2,541 research outputs found
Exact Cosmological Solutions of Theories via Hojman Symmetry
Nowadays, theory has been one of the leading modified gravity theories
to explain the current accelerated expansion of the universe, without invoking
dark energy. It is of interest to find the exact cosmological solutions of
theories. Besides other methods, symmetry has been proved as a powerful
tool to find exact solutions. On the other hand, symmetry might hint the deep
physical structure of a theory, and hence considering symmetry is also well
motivated. As is well known, Noether symmetry has been extensively used in
physics. Recently, the so-called Hojman symmetry was also considered in the
literature. Hojman symmetry directly deals with the equations of motion, rather
than Lagrangian or Hamiltonian, unlike Noether symmetry. In this work, we
consider Hojman symmetry in theories in both the metric and Palatini
formalisms, and find the corresponding exact cosmological solutions of
theories via Hojman symmetry. There exist some new solutions significantly
different from the ones obtained by using Noether symmetry in theories.
To our knowledge, they also have not been found previously in the literature.
This work confirms that Hojman symmetry can bring new features to cosmology and
gravity theories.Comment: 16 pages, revtex4; v2: discussions added, Nucl. Phys. B in press; v3:
published version. arXiv admin note: text overlap with arXiv:1505.0754
Van der Waals-like phase transition from holographic entanglement entropy in Lorentz breaking massive gravity
In this paper, phase transition of AdS black holes in lorentz breaking
massive gravity has been studied in the framework of holography. We find that
there is a first order phase transition(FPT) and second order phase
transition(SPT) both in Bekenstein-Hawking entropy(BHE)-temperature plane and
holographic entanglement entropy(HEE)-temperature plane. Furthermore, for the
FPT, the equal area law is checked and for the SPT, the critical exponent of
the heat capacity is also computed. Our results confirm that the phase
structure of HEE is similar to that of BHE in lorentz breaking massive gravity,
which implies that HEE and BHE have some potential underlying relationship.Comment: 10 pages, 10 figure
Graphene-plasmon polaritons: From fundamental properties to potential applications
With the unique possibilities for controlling light in nanoscale devices,
graphene plasmonics has opened new perspectives to the nanophotonics community
with potential applications in metamaterials, modulators, photodetectors, and
sensors. This paper briefly reviews the recent exciting progress in graphene
plasmonics. We begin with a general description for optical properties of
graphene, particularly focusing on the dispersion of graphene-plasmon
polaritons. The dispersion relation of graphene-plasmon polaritons of spatially
extended graphene is expressed in terms of the local response limit with
intraband contribution. With this theoretical foundation of graphene-plasmon
polaritons, we then discuss recent exciting progress, paying specific attention
to the following topics: excitation of graphene plasmon polaritons,
electron-phonon interactions in graphene on polar substrates, and tunable
graphene plasmonics with applications in modulators and sensors. Finally, we
seek to address some of the apparent challenges and promising perspectives of
graphene plasmonics.Comment: Invited minireview paper on graphene plasmon polaritons, 11 pages, 4
figure
Mutual correlation in the shock wave geometry
We probe the shock wave geometry with the mutual correlation in a spherically
symmetric Reissner Nordstr\"om AdS black hole on the basis of the gauge/gravity
duality. In the static background, we find that the regions living on the
boundary of the AdS black holes are correlated provided the considered regions
on the boundary are large enough. We also investigate the effect of the charge
on the mutual correlation and find that the bigger the value of the charge is,
the smaller the value of the mutual correlation will to be. As a small
perturbation is added at the AdS boundary, the horizon shifts and a dynamical
shock wave geometry forms after long time enough. In this dynamic background,
we find that the greater the shift of the horizon is, the smaller the mutual
correlation will to be. Especially for the case that the shift is large enough,
the mutual correlation vanishes, which implies that the considered regions on
the boundary are uncorrelated. The effect of the charge on the mutual
correlation in this dynamic background is found to be the same as that in the
static background.Comment: 10 page
Geometric bionics: Lotus effect helps polystyrene nanotube films get good blood compatibility
Various biomaterials have been widely used for manufacturing biomedical applications including artificial organs, medical devices and disposable clinical apparatus, such as vascular prostheses, blood pumps, artificial kidney, artificial hearts, dialyzers and plasma separators, which could be used in contact with blood^1^. However, the research tasks of improving hemocompatibility of biomaterials have been carrying out with the development of biomedical requirements^2^. Since the interactions that lead to surface-induced thrombosis occurring at the blood-biomaterial interface become a reason of familiar current complications with grafts therapy, improvement of the blood compatibility of artificial polymer surfaces is, therefore a major issue in biomaterials science^3^. After decades of focused research, various approaches of modifying biomaterial surfaces through chemical or biochemical methods to improve their hemocompatibility were obtained^1^. In this article, we report that polystyrene nanotube films with morphology similar to the papilla on lotus leaf can be used as blood-contacted biomaterials by virtue of Lotus effect^4^. Clearly, this idea, resulting from geometric bionics that mimicking the structure design of lotus leaf, is very novel technique for preparation of hemocompatible biomaterials
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