2,200 research outputs found
U(2,2) gravity on noncommutative space with symplectic structure
The classical Einstein's gravity can be reformulated from the constrained
U(2,2) gauge theory on the ordinary (commutative) four-dimensional spacetime.
Here we consider a noncommutative manifold with a symplectic structure and
construct a U(2,2) gauge theory on such a manifold by using the covariant
coordinate method. Then we use the Seiberg-Witten map to express noncommutative
quantities in terms of their commutative counterparts up to the first-order in
noncommutative parameters. After imposing constraints we obtain a
noncommutative gravity theory described by the Lagrangian with up to
nonvanishing first order corrections in noncommutative parameters. This result
coincides with our previous one obtained for the noncommutative SL(2,C)
gravity.Comment: 13 pages, no figures; v2: 14 pages, clarifications and references
added; v3: 16 pages, title changed, clarifications and references added; v4:
17 pages, clarifications added, this final version accepted by Physical
Review
An Investigation of Degradation of Mechanical Behaviour of Prestressing Strands Subjected to Chloride Attacking
Corrosion of reinforcing and prestressing steel due to chloride contamination is one of the primary causes of deterioration of concrete structures. A review of published literatures shows that the research on the deterioration of mechanical properties of reinforcing steel is more than that on prestressing strands, even though the corrosion of prestressing strands may trigger structural collapse without warnings due to higher stress levels in the steel. This paper aims to investigate the degradation of mechanical behaviour of corroded prestressing strands. Details of a comprehensive experiment designed to examine the mechanical behaviour of corroded prestressing strands in concrete structural members are presented. A micromechanical damage model for failure mechanism of corroded prestressing strands is proposed, and a model for damage factor is derived. Based on these models, a constitutive model for corroded prestressing strands is developed and verified with test results. It is found in the paper that both the strength and ductility of corroded prestressing strands decrease with the increase of corrosion and that the hemispherical model for the pit shape is more appropriate for the prediction of strength reduction of corroded prestressing strands. The paper concludes that the constitutive model developed in the paper can be used to predict the mechanical behaviour of corroded prestressing strands accurately, paving the way for the assessment of corrosion-induced flexural failure of prestressed concrete structures
Heterogeneity in structurally arrested hard spheres
When cooled or compressed sufficiently rapidly, a liquid vitrifies into a glassy amorphous state. Vitrification in a dense liquid is associated with jamming of the particles. For hard spheres, the density and degree of order in the final structure depend on the compression rate: simple intuition suggests, and previous computer simulation demonstrates, that slower compression results in states that are both denser and more ordered. In this work, we use the Lubachevsky-Stillinger algorithm to generate a sequence of structurally arrested hard-sphere states by varying the compression rate. We find that while the degree of order, as measured by both bond-orientation and translation order parameters, increases monotonically with decreasing compression rate, the density of the arrested state first increases, then decreases, then increases again, as the compression rate decreases, showing a minimum at an intermediate compression rate. Examination of the distribution of the local order parameters and the distribution of the root-mean-square fluctuation of the particle positions, as well as direct visual inspection of the arrested structures, reveal that they are structurally heterogeneous, consisting of disordered, amorphous regions and locally ordered crystal-like domains. In particular, the low-density arrested states correspond with many interconnected small crystal clusters that form a polycrystalline network interspersed in an amorphous background, suggesting that jamming by the domains may be an important mechanism for these states
The centre-to-limb variations of solar Fraunhofer lines imprinted upon lunar eclipse spectra - Implications for exoplanet transit observations
The atmospheres of exoplanets are commonly studied by observing the transit
of the planet passing in front of its parent star. The obscuration of part of
the stellar disk during a transit will reveal aspects of its surface structure
resulting from general centre-to-limb variations (CLVs). These become apparent
when forming the ratio between the stellar light in and out of transit. These
phenomena can be seen particularly clearly during the progress of a penumbral
lunar eclipse, where the Earth transits the solar disk and masks different
regions of the solar disk as the eclipse progresses. When inferring the
properties of the planetary atmosphere, it is essential that this effect
originating at the star is properly accounted for. Using the data observed from
the 2014-April-15 lunar eclipse with the ESPaDOnS spectrograph mounted on the
Canada France Hawaii Telescope (CFHT), we have obtained for the first time a
time sequence of the penumbral spectra. These penumbral spectra enable us to
study the centre-to-limb variations of solar Fraunhofer lines when the Earth is
transiting Sun. The Na i and Ca ii absorption features reported from previous
lunar eclipse observations are demonstrated to be CLV features, which dominate
the corresponding line profiles and mask possible planetary signal. Detecting
atmospheric species in exoplanets via transit spectroscopy must account for the
CLV effect.Comment: 9 pages, 11 figures, accepted, A&
Maximally localized states and quantum corrections of black hole thermodynamics in the framework of a new generalized uncertainty principle
As a generalized uncertainty principle (GUP) leads to the effects of the
minimal length of the order of the Planck scale and UV/IR mixing, some
significant physical concepts and quantities are modified or corrected
correspondingly. On the one hand, we derive the maximally localized states ---
the physical states displaying the minimal length uncertainty associated with a
new GUP proposed in our previous work. On the other hand, in the framework of
this new GUP we calculate quantum corrections to the thermodynamic quantities
of the Schwardzschild black hole, such as the Hawking temperature, the entropy,
and the heat capacity, and give a remnant mass of the black hole at the end of
the evaporation process. Moreover, we compare our results with that obtained in
the frameworks of several other GUPs. In particular, we observe a significant
difference between the situations with and without the consideration of the
UV/IR mixing effect in the quantum corrections to the evaporation rate and the
decay time. That is, the decay time can greatly be prolonged in the former
case, which implies that the quantum correction from the UV/IR mixing effect
may give rise to a radical rather than a tiny influence to the Hawking
radiation.Comment: 27 pages, 10 figures, 4 tables; v2: 30 pages, sections 3-6
substantially revised but conclusions unchanged; v3: 27 pages, clarifications
added; v4: 29 pages, clarifications and references added, final version to
appear in Advances in High Energy Physic
Kosterlitz-Thouless phase transition and reentrance in an anisotropic 3-state Potts model on the generalized Kagome lattice
The unusual reentrant phenomenon is observed in the anisotropic 3-state Potts
model on a gen- eralized Kagome lattice. By employing the linearized tensor
renormalization group method, we find that the reentrance can appear in the
region not only under a partial ordered phase as commonly known but also a
phase without a local order parameter, which is uncovered to fall into the uni-
versality of the Kosterlitz-Thouless (KT) type. The region of the reentrance
depends strongly on the ratios of the next nearest couplings {\alpha} = J2 /|J1
| and {\beta} = J3 /|J1 |. The phase diagrams in the plane of temperature
versus {\beta} for different {\alpha} are obtained. Through massive
calculations, it is also revealed that the quasi-entanglement entropy can be
used to accurately detect the KT transition temperature
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