306,967 research outputs found
Environmental Dependence of Cold Dark Matter Halo Formation
We use a high-resolution -body simulation to study how the formation of
cold dark matter (CDM) halos is affected by their environments, and how such
environmental effects produce the age-dependence of halo clustering observed in
recent -body simulations. We estimate, for each halo selected at redshift
, an `initial' mass defined to be the mass enclosed by the
largest sphere which contains the initial barycenter of the halo particles and
within which the mean linear density is equal to the critical value for
spherical collapse at . For halos of a given final mass, , the
ratio has large scatter, and the scatter is larger for
halos of lower final masses. Halos that form earlier on average have larger
, and so correspond to higher peaks in the initial density
field than their final masses imply. Old halos are more strongly clustered than
younger ones of the same mass because their initial masses are larger. The
age-dependence of clustering for low-mass halos is entirely due to the
difference in the initial/final mass ratio. Low-mass old halos are almost
always located in the vicinity of big structures, and their old ages are
largely due to the fact that their mass accretions are suppressed by the hot
environments produced by the tidal fields of the larger structure. The
age-dependence of clustering is weaker for more massive halos because the
heating by large-scale tidal fields is less important.Comment: 18 pages,19 figures, accepted by MNRA
Weak coupling d-wave BCS superconductivity and unpaired electrons in overdoped La_{2-x}Sr_{x}CuO_{4} single crystals
The low-temperature specific heat (SH) of overdoped La_{2-x}Sr_{x}CuO_{4}
single crystals (0.178=<x=<0.290) has been measured. For the superconducting
samples (0.178=<x=<0.238), the derived gap values (without any adjusting
parameters) approach closely onto the theoretical prediction
\Delta_{0}=2.14k_{B}T_{c} for the weak-coupling d-wave BCS superconductivity.
In addition, the residual term \gamma(0) of SH at H=0 increases with x
dramatically when beyond x~0.22, and finally evolves into the value of a
complete normal metallic state at higher doping levels, indicating growing
amount of unpaired electrons. We argue that this large \gamma(0) cannot be
simply attributed to the pair breaking induced by the impurity scattering,
instead the phase separation is possible.Comment: 6 pages, 6 figures; Contents added; Accepted for publication in Phys.
Rev.
On controllability of neuronal networks with constraints on the average of control gains
Control gains play an important role in the control of a natural or a technical system since they reflect how much resource is required to optimize a certain control objective. This paper is concerned with the controllability of neuronal networks with constraints on the average value of the control gains injected in driver nodes, which are in accordance with engineering and biological backgrounds. In order to deal with the constraints on control gains, the controllability problem is transformed into a constrained optimization problem (COP). The introduction of the constraints on the control gains unavoidably leads to substantial difficulty in finding feasible as well as refining solutions. As such, a modified dynamic hybrid framework (MDyHF) is developed to solve this COP, based on an adaptive differential evolution and the concept of Pareto dominance. By comparing with statistical methods and several recently reported constrained optimization evolutionary algorithms (COEAs), we show that our proposed MDyHF is competitive and promising in studying the controllability of neuronal networks. Based on the MDyHF, we proceed to show the controlling regions under different levels of constraints. It is revealed that we should allocate the control gains economically when strong constraints are considered. In addition, it is found that as the constraints become more restrictive, the driver nodes are more likely to be selected from the nodes with a large degree. The results and methods presented in this paper will provide useful insights into developing new techniques to control a realistic complex network efficiently
Energy dependence of Normal Branch Oscillation in Scorpius X-1
We report the energy dependence of normal branch oscillations (NBOs) in
Scorpius X-1, a low-mass X-ray binary Z-source. Three characteristic quantities
(centroid frequency, quality factor, and fractional root-mean-squared (rms)
amplitude) of a quasi-periodic oscillation signal as functions of photon energy
are investigated. We found that, although it is not yet statistically well
established, there is a signature indicating that the NBO centroid frequency
decreases with increasing photon energy when it is below 6-8 keV, which turns
out to be positively correlated with the photon energy at the higher energy
side. In addition, the rms amplitude increases significantly with the photon
energy below 13 keV and then decreases in the energy band of 13-20 keV. There
is no clear dependence on photon energy for the quality factor. Based on these
results, we suggest that the NBO originates mainly in the transition layer.Comment: 6 pages, 4 figure
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