333,545 research outputs found
Cosmological model of the interaction between dark matter and dark energy
In this paper, we test the dark matter-dark energy interacting cosmological
model with a dynamic equation of state , using
type Ia supernovae (SNe Ia), Hubble parameter data, baryonic acoustic
oscillation (BAO) measurements, and the cosmic microwave background (CMB)
observation. This interacting cosmological model has not been studied before.
The best-fitted parameters with uncertainties are , , and
with . At the
confidence level, we find , which means that the energy transfer
prefers from dark matter to dark energy. We also find that the SNe Ia are in
tension with the combination of CMB, BAO and Hubble parameter data. The
evolution of indicates that this interacting model is a
good approach to solve the coincidence problem, because the
decrease with scale factor . The transition redshift is in this model.Comment: 6 pages, 6 figures, published in A&
The velocities of intranetwork and network magnetic fields
We analyzed two sequences of quiet-Sun magnetograms obtained on June 4, 1992 and July 28, 1994. Both were observed during excellent seeing conditions such that the weak intranetwork (IN) fields are observed clearly during the entire periods. Using the local correlation tracking technique, we derived the horizontal velocity fields of IN and network magnetic fields. They consist of two components: (1) radial divergence flows which move IN fields from the network interior to the boundaries, and (2) lateral flows which move along the network boundaries and converge toward stronger magnetic elements. Furthermore, we constructed divergence maps based on horizonal velocities, which are a good representation of the vertical velocities of supergranules. For the June 4, 1992 data, the enhanced network area in the field of view has twice the flux density, 10% higher supergranular velocity and 20% larger cell sizes than the quiet, unenhanced network area. Based on the number densities and flow velocities of IN fields derived in this paper and a previous paper (Wang et al., 1995), we estimate that the lower limit of total energy released from the recycling of IN fields is 1.2 × 10²⁸ erg s⁻¹, which is comparable to the energy required for coronal heating
Polarized Curvature Radiation in Pulsar Magnetosphere
The propagation of polarized emission in pulsar magnetosphere is investigated
in this paper. The polarized waves are generated through curvature radiation
from the relativistic particles streaming along curved magnetic field lines and
co-rotating with the pulsar magnetosphere. Within the 1/{\deg} emission cone,
the waves can be divided into two natural wave mode components, the ordinary
(O) mode and the extraord nary (X) mode, with comparable intensities. Both
components propagate separately in magnetosphere, and are aligned within the
cone by adiabatic walking. The refraction of O-mode makes the two components
separated and incoherent. The detectable emission at a given height and a given
rotation phase consists of incoherent X-mode and O-mode components coming from
discrete emission regions. For four particle-density models in the form of
uniformity, cone, core and patches, we calculate the intensities for each mode
numerically within the entire pulsar beam. If the co-rotation of relativistic
particles with magnetosphere is not considered, the intensity distributions for
the X-mode and O-mode components are quite similar within the pulsar beam,
which causes serious depolarization. However, if the co-rotation of
relativistic particles is considered, the intensity distributions of the two
modes are very different, and the net polarization of out-coming emission
should be significant. Our numerical results are compared with observations,
and can naturally explain the orthogonal polarization modes of some pulsars.
Strong linear polarizations of some parts of pulsar profile can be reproduced
by curvature radiation and subsequent propagation effect.Comment: 12 pages, 9 figures, Accepted for publication in MNRA
Split Two-Higgs-Doublet Model and Neutrino Condensation
We split the two-Higgs-doublet model by assuming very different vevs for the
two doublets: the vev is at weak scale (174 GeV) for the doublet \Phi_1 and at
neutrino-mass scale (10^{-2} \sim 10^{-3} eV) for the doublet \Phi_2. \Phi_1 is
responsible for giving masses to all fermions except neutrinos; while \Phi_2 is
responsible for giving neutrino masses through its tiny vev without introducing
see-saw mechanism. Among the predicted five physical scalars H, h, A^0 and
H^{\pm}, the CP-even scalar h is as light as 10^{-2} \sim 10^{-3}eV while
others are at weak scale. We identify h as the cosmic dark energy field and the
other CP-even scalar H as the Standard Model Higgs boson; while the CP-odd A^0
and the charged H^{\pm} are the exotic scalars to be discovered at future
colliders. Also we demonstrate a possible dynamical origin for the doublet
\Phi_2 from neutrino condensation caused by some unknown dynamics.Comment: version in Europhys. Lett. (discussions added
GRBs and fundamental physics
Gamma-ray bursts (GRBs) are short and intense flashes at the cosmological
distances, which are the most luminous explosions in the Universe. The high
luminosities of GRBs make them detectable out to the edge of the visible
universe. So, they are unique tools to probe the properties of high-redshift
universe: including the cosmic expansion and dark energy, star formation rate,
the reionization epoch and the metal evolution of the Universe. First, they can
be used to constrain the history of cosmic acceleration and the evolution of
dark energy in a redshift range hardly achievable by other cosmological probes.
Second, long GRBs are believed to be formed by collapse of massive stars. So
they can be used to derive the high-redshift star formation rate, which can not
be probed by current observations. Moreover, the use of GRBs as cosmological
tools could unveil the reionization history and metal evolution of the
Universe, the intergalactic medium (IGM) properties and the nature of first
stars in the early universe. But beyond that, the GRB high-energy photons can
be applied to constrain Lorentz invariance violation (LIV) and to test
Einstein's Equivalence Principle (EEP). In this paper, we review the progress
on the GRB cosmology and fundamental physics probed by GRBs.Comment: 38 pages, 18 figures, Review based on ISSI workshop "Gamma-Ray
Bursts: a Tool to Explore the Young Universe" (2015, Beijing, China),
accepted for publication in Space Science Review
Investigation of the utilisation of social networks in e-learning at universities
Over the years universities have considered to use social networks for learning purposes as most of their students now engage on them. However, questions on the impact social networks would have on learning and how they can be utilised further for more effective teaching and learning are still unclear. To solve these questions, an in-depth investigation has been conducted to understand the benefits and drawback of social network features available for students. The investigation results show that students strongly believe that social network features will help enhance learning and the key ways of utilising such features have been suggested
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