603 research outputs found
Fractal and multifractal properties of a family of fractal networks
In this work, we study the fractal and multifractal properties of a family of
fractal networks introduced by Gallos {\it et al.} ({\it Proc. Natl. Acad. Sci.
U.S.A.}, 2007, {\bf 104}: 7746). In this fractal network model, there is a
parameter which is between and , and allows for tuning the level of
fractality in the network. Here we examine the multifractal behavior of these
networks, dependence relationship of fractal dimension and the multifractal
parameters on the parameter . First, we find that the empirical fractal
dimensions of these networks obtained by our program coincide with the
theoretical formula given by Song {\it et al.} ( {\it Nat. Phys}, 2006, {\bf
2}: 275). Then from the shape of the and curves, we find the
existence of multifractality in these networks. Last, we find that there exists
a linear relationship between the average information dimension and
the parameter .Comment: 12 pages, 7 figures, accepted by J. Stat. Mec
Multifractal analysis of weighted networks by a modified sandbox algorithm
Complex networks have attracted growing attention in many fields. As a
generalization of fractal analysis, multifractal analysis (MFA) is a useful way
to systematically describe the spatial heterogeneity of both theoretical and
experimental fractal patterns. Some algorithms for MFA of unweighted complex
networks have been proposed in the past a few years, including the sandbox (SB)
algorithm recently employed by our group. In this paper, a modified SB
algorithm (we call it SBw algorithm) is proposed for MFA of weighted
networks.First, we use the SBw algorithm to study the multifractal property of
two families of weighted fractal networks (WFNs): "Sierpinski" WFNs and "Cantor
dust" WFNs. We also discuss how the fractal dimension and generalized fractal
dimensions change with the edge-weights of the WFN. From the comparison between
the theoretical and numerical fractal dimensions of these networks, we can find
that the proposed SBw algorithm is efficient and feasible for MFA of weighted
networks. Then, we apply the SBw algorithm to study multifractal properties of
some real weighted networks ---collaboration networks. It is found that the
multifractality exists in these weighted networks, and is affected by their
edge-weights.Comment: 15 pages, 6 figures. Accepted for publication by Scientific Report
Solving and Completing the Rabi-Stark Model in the Ultrastrong Coupling Regime
In this work,we employ a unitary transformation with a suitable parameter to
convert the quantum Rabi-Stark model into a Jaynes-Cummings-like model.
Subsequently, we derive the analytical energy spectra in the ultrastrong
coupling regime. The energy spectra exhibit a phenomenon known as spectral
collapse, indicating the instability of the model due to the unboundedness of
its energy from below at higher coupling parameters. To stabilize the
Rabi-Stark model, we introduce a nonlinear photon-photon interaction term. We
then compare the modified model with the original model in the classical
oscillator (CO) limit. Interestingly, we observe a regular "staircase" pattern
in the mean photon number of the ground state. This pattern exhibits a fixed
slope and equal step width, which we determine analytically. Moreover, we
analytically determine the phase boundary, which slightly differs from that in
the original Rabi-Stark model. These findings offer insights into the
investigation of those superradiant phase transitions that are unbounded from
below due to the phenomenon of spectral collapse.Comment: 11 pages, 7 figure
2-(DibutylÂamino)-3-(4-fluoroÂphenÂyl)-5,6,7,8-tetraÂhydro-7-methyl-6,8-diÂphenylÂpyridineÂ[3′,4′:2,3]thieno[5,4-d]pyrimidin-4(3H)-one
In the crystal structure of the title compound, C36H39FN4OS, the two fused rings of the thienopyrimidine system are coplanar. The 4-fluoroÂphenyl ring is twisted with respect to the heterocyclic pyrimidinone ring by 67.21 (14)°. The piperidine ring shows a half-chair conformation. One of the n-butyl chains is disordered equally over two sites. The crystal packing is stabilized by C—H⋯O hydrogen bonds
Non-Gaussian features from the inverse volume corrections in loop quantum cosmology
In this paper we study the non-Gaussian features of the primordial
fluctuations in loop quantum cosmology with the inverse volume corrections. The
detailed analysis is performed in the single field slow-roll inflationary
models. However, our results reflect the universal characteristics of
bispectrum in loop quantum cosmology. The main corrections to the scalar
bispectrum come from two aspects: one is the modifications to the standard
Bunch-Davies vacuum, the other is the corrections to the background dependent
variables, such as slow-roll parameters. Our calculations show that the loop
quantum corrections make of the inflationary models increase
0.1%. Moreover, we find that two new shapes arise, namely and
. The former gives a unique loop quantum feature which is less
correlated with the local, equilateral and single types, while the latter is
highly correlated with the local one.Comment: matched to the published version. 30 pages, 4 figure
Production of proton-rich nuclei around Z=84-90 in fusion-evaporation reactions
Within the framework of the dinuclear system model, production cross sections
of proton-rich nuclei with charged numbers of Z=84-90 are investigated
systematically. Possible combinations with the Si, S, Ar
bombarding the target nuclides Ho, Tm, Yb,
Lu, Hf and Ta are analyzed thoroughly. The
optimal excitation energies and evaporation channels are proposed to produce
the proton-rich nuclei. The systems are feasible to be constructed in
experiments. It is found that the neutron shell closure of N=126 is of
importance during the evaporation of neutrons. The experimental excitation
functions in the Ar induced reactions can be nicely reproduced. The
charged particle evaporation is comparable with neutrons in cooling the excited
proton-rich nuclei, in particular for the channels with and proton
evaporation. The production cross section increases with the mass asymmetry of
colliding systems because of the decrease of the inner fusion barrier. The
channels with pure neutron evaporation depend on the isotopic targets. But it
is different for the channels with charged particles and more sensitive to the
odd-even effect.Comment: 15 pages, 10 figures. arXiv admin note: text overlap with
arXiv:0803.1117, arXiv:0707.258
- …