9,359 research outputs found
Positivity and Kodaira embedding theorem
Kodaira embedding theorem provides an effective characterization of
projectivity of a K\"ahler manifold in terms the second cohomology. Recently X.
Yang [21] proved that any compact K\"ahler manifold with positive holomorphic
sectional curvature must be projective. This gives a metric criterion of the
projectivity in terms of its curvature. In this note, we prove that any compact
K\"ahler manifold with positive 2nd scalar curvature (which is the average of
holomorphic sectional curvature over 2-dimensional subspaces of the tangent
space) must be projective. In view of generic 2-tori being non-abelian, this
new curvature characterization is sharp in certain sense
Properties and Origin of Galaxy Velocity Bias in the Illustris Simulation
We use the hydrodynamical galaxy formation simulations from the Illustris
suite to study the origin and properties of galaxy velocity bias, i.e., the
difference between the velocity distributions of galaxies and dark matter
inside halos. We find that galaxy velocity bias is a decreasing function of the
ratio of galaxy stellar mass to host halo mass. In general, central galaxies
are not at rest with respect to dark matter halos or the core of halos, with a
velocity dispersion above 0.04 times that of the dark matter. The central
galaxy velocity bias is found to be mostly caused by the close interactions
between the central and satellite galaxies. For satellite galaxies, the
velocity bias is related to their dynamical and tidal evolution history after
being accreted onto the host halos. It depends on the time after the accretion
and their distances from the halo centers, with massive satellites generally
moving more slowly than the dark matter. The results are in broad agreements
with those inferred from modeling small-scale redshift-space galaxy clustering
data, and the study can help improve models of redshift-space galaxy
clustering.Comment: 15 pages, 11 figures. Accepted for publication in Ap
Energy-Efficient Transmission Schedule for Delay-Limited Bursty Data Arrivals under Non-Ideal Circuit Power Consumption
This paper develops a novel approach to obtaining energy-efficient
transmission schedules for delay-limited bursty data arrivals under non-ideal
circuit power consumption. Assuming a-prior knowledge of packet arrivals,
deadlines and channel realizations, we show that the problem can be formulated
as a convex program. For both time-invariant and time-varying fading channels,
it is revealed that the optimal transmission between any two consecutive
channel or data state changing instants, termed epoch, can only take one of the
three strategies: (i) no transmission, (ii) transmission with an
energy-efficiency (EE) maximizing rate over part of the epoch, or (iii)
transmission with a rate greater than the EE-maximizing rate over the whole
epoch. Based on this specific structure, efficient algorithms are then
developed to find the optimal policies that minimize the total energy
consumption with a low computational complexity. The proposed approach can
provide the optimal benchmarks for practical schemes designed for transmissions
of delay-limited data arrivals, and can be employed to develop efficient online
scheduling schemes which require only causal knowledge of data arrivals and
deadline requirements.Comment: 30 pages, 7 figure
4-Cyanopyridinium bromide
In the title compound, C6H5N2
+·Br−, the pyridine N atom is protonated and involved in an intermolecular N—H⋯Br hydrogen bond which, together with weak C—H⋯N hydrogen bonds, results in the formation of a chain along the c axis. Weak intermolecular C—H⋯Br interactions between pyridine H atoms and Br− anions connect these chains into a network parallel to the bc plane
Oxalic acid–pyridine-4-carbonitrile (1/2)
In the title compound, 2C6H4N2·C2H2O4, the oxalic acid molecule lies about an inversion center. The pyridine ring of the pyridine-4-carbonitrile molecule is almost planar, the largest deviation from the least-squares plane being 0.006 (1) Å; the nitrile N atom deviates from this plane by 0.114 (1) Å. In the crystal, the oxalic acid molecules and the pyridine-4-carbonitrile molecules form stacks. Neighboring molecules within the stacks are related by translation in the a direction, with interplanar distances of 3.183 (1) and 3.331 (2) Å, respectively. Each oxalic acid molecule forms strong O—H⋯N hydrogen bonds with two molecules of pyridine-4-carbonitrile. Besides this, there are also weak C—H⋯O interactions
Probing signatures of bounce inflation with current observations
The aim of this paper is to probe the features of the bouncing cosmology with
the current observational data. Basing on bounce inflation model, with high
derivative term, we propose a general parametrization of primordial power
spectrum which includes the typical bouncing parameters, such as bouncing
time-scale, and energy scale. By applying Markov Chain Monto Carlo analysis
with current data combination of Planck 2015, BAO and JLA, we report the
posterior probability distributions of the parameters. We find that, bouncing
models can well explain CMB observations, especially the deficit and
oscillation on large scale in TT power spectrum.Comment: 17 pages, 8 figure
1,1′-(Phenylmethylene)dinaphthalen-2-ol
In the title compound, C27H20O2, the phenyl ring is oriented with respect to the naphthalene ring systems at 57.87 (6) and 85.12 (6)°. The two naphthalene ring systems make a dihedral angle of 70.10 (4)°. In the molecule, the hydroxy groups are involved in a strong intramolecular O—H⋯O hydrogen bond. In the crystal, inversion dimers linked by pairs of O—H⋯O hydrogen bonds occur. A weak C—H⋯π interaction is also observed in the crystal
- …