32,529 research outputs found
Topological properties and fractal analysis of recurrence network constructed from fractional Brownian motions
Many studies have shown that we can gain additional information on time
series by investigating their accompanying complex networks. In this work, we
investigate the fundamental topological and fractal properties of recurrence
networks constructed from fractional Brownian motions (FBMs). First, our
results indicate that the constructed recurrence networks have exponential
degree distributions; the relationship between and of recurrence networks decreases with the Hurst
index of the associated FBMs, and their dependence approximately satisfies
the linear formula . Moreover, our numerical results of
multifractal analysis show that the multifractality exists in these recurrence
networks, and the multifractality of these networks becomes stronger at first
and then weaker when the Hurst index of the associated time series becomes
larger from 0.4 to 0.95. In particular, the recurrence network with the Hurst
index possess the strongest multifractality. In addition, the
dependence relationships of the average information dimension on the Hurst index can also be
fitted well with linear functions. Our results strongly suggest that the
recurrence network inherits the basic characteristic and the fractal nature of
the associated FBM series.Comment: 25 pages, 1 table, 15 figures. accepted by Phys. Rev.
Experimental study on the compressive strength, damping and interfacial transition zone properties of modified recycled aggregate concrete
© 2019 The Authors. Published by the Royal Society under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/4.0/, which permits unrestricted use, provided the original author and source are credited. At present, many modification methods have been proposed to improve the performance of recycled aggregate concrete (RAC). In this study, tests on the compressive strength and damping properties of modified RAC with the addition of different proportions of recycled coarse aggregate (RCA) (0, 50, 100%), rubber powder (10, 15, 20%), steel fibre (5, 7.5, 10%) and fly ash (15, 20, 5%) are carried out. To elucidate the effect of the modification method on the interfacial transition zone (ITZ) performance of RAC, model ITZ specimens are used for push-out tests. The results show that when the replacement rate of RCA reaches 100%, the loss factor of the RAC is 6.0% higher than that of natural aggregate concrete; however, the compressive strength of the RAC decreases by 22.6%. With the addition of 20% rubber powder, the damping capacity of the modified RAC increases by 213.7%, while the compressive strength of the modified RAC decreases by 47.5%. However, with the addition of steel fibre and fly ash, both the compressive strength and loss factor of the RAC specimens increase. With a steel fibre content of 10 wt%, the compressive strength and loss factor of the RAC increase by 21.9% and 15.2%, respectively. With a fly ash content of 25 wt%, the compressive strength and loss factor of the RAC increase by 8.6% and 6.9%, respectively. This demonstrates that steel fibre and fly ash are effective in improving both the damping properties and compressive strength of RAC, and steel fibre is more effective than fly ash. Two methods were used for modification of the RAC: reinforcing the RCA through impregnation with a 0.5% polyvinyl alcohol (PVA) emulsion and nano-SiO2 solution, and strengthening the RAC integrally through the addition of fly ash as an admixture. Both of these techniques can improve the ITZ bond strength between the RAC and new mortar. Replacing 10% of the cement with fly ash in the new mortar is shown to be the best method to improve the ITZ strength
Global quark polarization in non-central collisions
Partons produced in the early stage of non-central heavy-ion collisions can
develop a longitudinal fluid shear because of unequal local number densities of
participant target and projectile nucleons. Under such fluid shear, local
parton pairs with non-vanishing impact parameter have finite local relative
orbital angular momentum along the direction opposite to the reaction plane.
Such finite relative orbital angular momentum among locally interacting quark
pairs can lead to global quark polarization along the same direction due to
spin-orbital coupling. Local longitudinal fluid shear is estimated within both
Landau fireball and Bjorken scaling model of initial parton production. Quark
polarization through quark-quark scatterings with the exchange of a thermal
gluon is calculated beyond small-angle scattering approximation in a
quark-gluon plasma. The polarization is shown to have a non-monotonic
dependence on the local relative orbital angular momentum dictated by the
interplay between electric and magnetic interaction. It peaks at a value of
relative orbital angular momentum which scales with the magnetic mass of the
exchanged gluons. With the estimated small longitudinal fluid shear in
semi-peripheral collisions at the RHIC energy, the final quark
polarization is found to be small in the weak coupling limit.
