4,913 research outputs found
Deconfinement and cold atoms in optical lattices
Despite the fact that by now one dimensional and three dimensional systems of
interacting particles are reasonably well understood, very little is known on
how to go from the one dimensional physics to the three dimensional one. This
is in particular true in a quasi-one dimensional geometry where the hopping of
particles between one dimensional chains or tubes can lead to a dimensional
crossover between a Luttinger liquid and more conventional high dimensional
states. Such a situation is relevant to many physical systems. Recently cold
atoms in optical traps have provided a unique and controllable system in which
to investigate this physics. We thus analyze a system made of coupled one
dimensional tubes of interacting fermions. We explore the observable
consequences, such as the phase diagram for isolated tubes, and the possibility
to realize unusual superfluid phases in coupled tubes systems.Comment: Proceedings of the conference on "Quantum Many Body Theories 13", to
be published by World Scientifi
Molecule formation as a diagnostic tool for second order correlations of ultra-cold gases
We calculate the momentum distribution and the second-order correlation
function in momentum space, for molecular dimers
that are coherently formed from an ultracold atomic gas by photoassociation or
a Feshbach resonance. We investigate using perturbation theory how the quantum
statistics of the molecules depend on the initial state of the atoms by
considering three different initial states: a Bose-Einstein condensate (BEC), a
normal Fermi gas of ultra-cold atoms, and a BCS-type superfluid Fermi gas. The
cases of strong and weak coupling to the molecular field are discussed. It is
found that BEC and BCS states give rise to an essentially coherent molecular
field with a momentum distribution determined by the zero-point motion in the
confining potential. On the other hand, a normal Fermi gas and the unpaired
atoms in the BCS state give rise to a molecular field with a broad momentum
distribution and thermal number statistics. It is shown that the first-order
correlations of the molecules can be used to measure second-order correlations
of the initial atomic state.Comment: revtex, 15 pages,8 figure
The Netherlands:The reinvention of consensus democracy
The authors examine the development of opposition party behaviour in the Dutch Tweede Kamer between 1998 and 2015. They look at the effect of three major events on opposition party behaviour: the entry of a major radical right-wing populist party (in 2002), the global financial crisis (in 2008) and the advent of minority governments (in 2012). The authors find that consensus democracy is alive. During the economic crisis, the established rules of the game were reinvented to allow for productive cooperation between effectively a minority government and ‘constructive’ opposition parties. Since the crisis, opposition parties with earlier government experience have been increasingly active
Bulk de novo mitogenome assembly from pooled total DNA elucidates the phylogeny of weevils (Coleoptera: Curculionoidea)
Complete mitochondrial genomes have been shown to be reliable markers for phylogeny reconstruction among diverse animal groups. However, the relative difficulty and high cost associated with obtaining de novo full mitogenomes have frequently led to conspicuously low taxon sampling in ensuing studies. Here, we report the successful use of an economical and accessible method for assembling complete or near-complete mitogenomes through shot-gun next-generation sequencing of a single library made from pooled total DNA extracts of numerous target species. To avoid the use of separate indexed libraries for each specimen, and an associated increase in cost, we incorporate standard polymerase chain reaction-based “bait” sequences to identify the assembled mitogenomes. The method was applied to study the higher level phylogenetic relationships in the weevils (Coleoptera: Curculionoidea), producing 92 newly assembled mitogenomes obtained in a single Illumina MiSeq run. The analysis supported a separate origin of wood-boring behavior by the subfamilies Scolytinae, Platypodinae, and Cossoninae. This finding contradicts morphological hypotheses proposing a close relationship between the first two of these but is congruent with previous molecular studies, reinforcing the utility of mitogenomes in phylogeny reconstruction. Our methodology provides a technically simple procedure for generating densely sampled trees from whole mitogenomes and is widely applicable to groups of animals for which bait sequences are the only required prior genome knowledge
Comment on piNN Coupling from High Precision np Charge Exchange at 162 MeV
In this updated and expanded version of our delayed Comment we show that the
np backward cross section, as presented by the Uppsala group, is seriously
flawed (more than 25 sd.). The main reason is the incorrect normalization of
the data. We show also that their extrapolation method, used to determine the
charged piNN coupling constant, is a factor of about 10 less accurate than
claimed by Ericson et al. The large extrapolation error makes the determination
of the coupling constant by the Uppsala group totally uninteresting.Comment: 5 pages, latex2e with a4wide.sty. This is an updated and extended
version of the Comment published in Phys. Rev. Letters 81, 5253 (1998
Degenerate fermion gas heating by hole creation
Loss processes that remove particles from an atom trap leave holes behind in
the single particle distribution if the trapped gas is a degenerate fermion
system. The appearance of holes increases the temperature and we show that the
heating is (i) significant if the initial temperature is well below the Fermi
temperature , and (ii) increases the temperature to
after half of the system's lifetime, regardless of the initial temperature. The
hole heating has important consequences for the prospect of observing
Cooper-pairing in atom traps.Comment: to be published in PR
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