8,055 research outputs found
Correlations and Scaling Laws in Human Mobility
Human mobility patterns deeply affect the dynamics of many social systems. In
this paper, we empirically analyze the real-world human movements based GPS
records, and observe rich scaling properties in the temporal-spatial patterns
as well as an abnormal transition in the speed-displacement patterns. We notice
that the displacements at the population level show significant positive
correlation, indicating a cascade-like nature in human movements. Furthermore,
our analysis at the individual level finds that the displacement distributions
of users with strong correlation of displacements are closer to power laws,
implying a relationship between the positive correlation of the series of
displacements and the form of an individual's displacement distribution. These
findings from our empirical analysis show a factor directly relevant to the
origin of the scaling properties in human mobility.Comment: 10 pages, 9 figure
1-[(2-Hydroxyphenyl)(pyrrolidin-1-yl)methyl]naphthalen-2-ol N,N-dimethylformamide monosolvate
The title compound, C21H21NO2·C3H7NO, was synthesized by solvent-free one-pot three-component reaction of naphthalen-2-ol, 2-hydroxybenzaldehyde and pyrrolidine. The dihedral angle between the naphthalene ring system and the benzene ring is 77.74 (6)°. The pyrrolidine ring assumes an envelope conformation. An intramolecular O—H⋯N and an intermolecular O—H⋯O hydrogen bond are observed
The progenitors of Type Ia supernovae with long delay times
The nature of the progenitors of Type Ia supernovae (SNe Ia) is still
unclear. In this paper, by considering the effect of the instability of
accretion disk on the evolution of white dwarf (WD) binaries, we performed
binary evolution calculations for about 2400 close WD binaries, in which a
carbon--oxygen WD accretes material from a main-sequence star or a slightly
evolved subgiant star (WD + MS channel), or a red-giant star (WD + RG channel)
to increase its mass to the Chandrasekhar (Ch) mass limit. According to these
calculations, we mapped out the initial parameters for SNe Ia in the orbital
period--secondary mass () plane for various WD
masses for these two channels, respectively. We confirm that WDs in the WD + MS
channel with a mass as low as can accrete efficiently and reach
the Ch limit, while the lowest WD mass for the WD + RG channel is . We have implemented these results in a binary population synthesis
study to obtain the SN Ia birthrates and the evolution of SN Ia birthrates with
time for both a constant star formation rate and a single starburst. We find
that the Galactic SN Ia birthrate from the WD + MS channel is according to our standard model, which is higher than
previous results. However, similar to previous studies, the birthrate from the
WD + RG channel is still low (). We also
find that about one third of SNe Ia from the WD + MS channel and all SNe Ia
from the WD + RG channel can contribute to the old populations (\ga1 Gyr) of
SN Ia progenitors.Comment: 11 pages, 9 figures, 1 table, accepted for publication in MNRA
- …