576 research outputs found
Dispersion management using betatron resonances in an ultracold-atom storage ring
Specific velocities of particles circulating in a storage ring can lead to
betatron resonances at which static perturbations of the particles' orbit yield
large transverse (betatron) oscillations. We have observed betatron resonances
in an ultracold-atom storage ring by direct observation of betatron motion.
These resonances caused a near-elimination of the longitudinal dispersion of
atomic beams propagating at resonant velocities, an effect which can improve
the performance of atom interferometric devices. Both the resonant velocities
and the strength of the resonances were varied by deliberate modifications to
the storage ring.Comment: 4 pages, 5 figures. Also available at
http://physics.berkeley.edu/research/ultracol
Microbial imbalance in inflammatory bowel disease patients at different taxonomic levels
Background
Inflammatory bowel disease (IBD), is a debilitating group of chronic diseases including Crohn’s Disease (CD) and ulcerative colitis (UC), which causes inflammation of the gut and affects millions of people worldwide. At different taxonomic levels, the structure of the gut microbiota is significantly altered in IBD patients compared to that of healthy individuals. However, it is unclear how these IBD-affected bacterial groups are related to other common bacteria in the gut, and how they are connected across different disease conditions at the global scale.
Results
In this study, using faecal samples from patients with IBD, we show through diversity analysis of the microbial community structure based on the 16S rRNA gene that the gut microbiome of IBD patients is less diverse compared to healthy individuals. Furthermore, we have identified which bacterial groups change in abundance in both CD and UC compared to healthy controls. A substantial imbalance was observed across four major bacterial phyla including Firmicutes, Bacteroidetes, Proteobacteria and Actinobacteria, which together constitute >98% of the gut microbiota. Next, we reconstructed a bacterial family co-abundance network based on the correlation of abundance profiles obtained from the public gut microbiome data of >22000 samples of faecal and gut biopsies taken from both diseased and healthy individuals. The data was compiled using the EBI metagenomics database [1]. By mapping IBD-altered bacterial families to the network, we show that the bacterial families which exhibit an increased abundance in IBD conditions are not well connected to other groups, implying that these families generally do not coexist together with common gut organisms. Whereas, the bacterial families whose abundance is reduced or did not change in IBD conditions compared to healthy conditions are very well connected to other bacterial groups, suggesting they are highly important groups of bacteria in the gut that can coexist with other bacteria across a range of conditions.
Conclusions
IBD patients exhibited a less diverse gut microbiome compared to healthy individuals. Bacterial groups which changed in IBD patients were found to be groups which do not co-exist well with common commensal gut bacteria, whereas bacterial groups which did not change in patients with IBD were found to commonly co-exist with commensal gut microbiota. This gives a potential insight into the dynamics of the gut microbiota in patients with IBD
Cavity Nonlinear Optics at Low Photon Numbers from Collective Atomic Motion
We report on Kerr nonlinearity and dispersive optical bistability of a
Fabry-Perot optical resonator due to the displacement of ultracold atoms
trapped within. In the driven resonator, such collective motion is induced by
optical forces acting upon up to Rb atoms prepared in the lowest
band of a one-dimensional intracavity optical lattice. The longevity of atomic
motional coherence allows for strongly nonlinear optics at extremely low cavity
photon numbers, as demonstrated by the observation of both branches of optical
bistability at photon numbers below unity.Comment: 4 pages, 3 figures. Modifed following reviewer comment
Bose-Einstein condensation in a circular waveguide
We have produced Bose-Einstein condensates in a ring-shaped magnetic
waveguide. The few-millimeter diameter non-zero bias ring is formed from a
time-averaged quadrupole ring. Condensates which propagate around the ring make
several revolutions within the time it takes for them to expand to fill the
ring. The ring shape is ideally suited for studies of vorticity in a
multiply-connected geometry and is promising as a rotation sensor.Comment: 4 pages, 4 figure
Collimated, single-pass atom source from a pulsed alkali metal dispenser for laser-cooling experiments
We have developed an improved scheme for loading atoms into a magneto-optical
trap (MOT) from a directed alkali metal dispenser in < 10^-10 torr ultra-high
vacuum conditions. A current-driven dispenser was surrounded with a cold
absorbing "shroud" held at < 0 C, pumping rubidium atoms not directed into the
MOT. This nearly eliminates background alkali atoms and reduces the detrimental
rise in pressure normally associated with these devices. The system can be
well-described as a current-controlled, rapidly-switched, two-temperature
thermal beam, and was used to load a MOT with 3 x 10^8 atoms.Comment: 5 pages, 4 figure
Thermodynamic activation energy for self-diffusion and order-order relaxation in intermetallic compounds
Collapse and revival of oscillations in a parametrically excited Bose-Einstein condensate in combined harmonic and optical lattice trap
In this work, we study parametric resonances in an elongated cigar-shaped BEC
in a combined harmonic trap and a time dependent optical lattice by using
numerical and analytical techniques. We show that there exists a relative
competition between the harmonic trap which tries to spatially localize the BEC
and the time varying optical lattice which tries to delocalize the BEC. This
competition gives rise to parametric resonances (collapse and revival of the
oscillations of the BEC width). Parametric resonances disappear when one of the
competing factors i.e strength of harmonic trap or the strength of optical
lattice dominates. Parametric instabilities (exponential growth of Bogoliubov
modes) arise for large variations in the strength of the optical lattice.Comment: 9 pages, 20 figure
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