4,222 research outputs found
Joint Workshop on Bibliometric-enhanced Information Retrieval and Natural Language Processing for Digital Libraries (BIRNDL 2017)
The large scale of scholarly publications poses a challenge for scholars in
information seeking and sensemaking. Bibliometrics, information retrieval (IR),
text mining and NLP techniques could help in these search and look-up
activities, but are not yet widely used. This workshop is intended to stimulate
IR researchers and digital library professionals to elaborate on new approaches
in natural language processing, information retrieval, scientometrics, text
mining and recommendation techniques that can advance the state-of-the-art in
scholarly document understanding, analysis, and retrieval at scale. The BIRNDL
workshop at SIGIR 2017 will incorporate an invited talk, paper sessions and the
third edition of the Computational Linguistics (CL) Scientific Summarization
Shared Task.Comment: 2 pages, workshop paper accepted at the SIGIR 201
Can chaos be observed in quantum gravity?
Full general relativity is almost certainly 'chaotic'. We argue that this
entails a notion of nonintegrability: a generic general relativistic model, at
least when coupled to cosmologically interesting matter, likely possesses
neither differentiable Dirac observables nor a reduced phase space. It follows
that the standard notion of observable has to be extended to include
non-differentiable or even discontinuous generalized observables. These cannot
carry Poisson-algebraic structures and do not admit a standard quantization;
one thus faces a quantum representation problem of gravitational observables.
This has deep consequences for a quantum theory of gravity, which we
investigate in a simple model for a system with Hamiltonian constraint that
fails to be completely integrable. We show that basing the quantization on
standard topology precludes a semiclassical limit and can even prohibit any
solutions to the quantum constraints. Our proposed solution to this problem is
to refine topology such that a complete set of Dirac observables becomes
continuous. In the toy model, it turns out that a refinement to a polymer-type
topology, as e.g. used in loop gravity, is sufficient. Basing quantization of
the toy model on this finer topology, we find a complete set of quantum Dirac
observables and a suitable semiclassical limit. This strategy is applicable to
realistic candidate theories of quantum gravity and thereby suggests a solution
to a long-standing problem which implies ramifications for the very concept of
quantization. Our work reveals a qualitatively novel facet of chaos in physics
and opens up a new avenue of research on chaos in gravity which hints at deep
insights into the structure of quantum gravity.Comment: 6 pages + references -- matches published version (clarifications
added for why GR with cosmologically interesting matter likely fails our
notion of weak-integrability
Feshbach resonances of harmonically trapped atoms
Employing a short-range two-channel description we derive an analytic model
of atoms in isotropic and anisotropic harmonic traps at a Feshbach resonance.
On this basis we obtain a new parameterization of the energy-dependent
scattering length which differs from the one previously employed. We validate
the model by comparison to full numerical calculations for Li-Rb and explain
quantitatively the experimental observation of a resonance shift and
trap-induced molecules in exited bands. Finally, we analyze the bound state
admixture and Landau-Zener transition probabilities.Comment: 4 pages, 2 figures; revised version with extension to anisotropic
traps and new paragraph on trap-induced molecules in excited band
Momentum-sector-selective metal-insulator transition in the eight-site dynamical mean-field approximation to the Hubbard model in two dimensions
We explore the momentum-sector-selective metal insulator transitions recently
found in the eight - site dynamical cluster approximation to the
two-dimensional Hubbard model. The phase diagram in the space of interaction
and second-neighbor hopping is established. The initial transitions from
Fermi-liquid like to sector-selective phases are found to be of second order,
caused by the continuous opening of an energy gap whereas the other transitions
are found to be of first order. In the sector-selective phase the Fermi surface
regions which are not gapped are found to have a non-Fermi-liquid self-energy.
We demonstrate that the phenomenon is not caused by the Van Hove divergence in
the density of states. The sector-selective and insulating phases are
characterized by a cluster spin correlation function that is strongly peaked at
the commensurate antiferromagnetic wave vector but the model has no
nematic instability. Comparison to dynamical mean-field studies on smaller
clusters is made
Efficient DMFT-simulation of the Holstein-Hubbard Model
We present a method for solving impurity models with electron-phonon
coupling, which treats the phonons efficiently and without approximations. The
algorithm is applied to the Holstein-Hubbard model in the dynamical mean field
approximation, where it allows access to strong interactions, very low
temperatures and arbitrary fillings. We show that a renormalized
Migdal-Eliashberg theory provides a reasonlable description of the phonon
contribution to the electronic self energy in strongly doped systems, but fails
if the quasiparticle energy becomes of order of the phonon frequency.Comment: Published versio
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