3,874 research outputs found
Creating a supersolid in one-dimensional Bose mixtures
We identify a one-dimensional supersolid phase in a binary mixture of
near-hardcore bosons with weak, local inter-species repulsion. We find
realistic conditions under which such a phase, defined here as the coexistence
of quasi-superfluidity and quasi-charge density wave order, can be produced and
observed in finite ultra-cold atom systems in a harmonic trap. Our analysis is
based on Luttinger liquid theory supported with numerical calculations using
the time-evolving block decimation method. Clear experimental signatures of
these two orders can be found, respectively, in time-of-flight interference
patterns, and the structure factor S(k) derived from density correlations.Comment: 4 pages, 5 figures, changed Fig. 4, and minor edit
Optimal Capacity Decisions in a Developing Fishery
The problem of estimating optimal fishing capacity for a developing fishery is discussed, using the methods of Bayesian decision analysis. The results obtained indicate that quite good decisions can often be made on the basis of limited prior information as to fish stock productivity, particularly if a conservative approach allowing for subsequent increases in capacity is employed.Environmental Economics and Policy, International Development, International Relations/Trade, Resource /Energy Economics and Policy,
SS433:the microquasar link with ULXs?
SS433 is the prototype microquasar in the Galaxy and may even be analogous to
the ULX sources if the jets' kinetic energy is taken into account. However, in
spite of 20 years of study, our constraints on the nature of the binary system
are extremely limited as a result of the difficulty of locating spectral
features that can reveal the nature and motion of the mass donor. Newly
acquired, high resolution blue spectra taken when the (precessing) disc is
edge-on suggest that the binary is close to a common-envelope phase, and hence
providing kinematic constraints is extremely difficult. Nevertheless, we do
find evidence for a massive donor, as expected for the inferred very high mass
transfer rate, and we compare SS433's properties with those of Cyg X-3.Comment: 4 pages, 3 figures, to appear in "Compact binaries in the Galaxy and
beyond
Immunocompetent murine models for the study of glioblastoma immunotherapy.
Glioblastoma remains a lethal diagnosis with a 5-year survival rate of less than 10%. (NEJM 352:987-96, 2005) Although immunotherapy-based approaches are capable of inducing detectable immune responses against tumor-specific antigens, improvements in clinical outcomes are modest, in no small part due to tumor-induced immunosuppressive mechanisms that promote immune escape and immuno-resistance. Immunotherapeutic strategies aimed at bolstering the immune response while neutralizing immunosuppression will play a critical role in improving treatment outcomes for glioblastoma patients. In vivo murine models of glioma provide an invaluable resource to achieving that end, and their use is an essential part of the preclinical workup for novel therapeutics that need to be tested in animal models prior to testing experimental therapies in patients. In this article, we review five contemporary immunocompetent mouse models, GL261 (C57BL/6), GL26 (C57BL/6) CT-2A (C57BL/6), SMA-560 (VM/Dk), and 4C8 (B6D2F1), each of which offer a suitable platform for testing novel immunotherapeutic approaches
Magic wavelengths for the np-ns transitions in alkali-metal atoms
Extensive calculations of the electric-dipole matrix elements in alkali-metal
atoms are conducted using the relativistic all-order method. This approach is a
linearized version of the coupled-cluster method, which sums infinite sets of
many-body perturbation theory terms. All allowed transitions between the lowest
ns, np_1/2, np_3/2 states and a large number of excited states are considered
in these calculations and their accuracy is evaluated. The resulting
electric-dipole matrix elements are used for the high-precision calculation of
frequency-dependent polarizabilities of the excited states of alkali-metal
atoms. We find magic wavelengths in alkali-metal atoms for which the ns and
np_1/2 and np_3/2 atomic levels have the same ac Stark shifts, which
facilitates state-insensitive optical cooling and trapping.Comment: 12 pages, 8 figure
Decay of a superfluid current of ultra-cold atoms in a toroidal trap
Using a numerical implementation of the truncated Wigner approximation, we
simulate the experiment reported by Ramanathan et al. in Phys. Rev. Lett. 106,
130401 (2011), in which a Bose-Einstein condensate is created in a toroidal
trap and set into rotation via a phase imprinting technique. A potential
barrier is then placed in the trap to study the decay of the superflow. We find
that the current decays via thermally activated phase slips, which can also be
visualized as vortices crossing the barrier region in the radial direction.
Adopting the notion of critical velocity used in the experiment, we determine
it to be lower than the local speed of sound at the barrier, in contradiction
to the predictions of the zero-temperature Gross-Pitaevskii equation. We map
out the superfluid decay rate and critical velocity as a function of
temperature and observe a strong dependence. Thermal fluctuations offer a
partial explanation of the experimentally observed reduction of the critical
velocity from the phonon velocity.Comment: 15 pages. 11 figure
Phase fluctuations in anisotropic Bose condensates: from cigars to rings
We study the phase-fluctuating condensate regime of ultra-cold atoms trapped
in a ring-shaped trap geometry, which has been realized in recent experiments.
We first consider a simplified box geometry, in which we identify the
conditions to create a state that is dominated by thermal phase-fluctuations,
and then explore the experimental ring geometry. In both cases we demonstrate
that the requirement for strong phase fluctuations can be expressed in terms of
the total number of atoms and the geometric length scales of the trap only. For
the ring-shaped trap we discuss the zero temperature limit in which a
condensate is realized where the phase is fluctuating due to interactions and
quantum fluctuations. We also address possible ways of detecting the phase
fluctuating regime in ring condensates.Comment: 10 pages, 5 figures, minor edit
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