18,064 research outputs found
Competing Nematic, Anti-ferromagnetic and Spin-flux orders in the Ground State of Bilayer Graphene
We analyze the phase diagram of the Bilayer graphene (BLG) at zero
temperature and doping. Assuming that at the high energies the electronic
system of BLG can be described within a weak coupling theory (consistent with
the experimental evidence), we systematically study the evolution of the
couplings with going from high to low energies. The divergences of the
couplings at some energies indicates the tendency towards certain symmetry
breakings. Carrying out this program, we found that the phase diagram is
determined by microscopic couplings defined on the short distances (initial
conditions). We explored all plausible space of these initial conditions and
found that the three states have the largest phase volume of the initial
couplings: nematic, antiferromagnetic and spin flux (a.k.a quantum spin Hall).
In addition, ferroelectric and two superconducting phases and appear only near
the very limits of the applicability of the weak coupling approach.
The paper also contains the derivation and analysis of the renormalization
group equations and the group theory classification of all the possible phases
which might arise from the symmetry breakings of the lattice, spin rotation,
and gauge symmetries of graphene.Comment: 19 pages, 16 figure
On First-Order Generalized Maxwell Equations
The generalized Maxwell equations including an additional scalar field are
considered in the first-order formalism. The gauge invariance of the Lagrangian
and equations is broken resulting the appearance of a scalar field. We find the
canonical and symmetrical Belinfante energy-momentum tensors. It is shown that
the traces of the energy-momentum tensors are not equal to zero and the
dilatation symmetry is broken in the theory considered. The matrix Hamiltonian
form of equations is obtained after the exclusion of the nondynamical
components. The canonical quantization is performed and the propagator of the
fields is found in the first-order formalism.Comment: 14 pages, corrections in Eq.(38),(39),(59
Spatially-averaged oscillatory flow over a rough bed
Peer reviewedPublisher PD
Identifying Unclear Questions in Community Question Answering Websites
Thousands of complex natural language questions are submitted to community
question answering websites on a daily basis, rendering them as one of the most
important information sources these days. However, oftentimes submitted
questions are unclear and cannot be answered without further clarification
questions by expert community members. This study is the first to investigate
the complex task of classifying a question as clear or unclear, i.e., if it
requires further clarification. We construct a novel dataset and propose a
classification approach that is based on the notion of similar questions. This
approach is compared to state-of-the-art text classification baselines. Our
main finding is that the similar questions approach is a viable alternative
that can be used as a stepping stone towards the development of supportive user
interfaces for question formulation.Comment: Proceedings of the 41th European Conference on Information Retrieval
(ECIR '19), 201
Kinetics of the Phase Separation Transition in Cold-Atom Boson-Fermion Mixtures
We study the kinetics of the first order phase separation transition in
boson-fermion cold-atom mixtures. At sufficiently low temperatures such a
transition is driven by quantum fluctuations responsible for the formation of
critical nuclei of a stable phase. Based on a microscopic description of
interacting boson-fermion mixtures we derive an effective action for the
critical droplet and obtain an asymptotic expression for the nucleation rate in
the vicinity of the phase transition and near the spinodal instability of the
mixed phase. We also discuss effects of dissipation which play a dominant role
close to the transition point, and identify the regimes where quantum
nucleation can be experimentally observed in cold-atom systems.Comment: 4 pages 1 figure, typos correcte
Inversion of polarimetric data from eclipsing binaries
We describe a method for determining the limb polarization and limb darkening
of stars in eclipsing binary systems, by inverting photometric and polarimetric
light curves.
Because of the ill-conditioning of the problem, we use the Backus-Gilbert
method to control the resolution and stability of the recovered solution, and
to make quantitative estimates of the maximum accuracy possible. Using this
method we confirm that the limb polarization can indeed be recovered, and
demonstrate this with simulated data, thus determining the level of
observational accuracy required to achieve a given accuracy of reconstruction.
This allows us to set out an optimal observational strategy, and to critcally
assess the claimed detection of limb polarization in the Algol system.
The use of polarization in stars has been proposed as a diagnostic tool in
microlensing surveys by Simmons et al. (1995), and we discuss the extension of
this work to the case of microlensing of extended sources.Comment: 10pp, 5 figures. To appear in A&
Double-averaged velocity and stress distributions for hydraulically-smooth and transitionally-rough turbulent flows
Peer reviewedPreprin
Scaling tests with dynamical overlap and rooted staggered fermions
We present a scaling analysis in the 1-flavor Schwinger model with the full
overlap and the rooted staggered determinant. In the latter case the chiral and
continuum limit of the scalar condensate do not commute, while for overlap
fermions they do. For the topological susceptibility a universal continuum
limit is suggested, as is for the partition function and the Leutwyler-Smilga
sum rule. In the heavy-quark force no difference is visible even at finite
coupling. Finally, a direct comparison between the complete overlap and the
rooted staggered determinant yields evidence that their ratio is constant up to
effects.Comment: 28 pages, 20 figures containg 37 graphs. v2: 6 new references, 2 new
footnotes (to match published version
Our Whole Future is Bound up in this Project: The Making of Buford Dam
Twentieth Century Americans witnessed the construction of numerous massive dams that controlled the flow of rivers across the country. Many of these dams were built by the U.S. Army Corps of Engineers to improve navigation and to provide inexpensive electricity and flood control. This paper will seek to shed light on Georgia’s current water crisis by analyzing the initial purposes behind the building of Buford Dam in North Georgia, investigating how water supply issues were addressed in the first half of the twentieth century, and exploring how expectations of the Chattahoochee River changed over time due in part to metropolitan Atlanta’s population growth. This paper will show that Atlanta area leaders secured appropriations for Buford Dam primarily to obtain a reliable water supply and additional electricity for their burgeoning community
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