58,843 research outputs found
Comment on ``Force Balance at the Transition from Selective Withdrawal to Viscous Entrainment
Comment on paper by Blanchette and Zhang, Phys. Rev. Lett. 102, 144501
(2009)
Recent results in Euclidean dynamical triangulations
We study a formulation of lattice gravity defined via Euclidean dynamical
triangulations (EDT). After fine-tuning a non-trivial local measure term we
find evidence that four-dimensional, semi-classical geometries are recovered at
long distance scales in the continuum limit. Furthermore, we find that the
spectral dimension at short distance scales is consistent with 3/2, a value
that is also observed in the causal dynamical triangulation (CDT) approach to
quantum gravity.Comment: 7 pages, 3 figures. Proceedings for the 3rd conference of the Polish
society on relativit
Microscopy of glazed layers formed during high temperature sliding wear at 750C
The evolution of microstructures in the glazed layer formed during high temperature sliding wear of Nimonic 80A against Stellite 6 at 750 ◦C using a speed of 0.314ms−1 under a load of 7N has been investigated using scanning electron microscopy (SEM), energy dispersive analysis by X-ray (EDX), X-ray diffraction (XRD) analysis, scanning tunnelling microscopy (STM) and transmission electron microscopy (TEM). The results indicate the formation of a wear resistant nano-structured glazed layer. The mechanisms responsible for the formation of the nano-polycrystalline glazed layer are discussed
Lattice Quantum Gravity and Asymptotic Safety
We study the nonperturbative formulation of quantum gravity defined via
Euclidean dynamical triangulations (EDT) in an attempt to make contact with
Weinberg's asymptotic safety scenario. We find that a fine-tuning is necessary
in order to recover semiclassical behavior. Such a fine-tuning is generally
associated with the breaking of a target symmetry by the lattice regulator; in
this case we argue that the target symmetry is the general coordinate
invariance of the theory. After introducing and fine-tuning a nontrivial local
measure term, we find no barrier to taking a continuum limit, and we find
evidence that four-dimensional, semiclassical geometries are recovered at long
distance scales in the continuum limit. We also find that the spectral
dimension at short distance scales is consistent with 3/2, a value that could
resolve the tension between asymptotic safety and the holographic entropy
scaling of black holes. We argue that the number of relevant couplings in the
continuum theory is one, once symmetry breaking by the lattice regulator is
accounted for. Such a theory is maximally predictive, with no adjustable
parameters. The cosmological constant in Planck units is the only relevant
parameter, which serves to set the lattice scale. The cosmological constant in
Planck units is of order 1 in the ultraviolet and undergoes renormalization
group running to small values in the infrared. If these findings hold up under
further scrutiny, the lattice may provide a nonperturbative definition of a
renormalizable quantum field theory of general relativity with no adjustable
parameters and a cosmological constant that is naturally small in the infrared.Comment: 69 pages, 25 figures. Revised discussion of target symmetry
throughout paper. Numerical results unchanged and main conclusions largely
unchanged. Added references and corrected typos. Conforms with version
published in Phys. Rev.
Oscillatory Magneto-Thermopower and Resonant Phonon Drag in a High-Mobility 2D Electron Gas
Experimental and theoretical evidence is presented for new low-magnetic-field
( kG) 1/B-oscillations in the thermoelectric power of a high-mobility
GaAs/AlGaAs two-dimensional (2D) electron gas. The oscillations result from
inter-Landau-Level resonances of acoustic phonons carrying a momentum equal to
twice the Fermi wavenumber at . Numerical calculations show that both 3D
and 2D phonons can contribute to this effect.Comment: 4 pages, 5 figure
Comment on "Self-Purification in Semiconductor Nanocrystals"
In a recent Letter [PRL 96, 226802 (2006)], Dalpian and Chelikowsky claimed
that formation energies of Mn impurities in CdSe nanocrystals increase as the
size of the nanocrystal decreases, and argued that this size dependence leads
to "self-purification" of small nanocrystals. They presented
density-functional-theory (DFT) calculations showing a strong size dependence
for Mn impurity formation energies, and proposed a general explanation. In this
Comment we show that several different DFT codes, pseudopotentials, and
exchange-correlation functionals give a markedly different result: We find no
such size dependence. More generally, we argue that formation energies are not
relevant to substitutional doping in most colloidally grown nanocrystals.Comment: 1 page, 1 figur
Two-Photon Beatings Using Biphotons Generated from a Two-Level System
We propose a two-photon beating experiment based upon biphotons generated
from a resonant pumping two-level system operating in a backward geometry. On
the one hand, the linear optical-response leads biphotons produced from two
sidebands in the Mollow triplet to propagate with tunable refractive indices,
while the central-component propagates with unity refractive index. The
relative phase difference due to different refractive indices is analogous to
the pathway-length difference between long-long and short-short in the original
Franson interferometer. By subtracting the linear Rayleigh scattering of the
pump, the visibility in the center part of the two-photon beating interference
can be ideally manipulated among [0, 100%] by varying the pump power, the
material length, and the atomic density, which indicates a Bell-type inequality
violation. On the other hand, the proposed experiment may be an interesting way
of probing the quantum nature of the detection process. The interference will
disappear when the separation of the Mollow peaks approaches the fundamental
timescales for photon absorption in the detector.Comment: to appear in Phys. Rev. A (2008
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