15,620 research outputs found
Pinning quantum phase transition of photons in a hollow-core fiber
We show that a pinning quantum phase transition for photons could be observed
in a hollow-core one-dimensional fiber loaded with a cold atomic gas. Utilizing
the strong light confinement in the fiber, a range of different strongly
correlated polaritonic and photonic states, corresponding to both strong and
weak interactions can be created and probed. The key ingredient is the creation
of a tunable effective lattice potential acting on the interacting polaritonic
gas which is possible by slightly modulating the atomic density. We analyze the
relevant phase diagram corresponding to the realizable Bose-Hubbard (weak) and
sine-Gordon (strong) interacting regimes and conclude by describing the
measurement process. The latter consists of mapping the stationary excitations
to propagating light pulses whose correlations can be efficiently probed once
they exit the fiber using available optical technologiesComment: 4 pages, 4 figures. Comments welcome
Efficient quantum transport simulation for bulk graphene heterojunctions
The quantum transport formalism based on tight-binding models is known to be
powerful in dealing with a wide range of open physical systems subject to
external driving forces but is, at the same time, limited by the memory
requirement's increasing with the number of atomic sites in the scattering
region. Here we demonstrate how to achieve an accurate simulation of quantum
transport feasible for experimentally sized bulk graphene heterojunctions at a
strongly reduced computational cost. Without free tuning parameters, we show
excellent agreement with a recent experiment on Klein backscattering [A. F.
Young and P. Kim, Nature Phys. 5, 222 (2009)].Comment: 5 pages, 3 figure
meson effects on neutron stars in the modified quark-meson coupling model
The properties of neutron stars are investigated by including meson
field in the Lagrangian density of modified quark-meson coupling model. The
population with meson is larger than that without
meson at the beginning, but it becomes smaller than that without meson
as the appearance of . The meson has opposite effects on
hadronic matter with or without hyperons: it softens the EOSes of hadronic
matter with hyperons, while it stiffens the EOSes of pure nucleonic matter.
Furthermore, the leptons and the hyperons have the similar influence on
meson effects. The meson increases the maximum masses of
neutron stars. The influence of on the meson effects
are also investigated.Comment: 10 pages, 6 figures, 4 table
TeV Scale Lee-Wick Fields out of Large Extra Dimensional Gravity
We study the gravitational corrections to the Maxwell, Dirac and Klein-Gorden
theories in the large extra dimension model in which the gravitons propagate in
the (4+n)-dimensional bulk, while the gauge and matter fields are confined to
the four-dimensional world. The corrections to the two-point Green's functions
of the gauge and matter fields from the exchanges of virtual Kaluza-Klein
gravitons are calculated in the gauge independent background field method. In
the framework of effective field theory, we show that the modified one-loop
renormalizable Lagrangian due to quantum gravitational effects contains a TeV
scale Lee-Wick partner of every gauge and matter field as extra degrees of
freedom in the theory. Thus the large extra dimension model of gravity provides
a natural mechanism to the emergence of these exotic particles which were
recently used to construct an extension of the Standard Model.Comment: 17 pages, 3 figures, references added, to appear in Phys. Rev.
Freeform Extrusion of High Solids Loading Ceramic Slurries, Part II: Extrusion Process Control
Part I of this paper provided a detailed description of a novel fabrication machine for high solids
loading ceramic slurry extrusion and presented an empirical model of the ceramic extrusion
process, with ram velocity as the input and extrusion force as the output. A constant force is
desirable in freeform extrusion processes as it correlates with a constant material deposition rate
and, thus, good part quality. The experimental results in Part I demonstrated that a constant ram
velocity will produce a transient extrusion force. In some instances the extrusion force increased
until ram motor skipping occurred. Further, process disturbances, such as air bubble release and
nozzle clogging that cause sudden changes in extrusion force, were often present. In this paper a
feedback controller for the ceramic extrusion process is designed and experimentally
implemented. The controller intelligently adjusts the ram motor velocity to maintain a constant
extrusion force. Since there is tremendous variability in the extrusion process characteristics, an
on-off controller is utilized in this paper. Comparisons are made between parts fabricated with
and without the feedback control. It is demonstrated that the use of the feedback control reduces
the effect of process disturbances (i.e., air bubble release and nozzle clogging) and dramatically
improves part quality.Mechanical Engineerin
Freeform Extrusion of High Solids Loading Ceramic Slurries, Part I: Extrusion Process Modeling
A novel solid freeform fabrication method has been developed for the manufacture of
ceramic-based components in an environmentally friendly fashion. The method is based on the
extrusion of ceramic slurries using water as the binding media. Aluminum oxide (Al2O3) is
currently being used as the part material and solids loading as high as 60 vol. % has been
achieved. This paper describes a manufacturing machine that has been developed for the
extrusion of high solids loading ceramic slurries. A critical component of the machine is the
deposition system, which consists of a syringe, a plunger, a ram actuated by a motor that forces
the plunger down to extrude material, and a load cell to measure the extrusion force. An
empirical, dynamic model of the ceramic extrusion process, where the input is the commanded
ram velocity and the output is the extrusion force, is developed. Several experiments are
conducted and empirical modeling techniques are utilized to construct the dynamic model. The
results demonstrate that the ceramic extrusion process has a very slow dynamic response, as
compared to other non-compressible fluids such as water. A substantial amount of variation
exists in the ceramic extrusion process, most notably in the transient dynamics, and a constant
ram velocity may either produce a relatively constant steady-state extrusion force or it may cause
the extrusion force to steadily increase until the ram motor skips. The ceramic extrusion process
is also subjected to significant disturbances such as air bubble release, which causes a dramatic
decrease in the extrusion force, and nozzle clogging, which causes the extrusion force to slowly
increase until the clog is released or the ram motor skips.Mechanical Engineerin
The spontaneous emergence of ordered phases in crumpled sheets
X-ray tomography is performed to acquire 3D images of crumpled aluminum
foils. We develop an algorithm to trace out the labyrinthian paths in the three
perpendicular cross sections of the data matrices. The tangent-tangent
correlation function along each path is found to decay exponentially with an
effective persistence length that shortens as the crumpled ball becomes more
compact. In the mean time, we observed ordered domains near the crust, similar
to the lamellae phase mixed by the amorphous portion in lyotropic liquid
crystals. The size and density of these domains grow with further compaction,
and their orientation favors either perpendicular or parallel to the radial
direction. Ordering is also identified near the core with an arbitrary
orientation, exemplary of the spontaneous symmetry breaking
Symplectic Geometry on Quantum Plane
A study of symplectic forms associated with two dimensional quantum planes
and the quantum sphere in a three dimensional orthogonal quantum plane is
provided. The associated Hamiltonian vector fields and Poissonian algebraic
relations are made explicit.Comment: 12 pages, Late
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