Possible behavior of the quark polarization in the strong coupling limit and
implications on the experimental detection of such global quark polarization at
RHIC and LHC are also discussed.Comment: 28 pages,11 figure
A comparison of the local spiral structure from Gaia DR2 and VLBI maser parallaxes
Context. The Gaia mission has released the second data set (Gaia DR2), which
contains parallaxes and proper motions for a large number of massive, young
stars. Aims. We investigate the spiral structure in the solar neighborhood
revealed by Gaia DR2 and compare it with that depicted by VLBI maser
parallaxes. Methods. We examined three samples with different constraints on
parallax uncertainty and distance errors and stellar spectral types: (1) all OB
stars with parallax errors of less than 10%; (2) only O-type stars with 0.1 mas
errors imposed and with parallax distance errors of less than 0.2 kpc; and (3)
only O-type stars with 0.05 mas errors imposed and with parallax distance
errors of less than 0.3 kpc. Results. In spite of the significant distance
uncertainties for stars in DR2 beyond 1.4 kpc, the spiral structure in the
solar neighborhood demonstrated by Gaia agrees well with that illustrated by
VLBI maser results. The O-type stars available from DR2 extend the spiral arm
models determined from VLBI maser parallaxes into the fourth Galactic quadrant,
and suggest the existence of a new spur between the Local and Sagittarius arms.Comment: 4 pages, 3 figures, 1 table, accepted for publication in A&
Solidification of Al-Sn-Cu based immiscible alloys under intense shearing
The official published version of the Article can be accessed from the link below - Copyright @ 2009 The Minerals, Metals & Materials Society and ASM InternationalThe growing importance of Al-Sn based alloys as materials for engineering applications
necessitates the development of uniform microstructures with improved performance. Guided by the recently thermodynamically assessed Al-Sn-Cu system, two model immiscible alloys, Al-45Sn-10Cu and Al-20Sn-10Cu, were selected to investigate the effects of intensive melt shearing provided by the novel melt conditioning by advanced shear technology (MCAST) unit on the uniform dispersion of the soft Sn phase in a hard Al matrix. Our experimental results have confirmed that intensive melt shearing is an effective way to achieve fine and uniform
dispersion of the soft phase without macro-demixing, and that such dispersed microstructure can be further refined in alloys with precipitation of the primary Al phase prior to the demixing reaction. In addition, it was found that melt shearing at 200 rpm and 60 seconds will be adequate to produce fine and uniform dispersion of the Sn phase, and that higher shearing speed and prolonged shearing time can only achieve minor further refinement.This work is funded by the EPSRC and
DT
Possible approach to improve sensitivity of a Michelson interferometer
We propose a possible approach to achieve an 1/N sensitivity of Michelson
interferometer by using a properly designed random phase modulation. Different
from other approaches, the sensitivity improvement does not depend on
increasing optical powers or utilizing the quantum properties of light.
Moreover the requirements for optical losses and the quantum efficiencies of
photodetection systems might be lower than the quantum approaches and the
sensitivity improvement is frequency independent in all detection band.Comment: 8 pages, 3 figures, new versio
Pressure shift of the superconducting T_c of LiFeAs
The effect of hydrostatic pressure on the superconductivity in LiFeAs is
investigated up to 1.8 GPa. The superconducting transition temperature, T_c,
decreases linearly with pressure at a rate of 1.5 K/GPa. The negative pressure
coefficient of T_c and the high ambient pressure T_c indicate that LiFeAs is
the high-pressure analogue of the isoelectronic SrFe_2As_2 and BaFe_2As_2.Comment: 3 pages, 2 figure
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