291 research outputs found
Interacting Agegraphic Dark Energy
A new dark energy model, named "agegraphic dark energy", has been proposed
recently, based on the so-called K\'{a}rolyh\'{a}zy uncertainty relation, which
arises from quantum mechanics together with general relativity. In this note,
we extend the original agegraphic dark energy model by including the
interaction between agegraphic dark energy and pressureless (dark) matter. In
the interacting agegraphic dark energy model, there are many interesting
features different from the original agegraphic dark energy model and
holographic dark energy model. The similarity and difference between agegraphic
dark energy and holographic dark energy are also discussed.Comment: 10 pages, 5 figures, revtex4; v2: references added; v3: accepted by
Eur. Phys. J. C; v4: published versio
Dispersive Manipulation of Paired Superconducting Qubits
We combine the ideas of qubit encoding and dispersive dynamics to enable
robust and easy quantum information processing (QIP) on paired superconducting
charge boxes sharing a common bias lead. We establish a decoherence free
subspace on these and introduce universal gates by dispersive interaction with
a LC resonator and inductive couplings between the encoded qubits. These gates
preserve the code space and only require the established local symmetry and the
control of the voltage bias.Comment: 5 pages, incl. 1 figur
Existence and uniqueness of solutions for systems of fractional differential equations with Riemann–Stieltjes integral boundary condition
In this article, we first establish an existence and uniqueness result for a class of systems of nonlinear operator equations under more general conditions by means of the cone theory and monotone iterative technique. Furthermore, the iterative sequence of the solution and the error estimation of the system are given. Then we use this new result to study the existence and uniqueness of the solution for boundary value problems of systems of fractional differential equations with a Riemann–Stieltjes integral boundary condition in real Banach spaces. The results obtained in this paper are more general than many previous results and complement them
Running coupling: Does the coupling between dark energy and dark matter change sign during the cosmological evolution?
In this paper we put forward a running coupling scenario for describing the
interaction between dark energy and dark matter. The dark sector interaction in
our scenario is free of the assumption that the interaction term is
proportional to the Hubble expansion rate and the energy densities of dark
sectors. We only use a time-variable coupling (with the scale factor
of the universe) to characterize the interaction . We propose a
parametrization form for the running coupling in which the
early-time coupling is given by a constant , while today the coupling is
given by another constant, . For investigating the feature of the running
coupling, we employ three dark energy models, namely, the cosmological constant
model (), the constant model (), and the time-dependent
model (). We constrain the models with the current
observational data, including the type Ia supernova, the baryon acoustic
oscillation, the cosmic microwave background, the Hubble expansion rate, and
the X-ray gas mass fraction data. The fitting results indicate that a
time-varying vacuum scenario is favored, in which the coupling crosses
the noninteracting line () during the cosmological evolution and the sign
changes from negative to positive. The crossing of the noninteracting line
happens at around , and the crossing behavior is favored at about
1 confidence level. Our work implies that we should pay more attention
to the time-varying vacuum model and seriously consider the phenomenological
construction of a sign-changeable or oscillatory interaction between dark
sectors.Comment: 8 pages, 5 figures; refs added; to appear in EPJ
Facile Synthesis of ZnO Nanorods by Microwave Irradiation of Zinc–Hydrazine Hydrate Complex
ZnO nanorods have been successfully synthesized by a simple microwave-assisted solution phase approach. Hydrazine hydrate has been used as a mineralizer instead of sodium hydroxide. XRD and FESEM have been used to characterize the product. The FESEM images show that the diameter of the nanorods fall in the range of about 25–75 nm and length in the range of 500–1,500 nm with an aspect ratio of about 20–50. UV–VIS and photoluminescence spectra of the nanorods in solution have been taken to study their optical properties. A mechanism for microwave synthesis of the ZnO nanorods using hydrazine hydrate precursor has also been proposed
Dark Energy and Neutrino CPT Violation
In this paper we study the dynamical CPT violation in the neutrino sector
induced by the dark energy of the Universe. Specifically we consider a dark
energy model where the dark energy scalar derivatively interacts with the
right-handed neutrinos. This type of derivative coupling leads to a
cosmological CPT violation during the evolution of the background field of the
dark energy. We calculate the induced CPT violation of left-handed neutrinos
and find the CPT violation produced in this way is consistent with the present
experimental limit and sensitive to the future neutrino oscillation
experiments, such as the neutrino factory.Comment: 10 pages, 2 figures. Typos corrected and references added. To be
published in EPJ
The Stability of Al11Sm3 (Al4Sm) Phases in the Al-Sm Binary System
The relative stability of Al11Sm3 (Al4Sm) intermetallic phases was experimentally investigated through a series of heat treatments followed by microstructural, microchemical, and X-ray diffraction (XRD) analyses. The principal findings are that the high-temperature tetragonal phase is stable from 1655 to 1333 K and that the low-temperature orthorhombic phases, α and γ, have no range of full stability but are metastable with respect to the crystalline Al and Sm reference states down to 0 K. Thermodynamic modeling is used to describe the relative energetics of stable and metastable phases along with the associated two-phase mixtures. Issues regarding transition energetics and kinetics are discussed
Structure of the icosahedral Ti-Zr-Ni quasicrystal
The atomic structure of the icosahedral Ti-Zr-Ni quasicrystal is determined
by invoking similarities to periodic crystalline phases, diffraction data and
the results from ab initio calculations. The structure is modeled by
decorations of the canonical cell tiling geometry. The initial decoration model
is based on the structure of the Frank-Kasper phase W-TiZrNi, the 1/1
approximant structure of the quasicrystal. The decoration model is optimized
using a new method of structural analysis combining a least-squares refinement
of diffraction data with results from ab initio calculations. The resulting
structural model of icosahedral Ti-Zr-Ni is interpreted as a simple decoration
rule and structural details are discussed.Comment: 12 pages, 8 figure
NMR and Mossbauer study of spin dynamics and electronic structure of Fe{2+x}V{1-x}Al and Fe2VGa
In order to assess the magnetic ordering process in Fe2VAl and the related
material Fe2VGa, we have carried out nuclear magnetic resonance (NMR) and
Mossbauer studies. 27Al NMR relaxation measurements covered the temperature
range 4 -- 500 K in Fe(2+x)V(1-x)Al samples. We found a peak in the NMR
spin-lattice relaxation rate, 27T1^-1, corresponding to the magnetic
transitions in each of these samples. These peaks appear at 125 K, 17 K, and
165 K for x = 0.10, 0, and - 0.05 respectively, and we connect these features
with critical slowing down of the localized antisite defects. Mossbauer
measurements for Fe2VAl and Fe2VGa showed lines with no hyperfine splitting,
and isomer shifts nearly identical to those of the corresponding sites in Fe3Al
and Fe3Ga, respectively. We show that a model in which local band filling leads
to magnetic regions in the samples, in addition to the localized antisite
defects, can account for the observed magnetic ordering behavior.Comment: 5 pages, 3 figure
- …