4,214 research outputs found
Bright soliton trains of trapped Bose-Einstein condensates
We variationally determine the dynamics of bright soliton trains composed of
harmonically trapped Bose-Einstein condensates with attractive interatomic
interactions. In particular, we obtain the interaction potential between two
solitons. We also discuss the formation of soliton trains due to the quantum
mechanical phase fluctuations of a one-dimensional condensate.Comment: 4 pages, 2 figures, submitted to PR
Bright matter wave solitons in Bose-Einstein condensates
We review recent experimental and theoretical work on the creation
of bright matter wave solitons in Bose–Einstein condensates. In two recent experiments,
solitons are formed from Bose–Einstein condensates of 7Li by utilizing
a Feshbach resonance to switch from repulsive to attractive interactions.
The solitons are made to propagate in a one-dimensional potential formed by a
focused laser beam. For repulsive interactions, the wavepacket undergoes dispersivewavepacket
spreading, while for attractive interactions, localized solitons are
formed. In our experiment, a multi-soliton train containing up to ten solitons is
observed to propagate without spreading for a duration of 2 s. Adjacent solitons
are found to interact repulsively, in agreement with a calculation based on the
nonlinear Schr¨odinger equation assuming that the soliton train is formed with an
alternating phase structure. The origin of this phase structure is not entirely clear
Conversion of an Atomic Fermi Gas to a Long-Lived Molecular Bose Gas
We have converted an ultracold Fermi gas of Li atoms into an ultracold
gas of Li molecules by adiabatic passage through a Feshbach resonance.
Approximately molecules in the least-bound, ,
vibrational level of the X singlet state are produced with an
efficiency of 50%. The molecules remain confined in an optical trap for times
of up to 1 s before we dissociate them by a reverse adiabatic sweep.Comment: Accepted for publication in Phys. Rev. Letter
Optically Faint Microjansky Radio Sources
We report on the identifications of radio sources from our survey of the
Hubble Deep Field and the SSA13 fields, both of which comprise the deepest
radio surveys to date at 1.4 GHz and 8.5 GHz respectively. About 80% of the
microjansky radio sources are associated with moderate redshift starburst
galaxies or AGNs within the I magnitude range of 17 to 24 with a median of I =
22 mag. Thirty-one (20%) of the radio sources are: 1) fainter than 25 mag,
with two objects in the HDF 28.5, 2) often identified with very red
objects 4, and 3) not significantly different in radio properties than
the brighter objects. We suggest that most of these objects are associated with
heavily obscured starburst galaxies with redshifts between 1 and 3. However,
other mechanisms are discussed and cannot be ruled out with the present
observations.Comment: to appear in Astrophysical Journal Letters, 3 figures, 1 tabl
Characterization of Dicer-deficient murine embryonic stem cells
Dicer is an RNase III-family nuclease that initiates RNA interference (RNAi) and related phenomena by generation of the small RNAs that determine the specificity of these gene silencing pathways. We have previously shown that Dicer is essential for mammalian development, with Dicer-deficient mice dying at embryonic day 7.5 with a lack of detectable multipotent stem cells. To permit a more detailed investigation of the biological roles of Dicer, we have generated embryonic stem cell lines in which their single Dicer gene can be conditionally inactivated. As expected, Dicer loss compromises maturation of microRNAs and leads to a defect in gene silencing triggered by long dsRNAs. However, the absence of Dicer does not affect the ability of small interfering RNAs to repress gene expression. Of interest, Dicer loss does compromise the proliferation of ES cells, possibly rationalizing the phenotype previously observed in Dicer-null animals. Dicer loss also affects the abundance of transcripts from mammalian centromeres but does so without a pronounced affect on histone modification status at pericentric repeats or methylation of centromeric DNA. These studies provide a conditional model of RNAi deficiency in mammals that will permit the dissection of the biological roles of the RNAi machinery in cultured mammalian cells
Three-dimensional correlated-fermion phase separation from analysis of the geometric mean of the individual susceptibilities
A quasi-Gaussian approximation scheme is formulated to study the strongly
correlated imbalanced fermions thermodynamics, where the mean-field theory is
not applicable. The non-Gaussian correlation effects are understood to be
captured by the statistical geometric mean of the individual susceptibilities.
In the three-dimensional unitary fermions ground state, an {\em universal}
non-linear scaling transformation relates the physical chemical potentials with
the individual Fermi kinetic energies. For the partial polarization phase
separation to full polarization, the calculated critical polarization ratio is
. The defines
the ratio of the symmetric ground state energy density to that of the ideal
fermion gas.Comment: Minor changes with typos correcte
Asymmetric Fermi superfluid with different atomic species in a harmonic trap
We study the dilute fermion gas with pairing between two species and unequal
concentrations in a harmonic trap using the mean field theory and the local
density approximation. We found that the system can exhibit a superfluid shell
structure sandwiched by the normal fermions. This superfluid shell structure
occurs if the mass ratio is larger then certain critical value which increases
from the weak-coupling BCS region to the strong-coupling BEC side. In the
strong coupling BEC regime, the radii of superfluid phase are less sensitive to
the mass ratios and are similar to the case of pairing with equal masses.
