also for this general
situation the photon reabsorption can help to increase the condensate fraction.
Such effect could be employed to realize a continuous atom laser, and to
overcome condensate losses.Comment: 7 pages, 5 eps figures, uses epl.st
Optical-NIR analysis of globular clusters in the IKN dwarf spheroidal: a complex star formation history
Age, metallicity and spatial distribution of globular clusters (GCs) provide
a powerful tool to reconstruct major star-formation episodes in galaxies. IKN
is a faint dwarf spheroidal (dSph) in the M81 group of galaxies. It contains
five old GCs, which makes it the galaxy with the highest known specific
frequency (SN=126). We estimate the photometric age, metallicity and spatial
distribution of the poorly studied IKN GCs. We search SDSS for GC candidates
beyond the HST field of view, which covers half of IKN. To break the
age-metallicity degeneracy in the V-I colour we use WHT/LIRIS Ks-band
photometry and derive photometric ages and metallicities by comparison with SSP
models in the V,I,Ks colour space. IKN GCs' VIKs colours are consistent with
old ages ( Gyr) and a metallicity distribution with a higher mean than
typical for such a dSph ([Fe/H dex). Their
photometric masses range () implies
a high mass ratio between GCs and field stars, of . Mixture model
analysis of the RGB field stars' metallicity suggests that 72\% of the stars
may have formed together with the GCs. Using the most massive GC-SFR relation
we calculate a SFR of yr during its formation epoch. We note
that the more massive GCs are closer to the galaxy photometric centre. IKN GCs
also appear spatially aligned along a line close to the IKN major-axis and
nearly orthogonal to the plane of spatial distribution of galaxies in the M81
group. We identify one new IKN GC candidate based on colour and PSF analysis of
the SDSS data. The evidence towards i) broad and high metallicity distribution
of the field IKN RGB stars and its GCs, ii) high fraction and iii), spatial
alignment of IKN GCs, supports a scenario for tidally triggered complex IKN's
SFH in the context of interactions with galaxies in the M81 group.Comment: 12 pages, 9 figures, accepted to A&
Quantum interference-induced stability of repulsively bound pairs of excitations
We study the dynamics of two types of pairs of excitations which are bound
despite their strong repulsive interaction. One corresponds to doubly occupied
sites in one-dimensional Bose-Hubbard systems, the so-called doublons. The
other is pairs of neighboring excited spins in anisotropic Heisenberg spin-1/2
chains. We investigate the possibility of decay of the bound pairs due to
resonant scattering by a defect or due to collisions of the pairs. We find that
the amplitudes of the corresponding transitions are very small. This is a
result of destructive quantum interference and explains the stability of the
bound pairs.Comment: 12 pages, 3 figure
Many-particle confinement by constructed disorder and quantum computing
Many-particle confinement (localization) is studied for a 1D system of
spinless fermions with nearest-neighbor hopping and interaction, or
equivalently, for an anisotropic Heisenberg spin-1/2 chain. This system is
frequently used to model quantum computers with perpetually coupled qubits. We
construct a bounded sequence of site energies that leads to strong
single-particle confinement of all states on individual sites. We show that
this sequence also leads to a confinement of all many-particle states in an
infinite system for a time that scales as a high power of the reciprocal
hopping integral. The confinement is achieved for strong interaction between
the particles while keeping the overall bandwidth of site energies
comparatively small. The results show viability of quantum computing with
time-independent qubit coupling.Comment: An invited paper for the topical issue of J. Opt. B on quantum
contro
New family of potentials with analytical twiston-like solutions
In this letter we present a new approach to find analytical twiston models.
The effective two-field model was constructed by a non-trivial combination of
two one field systems. In such an approach we successfully build analytical
models which are satisfied by a combination of two defect-like solutions, where
one is responsible to twist the molecular chain by , while the other
implies in a longitudinal movement. Such a longitudinal movement can be fitted
to have the size of the distance between adjacent molecular groups. The
procedure works nicely and can be used to describe the dynamics of several
other molecular chains.Comment: 7 pages, 3 figure
Morbilidade Neonatal e Cesariana Electiva em Recém-Nascidos de Termo
INTRODUCTION:
International guidelines suggest that non-urgent planned deliveries be scheduled at or after 39 weeks. Despite this recommendation elective cesarean often occurs before 39 weeks. Some research has demonstrated that elective cesarean before 39 weeks poses a greater risk to the infants than at or after 39 weeks.
OBJECTIVE:
To evaluate neonatal morbidity in term newborns born by elective cesarean section.
MATERIAL AND METHODS:
Retrospective study of all term elective cesarean sections (scheduled and without labor) performed in level III maternity, in the last 11 years (2003 - 2013). High risk pregnancies were excluded: twins, premature rupture of membranes, preeclampsia, poorly controlled diabetes mellitus, Rh isoimmunization and congenital malformations. Two groups of newborns with gestational age less than 39 weeks and equal or greater than 39 weeks gestational age were compared.
RESULTS:
In our sample, 45% of elective caesarean sections were performed before 39 weeks. Infants born before 39 weeks were more frequently admitted in neonatal intensive care, odds ratio 2.4 [1.4 - 4.1] p = 0.001, had more respiratory morbidity, odds ratio 2.4 [1.6 - 3.8] p < 0.001, more hyperbilirubinaemia odds ratio 2.3 [1.5 - 3.7] p < 0.001, more hypoglycaemia and/or feeding difficulties odds ratio 1.6 [1.2 - 2.4] p = 0.006, and longer admissions (more than five days), odds ratio 2.0 [1.4 - 3] p < 0.001.
DISCUSSION:
As in other studies 'early term' had higher respiratory and metabolic morbidity and consequently had a longer hospital stay.
CONCLUSION:
These findings support recommendations to delay elective cesarean delay until 39 weeks of gestation.info:eu-repo/semantics/publishedVersio
Manipulation of the dynamics of many-body systems via quantum control methods
We investigate how dynamical decoupling methods may be used to manipulate the
time evolution of quantum many-body systems. These methods consist of sequences
of external control operations designed to induce a desired dynamics. The
systems considered for the analysis are one-dimensional spin-1/2 models, which,
according to the parameters of the Hamiltonian, may be in the integrable or
non-integrable limits, and in the gapped or gapless phases. We show that an
appropriate control sequence may lead a chaotic chain to evolve as an
integrable chain and a system in the gapless phase to behave as a system in the
gapped phase. A key ingredient for the control schemes developed here is the
possibility to use, in the same sequence, different time intervals between
control operations.Comment: 10 pages, 3 figure
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