184,252 research outputs found
Quantization of static space-times
A 4-dimensional Lorentzian static space-time is equivalent to 3-dimensional
Euclidean gravity coupled to a massless Klein-field. By canonically quantizing
the coupling model in the framework of loop quantum gravity, we obtain a
quantum theory which actually describes quantized static space-times. The
Kinematical Hilbert space is the product of the Hilbert space of gravity with
that of imaginary scalar fields. It turns out that the Hamiltonian constraint
of the 2+1 model corresponds to a densely defined operator in the underlying
Hilbert space, and hence it is finite without renormalization. As a new point
of view, this quantized model might shed some light on a few physical problems
concerning quantum gravity.Comment: 14 pages, made a few modifications, added Journal-re
Numerical framework for transcritical real-fluid reacting flow simulations using the flamelet progress variable approach
An extension to the classical FPV model is developed for transcritical
real-fluid combustion simulations in the context of finite volume, fully
compressible, explicit solvers. A double-flux model is developed for
transcritical flows to eliminate the spurious pressure oscillations. A hybrid
scheme with entropy-stable flux correction is formulated to robustly represent
large density ratios. The thermodynamics for ideal-gas values is modeled by a
linearized specific heat ratio model. Parameters needed for the cubic EoS are
pre-tabulated for the evaluation of departure functions and a quadratic
expression is used to recover the attraction parameter. The novelty of the
proposed approach lies in the ability to account for pressure and temperature
variations from the baseline table. Cryogenic LOX/GH2 mixing and reacting cases
are performed to demonstrate the capability of the proposed approach in
multidimensional simulations. The proposed combustion model and numerical
schemes are directly applicable for LES simulations of real applications under
transcritical conditions.Comment: 55th AIAA Aerospace Sciences Meeting, Dallas, T
Information processing with topologically protected vortex memories in exciton-polariton condensates
We show that in a non-equilibrium system of an exciton-polariton condensate,
where polaritons are generated from incoherent pumping, a ring-shaped pump
allows for stationary vortex memory elements of topological charge or
. Using simple potential guides we can choose whether to copy the same
charge or invert it onto another spatially separate ring pump. Such
manipulation of binary information opens the possibility of a new type
processing using vortices as topologically protected memory components
Instability-induced formation and non-equilibrium dynamics of phase defects in polariton condensates
We study, theoretically and numerically, the onset and development of
modulational instability in an incoherently pumped spatially homogeneous
polariton condensate. Within the framework of mean-field theory, we identify
regimes of modulational instability in two cases: 1) Strong feedback between
the condensate and reservoir, which may occur in scalar condensates, and 2)
Parametric scattering in the presence of polarization splitting in spinor
condensates. In both cases we investigate the instability induced textures in
space and time including non-equilibrium dynamics of phase dislocations and
vortices. In particular we discuss the mechanism of vortex destabilization and
formation of spiraling waves. We also identify the presence of topological
defects, which take the form of half-vortex pairs in the spinor case, giving an
"eyelet" structure in intensity and dipole type structure in the spin
polarization. In the modulationally stable parameter domains, we observe
formation of the phase defects in the process of condensate formation from an
initially spatially incoherent low-density state. In analogy to the
Kibble-Zurek type scaling for nonequilibrium phase transitions, we find that
the defect density scales with the pumping rate.Comment: 13 pages, 9 figures, revised manuscript sent to Phys. Rev.
Semi-classical States in Homogeneous Loop Quantum Cosmology
Semi-classical states in homogeneous loop quantum cosmology (LQC) are
constructed by two different ways. In the first approach, we firstly construct
an exponentiated annihilation operator. Then a kind of semi-classical
(coherent) state is obtained by solving the eigen-equation of that operator.
Moreover, we use these coherent states to analyze the semi-classical limit of
the quantum dynamics. It turns out that the Hamiltonian constraint operator
employed currently in homogeneous LQC has correct classical limit with respect
to the coherent states. In the second approach, the other kind of
semi-classical state is derived from the mathematical construction of coherent
states for compact Lie groups due to Hall.Comment: 13 pages, submitted to CQ
Nonequilibrium phase transition in surface growth
Conserved growth models that exhibit a nonlinear instability in which the
height (depth) of isolated pillars (grooves) grows in time are studied by
numerical integration and stochastic simulation. When this instability is
controlled by the introduction of an infinite series of higher-order nonlinear
terms, these models exhibit, as function of a control parameter, a
non-equilibrium phase transition between a kinetically rough phase with
self-affine scaling and a phase that exhibits mound formation, slope selection
and power-law coarsening.Comment: 7 pages, 4 .eps figures (Minor changes in text and references.
Dynamics of Scalar Field in Polymer-like Representation
In recent twenty years, loop quantum gravity, a background independent
approach to unify general relativity and quantum mechanics, has been widely
investigated. We consider the quantum dynamics of a real massless scalar field
coupled to gravity in this framework. A Hamiltonian operator for the scalar
field can be well defined in the coupled diffeomorphism invariant Hilbert
space, which is both self-adjoint and positive. On the other hand, the
Hamiltonian constraint operator for the scalar field coupled to gravity can be
well defined in the coupled kinematical Hilbert space. There are 1-parameter
ambiguities due to scalar field in the construction of both operators. The
results heighten our confidence that there is no divergence within this
background independent and diffeomorphism invariant quantization approach of
matter coupled to gravity. Moreover, to avoid possible quantum anomaly, the
master constraint programme can be carried out in this coupled system by
employing a self-adjoint master constraint operator on the diffeomorphism
invariant Hilbert space.Comment: 24 pages, accepted for pubilcation in Class. Quant. Gra
The Interaction of Venus-like, M-dwarf Planets with the Stellar Wind of Their Host Star
We study the interaction between the atmospheres of Venus-like,
non-magnetized exoplanets orbiting an M-dwarf star, and the stellar wind using
a multi-species Magnetohydrodynaic (MHD) model. We focus our investigation on
the effect of enhanced stellar wind and enhanced EUV flux as the planetary
distance from the star decreases. Our simulations reveal different topologies
of the planetary space environment for sub- and super-Alfvenic stellar wind
conditions, which could lead to dynamic energy deposition in to the atmosphere
during the transition along the planetary orbit. We find that the stellar wind
penetration for non-magnetized planets is very deep, up to a few hundreds of
kilometers. We estimate a lower limit for the atmospheric mass-loss rate and
find that it is insignificant over the lifetime of the planet. However, we
predict that when accounting for atmospheric ion acceleration, a significant
amount of the planetary atmosphere could be eroded over the course of a billion
years.Comment: 13 pages, 7 figures, accepted to Ap
easySTORM: a robust, lower-cost approach to localisation and TIRF microscopy
TIRF and STORM microscopy are super-resolving fluorescence imaging modalities for which current implementations on standard microscopes can present significant complexity and cost. We present a straightforward and low-cost approach to implement STORM and TIRF taking advantage of multimode optical fibres and multimode diode lasers to provide the required excitation light. Combined with open source software and relatively simple protocols to prepare samples for STORM, including the use of Vectashield for non-TIRF imaging, this approach enables TIRF and STORM imaging of cells labelled with appropriate dyes or expressing suitable fluorescent proteins to become widely accessible at low cost
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