However, the lighter leftover fermions are easier to mix with the superfluid
core than the heavier ones. A partially polarized superfluid can be found if
the majority fermions are lighter, whereas phase separation is still found if
they are heavier.Comment: 12 pages, 7 figure
Initial Metabolic Profiles Are Associated with 7-Day Survival among Infants Born at 22-25 Weeks of Gestation.
OBJECTIVE:To evaluate the association between early metabolic profiles combined with infant characteristics and survival past 7 days of age in infants born at 22-25 weeks of gestation. STUDY DESIGN:This nested case-control consisted of 465 singleton live births in California from 2005 to 2011 at 22-25 weeks of gestation. All infants had newborn metabolic screening data available. Data included linked birth certificate and mother and infant hospital discharge records. Mortality was derived from linked death certificates and death discharge information. Each death within 7 days was matched to 4 surviving controls by gestational age and birth weight z score category, leaving 93 cases and 372 controls. The association between explanatory variables and 7-day survival was modeled via stepwise logistic regression. Infant characteristics, 42 metabolites, and 12 metabolite ratios were considered for model inclusion. Model performance was assessed via area under the curve. RESULTS:The final model included 1 characteristic and 11 metabolites. The model demonstrated a strong association between metabolic patterns and infant survival (area under the curve [AUC] 0.885, 95% CI 0.851-0.920). Furthermore, a model with just the selected metabolites performed better (AUC 0.879, 95% CI 0.841-0.916) than a model with multiple clinical characteristics (AUC 0.685, 95% CI 0.627-0.742). CONCLUSIONS:Use of metabolomics significantly strengthens the association with 7-day survival in infants born extremely premature. Physicians may be able to use metabolic profiles at birth to refine mortality risks and inform postnatal counseling for infants born at <26 weeks of gestation
Spin-Imbalance in a One-Dimensional Fermi Gas
Superconductivity and magnetism generally do not coexist. Changing the
relative number of up and down spin electrons disrupts the basic mechanism of
superconductivity, where atoms of opposite momentum and spin form Cooper pairs.
Nearly forty years ago Fulde and Ferrell and Larkin and Ovchinnikov proposed an
exotic pairing mechanism (FFLO) where magnetism is accommodated by formation of
pairs with finite momentum. Despite intense theoretical and experimental
efforts, however, polarized superconductivity remains largely elusive. Here we
report experimental measurements of density profiles of a two spin mixture of
ultracold 6Li atoms trapped in an array of one dimensional (1D) tubes, a system
analogous to electrons in 1D wires. At finite spin imbalance, the system phase
separates with an inverted phase profile in comparison to the three-dimensional
case. In 1D we find a partially polarized core surrounded by wings composed of
either a completely paired BCS superfluid or a fully polarized Fermi gas,
depending on the degree of polarization. Our observations are in quantitative
agreement with theoretical calculations in which the partially polarized phase
is found to be a 1D analogue of the FFLO state. This study demonstrates how
ultracold atomic gases in 1D may be used to create non-trivial new phases of
matter, and also paves the way for direct observation and further study of the
FFLO phase.Comment: 30 pages, 7 figure
The Radio/Optical Catalog of the SSA13 Field
We present a 1.4-GHz catalog of 810 radio sources (560 sources in the
complete sample) with 1.8" resolution found within a 17' radius in the SSA13
field (RA=13h12m,DEC=42d38'). The radio image from the VLA has an rms noise
level of 4.82 microJy/beam at the field center, and Subaru optical images in
r-band (6300A) and z-band (9200A) have a three-sigma detection magnitude of
26.1 and 24.9, respectively. 88% of the radio sources are identified with an
optical counterpart, and there is significantly more reddening for objects
fainter than 24-mag. The radio and optical parameters are tabulated, and source
morphologies are displayed by radio contours overlaying optical false-color
images. The radio structures show a wealth of complexity and these are
classified into a small number of categories. About one-third of the radio
sources are larger than 1.2" and their orientation is often similar to that of
the associated galaxy or binary-galaxy system. The density of sources in the
SSA13 field above 75 microJy is 0.40 per square arcmin, with a slope of -2.43
in the differential counts. The radio spectral index may steepen for sources
below 75 microJy. We estimate that at most 40% of the microJansky radio sources
are dominated by AGN processes.Comment: 50 pages, 14 figures of which fig 6 contains 33 parts. In press,
Astrophysical Journal, Supp
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