4,861 research outputs found
Extreme tunability of interactions in a Li Bose-Einstein condensate
We use a Feshbach resonance to tune the scattering length a of a
Bose-Einstein condensate of 7Li in the |F = 1, m_F = 1> state. Using the
spatial extent of the trapped condensate we extract a over a range spanning 7
decades from small attractive interactions to extremely strong repulsive
interactions. The shallow zero-crossing in the wing of the Feshbach resonance
enables the determination of a as small as 0.01 Bohr radii. In this regime,
evidence of the weak anisotropic magnetic dipole interaction is obtained by
comparison with different trap geometries
A variational analysis of Einstein-scalar field Lichnerowicz equations on compact Riemannian manifolds
We establish new existence and non-existence results for positive solutions
of the Einstein-scalar field Lichnerowicz equation on compact manifolds. This
equation arises from the Hamiltonian constraint equation for the
Einstein-scalar field system in general relativity. Our analysis introduces
variational techniques, in the form of the mountain pass lemma, to the analysis
of the Hamiltonian constraint equation, which has been previously studied by
other methods.Comment: 15 page
Dynamics in shear flow studied by X-ray Photon Correlation Spectroscopy
X-ray photon correlation spectroscopy was used to measure the diffusive
dynamics of colloidal particles in a shear flow. The results presented here
show how the intensity autocorrelation functions measure both the diffusive
dynamics of the particles and their flow-induced, convective motion. However,
in the limit of low flow/shear rates, it is possible to obtain the diffusive
component of the dynamics, which makes the method suitable for the study of the
dynamical properties of a large class of complex soft-matter and biological
fluids. An important benefit of this experimental strategy over more
traditional X-ray methods is the minimization of X-ray induced beam damage.
While the method can be applied also for photon correlation spectroscopy in the
visible domain, our analysis shows that the experimental conditions under which
it is possible to measure the diffusive dynamics are easier to achieve at
higher q values (with X-rays).Comment: 9 pages, 7 figures, to appear in Eur. Phys. J.
Gluing Initial Data Sets for General Relativity
We establish an optimal gluing construction for general relativistic initial
data sets. The construction is optimal in two distinct ways. First, it applies
to generic initial data sets and the required (generically satisfied)
hypotheses are geometrically and physically natural. Secondly, the construction
is completely local in the sense that the initial data is left unaltered on the
complement of arbitrarily small neighborhoods of the points about which the
gluing takes place. Using this construction we establish the existence of
cosmological, maximal globally hyperbolic, vacuum space-times with no constant
mean curvature spacelike Cauchy surfaces.Comment: Final published version - PRL, 4 page
A late Quaternary climate reconstruction based on borehole heat flux data, borehole temperature data, and the instrumental record
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95180/1/grl24686.pd
Identification of the Early Fermi LAT Gamma-Ray Bright Objects with Extragalactic VLBI sources
A list of 205 gamma-ray strong objects was reported recently as a result of a
3-month integration with the Large Area Telescope on board the Fermi Gamma-Ray
Space Telescope. We attempted identification of these objects,
cross-correlating the gamma-ray positions with VLBI positions of a large
all-sky sample of extragalactic radio sources selected on the basis of their
parsec-scale flux density. The original associations reported by the Fermi team
are confirmed and six new identifications are suggested. A Monte-Carlo analysis
shows that the fraction of chance associations in our analysis is less than 5
per cent, and confirms that the vast majority of gamma-ray bright extragalactic
sources are radio loud blazars with strong parsec-scale jets. A correlation
between the parsec-scale radio and gamma-ray flux is supported by our analysis
of a complete VLBI flux-density-limited sample of extragalactic jets. The
effectiveness of using a VLBI catalog to find associations between gamma-ray
detections and compact extragalactic radio sources, especially near the
Galactic plane, is demonstrated. It is suggested that VLBI catalogs should be
used for future identification of Fermi LAT objects.Comment: 5 pages, 4 figures, 1 table, accepted by the Astrophysical Journal
Letters; minor corrections to the text are made, one panel is added to Figure
1; full table 1 in electronic form can be extracted from the preprint sourc
Droplet microactuator system
The present invention relates to a droplet microactuator system. According to one embodiment, the droplet microactuator system includes: (a) a droplet microactuator configured to conduct droplet operations; (b) a magnetic field source arranged to immobilize magnetically responsive beads in a droplet during droplet operations; (c) a sensor configured in a sensing relationship with the droplet microactuator, such that the sensor is capable of sensing a signal from and/or a property of one or more droplets on the droplet microactuator; and (d) one or more processors electronically coupled to the droplet microactuator and programmed to control electrowetting-mediated droplet operations on the droplet actuator and process electronic signals from the sensor
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